The small rotorcraft made history, hovering above Jezero Crater, demonstrating that powered, controlled flight on another planet is possible.
Monday, NASA’s Ingenuity Mars Helicopter became the first aircraft in history to make a powered, controlled flight on another planet. The Ingenuity team at the agency’s Jet Propulsion Laboratory in Southern California confirmed the flight succeeded after receiving data from the helicopter via NASA’s Perseverance Mars rover at 6:46 a.m. EDT (3:46 a.m. PDT).
“Ingenuity is the latest in a long and storied tradition of NASA projects achieving a space exploration goal once thought impossible,” said acting NASA Administrator Steve Jurczyk. “The X-15 was a pathfinder for the space shuttle. Mars Pathfinder and its Sojourner rover did the same for three generations of Mars rovers. We don’t know exactly where Ingenuity will lead us, but today’s results indicate the sky – at least on Mars – may not be the limit.”
The solar-powered helicopter first became airborne at 3:34 a.m. EDT (12:34 a.m. PDT) – 12:33 Local Mean Solar Time (Mars time) – a time the Ingenuity team determined would have optimal energy and flight conditions. Altimeter data indicate Ingenuity climbed to its prescribed maximum altitude of 10 feet (3 meters) and maintained a stable hover for 30 seconds. It then descended, touching back down on the surface of Mars after logging a total of 39.1 seconds of flight. Additional details on the test are expected in upcoming downlinks.
Ingenuity’s initial flight demonstration was autonomous – piloted by onboard guidance, navigation, and control systems running algorithms developed by the team at JPL. Because data must be sent to and returned from the Red Planet over hundreds of millions of miles using orbiting satellites and NASA’s Deep Space Network, Ingenuity cannot be flown with a joystick, and its flight was not observable from Earth in real time.
NASA Associate Administrator for Science Thomas Zurbuchen announced the name for the Martian airfield on which the flight took place.
“Now, 117 years after the Wright brothers succeeded in making the first flight on our planet, NASA’s Ingenuity helicopter has succeeded in performing this amazing feat on another world,” Zurbuchen said. “While these two iconic moments in aviation history may be separated by time and 173 million miles of space, they now will forever be linked. As an homage to the two innovative bicycle makers from Dayton, this first of many airfields on other worlds will now be known as Wright Brothers Field, in recognition of the ingenuity and innovation that continue to propel exploration.”
Oxygen in the atmosphere may not be an entirely reliable ‘biosignature,’ but there are ways to distinguish false positives from signs of life, scientists say.
In the search for life on other planets, the presence of oxygen in a planet’s atmosphere is one potential sign of biological activity that might be detected by future telescopes. A new study, however, describes several scenarios in which a lifeless rocky planet around a sun-like star could evolve to have oxygen in its atmosphere.
The new findings, published April 13 in AGU Advances, highlight the need for next-generation telescopes that are capable of characterizing planetary environments and searching for multiple lines of evidence for life in addition to detecting oxygen.
“This is useful because it shows there are ways to get oxygen in the atmosphere without life, but there are other observations you can make to help distinguish these false positives from the real deal,” said first author Joshua Krissansen-Totton, a Sagan Fellow in the Department of Astronomy and Astrophysics at UC Santa Cruz. “For each scenario, we try to say what your telescope would need to be able to do to distinguish this from biological oxygen.”
In the coming decades, perhaps by the late 2030s, astronomers hope to have a telescope capable of taking images and spectra of potentially Earth-like planets around sun-like stars. Coauthor Jonathan Fortney, professor of astronomy and astrophysics and director of UCSC’s Other Worlds Laboratory, said the idea would be to target planets similar enough to Earth that life might have emerged on them and characterize their atmospheres.
“There has a been a lot of discussion about whether detection of oxygen is ‘enough’ of a sign of life,” he said. “This work really argues for needing to know the context of your detection. What other molecules are found in addition to oxygen, or not found, and what does that tell you about the planet’s evolution?”
This means astronomers will want a telescope that is sensitive to a broad range of wavelengths in order to detect different types of molecules in a planet’s atmosphere.
The researchers based their findings on a detailed, end-to-end computational model of the evolution of rocky planets, starting from their molten origins and extending through billions of years of cooling and geochemical cycling. By varying the initial inventory of volatile elements in their model planets, the researchers obtained a surprisingly wide range of outcomes.
Oxygen can start to build up in a planet’s atmosphere when high-energy ultraviolet light splits water molecules in the upper atmosphere into hydrogen and oxygen. The lightweight hydrogen preferentially escapes into space, leaving the oxygen behind. Other processes can remove oxygen from the atmosphere. Carbon monoxide and hydrogen released by outgassing from molten rock, for example, will react with oxygen, and weathering of rock also mops up oxygen. These are just a few of the processes the researchers incorporated into their model of the geochemical evolution of a rocky planet.
“If you run the model for Earth, with what we think was the initial inventory of volatiles, you reliably get the same outcome every time–without life you don’t get oxygen in the atmosphere,” Krissansen-Totton said. “But we also found multiple scenarios where you can get oxygen without life.”
For example, a planet that is otherwise like Earth but starts off with more water will end up with very deep oceans, putting immense pressure on the crust. This effectively shuts down geological activity, including all of the processes such as melting or weathering of rocks that would remove oxygen from the atmosphere.
In the opposite case, where the planet starts off with a relatively small amount of water, the magma surface of the initially molten planet can freeze quickly while the water remains in the atmosphere. This “steam atmosphere” puts enough water in the upper atmosphere to allow accumulation of oxygen as the water breaks up and hydrogen escapes.
“The typical sequence is that the magma surface solidifies simultaneously with water condensing out into oceans on the surface,” Krissansen-Totton said. “On Earth, once water condensed on the surface, escape rates were low. But if you retain a steam atmosphere after the molten surface has solidified, there’s a window of about a million years when oxygen can build up because there are high water concentrations in the upper atmosphere and no molten surface to consume the oxygen produced by hydrogen escape.”
A third scenario that can lead to oxygen in the atmosphere involves a planet that is otherwise like Earth but starts off with a higher ratio of carbon dioxide to water. This leads to a runaway greenhouse effect, making it too hot for water to ever condense out of the atmosphere onto the surface of the planet.
“In this Venus-like scenario, all the volatiles start off in the atmosphere and few are left behind in the mantle to be outgassed and mop up oxygen,” Krissansen-Totton said.
He noted that previous studies have focused on atmospheric processes, whereas the model used in this study explores the geochemical and thermal evolution of the planet’s mantle and crust, as well as the interactions between the crust and atmosphere.
“It’s not computationally intensive, but there are a lot of moving parts and interconnected processes,” he said.
First we need to know more about molecules in the atmosphere. Scientists shed more light on molecules linked to life on other planets.
To confirm life on other planets, we need to detect far more molecules in their atmospheres than we currently do to rule out non-biological chemical processes.
The search for life on other planets has received a major boost after scientists revealed the spectral signatures of almost 1000 atmospheric molecules that may be involved in the production or consumption of phosphine, a study led by UNSW Sydney revealed.
Scientists have long conjectured that phosphine – a chemical compound made of one phosphorous atom surrounded by three hydrogen atoms (PH3) – may indicate evidence of life if found in the atmospheres of small rocky planets like our own, where it is produced by the biological activity of bacteria.
So when an international team of scientists last year claimed to have detected phosphine in the atmosphere of Venus, it raised the tantalising prospect of the first evidence of life on another planet – albeit the primitive, single-celled variety.
Now an international team, led by UNSW Sydney scientists, has made a key contribution to this and any future searches for life on other planets by demonstrating how an initial detection of a potential biosignature must be followed by searches for related molecules.
In a paper published today in the journal Frontiers in Astronomy and Space Sciences, they described how the team used computer algorithms to produce a database of approximate infrared spectral barcodes for 958 molecular species containing phosphorous.
Look and learn
As UNSW School of Chemistry’s Dr Laura McKemmish explains, when scientists look for evidence of life on other planets, they don’t need to go into space, they can simply point a telescope at the planet in question.
