Since its launch in late 2021, NASA’s James Webb Space Telescope has raised the possibility that we could detect signs of life on exoplanets, or planets outside our solar system.

Top candidates in this search are rocky, rather than gaseous, planets orbiting low-mass stars called M-dwarfs — easily the most common stars in the universe. One nearby M-dwarf is , a star about 40 light years away that hosts a system of orbiting planets under intense scrutiny in the search for life on planets orbiting stars other than the sun.

Previous research questioned the habitability of planets orbiting TRAPPIST-1, finding that intense UV rays would burn away their surface water. That would leave the planet’s surface desiccated and — if only the hydrogen part of the water vapor molecules escapes — potentially with huge amounts of reactive oxygen that would inhibit origin-of-life chemistry.

Now, a 91̽��-led recently published in Nature Communications finds that a sequence of events during the evolution of certain rocky planets orbiting M-dwarfs creates an atmosphere that would be stable over time.

“One of the most intriguing questions right now in exoplanet astronomy is: Can rocky planets orbiting M-dwarf stars maintain atmospheres that could support life?” said lead author , a 91̽��assistant professor of Earth and space sciences. “Our findings give reason to expect that some of these planets do have atmospheres, which significantly enhances the chances that these common planetary systems could support life.”

The James Webb Space Telescope is sensitive enough that it can observe a select few of these planetary systems. Data coming back so far suggests that the hottest rocky planets, closest to the TRAPPIST-1 star, do lack significant atmospheres. But the telescope has not yet been able to clearly characterize planets in the “Goldilocks zone,” slightly farther from their star, at a distance most favorable to supporting liquid water and life.

The new study modeled a rocky planet through the course of its molten formation and cooling over hundreds of millions of years into a solid terrestrial planet. Results showed that hydrogen or other light gases did initially escape into outer space. But for planets farther away from the star, where the temperature is more moderate, hydrogen also reacted with oxygen and iron in the planet’s interior. This produced water and other, heavier, gases, forming an atmosphere that results show is stable over time.

Results also showed that for these “Goldilocks zone” planets, water rains out of the atmosphere fairly quickly, making the water less likely to escape.

“It’s easier for the JWST to observe hotter planets closest to the star because they emit more thermal radiation, which isn’t as affected by the interference from the star. For those planets we have a fairly unambiguous answer: They don’t have a thick atmosphere,” Krissansen-Totton said. “For me, this result is interesting because it suggests that the more temperate planets may have atmospheres and ought to be carefully scrutinized with telescopes, especially given their habitability potential.”

The JWST has not yet been able to see whether the planets a little farther from the TRAPPIST-1 star have atmospheres. But if they do, that means they could have surface liquid water and a temperate climate conducive to life.

“With the telescopes that we have now, the James Webb and the extremely large ground-based telescopes coming soon, we’re really only going to be able to look at a very small number of habitable zone rocky planets’ atmospheres — it’s the TRAPPIST-1 planets and a couple of others,” Krissansen-Totton said. “Given the huge interest in the search for life elsewhere, our result suggests that it’s worthwhile investing telescope time to continue studying the habitability of these systems with the technology we have now, rather than waiting for the next generation of more powerful telescopes.”

Co-authors are Nicholas Wogan, who did this work as a 91̽��graduate student and is now at NASA; Maggie Thompson at Carnegie Institution for Science in Washington, D.C.; and Jonathan Fortney at the University of California, Santa Cruz. This research was supported by NASA.

For more information, contact Krissansen-Totton at joshkt@uw.edu.��

Exoplanets are experiencing a stratospheric rise. In the three decades since the first confirmed planet orbiting another star, scientists have catalogued more than 4,000 of them. As the list grows, so too does the desire to find Earth-like exoplanets — and to determine whether they could be life-sustaining oases like our own globe.

The coming decades should see the launch of new missions that can gather ever-larger amounts of data about exoplanets. Anticipating these future endeavors, a team at the 91̽�� and the University of Bern has computationally simulated more than 200,000 hypothetical Earth-like worlds — planets that have the same size, mass, atmospheric composition and geography as modern Earth — all in orbit of stars like our sun. Their goal was to model what types of environments astronomers can expect to find on real Earth-like exoplanets.