“To identify life on a planet, we need spectral data,” she says.
“With the right spectral data, light from a planet can tell you what molecules are in the planet’s atmosphere.”
Phosphorus is an essential element for life, yet up until now, she says, astronomers could only look for one polyatomic phosphorus-containing molecule, phosphine.
“Phosphine is a very promising biosignature because it is only produced in tiny concentrations by natural processes. However, if we can’t trace how it is produced or consumed, we can’t answer the question of whether it is unusual chemistry or little green men who are producing phosphine on a planet,” says Dr McKemmish.
To provide insight, Dr McKemmish brought together a large interdisciplinary team to understand how phosphorus behaves chemically, biologically and geologically and ask how this can be investigated remotely through atmospheric molecules alone.
“What was great about this study is that it brought together scientists from disparate fields – chemistry, biology, geology – to address these fundamental questions around the search for life elsewhere that one field alone could not answer,” says astrobiologist and co-author on the study, Associate Professor Brendan Burns.
Dr McKemmish continues: “At the start, we looked for which phosphorous-bearing molecules – what we called P-molecules – are most important in atmospheres but it turns out very little is known. So we decided to look at a large number of P-molecules that could be found in the gas-phase which would otherwise go undetected by telescopes sensitive to infrared light.”
Barcode data for new molecular species are normally produced for one molecule at a time, Dr McKemmish says, a process that often takes years. But the team involved in this research used what she calls “high-throughput computational quantum chemistry” to predict the spectra of 958 molecules within only a couple of weeks.
“Though this new dataset doesn’t yet have the accuracy to enable new detections, it can help prevent misassignments by highlighting the potential for multiple molecular species having similar spectral barcodes – for example, at low resolution with some telescopes, water and alcohol could be indistinguishable.
“The data can also be used to rank how easy a molecule is to detect. For example, counter-intuitively, alien astronomers looking at Earth would find it much easier to detect 0.04% CO2 in our atmosphere than the 20% O2. This is because CO2 absorbs light much more strongly than O2 – this is actually what causes the greenhouse effect on Earth.”
Life on exoplanets
Regardless of the outcomes from the debate about the existence of phosphine in Venus’s atmosphere and the potential signs of life on the planet, this recent addition to the knowledge of what can be detected using telescopes will be important in the detection of potential signs of life on exoplanets – planets in other solar systems.
“The only way we’re going to be able to look at exoplanets and see whether there’s life there is to use spectral data collected by telescopes – that is our one and only tool,” says Dr McKemmish.
“Our paper provides a novel scientific approach to following up the detection of potential biosignatures and has relevance to the study of astrochemistry within and outside the Solar System,” says Dr McKemmish. “Further studies will rapidly improve the accuracy of the data and expand the range of molecules considered, paving the way for its use in future detections and identifications of molecules.”
Fellow co-author and CSIRO astronomer Dr Chenoa Tremblay says the team’s contribution will be beneficial as more powerful telescopes come online in the near future.
“This information has come at a critical time in astronomy,” she says.
“A new infrared telescope called the James Web Space Telescope is due to launch later this year and it will be far more sensitive and cover more wavelengths than its predecessors like the Herschel Space Observatory. We will need this information at a very rapid rate to identify new molecules in the data.”
She says although the team’s work was focused on the vibrational motions of molecules detected with telescopes sensitive to infrared light, they are currently working to extend the technique to the radio wavelengths as well.
“This will be important for current and new telescopes like the upcoming Square Kilometre Array to be built in Western Australia.”
When the Huygens probe descended from the Cassini spacecraft in 2005 and gave humans a close-up of Titan’s dense atmosphere, scientists began dreaming of a future mission that would further explore Saturn’s largest moon. Thus, the seeds of the Dragonfly mission were sown. This groundbreaking mission may provide clues to Titan’s habitability, as well as to the chemical processes that lay the groundwork for the emergence of life.
What is Dragonfly?
The Dragonfly mission is scheduled to last at least 32 months and may be extended if the vehicle and instruments on board remain functional. In order to perform its scientific tasks, Dragonfly will travel around the moon using an “8-bladed rotorcraft,” or a drone. Exploring Titan via drone presents many unique challenges. Because Titan’s atmosphere is so dense (1.5 times denser than Earth’s), it may actually be easier for a drone to take flight on the moon. However, because of Titan’s distance from Earth, communication takes too long for NASA scientists to relay real-time commands to the vehicle. Thus, Dragonfly needs to operate autonomously, which includes checking for favorable weather conditions before lifting off.
Designed for Titan’s dense atmosphere and surface conditions, Dragonfly will contain a number of instruments to measure chemical, meteorological, and geological processes: a mass spectrometer for molecular identification, a neutron and gamma-ray spectrometer for surface analysis, a seismometer to measure tectonic movement, flight sensors and radars, and a number of cameras. Dragonfly will collect and test surface material onboard and can return to spots where sample analysis proves tantalizing or inconclusive.
Dr. Rosaly Lopes, a Senior Research Scientist at NASA’s Jet Propulsion Laboratory currently studying geological data from the Cassini mission, said that when the idea of flying a drone on Titan was first proposed, the concept “had not been proven anywhere yet.” NASA’s Ingenuity helicopter is scheduled to explore Mars in spring 2021 as part of the Mars 2020 mission and will represent the first powered flight on another world, if successful. Dragonfly could be the second.
Titan is the Solar System’s second largest moon and is bigger than the planet Mercury. At roughly 886 million miles away, it’s about ten times farther away from the Sun than Earth is. One year on Titan is equivalent to about 29 Earth years. Temperatures can plunge to nearly -300° Fahrenheit on the surface. Those characteristics might make Titan seem like a strange place to seek clues about the emergence of life, but according to Dr. Elizabeth Turtle, Principal Investigator of the Dragonfly Mission, Titan has chemical similarities to early Earth.
“There’s organic material, water at impact craters, cryo-volcanoes, and sunlight as the energy driving the whole thing,” says Turtle. “All the ingredients for life as we know it exist and interact on the surface.”
Titan is the only celestial body apart from Earth that is known to support bodies of liquid like rivers and lakes. However, unlike on the Earth, these features on Titan are comprised of hydrocarbons, such as liquid methane and ethane. Dragonfly will provide data to assess precipitation cycles, moisture evaporation, and cloud formation on the moon.
Understanding the relationship between the moon’s atmosphere and its surface will also help geologists, as, according to Lopes, “[Titan] has the major geologic features that Earth does…including dunes, lakes and seas, erosion by rivers, mountains, and volcanoes.”
What Do Scientists Hope to Learn?
The main objective of Dragonfly is to gain a better understanding of Titan’s chemical progression. Early Earth had a chemical environment similar to Titan and, on Earth, “that chemistry became biology,” says Turtle. But Titan’s chemical past is unknown, and it’s unclear whether it has followed, is following, or will follow a path similar to Earth’s; scientists only know that similar ingredients existed.
“We want to understand those early chemical steps and how far the chemistry has progressed on Titan,” Turtle says.
Much of that chemistry occurs in its atmosphere, which is 95% nitrogen (N2) and 5% methane (CH4). The methane molecules split as they are accelerated by Saturn’s magnetism and the Sun’s ultraviolet light, allowing hydrogen to escape and other molecules to recombine into hydrocarbons. Given the current amount of methane in Titan’s atmosphere, Turtle estimates that “the lifetime of that methane is on the order of 10 million years,” which means Dragonfly will search for information about the methane’s origin and Titan’s atmospheric longevity. Scientists aren’t quite sure how Titan’s atmosphere gets resupplied with methane—it could be stored in reservoirs in the moon’s crust, result from cryo-volcanic eruptions, or emerge from underwater sulfuric vents. Dragonfly may have the opportunity to witness this process firsthand.
The Dragonfly mission will return a plethora of data concerning Titan, data that will shape the scientific path of many early career astrobiologists in the years to come. Dr. Natalie Grefenstette, a postdoctoral fellow at the Santa Fe Institute who holds a PhD in prebiotic chemistry, says the scientific community is “excited to see what the environment [on Titan] is naturally producing.”
The mission’s focus on the moon’s chemistry will provide insights about whether Titan could support life now or in the past. Instead of restricting Dragonfly’s analysis of samples to the molecules scientists have identified as fundamental to terrestrial life, Grefenstette hopes the mission will uncover unexpected “evidence of proto-life or life-like systems.” Such discoveries could aid astrobiologists’ understanding of how lifeforms function on other worlds and whether the particular expression of life on Earth is unique.
“Being able to see what happened in [Titan’s] environment will give us perspective on what happened in other environments, as well as on habitability in general,” Turtle says.
Scientists from Japan and NASA have confirmed the presence in meteorites of a key organic molecule which may have been used to build other organic molecules, including some used by life. The discovery validates theories of the formation of organic compounds in extraterrestrial environments.
The chemistry of life runs on organic compounds, molecules containing carbon and hydrogen, which also may include oxygen, nitrogen and other elements. While commonly associated with life, organic molecules also can be created by non-biological processes and are not necessarily indicators of life. An enduring mystery regarding the origin of life is how biology could have arisen from non-biological chemical processes, called prebiotic chemistry. Organic molecules from meteorites may be one of the sources of organic compounds that led to the emergence of life on Earth.
Associate Professor Yasuhiro Oba from Hokkaido University, Japan, led an international team of researchers who discovered the presence of a prebiotic organic molecule called hexamethylenetetramine (HMT) in three different carbon-rich meteorites. Their discovery validates models and theories that propose HMT as an important molecule in the formation of organic compounds in interstellar environments.
“HMT is a key piece of a puzzle which draws the whole picture of chemical evolution in space,” said Oba, lead author of a paper about the research published December 7 in the journal Nature Communications. “To explain the formation of meteoritic organic molecules such as amino acids and sugars, two easily vaporized (volatile) molecules, formaldehyde and ammonia, are necessary in asteroids, the parent bodies of many meteorites. However, since they are easily lost from asteroidal environments due to their high volatility, scientists question how enough could have been available to build the meteoritic organic molecules being found. HMT does not vaporize even at room temperature, and it can produce both molecules if it is heated with liquid water inside asteroids. Finding HMT in meteorites confirms the hypothesis that it is a stable source for ammonia and formaldehyde in asteroids.”
Early in the solar system’s history, many asteroids could have been heated by collisions or the decay of radioactive elements. If some asteroids were warm enough and had liquid water, HMT could have broken down to provide building blocks such as formaldehyde and ammonia that in turn reacted to make other important biological molecules which have been found in meteorites, including amino acids. Some types of amino acids are used by life to make proteins, which are used to build structures like hair and nails, or to speed up or regulate chemical reactions.
“These results shed light on the various ways amino acids can form in extraterrestrial environments,” said Jason Dworkin, a co-author of the paper at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This can be explored further when comparing the samples from Japan’s Hayabusa2 and NASA’s OSIRIS-REx missions. These spacecraft collected material from asteroids with what appears to be different histories of liquid water. If there is a mission to return a sample from a comet nucleus someday, perhaps we can see if there is a connection between HMT in comets and asteroids.”
While the diversity of organic compounds in meteorites is well-documented, many questions remain about the processes by which these compounds were formed. The most important meteorites in this area of research are carbonaceous chondrites, stony meteorites that contain high percentages of water and organic compounds. Experimental models have shown that a combination of water, ammonia and methanol, when subjected to photochemical and thermal conditions common in extraterrestrial environments, give rise to a number of organic compounds, the most common of which is HMT. Interstellar ice is rich in methanol. Hypothetically, HMT should be common in water-containing extraterrestrial materials, but, until this study, it had not been detected.
HMT is likely to break apart when exposed to processes commonly used in the analysis of organic compounds in meteorites, and therefore, may not have been detected in other studies even though it was present. The scientists developed a method that specifically extracted HMT from meteorites with minimal breakdown. This method allowed them to isolate significant quantities of HMT and HMT derivatives from the meteorites Murchison, Murray and Tagish Lake.
Since Earth has abundant life, the researchers had to be confident that the HMT found in the meteorites was in fact extraterrestrial, and not just from contamination by terrestrial life. “The Murchison fragment used in this study was from the Chicago Field Museum that had been stored for many years inside a sealed container, and is the least contaminated and most pristine piece of Murchison we have ever studied for amino acids, giving us more confidence that the HMT detected in this meteorite is in fact extraterrestrial in origin,” said Daniel Glavin of NASA Goddard, a co-author on the study.
This work was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI (JP15H05749, JP16H04083, JP17H04862, JP20H00202), the National Aeronautics and Space Administration (NASA) Astrobiology Institute through the Goddard Center for Astrobiology (13-13NAI7-0032), NASA’s Planetary Science Division Internal Scientist Funding Program through the Fundamental Laboratory Research (FLaRe) work package at NASA Goddard Space Flight Center, and the Simons Foundation (SCOL award 302497).
Yasuhiro Oba is part of the Astrophysical Chemistry/Ice & Planetary Science Group at the Institute of Low Temperature Science, where he studies chemical evolution of compounds at scales from molecular clouds to planetary systems.
A planet in an unlikely orbit around a double star 336 light-years away may offer a clue to a mystery much closer to home: a hypothesized, distant body in our solar system dubbed “Planet Nine.”
This is the first time that astronomers have been able to measure the motion of a massive Jupiter-like planet that is orbiting very far away from its host stars and visible debris disk. This disk is similar to our Kuiper Belt of small, icy bodies beyond Neptune. In our own solar system, the suspected Planet Nine would also lie far outside of the Kuiper Belt on a similarly strange orbit. Though the search for a Planet Nine continues, this exoplanet discovery is evidence that such oddball orbits are possible.
“This system draws a potentially unique comparison with our solar system,” explained the paper’s lead author, Meiji Nguyen of the University of California, Berkeley. “It’s very widely separated from its host stars on an eccentric and highly misaligned orbit, just like the prediction for Planet Nine. This begs the question of how these planets formed and evolved to end up in their current configuration.”
The system where this gas giant resides is only 15 million years old. This suggests that our Planet Nine — if it does exist — could have formed very early on in the evolution of our 4.6-billion-year-old solar system.
An Extreme Orbit
The 11-Jupiter-mass exoplanet called HD 106906 b was discovered in 2013 with the Magellan Telescopes at the Las Campanas Observatory in the Atacama Desert of Chile. However, astronomers did not know anything about the planet’s orbit. This required something only the Hubble Space Telescope could do: collect very accurate measurements of the vagabond’s motion over 14 years with extraordinary precision. The team used data from the Hubble archive that provided evidence for this motion.
The exoplanet resides extremely far from its host pair of bright, young stars — more than 730 times the distance of Earth from the Sun, or nearly 68 billion miles. This wide separation made it enormously challenging to determine the 15,000-year-long orbit in such a relatively short time span of Hubble observations. The planet is creeping very slowly along its orbit, given the weak gravitational pull of its very distant parent stars.
The Hubble team was surprised to find that the remote world has an extreme orbit that is very misaligned, elongated and external to the debris disk that surrounds the exoplanet’s twin host stars. The debris disk itself is very unusual-looking, perhaps due to the gravitational tug of the wayward planet.
How Did It Get There?
So how did the exoplanet arrive at such a distant and strangely inclined orbit? The prevailing theory is that it formed much closer to its stars, about three times the distance that Earth is from the Sun. But drag within the system’s gas disk caused the planet’s orbit to decay, forcing it to migrate inward toward its stellar pair. The gravitational effects from the whirling twin stars then kicked it out onto an eccentric orbit that almost threw it out of the system and into the void of interstellar space. Then a passing star from outside the system stabilized the exoplanet’s orbit and prevented it from leaving its home system.
Using precise distance and motion measurements from the European Space Agency’s Gaia survey satellite, candidate passing stars were identified in 2019 by team members Robert De Rosa of the European Southern Observatory in Santiago, Chile, and Paul Kalas of the University of California.