As they report in a paper accepted to the Planetary Science Journal and Dec. 6 to the preprint site arXiv, on these simulated exoplanets, one common feature of present-day Earth was often lacking: partial ice coverage.

“We essentially simulated Earth’s climate on worlds around different types of stars, and we find that in 90% of cases with liquid water on the surface, there are no ice sheets, like polar caps,” said co-author , a 91̽��professor of astronomy and scientist with the UW’s . “When ice is present, we see that ice belts — permanent ice along the equator — are actually more likely than ice caps.”

The findings shed light on the complex interplay between liquid water and ice on Earth-like worlds, according to lead author Caitlyn Wilhelm, who led the study as an undergraduate student in the 91̽��Department of Astronomy.

“Looking at ice coverage on an Earth-like planet can tell you a lot about whether it’s habitable,” said Wilhelm, who is now a research scientist with the Virtual Planetary Laboratory. “We wanted to understand all the parameters — the shape of the orbit, the axial tilt, the type of star — that affect whether you have ice on the surface, and if so, where.”

The team used a 1-D energy balance model, which computationally imitates the energy flow between a planet’s equator and poles, to simulate the climates on thousands of hypothetical exoplanets in various orbital configurations around F-, G- or K-type stars. These classes of stars, which include our own G-type sun, are promising candidates for hosting life-friendly worlds in their , also known as the “Goldilocks” zone. F-type stars are a bit hotter and larger than our sun; K-type stars are slightly cooler and smaller.

In their simulations, the orbits of the exoplanets ranged from circular to a pronounced oval. The team also considered axial tilts ranging from 0 to 90 degrees. Earth’s axial tilt is a moderate 23.5 degrees. A planet with a 90-degree tilt would “sit on its side” and experience extreme seasonal variations in climate, much like the planet Uranus.

According to the simulations, which encompassed a 1-million-year timespan on each world, Earth-like worlds showed climates ranging from planet-wide “” climates — with ice present at all latitudes — to a steaming “moist greenhouse,” which is probably similar to Venus’ climate before a made its surface hot enough to melt lead. But even though most environments in the simulations fell somewhere between those extremes, partial surface ice was present on only about 10% of hypothetical, habitable exoplanets.

The model included natural variations over time in each world’s axial tilt and orbit, which in part explains the general lack of ice on habitable exoplanets, according to co-author , a postdoctoral scientist at the University of Bern and researcher with the Virtual Planetary Laboratory.

“Orbits and axial tilts are always changing,” said Deitrick. “On Earth, these variations are called , and are very small in amplitude. But for exoplanets, these changes can be quite large, which can eliminate ice altogether or trigger ‘snowball’ states.”

When partial ice was present, its distribution varied by star. Around F-type stars, polar ice caps — like what Earth sports currently — were found about three times more often than ice belts, whereas ice belts occurred twice as often as caps for planets around G- and K-type stars. Ice belts were also more common on worlds with extreme axial tilts, likely because seasonal extremes keep the polar climates more volatile than equatorial regions, according to Wilhelm.

The team’s findings about ice on these simulated Earth-like worlds should help in the search for potentially habitable worlds by showing astronomers what they can expect to find, especially regarding ice distribution and the types of climates.

“Surface ice is very reflective, and can shape how an exoplanet ‘looks’ through our instruments,” said Wilhelm. “Whether or not ice is present can also shape how a climate will change over the long term, whether it goes to an extreme — like a ‘snowball Earth’ or a runaway greenhouse — or something more moderate.”

Ice alone, or its absence, does not determine habitability, though.

“Habitability encompasses a lot of moving parts, not just the presence or absence of ice,” said Wilhelm.

Life on Earth has survived snowball periods, as well as hundreds of millions of ice-free years, according to Barnes.