A Messy Disk
In a study published in 2015, Kalas led a team that found circumstantial evidence for the runaway planet’s behavior: the system’s debris disk is strongly asymmetric, rather than being a circular “pizza pie” distribution of material. One side of the disk is truncated relative to the opposite side, and it is also disturbed vertically rather than being restricted to a narrow plane as seen on the opposite side of the stars.
“The idea is that every time the planet comes to its closest approach to the binary star, it stirs up the material in the disk,” explains De Rosa. “So every time the planet comes through, it truncates the disk and pushes it up on one side. This scenario has been tested with simulations of this system with the planet on a similar orbit — this was before we knew what the orbit of the planet was.”
“It’s like arriving at the scene of a car crash, and you’re trying to reconstruct what happened,” explained Kalas. “Is it passing stars that perturbed the planet, then the planet perturbed the disk? Is it the binary in the middle that first perturbed the planet, and then it perturbed the disk? Or did passing stars disturb both the planet and disk at the same time? This is astronomy detective work, gathering the evidence we need to come up with some plausible storylines about what happened here.”
A Planet Nine Proxy?
This scenario for HD 106906 b’s bizarre orbit is similar in some ways to what may have caused the hypothetical Planet Nine to end up in the outer reaches of our own solar system, well beyond the orbit of the other planets and beyond the Kuiper Belt. Planet Nine could have formed in the inner solar system and been kicked out by interactions with Jupiter. However, Jupiter — the proverbial 800-pound gorilla in our solar system — would very likely have flung Planet Nine far beyond Pluto. Passing stars may have stabilized the orbit of the kicked-out planet by pushing the orbit path away from Jupiter and the other planets in the inner solar system.
“It’s as if we have a time machine for our own planetary system going back 4.6 billion years to see what may have happened when our young solar system was dynamically active and everything was being jostled around and rearranged,” said Kalas.
To date, astronomers only have circumstantial evidence for Planet Nine. They’ve found a cluster of small celestial bodies beyond Neptune that move in unusual orbits compared with the rest of the solar system. This configuration, some astronomers say, suggests these objects were shepherded together by the gravitational pull of a huge, unseen planet. An alternative theory is that there is not one giant perturbing planet, but instead the imbalance is due to the combined gravitational influence of multiple, much smaller objects. Another theory is that Planet Nine does not exist at all and the clustering of smaller bodies may be just a statistical anomaly.
A Target for the Webb Telescope
Scientists using NASA’s upcoming James Webb Space Telescope plan to get data on HD 106906 b to understand the planet in detail. “One question you could ask is: Does the planet have its own debris system around it? Does it capture material every time it goes close to the host stars? And you’d be able to measure that with the thermal infrared data from Webb,” said De Rosa. “Also, in terms of helping to understand the orbit, I think Webb would be useful for helping to confirm our result.”
Because Webb is sensitive to smaller, Saturn-mass planets, it may be able to detect other exoplanets that have been ejected from this and other inner planetary systems. “With Webb, we can start to look for planets that are both a little bit older and a little bit fainter,” explained Nguyen. The unique sensitivity and imaging capabilities of Webb will open up new possibilities for detecting and studying these unconventional planets and systems.
The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.
An international team of scientists have shown that glycine, the simplest amino acid and an important building block of life, can form under the harsh conditions that govern chemistry in space.
The results, published in Nature Astronomy, suggest that glycine, and very likely other amino acids, form in dense interstellar clouds well before they transform into new stars and planets.
Comets are the most pristine material in our Solar System and reflect the molecular composition present at the time our Sun and planets were just about to form. The detection of glycine in the coma of comet 67P/Churyumov-Gerasimenko and in samples returned to Earth from the Stardust mission suggests that amino acids, such as glycine, form long before stars. However until recently, it was thought that glycine formation required energy, setting clear constraints to the environment in which it can be formed.
In the new study the international team of astrophysicists and astrochemical modelers, mostly based at the Laboratory for Astrophysics at Leiden Observatory, the Netherlands, have shown that it is possible for glycine to form on the surface of icy dust grains, in the absence of energy, through ‘dark chemistry’. The findings contradict previous studies that have suggested UV radiation was required to produce this molecule.
Dr Sergio Ioppolo, from Queen Mary University of London and lead author of the article, said: “Dark chemistry refers to chemistry without the need of energetic radiation. In the laboratory we were able to simulate the conditions in dark interstellar clouds where cold dust particles are covered by thin layers of ice and subsequently processed by impacting atoms causing precursor species to fragment and reactive intermediates to recombine.”
The scientists first showed methylamine, the precursor species of glycine that was detected in the coma of the comet 67P, could form. Then, using a unique ultra-high vacuum setup, equipped with a series of atomic beam lines and accurate diagnostic tools, they were able to confirm glycine could also be formed, and that the presence of water ice was essential in this process.
Further investigation using astrochemical models confirmed the experimental results and allowed the researchers to extrapolate data obtained on a typical laboratory timescale of just one day to interstellar conditions, bridging millions of years. “From this we find that low but substantial amounts of glycine can be formed in space with time,” said Professor Herma Cuppen from Radboud University, Nijmegen, who was responsible for some of the modelling studies within the paper.
“The important conclusion from this work is that molecules that are considered building blocks of life already form at a stage that is well before the start of star and planet formation,” said Harold Linnartz, Director of the Laboratory for Astrophysics at Leiden Observatory. “Such an early formation of glycine in the evolution of star-forming regions implies that this amino acid can be formed more ubiquitously in space and is preserved in the bulk of ice before inclusion in comets and planetesimals that make up the material from which ultimately planets are made.”
“Once formed, glycine can also become a precursor to other complex organic molecules,” concluded Dr Ioppolo. “Following the same mechanism, in principle, other functional groups can be added to the glycine backbone, resulting in the formation of other amino acids, such as alanine and serine in dark clouds in space. In the end, this enriched organic molecular inventory is included in celestial bodies, like comets, and delivered to young planets, as happened to our Earth and many other planets.”
In a new video from the NASA Astrobiology Program, astrobiologists Dr. Jason Dworkin and Dr. Scott Sandford explain the importance of the OSIRIS-REx mission in the quest to understand the role that asteroids and other small bodies play in the origins of life on Earth.
OSIRIS-REx & the Origin of Life
Dr. Jason Dworkin(NASA Goddard Space Flight Center): Asteroids are remnants of the early solar system. They are leftover pieces as the solar system was forming, and around the same time that life was forming on the early earth or other bodies. And so the same chemistry that was happening that could have influenced the origin of life is preserved on these relics of the solar system.
Dr. Scott Sandford(NASA Ames Research Center): You know, you can’t have a life on a planet unless you have a biosphere, which means you have to have all the appropriate carbon, oxygen, hydrogen, nitrogen, all kinds of elements you need for life, and so, if those aren’t delivered then you’re not going to get anywhere.
Obviously, OSIRIS-REx is visiting one of these objects and it’s not just visiting any old asteroid; it’s visiting a really appropriate one for these questions about astrobiology because it’s a class of asteroid which we believe is associated with a type of meteorite called carbonaceous chondrites, which are amongst the most richest meteorites in terms of their carbon abundance, and also their molecular complexity.
So, OSIRIS-REx can then attack these various issues in several ways. Of course, one is we have some instruments on board the spacecraft which will give us a global look at the asteroid.
Dworkin: Sample return is the prime objective for the OSIRIS-REx mission. So, for fun, here is a LEGO version of the spacecraft: it has articulated solar arrays, a sample return canister and this three-meter long arm, and at the end of this is sort of like an old, car air filter but, of course, a bespoke design for this mission and for this asteroid, to collect a sample of material and bring it back to earth by touching the surface of the asteroid, collecting at least 60 grams, and as much as two kilograms of material; then, go up and measure the mass of the material, and then stow it in the sample return canister and bring it back to earth.
So when we get these samples back we’re going to be interested in these aspects of the samples: what are their bulk elemental abundances? And also, what kinds of specific compounds are present and what can they tell us about how they formed and where they formed and when they form? And, in particular, could any of these molecules have played a role in helping get life started on the Earth, or you know, any other place?
One of the huge advantages of a sample return mission is that when you get the sample back to the Earth you’ve effectively added all the world’s analytical instruments to the payload of your spacecraft. Okay, so you can afford to do analyses of the return samples that would never happen on the spacecraft. Some of the instruments we’ll use to study the return samples are not just bigger than the spacecraft, they’re bigger than the launch pad the spacecraft left from!
That will allow us to take a portion of the asteroid and really dig deep into what’s there, and then, because we have the global data from the in-situ instruments, we can then put all that information in the context of the asteroid as a whole.Samples will be studied by people not yet born, using techniques not yet invented, to answer questions not yet asked. DR. JASON DWORKINNASA Goddard Space Flight Center
Dworkin: 60 grams of sample is a bounty. If you look at, say the Stardust mission, it brought back maybe a milligram of material from comet Wild-2. That revolutionized our understanding of solar system dynamics and solar system formation.
So 60 grams, which is our baseline, is a huge bounty for the chemistry and astrobiology community. The most exciting aspect of this mission is that when we collect the sample, 75 percent of this is archived for future generations. So, samples will be studied by people not yet born, using techniques not yet invented, to answer questions not yet asked.
People who are in school now can make life choices to enable them to study the samples and ask questions that you just can’t think of today or just don’t have the ability to analyze.
Sandford: It’s just hard to overstate the power the scientific power you get out of this this is why missions like OSIRIS-REx are just so powerful it’s because mission gives you a legacy that just extends on into the future and never really ends.
As the icy, ocean-filled moon Europa orbits Jupiter, it withstands a relentless pummeling of radiation. Jupiter zaps Europa’s surface night and day with electrons and other particles, bathing it in high-energy radiation. But as these particles pound the moon’s surface, they may also be doing something otherworldly: making Europa glow in the dark.
New research from scientists at NASA’s Jet Propulsion Laboratory in Southern California details for the first time what the glow would look like, and what it could reveal about the composition of ice on Europa’s surface. Different salty compounds react differently to the radiation and emit their own unique glimmer. To the naked eye, this glow would look sometimes slightly green, sometimes slightly blue or white and with varying degrees of brightness, depending on what material it is.
Scientists use a spectrometer to separate the light into wavelengths and connect the distinct “signatures,” or spectra, to different compositions of ice. Most observations using a spectrometer on a moon like Europa are taken using reflected sunlight on the moon’s dayside, but these new results illuminate what Europa would look like in the dark.
“We were able to predict that this nightside ice glow could provide additional information on Europa’s surface composition. How that composition varies could give us clues about whether Europa harbors conditions suitable for life,” said JPL’s Murthy Gudipati, lead author of the work published Nov. 9 in Nature Astronomy.
That’s because Europa holds a massive, global interior ocean that could percolate to the surface through the moon’s thick crust of ice. By analyzing the surface, scientists can learn more about what lies beneath.
Shining a Light
Scientists have inferred from prior observations that Europa’s surface could be made of a mix of ice and commonly known salts on Earth, such as magnesium sulfate (Epsom salt) and sodium chloride (table salt). The new research shows that incorporating those salts into water ice under Europa-like conditions and blasting it with radiation produces a glow.
That much was not a surprise. It’s easy to imagine an irradiated surface glowing. Scientists know the shine is caused by energetic electrons penetrating the surface, energizing the molecules underneath. When those molecules relax, they release energy as visible light.
“But we never imagined that we would see what we ended up seeing,” said JPL’s Bryana Henderson, who co-authored the research. “When we tried new ice compositions, the glow looked different. And we all just stared at it for a while and then said, ‘This is new, right? This is definitely a different glow?’ So we pointed a spectrometer at it, and each type of ice had a different spectrum.”
To study a laboratory mockup of Europa’s surface, the JPL team built a unique instrument called Ice Chamber for Europa’s High-Energy Electron and Radiation Environment Testing (ICE-HEART). They took ICE-HEART to a high-energy electron beam facility in Gaithersburg, Maryland, and started the experiments with an entirely different study in mind: to see how organic material under Europa ice would react to blasts of radiation.
They didn’t expect to see variations in the glow itself tied to different ice compositions. It was – as the authors called it – serendipity.
“Seeing the sodium chloride brine with a significantly lower level of glow was the ‘aha’ moment that changed the course of the research,” said Fred Bateman, co-author of the paper. He helped conduct the experiment and delivered radiation beams to the ice samples at the Medical Industrial Radiation Facility at the National Institute of Standards and Technology in Maryland.
A moon that’s visible in a dark sky may not seem unusual; we see our own Moon because it reflects sunlight. But Europa’s glow is caused by an entirely different mechanism, the scientists said. Imagine a moon that glows continuously, even on its nightside – the side facing away from the Sun.
“If Europa weren’t under this radiation, it would look the way our moon looks to us – dark on the shadowed side,” Gudipati said. “But because it’s bombarded by the radiation from Jupiter, it glows in the dark.”
Set to launch in the mid-2020s, NASA’s upcoming flagship mission Europa Clipper will observe the moon’s surface in multiple flybys while orbiting Jupiter. Mission scientists are reviewing the authors’ findings to evaluate if a glow would be detectable by the spacecraft’s science instruments. It’s possible that information gathered by the spacecraft could be matched with the measurements in the new research to identify the salty components on the moon’s surface or narrow down what they might be.
“It’s not often that you’re in a lab and say, ‘We might find this when we get there,'” Gudipati said. “Usually it’s the other way around – you go there and find something and try to explain it in the lab. But our prediction goes back to a simple observation, and that’s what science is about.”
Missions such as Europa Clipper help contribute to the field of astrobiology, the interdisciplinary research on the variables and conditions of distant worlds that could harbor life as we know it. While Europa Clipper is not a life-detection mission, it will conduct detailed reconnaissance of Europa and investigate whether the icy moon, with its subsurface ocean, has the capability to support life. Understanding Europa’s habitability will help scientists better understand how life developed on Earth and the potential for finding life beyond our planet.
NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) has confirmed, for the first time, water on the sunlit surface of the Moon. This discovery indicates that water may be distributed across the lunar surface, and not limited to cold, shadowed places.
SOFIA has detected water molecules (H2O) in Clavius Crater, one of the largest craters visible from Earth, located in the Moon’s southern hemisphere. Previous observations of the Moon’s surface detected some form of hydrogen, but were unable to distinguish between water and its close chemical relative, hydroxyl (OH). Data from this location reveal water in concentrations of 100 to 412 parts per million – roughly equivalent to a 12-ounce bottle of water – trapped in a cubic meter of soil spread across the lunar surface. The results are published in the latest issue of Nature Astronomy.
“We had indications that H2O – the familiar water we know – might be present on the sunlit side of the Moon,” said Paul Hertz, director of the Astrophysics Division in the Science Mission Directorate at NASA Headquarters in Washington. “Now we know it is there. This discovery challenges our understanding of the lunar surface and raises intriguing questions about resources relevant for deep space exploration.”
As a comparison, the Sahara desert has 100 times the amount of water than what SOFIA detected in the lunar soil. Despite the small amounts, the discovery raises new questions about how water is created and how it persists on the harsh, airless lunar surface.
Water is a precious resource in deep space and a key ingredient of life as we know it. Whether the water SOFIA found is easily accessible for use as a resource remains to be determined. Under NASA’s Artemis program, the agency is eager to learn all it can about the presence of water on the Moon in advance of sending the first woman and next man to the lunar surface in 2024 and establishing a sustainable human presence there by the end of the decade.
SOFIA’s results build on years of previous research examining the presence of water on the Moon. When the Apollo astronauts first returned from the Moon in 1969, it was thought to be completely dry. Orbital and impactor missions over the past 20 years, such as NASA’s Lunar Crater Observation and Sensing Satellite, confirmed ice in permanently shadowed craters around the Moon’s poles. Meanwhile, several spacecraft – including the Cassini mission and Deep Impact comet mission, as well as the Indian Space Research Organization’s Chandrayaan-1 mission – and NASA’s ground-based Infrared Telescope Facility, looked broadly across the lunar surface and found evidence of hydration in sunnier regions. Yet those missions were unable to definitively distinguish the form in which it was present – either H2O or OH.