“Our own planet has seen some of these extremes in its own history,” said Barnes. “We hope this study lays the groundwork for upcoming missions to look for habitable signatures in exoplanet atmospheres — and to even image exoplanets directly — by showing what’s possible, what’s common and what’s rare.”

Rachel Mellman, a recent 91̽��graduate in astronomy, is a co-author on the paper. The research was funded by NASA through grants to the Virtual Planetary Laboratory.

For more information, contact Barnes at rkb9@uw.edu and Wilhelm at cwilhelm@uw.edu.

Grant numbers: NNA13AA93A, 80NSSC18K0829.

For centuries, humans have blamed the moon for our moods, accidents and even natural disasters. But new research indicates that our planet’s celestial companion impacts something else entirely — our sleep.

In a published Jan. 27 in Science Advances, scientists at the 91̽��, the National University of Quilmes in Argentina and Yale University report that sleep cycles in people oscillate during the : In the days leading up to a full moon, people go to sleep later in the evening and sleep for shorter periods of time. The research team, led by 91̽��professor of biology , observed these variations in both the time of sleep onset and the duration of sleep in urban and rural settings — from Indigenous communities in northern Argentina to college students in Seattle, a city of more than 750,000. They saw the oscillations regardless of an individual’s access to electricity, though the variations are less pronounced in individuals living in urban environments.

The pattern’s ubiquity may indicate that our natural circadian rhythms are somehow synchronized with — or entrained to — the phases of the lunar cycle.

“We see a clear lunar modulation of sleep, with sleep decreasing and a later onset of sleep in the days preceding a full moon,” said de la Iglesia. “And although the effect is more robust in communities without access to electricity, the effect is present in communities with electricity, including undergraduates at the 91̽��.”

Using wrist monitors, the team tracked sleep patterns among 98 individuals living in three Toba-Qom Indigenous communities in the Argentine province of Formosa. The communities differed in their access to electricity during the study period: One rural community had no electricity access, a second rural community had only limited access to electricity — such as a single source of artificial light in dwellings — while a third community was located in an urban setting and had full access to electricity. For nearly three-quarters of the Toba-Qom participants, researchers collected sleep data for one to two whole lunar cycles.

Past studies by de la Iglesia’s team and other research groups have shown that access to electricity impacts sleep, which the researchers also saw in their study: Toba-Qom in the urban community went to bed later and slept less than rural participants with limited or no access to electricity.

But study participants in all three communities also showed the same sleep oscillations as the moon progressed through its 29.5-day cycle. Depending on the community, the total amount of sleep varied across the lunar cycle by an average of 46 to 58 minutes, and bedtimes seesawed by around 30 minutes. For all three communities, on average, people had the latest bedtimes and the shortest amount of sleep in the nights three to five days leading up to a full moon.

When they discovered this pattern among the Toba-Qom participants, the team analyzed sleep-monitor data from 464 Seattle-area college students that had been collected for a separate study. They found the same oscillations.

The team confirmed that the evenings leading up to the full moon — when participants slept the least and went to bed the latest — have more natural light available after dusk: The waxing moon is increasingly brighter as it progresses toward a full moon, and generally rises in the late afternoon or early evening, placing it high in the sky during the evening after sunset. The latter half of the full moon phase and waning moons also give off significant light, but in the middle of the night, since the moon rises so late in the evening at those points in the lunar cycle.

“We hypothesize that the patterns we observed are an innate adaptation that allowed our ancestors to take advantage of this natural source of evening light that occurred at a specific time during the lunar cycle,” said lead author , a 91̽��postdoctoral researcher in the Department of Biology.

Whether the moon affects our sleep has been a controversial issue among scientists. Some studies hint at lunar effects only to be contradicted by others. De la Iglesia and Casiraghi believe this study showed a clear pattern in part because the team employed wrist monitors to collect sleep data, as opposed to user-reported sleep diaries or other methods. More importantly, they tracked individuals across lunar cycles, which helped filter out some of the “noise” in data caused by individual variations in sleep patterns and major differences in sleep patterns between people with and without access to electricity.