“Prior to the SOFIA observations, we knew there was some kind of hydration,” said Casey Honniball, the lead author who published the results from her graduate thesis work at the University of Hawaii at Mānoa in Honolulu. “But we didn’t know how much, if any, was actually water molecules – like we drink every day – or something more like drain cleaner.”
SOFIA offered a new means of looking at the Moon. Flying at altitudes of up to 45,000 feet, this modified Boeing 747SP jetliner with a 106-inch diameter telescope reaches above 99% of the water vapor in Earth’s atmosphere to get a clearer view of the infrared universe. Using its Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST), SOFIA was able to pick up the specific wavelength unique to water molecules, at 6.1 microns, and discovered a relatively surprising concentration in sunny Clavius Crater.
“Without a thick atmosphere, water on the sunlit lunar surface should just be lost to space,” said Honniball, who is now a postdoctoral fellow at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Yet somehow we’re seeing it. Something is generating the water, and something must be trapping it there.”
Several forces could be at play in the delivery or creation of this water. Micrometeorites raining down on the lunar surface, carrying small amounts of water, could deposit the water on the lunar surface upon impact. Another possibility is there could be a two-step process whereby the Sun’s solar wind delivers hydrogen to the lunar surface and causes a chemical reaction with oxygen-bearing minerals in the soil to create hydroxyl. Meanwhile, radiation from the bombardment of micrometeorites could be transforming that hydroxyl into water.
How the water then gets stored – making it possible to accumulate – also raises some intriguing questions. The water could be trapped into tiny beadlike structures in the soil that form out of the high heat created by micrometeorite impacts. Another possibility is that the water could be hidden between grains of lunar soil and sheltered from the sunlight – potentially making it a bit more accessible than water trapped in beadlike structures.
For a mission designed to look at distant, dim objects such as black holes, star clusters, and galaxies, SOFIA’s spotlight on Earth’s nearest and brightest neighbor was a departure from business as usual. The telescope operators typically use a guide camera to track stars, keeping the telescope locked steadily on its observing target. But the Moon is so close and bright that it fills the guide camera’s entire field of view. With no stars visible, it was unclear if the telescope could reliably track the Moon. To determine this, in August 2018, the operators decided to try a test observation.
“It was, in fact, the first time SOFIA has looked at the Moon, and we weren’t even completely sure if we would get reliable data, but questions about the Moon’s water compelled us to try,” said Naseem Rangwala, SOFIA’s project scientist at NASA’s Ames Research Center in California’s Silicon Valley. “It’s incredible that this discovery came out of what was essentially a test, and now that we know we can do this, we’re planning more flights to do more observations.”
SOFIA’s follow-up flights will look for water in additional sunlit locations and during different lunar phases to learn more about how the water is produced, stored, and moved across the Moon. The data will add to the work of future Moon missions, such as NASA’s Volatiles Investigating Polar Exploration Rover (VIPER), to create the first water resource maps of the Moon for future human space exploration.
In the same issue of Nature Astronomy, scientists have published a paper using theoretical models and NASA’s Lunar Reconnaissance Orbiter data, pointing out that water could be trapped in small shadows, where temperatures stay below freezing, across more of the Moon than currently expected. The results can be found here.
“Water is a valuable resource, for both scientific purposes and for use by our explorers,” said Jacob Bleacher, chief exploration scientist for NASA’s Human Exploration and Operations Mission Directorate. “If we can use the resources at the Moon, then we can carry less water and more equipment to help enable new scientific discoveries.”
SOFIA is a joint project of NASA and the German Aerospace Center. Ames manages the SOFIA program, science, and mission operations in cooperation with the Universities Space Research Association, headquartered in Columbia, Maryland, and the German SOFIA Institute at the University of Stuttgart. The aircraft is maintained and operated by NASA’s Armstrong Flight Research Center Building 703, in Palmdale, California.
Three decades after Cornell astronomer Carl Sagan suggested that Voyager 1 snap Earth’s picture from billions of miles away – resulting in the iconic Pale Blue Dot photograph – two astronomers now offer another unique cosmic perspective. Some exoplanets – planets from beyond our own solar system – have a direct line of sight to observe Earth’s biological qualities from far, far away.
Lisa Kaltenegger, associate professor of astronomy in the College of Arts and Sciences and director of Cornell’s Carl Sagan Institute; and Joshua Pepper, associate professor of physics at Lehigh University, have identified 1,004 main-sequence stars (similar to our sun) that might contain Earth-like planets in their own habitable zones – all within about 300 light-years of Earth – and which should be able to detect Earth’s chemical traces of life.
“Let’s reverse the viewpoint to that of other stars and ask from which vantage point other observers could find Earth as a transiting planet,” Kaltenegger said. A transiting planet is one that passes through the observer’s line of sight to another star, such as the sun, revealing clues as to the makeup of the planet’s atmosphere.
“If observers were out there searching, they would be able to see signs of a biosphere in the atmosphere of our Pale Blue Dot,” she said, “And we can even see some of the brightest of these stars in our night sky without binoculars or telescopes.”
Transit observations are a crucial tool for Earth’s astronomers to characterize inhabited extrasolar planets, Kaltenegger said, which astronomers will start to use with the launch of NASA’s James Webb Space telescope next year.
But which stars systems could find us? Holding the key to this science is Earth’s ecliptic – the plane of Earth’s orbit around the Sun. The ecliptic is where the exoplanets with a view of Earth would be located, as they will be the places able to see Earth crossing its own sun – effectively providing observers a way to discover our planet’s vibrant biosphere.
“Only a very small fraction of exoplanets will just happen to be randomly aligned with our line of sight so we can see them transit.” Pepper said. ”But all of the thousand stars we identified in our paper in the solar neighborhood could see our Earth transit the sun, calling their attention.”
“If we found a planet with a vibrant biosphere, we would get curious about whether or not someone is there looking at us too,” Kaltenegger said.
“If we’re looking for intelligent life in the universe, that could find us and might want to get in touch” she said, “we’ve just created the star map of where we should look first.”
This work was funded by the Carl Sagan Institute and the Breakthrough Initiative.
A growing body of research suggests the planet Venus may have had an Earth-like environment billions of years ago, with water and a thin atmosphere.
Yet testing such theories is difficult without geological samples to examine. The solution, according to Yale astronomers Samuel Cabot and Gregory Laughlin, may be closer than anyone realized.
Cabot and Laughlin say pieces of Venus — perhaps billions of them — are likely to have crashed on the moon. A new study explaining the theory has been accepted by the Planetary Science Journal.
The researchers said asteroids and comets slamming into Venus may have dislodged as many as 10 billion rocks and sent them into an orbit that intersected with Earth and Earth’s moon. “Some of these rocks will eventually land on the moon as Venusian meteorites,” said Cabot, a Yale graduate student and lead author of the study.
Cabot said catastrophic impacts such as these only happen every hundred million years or so — and occurred more frequently billions of years ago.
“The moon offers safe keeping for these ancient rocks,” Cabot said. “Anything from Venus that landed on Earth is probably buried very deep, due to geological activity. These rocks would be much better preserved on the moon.”
Many scientists believe that Venus might have had an Earth-like atmosphere as recently as 700 million years ago. After that, Venus experienced a runaway greenhouse effect and developed its current climate. The Venusian atmosphere is so thick today that no rocks could possibly escape after an impact with an asteroid or comet, Cabot said.
Laughlin and Cabot cited two factors supporting their theory. The first is that asteroids hitting Venus are usually going faster than those that hit Earth, launching even more material. The second is that a huge fraction of the ejected material from Venus would have come close to Earth and the moon.