These lunar effects may also explain why access to electricity causes such pronounced changes to our sleep patterns, de la Iglesia added.

“In general, artificial light disrupts our innate circadian clocks in specific ways: It makes us go to sleep later in the evening; it makes us sleep less. But generally we don’t use artificial light to ‘advance’ the morning, at least not willingly. Those are the same patterns we observed here with the phases of the moon,” said de la Iglesia.

“At certain times of the month, the moon is a significant source of light in the evenings, and that would have been clearly evident to our ancestors thousands of years ago,” said Casiraghi.

The team also found a second, “semilunar” oscillation of sleep patterns in the Toba-Qom communities, which seemed to modulate the main lunar rhythm with a 15-day cycle around the new and full moon phases. This semilunar effect was smaller and only noticeable in the two rural Toba-Qom communities. Future studies would have to confirm this semilunar effect, which may suggest that these lunar rhythms are due to effects other than from light, such as the moon’s maximal gravitational “tug” on the Earth at the new and full moons, according to Casiraghi.

Regardless, the lunar effect the team discovered will impact sleep research moving forward, the researchers said.

“In general, there has been a lot of suspicion on the idea that the phases of the moon could affect a behavior such as sleep — even though in urban settings with high amounts of light pollution, you may not know what the moon phase is unless you go outside or look out the window,” said Casiraghi. “Future research should focus on how: Is it acting through our innate circadian clock? Or other signals that affect the timing of sleep? There is a lot to understand about this effect.”

Co-authors are Ignacio Spiousas at the National University of Quilmes; former 91̽��researchers Gideon Dunster and Kaitlyn McGlothlen; and Eduardo Fernández-Duque and Claudia Valeggia at Yale University. The research was funded by the National Science Foundation and the Leakey Foundation.

For more information, contact de la Iglesia at horaciod@uw.edu and Casiraghi at lcasira@uw.edu.

In September, a team led by astronomers in the United Kingdom that they had detected the chemical phosphine in the thick clouds of Venus. The team’s reported detection, based on observations by two Earth-based radio telescopes, surprised many Venus experts. Earth’s atmosphere contains small amounts of phosphine, which may be produced by life. Phosphine on Venus generated buzz that the planet, often succinctly touted as a “,” could somehow harbor life within its acidic clouds.

Since that initial claim, other science teams have on the reliability of the phosphine detection. Now, a team led by researchers at the 91̽�� has used a robust model of the conditions within the atmosphere of Venus to revisit and comprehensively reinterpret the radio telescope observations underlying the initial phosphine claim. As they report in a accepted to the Astrophysical Journal and posted Jan. 25 to the preprint site arXiv, the U.K.-led group likely wasn’t detecting phosphine at all.

“Instead of phosphine in the clouds of Venus, the data are consistent with an alternative hypothesis: They were detecting sulfur dioxide,” said co-author , a 91̽��professor of astronomy. “Sulfur dioxide is the third-most-common chemical compound in Venus’ atmosphere, and it is not considered a sign of life.”

The team behind the new study also includes scientists at NASA’s Caltech-based Jet Propulsion Laboratory, the NASA Goddard Space Flight Center, the Georgia Institute of Technology, the NASA Ames Research Center and the University of California, Riverside.

The UW-led team shows that sulfur dioxide, at levels plausible for Venus, can not only explain the observations but is also more consistent with what astronomers know of the planet’s atmosphere and its punishing chemical environment, which includes clouds of sulfuric acid. In addition, the researchers show that the initial signal originated not in the planet’s cloud layer, but far above it, in an upper layer of Venus’ atmosphere where phosphine molecules would be destroyed within seconds. This lends more support to the hypothesis that sulfur dioxide produced the signal.

Both the purported phosphine signal and this new interpretation of the data center on radio astronomy. Every chemical compound absorbs unique wavelengths of the , which includes radio waves, X-rays and visible light. Astronomers use radio waves, light and other emissions from planets to learn about their chemical composition, among other properties.

In 2017 using the , or JCMT, the U.K.-led team discovered a feature in the radio emissions from Venus at 266.94 gigahertz. Both phosphine and sulfur dioxide absorb radio waves near that frequency. To differentiate between the two, in 2019 the same team obtained follow-up observations of Venus using the , or ALMA. Their analysis of ALMA observations at frequencies where only sulfur dioxide absorbs led the team to conclude that sulfur dioxide levels in Venus were too low to account for the signal at 266.94 gigahertz, and that it must instead be coming from phosphine.

In this new study by the UW-led group, the researchers started by modeling conditions within Venus’ atmosphere, and using that as a basis to comprehensively interpret the features that were seen — and not seen — in the JCMT and ALMA datasets.

“This is what’s known as a radiative transfer model, and it incorporates data from several decades’ worth of observations of Venus from multiple sources, including observatories here on Earth and spacecraft missions like ,” said lead author Andrew Lincowski, a researcher with the 91̽��Department of Astronomy.

The team used that model to simulate signals from phosphine and sulfur dioxide for different levels of Venus’ atmosphere, and how those signals would be picked up by the JCMT and ALMA in their 2017 and 2019 configurations. Based on the shape of the 266.94-gigahertz signal picked up by the JCMT, the absorption was not coming from Venus’ cloud layer, the team reports. Instead, most of the observed signal originated some 50 or more miles above the surface, in Venus’ mesosphere. At that altitude, harsh chemicals and ultraviolet radiation would shred phosphine molecules within seconds.

“Phosphine in the mesosphere is even more fragile than phosphine in Venus’ clouds,” said Meadows. “If the JCMT signal were from phosphine in the mesosphere, then to account for the strength of the signal and the compound’s sub-second lifetime at that altitude, phosphine would have to be delivered to the mesosphere at about 100 times the rate that oxygen is pumped into Earth’s atmosphere by photosynthesis.”

The researchers also discovered that the ALMA data likely significantly underestimated the amount of sulfur dioxide in Venus’ atmosphere, an observation that the U.K.-led team had used to assert that the bulk of the 266.94-gigahertz signal was from phosphine.

“The antenna configuration of ALMA at the time of the 2019 observations has an undesirable side effect: The signals from gases that can be found nearly everywhere in Venus’ atmosphere — like sulfur dioxide — give off weaker signals than gases distributed over a smaller scale,” said co-author Alex Akins, a researcher at the Jet Propulsion Laboratory.

This phenomenon, known as spectral line dilution, would not have affected the JCMT observations, leading to an underestimate of how much sulfur dioxide was being seen by JCMT.

“They inferred a low detection of sulfur dioxide because of that artificially weak signal from ALMA,” said Lincowski. “But our modeling suggests that the line-diluted ALMA data would have still been consistent with typical or even large amounts of Venus sulfur dioxide, which could fully explain the observed JCMT signal.”

“When this new discovery was announced, the reported low sulfur dioxide abundance was at odds with what we already know about Venus and its clouds,” said Meadows. “Our new work provides a complete framework that shows how typical amounts of sulfur dioxide in the Venus mesosphere can explain both the signal detections, and non-detections, in the JCMT and ALMA data, without the need for phosphine.”

With science teams around the world following up with fresh observations of Earth’s cloud-shrouded neighbor, this new study provides an alternative explanation to the claim that something geologically, chemically or biologically must be generating phosphine in the clouds. But though this signal appears to have a more straightforward explanation — with a toxic atmosphere, bone-crushing pressure and some of our solar system’s hottest temperatures outside of the sun — Venus remains a world of mysteries, with much left for us to explore.

Additional co-authors are at the JPL, at UC Riverside, and at the Goddard Space Flight Center, 91̽��researcher , at Georgia Tech and at NASA Ames. The research was funded by the NASA Astrobiology Program and performed at the NExSS Virtual Planetary Laboratory.

For more information, contact Meadows at meadows@uw.edu, Akins at alexander.akins@jpl.nasa.gov and Lincowski at alinc@uw.edu.