“There is a commensurability between the orbits of Venus and Earth that provides a ready route for rocks blasted off Venus to travel to Earth’s vicinity,” said Laughlin, who is professor of astronomy and astrophysics at Yale. “The moon’s gravity then aids in sweeping up some of these Venusian arrivals.”
Upcoming missions to the moon could give Cabot and Laughlin their answer soon. The researchers said NASA’s Artemis program is the perfect opportunity to collect and analyze unprecedented amounts of lunar soil.
Laughlin said there are several standard chemical analyses that can pinpoint the origin of moon rocks, including any that came from Venus. Different ratios of specific elements and isotopes offer a kind of fingerprint for each planet in the solar system.
“An ancient fragment of Venus would contain a wealth of information,” Laughlin said. “Venus’ history is closely tied to important topics in planetary science, including the past influx of asteroids and comets, atmospheric histories of the inner planets, and the abundance of liquid water.”
The origins of life on Earth remains one of science’s biggest mysteries. Scientists have long tried to figure out the precursors to both RNA (ribonucleic acid) and DNA (deoxyribonucleic acid), as well as how the two emerged. Dr. Ramanarayanan Krishnamurthy of the Scripps Research Institute investigates possible chemical origins of both RNA and DNA, and his recent publication in Nature Communications raises an intriguing question: could RNA and DNA have arisen together, rather than one emerging before the other?
Scientists agree that the creation of RNA and DNA requires ribose and nucleobases, but they disagree on “what is defined and universally accepted as prebiotically plausible conditions,” writes Krishnamurthy. The fundamental disagreement stems from difficulties of accurately deciphering early fossils, the rarity of those early fossils, the possibility of contamination from currently existing life, and potential analytical errors in their examination. Given those constraints, “There can be no single solution,” says Krishnamurthy. Instead, myriad possibilities remain for how the stage was set for life, not to mention how life actually came to be.
Given the massive time frame of this evolution and the lack of scientific consensus regarding early Earth conditions, trying to figure out the exact combination of chemicals and conditions leading to RNA and DNA is harder than searching for a needle in a haystack. Instead of looking for a single needle, scientists are searching for pieces of infinite different needles and then trying to make sense of what they find.
Exit RNA World Theory?
One popular idea about the emergence of life on Earth, RNA World Theory, was developed by scientists Carl Woese, Francis Crick, and Leslie Orgel in the 1960s. RNA is simpler and more versatile than DNA, so many scientists believe RNA’s nucleic acids comprised life’s main building blocks, which later created proteins that gave rise to DNA. In the 1980s, scientists discovered ribozymes, RNA enzymes that cause chemical reactions. The finding seemed to support RNA World Theory: ribozymes create protein chains by linking amino acids, and they’re involved in processes that enable RNA splicing and reproduction.
However, scientists cast doubt on RNA World Theory for a variety of reasons, including a growing belief in RNA precursor insufficiency. “RNA has catalytic capabilities and information that translates into proteins, but the building blocks of RNA don’t do much,” Krishnamurthy explained. Nearly 60 years after proposing RNA World Theory, scientists still lack evidence of a causal chain linking RNA precursors to life as we know it, and Krishnamurthy’s work has caused at least one scientist to reverse his position on the theory. A 2012 Biology Direct publication called RNA world hypothesis “the worst theory of the early evolution of life (except for all the others).”
If RNA Didn’t Come First, What Did?
In their 1952 “spark” experiment, chemists Stanley Miller and Harold Urey sought to reproduce conditions on early Earth. They used an electric current to replicate a lightning strike to see how it might impact atmospheric gases, which resulted in the production of amino acids. The idea that non-biological molecules can create biological ones has narrowed the focus of further investigations almost solely on amino acids. Life requires amino acids, but “focusing on them hasn’t given us the answer to the chemical origins of life,” Krishnamurthy says. “It’s our duty to see what else is possible.”
Alternatives to RNA World Theory have been springing up, including in Krishnamurthy’s lab. Other nucleotides similar to RNA’s building blocks could have emerged together and other mechanisms could have arisen along with RNA that paved the way for later systems. RNA World Theory is “outliving its usefulness” and according to Krishnamurthy, it “constricts scientists’ views and doesn’t allow new ideas to develop.”
Dr. Martha Grover, Professor of Chemical and Biomolecular Engineering at Georgia’s Institute of Technology, agrees: “constructs like the RNA World Theory are useful to frame our thinking, but they should not be interpreted too strictly.” If scientists cling to the theory, then they’ll look for source molecules and pathways that culminate exclusively in RNA, which eliminates countless other possibilities from the start.
Krishnamurthy’s work suggests that RNA and DNA could have arisen from the same source molecules. His lab identifies plausible pathways for that idea, including one involving diamidophosphate, a molecule that may have been present on prebiotic Earth and that may, via a phosphorus-nitrogen bond, have helped turn both RNA and DNA precursors into strands. Other chemical researchers, such as John Sutherland of the MRC Laboratory of Molecular Biology and Noble Prize-winning geneticist Jack Szostak maintain positions similar to Krishnamurthy’s. Sutherland has proposed that precursors to RNA and DNA might have combined to make the first genes. Dr. Claudia Bonfio of the MRC Laboratory of Molecular Biology said that she finds it “truly intriguing that DNA nucleotides could have been present on early Earth before the advent of life, potentially resulting from the same chemistry that also produces RNA building blocks, amino acids, and lipids.”
The importance of keeping an open mind
Krishnamurthy hopes his work will galvanize a shift when it comes to not limiting origin of life experiments to RNA-first scenarios. Bonfio agrees that the “co-presence of DNA and RNA nucleotides opens the door to an expanded and more comprehensive view where DNA and RNA could have been different, yet complementary roles in the emergence of life.” Grover similarly underscores the importance of “posing hypotheses and then working hard and sincerely to invalidate them,” which is the essence of scientific experimentation, given how much easier is it to disprove rather than prove a theory. That might sound counter-intuitive, but proving oneself wrong in science is just as valuable as proving oneself right. “In the modern research environment, there may be pressure to pose a hypothesis, become personally invested in the hypothesis, and work to find evidence to support that hypothesis,” Grover says. “However, that is really not the best way to go about hypothesis-driven research.”
If scientists struggle to figure out how RNA and DNA emerged on early Earth, then trying to figure out what might comprise life’s building blocks on other planets might seem impossible, especially considering the existence of molecules we haven’t discovered yet. Bonfio acknowledges that these unknowns could inhibit progress: “Even though new building blocks could be synthesized and new chemical pathways revealed by expanding our chemical space, such advancement could potentially be compromised by prebiotic implausibility or biological irrelevance. Nevertheless, such discoveries could provide useful insights in the search of life in extra-terrestrial environments.”
Grover points out that while “life on other planets might be completely different, but if the planet is Earth-like, it’s possible that it might choose similar building blocks.” But who knows? That’s why Krishnamurthy applies his open-minded approach to exoplanets. “Starting with a mixture is quite general,” Krishnamurthy explained. “It’s specific to any two systems that do base-pair replication, but not specific to RNA or DNA.” If scientists limit themselves to organisms that exist in Earth-based biology, they’re likely to come up empty-handed.
Taking a more general approach invites scientists to think of other structures and systems that would have similar properties but would lead to entirely different building blocks. Different chemistries exist on different planets, and “maybe the structures on exoplanet A aren’t similar to RNA but have similar chemical or physical properties,” said Krishnamurthy. Considering those alternatives is important to Grover as well: “Even if life on other planets uses the same building blocks, like nucleobases, the environments might lead to different evolutionary pathways.”
Krishnamurthy acknowledges that scientists are “trying to recreate a situation with very little chemical clues as to what exactly happened.” Even if he published a paper tomorrow showing how his lab mixed chemicals that turned into life, “you still wouldn’t know if that’s what happened 4 billion years ago.” The big takeaway here, according to Krishnamurthy, is to embrace possibilities rather than ruling things out. After all, figuring out the origins of life on Earth is “not like being Columbo,” Krishnamurthy said. “You might catch the thief, but that doesn’t mean you know how he committed the crime.”
An international team of astronomers, led by Professor Jane Greaves of Cardiff University, today announced the discovery of a rare molecule – phosphine – in the clouds of Venus. On Earth, this gas is only made industrially, or by microbes that thrive in oxygen-free environments.
Astronomers have speculated for decades that high clouds on Venus could offer a home for microbes – floating free of the scorching surface, but still needing to tolerate very high acidity. The detection of phosphine molecules, which consist of hydrogen and phosphorus, could point to this extra-terrestrial ‘aerial’ life. The new discovery is described in a paper in Nature Astronomy.
The team first used the James Clerk Maxwell Telescope (JCMT) in Hawaii to detect the phosphine, and were then awarded time to follow up their discovery with 45 telescopes of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. Both facilities observed Venus at a wavelength of about 1 millimetre, much longer than the human eye can see – only telescopes at high altitude can detect this wavelength effectively.
Professor Greaves says, “This was an experiment made out of pure curiosity, really – taking advantage of JCMT’s powerful technology, and thinking about future instruments. I thought we’d just be able to rule out extreme scenarios, like the clouds being stuffed full of organisms. When we got the first hints of phosphine in Venus’ spectrum, it was a shock!”
Naturally cautious about the initial findings, Greaves and her team were delighted to get three hours of time with the more sensitive ALMA observatory. Bad weather added a frustrating delay, but after six months of data processing, the discovery was confirmed.
Team member Dr Anita Richards, of the UK ALMA Regional Centre and the University of Manchester, adds: “To our great relief, the conditions were good at ALMA for follow-up observations while Venus was at a suitable angle to Earth. Processing the data was tricky, though, as ALMA isn’t usually looking for very subtle effects in very bright objects like Venus.”
Greaves adds: “In the end, we found that both observatories had seen the same thing – faint absorption at the right wavelength to be phosphine gas, where the molecules are backlit by the warmer clouds below.”
Professor Hideo Sagawa of Kyoto Sangyo University then used his models for the Venusian atmosphere to interpret the data, finding that phosphine is present but scarce – only about twenty molecules in every billion.
The astronomers then ran calculations to see if the phosphine could come from natural processes on Venus. They caution that some information is lacking – in fact, the only other study of phosphorus on Venus came from one lander experiment, carried by the Soviet Vega 2 mission in 1985.
Massachusetts Institute of Technology scientist Dr William Bains led the work on assessing natural ways to make phosphine. Some ideas included sunlight, minerals blown upwards from the surface, volcanoes, or lightning, but none of these could make anywhere near enough of it. Natural sources were found to make at most one ten thousandth of the amount of phosphine that the telescopes saw.
To create the observed quantity of phosphine on Venus, terrestrial organisms would only need to work at about 10% of their maximum productivity, according to calculations by Dr Paul Rimmer of Cambridge University. Any microbes on Venus will likely be very different to their Earth cousins though, to survive in hyper-acidic conditions.
Earth bacteria can absorb phosphate minerals, add hydrogen, and ultimately expel phosphine gas. It costs them energy to do this, so why they do it is not clear. The phosphine could be just a waste product, but other scientists have suggested purposes like warding off rival bacteria.
Another MIT team-member, Dr Clara Sousa Silva, was also thinking about searching for phosphine as a ‘biosignature’ gas of non-oxygen-using life on planets around other stars, because normal chemistry makes so little of it.
She comments: “Finding phosphine on Venus was an unexpected bonus! The discovery raises many questions, such as how any organisms could survive. On Earth, some microbes can cope with up to about 5% of acid in their environment – but the clouds of Venus are almost entirely made of acid.”
Other possible biosignatures in the Solar System may exist, like methane on Mars and water venting from the icy moons Europa and Enceladus. On Venus, it has been suggested that dark streaks where ultraviolet light is absorbed could come from colonies of microbes. The Akatsuki spacecraft, launched by the Japanese space agency JAXA, is currently mapping these dark streaks to understand more about this “unknown ultraviolet absorber”.
The team believes their discovery is significant because they can rule out many alternative ways to make phosphine, but they acknowledge that confirming the presence of “life” needs a lot more work. Although the high clouds of Venus have temperatures up to a pleasant 30 degrees centigrade, they are incredibly acidic – around 90% sulphuric acid – posing major issues for microbes to survive there. Professor Sara Seager and Dr Janusz Petkowski, also both at MIT, are investigating how microbes could shield themselves inside droplets.
The team are now eagerly awaiting more telescope time, for example to establish whether the phosphine is in a relatively temperate part of the clouds, and to look for other gases associated with life. New space missions could also travel to our neighbouring planet, and sample the clouds in situ to further search for signs of life.
Professor Emma Bunce, President of the Royal Astronomical Society, congratulated the team on their work:
“A key question in science is whether life exists beyond Earth, and the discovery by Professor Jane Greaves and her team is a key step forward in that quest. I’m particularly delighted to see UK scientists leading such an important breakthrough – something that makes a strong case for a return space mission to Venus.”
Science Minister Amanda Solloway said:
“Venus has for decades captured the imagination of scientists and astronomers across the world.”
“This discovery is immensely exciting, helping us increase our understanding of the universe and even whether there could be life on Venus. I am incredibly proud that this fascinating detection was led by some of the UK’s leading scientists and engineers using state of the art facilities built on our own soil.”
Imagine microscopic life-forms, such as bacteria, transported through space, and landing on another planet. The bacteria finding suitable conditions for its survival could then start multiplying again, sparking life at the other side of the universe. This theory, called “panspermia”, support the possibility that microbes may migrate between planets and distribute life in the universe. Long controversial, this theory implies that bacteria would survive the long journey in outer space, resisting to space vacuum, temperature fluctuations, and space radiations.
“The origin of life on Earth is the biggest mystery of human beings. Scientists can have totally different points of view on the matter. Some think that life is very rare and happened only once in the Universe, while others think that life can happen on every suitable planet. If panspermia is possible, life must exist much more often than we previously thought,” says Dr. Akihiko Yamagishi, a Professor at Tokyo University of Pharmacy and Life Sciences and principal investigator of the space mission Tanpopo.
In 2018, Dr. Yamagishi and his team tested the presence of microbes in the atmosphere. Using an aircraft and scientific balloons, the researchers, found Deinococcal bacteria floating 12 km above the earth. But while Deinococcus are known to form large colonies (easily larger than one millimeter) and be resistant to environmental hazards like UV radiation, could they resist long enough in space to support the possibility of panspermia?
To answer this question, Dr. Yamagishi and the Tanpopo team, tested the survival of the radioresistant bacteria Deinococcus in space. The study, now published in Frontiers in Microbiology, shows that thick aggregates can provide sufficient protection for the survival of bacteria during several years in the harsh space environment.
Dr. Yamagishi and his team came to this conclusion by placing dried Deinococcus aggregates in exposure panels outside of the International Space Station (ISS). The samples of different thicknesses were exposed to space environment for one, two, or three years and then tested for their survival.
After three years, the researchers found that all aggregates superior to 0.5 mm partially survived to space conditions. Observations suggest that while the bacteria at the surface of the aggregate died, it created a protective layer for the bacteria beneath ensuring the survival of the colony. Using the survival data at one, two, and three years of exposure, the researchers estimated that a pellet thicker than 0.5 mm would have survived between 15 and 45 years on the ISS. The design of the experiment allowed the researcher to extrapolate and predict that a colony of 1 mm of diameter could potentially survive up to 8 years in outer space conditions.
“The results suggest that radioresistant Deinococcus could survive during the travel from Earth to Mars and vice versa, which is several months or years in the shortest orbit,” says Dr. Yamagishi.
This work provides, to date, the best estimate of bacterial survival in space. And, while previous experiments prove that bacteria could survive in space for a long period when benefitting from the shielding of rock (i.e. lithopanspermia), this is the first long-term space study raising the possibility that bacteria could survive in space in the form of aggregates, raising the new concept of “massapanspermia”. Yet, while we are one step closer to prove panspermia possible, the microbe transfer also depends on other processes such as ejection and landing, during which the survival of bacteria still needs to be assessed.