The TRAPPIST-1 star system is home to the largest batch of roughly Earth-size planets ever found outside our solar system. some 40 light-years away, these seven rocky siblings offer a glimpse at the tremendous variety of planetary systems that likely fill the universe.

A accepted by the Planetary Science Journal shows that the planets share similar densities. That could mean they all contain roughly the same ratio of materials thought to be common to rocky planets, such as iron, oxygen, magnesium and silicon. If so, then while the might be similar to each other, they appear to differ notably from Earth: They’re about 8% less dense than they would be if they had the same chemical composition as our planet.

These findings give astronomers new data that they’re using to try to pin down the precise composition of these planets, and compare them not just to Earth, but to all the rocky planets in our solar system, according to lead author , a 91̽�� professor of astronomy.

“This is one of the most precise characterizations of a set of rocky exoplanets, which gave us high-confidence measurements of their diameters, densities and masses,” said Agol. “This is the information we needed to make hypotheses about their composition and understand how these planets differ from the rocky planets in our solar system.”

Since the initial detection in 2016 of the TRAPPIST-1 worlds, scientists have studied this planetary family with multiple space- and ground-based telescopes, including NASA’s now-retired and . Spitzer alone provided over 1,000 hours of targeted observations of the system before . Since they’re too small and faint to view directly, all seven exoplanets were found via the so-called transit method: looking for dips in the star’s brightness created when the planets cross in front of it.

had shown that the planets are roughly the size and mass of Earth and thus must also be — as opposed to gas-dominated worlds like Jupiter and Saturn. This new study offers the most precise density measurements to date for any group of exoplanets.

“The night sky is full of planets, and it’s only been within the last 30 years that we’ve been able to start unraveling their mysteries,” said co-author of the University of Zurich. “The TRAPPIST-1 system is fascinating because around this one star we can learn about the diversity of rocky planets within a single system. And we can actually learn more about a planet by studying its neighbors as well, so this system is perfect for that.”

The team — which includes scientists based in the United States, Switzerland, France, the United Kingdom and Morocco — used observations of the starlight dips and precise measurements of the timing of the planets’ orbits to make detailed measurements of each planet’s mass and diameter, and from there to determine its density. Agol and 91̽��co-authors Zachary Langford and , a professor of astronomy, analyzed data and performed computer simulations that constrained the orbits of the TRAPPIST-1 planets and calculated their densities.

With more precise measurements of an object’s density, we can know more about its composition. A baseball and a paperweight may be the same size, but the baseball is much lighter. Width and weight together reveal each object’s density, and from there it is possible to infer that the baseball is made of lighter materials, like string and leather, while the paperweight has a heavier composition, like glass or metal.

In our own solar system, the densities of the eight planets vary widely. The gas giants — Jupiter, Saturn, Uranus and Neptune — are larger, but much less dense than the four rocky planets. Earth, Venus and Mars have similar densities, but Mercury contains a much higher percentage of iron, so although it is the solar system’s smallest planet in diameter, Mercury has the second highest density of all eight planets.

The seven TRAPPIST-1 planets, on the other hand, all share a similar density, which makes the system quite different from our own. The difference in density between the TRAPPIST-1 planets and Earth, Venus and Mars, may seem small — about 8% — but it is significant on a planetary scale. For example, one way to explain the lower density is that the TRAPPIST-1 planets have a similar composition to Earth, but with a lower percentage of iron — about 21% compared to Earth’s 32%, according to the study.

Alternatively, the iron in the TRAPPIST-1 planets might be infused with high levels of oxygen, forming iron oxide, or rust. The additional oxygen would decrease the planets’ densities. The surface of Mars gets its red tint from iron oxide, but like its three terrestrial siblings, it has a core composed of non-oxidized iron. By contrast, if the lower density of the TRAPPIST-1 planets were caused entirely by oxidized iron, then the planets would have to be rusty throughout and could not have iron cores.

Agol said the answer might be a combination of the two scenarios — less iron overall and some oxidized iron.

The team also looked into whether the surface of each planet could be covered with water, which is even lighter than rust and which would change the planet’s overall density. If that were the case, water would have to account for about 5% of the total mass of the outer four planets. By comparison, water makes up less than 0.1% of Earth’s total mass. The three inner TRAPPIST-1 planets, positioned too close to their star for water to remain a liquid under most circumstances, would require hot, dense atmospheres like on Venus, where water could remain bound to the planet as steam. But this explanation seems less likely because it would be a coincidence for all seven planets to have just enough water present to have such similar densities, according to Agol.

When it launches, NASA’s James Webb Space Telescope should have the capabilities to probe this system further, including gathering more detailed information about the atmospheres of the seven TRAPPIST-1 worlds.

“There are many more questions to answer about TRAPPIST-1 and its worlds,” said Agol. “And in a way, answering them helps us understand our own solar system, too.”

Agol and Meadows are members of the NASA NExSS Virtual Planetary Laboratory team and the 91̽��Astrobiology Program. Agol’s involvement in the study was funded by the National Science Foundation, NASA, the Guggenheim Foundation and the Virtual Planetary Laboratory.

For more information, contact Agol at agol@uw.edu.

Adapted from a by NASA’s Jet Propulsion Laboratory.

The subsurface ocean of Saturn’s moon probably has higher than previously known concentrations of carbon dioxide and hydrogen and a more Earthlike pH level, possibly providing conditions favorable to life, according to new research from planetary scientists at the 91̽��.

The presence of such high concentrations could provide fuel — a sort of chemical “free lunch” — for living microbes, said lead researcher a 91̽��doctoral student in Earth and space sciences. Or, it could mean “that there is hardly anyone around to eat it.”

The new information about the composition of Enceladus’ ocean gives planetary scientists a better understanding of the ocean world’s capacity to host life. Fifer said.

Enceladus is a small moon, an ocean world about 310 miles (500 kilometers) across. Its salty subsurface ocean is of interest because of the similarity in pH, salinity and temperature to Earth’s oceans. Plumes of water vapor and ice particles — spotted and studied by the spacecraft — erupting hundreds of miles into space from the ocean through cracks in Enceladus’s ice-encased surface provide a tantalizing glimpse into what the moon’s subsurface ocean might contain.

But Fifer and colleagues found that the plumes aren’t chemically the same as the ocean from which they erupt at 800 miles an hour; the eruption process itself changes their composition. He is working with ESS faculty members and . They will present their work June 24 at the .

Fifer and colleagues say the plumes provide an “imperfect window” to the composition of Enceladus’s global subsurface ocean and that the plume composition and ocean composition could be much different. That, they find, is due to plume , or the separation of gases, which preferentially allows some components of the plume to erupt while others are left behind.

This in mind, the team returned to data from the Cassini mission with a computer simulation that accounts for the effects of fractionation, to get a clearer idea of the composition of Enceladus’s inner ocean’s. They found “significant differences” between Enceladus’s plume and ocean chemistry. Previous interpretations, they found, underestimate the presence of hydrogen, methane and carbon dioxide in the ocean.

“It’s better to find high gas concentrations than none at all,” said Fifer. “It seems unlikely that life would evolve to consume this chemical free lunch if the gases were not abundant in the ocean.”

Those high levels of carbon dioxide also imply a lower and more Earthlike pH level in the ocean of Enceladus than previous studies have shown. This bodes well for possible life, too, Fifer said.

“Although there are exceptions, most life on Earth functions best living in or consuming water with near-neutral pH, so similar conditions on Enceladus could be encouraging,” he said. “And they make it much easier to compare this strange ocean world to an environment that is more familiar.”

There could be high concentrations of ammonium as well, which is also a potential fuel for life. And though the high concentrations of gases might indicate a lack of living organisms to consume it all, Fifer said, that does not necessarily mean Enceladus is devoid of life. It might mean microbes just aren’t abundant enough to consume all the available chemical energy.

The researchers can use the gas concentrations to determine an upper limit for certain types of possible life that could exist in the icy ocean of Enceladus.

In other words, he said: “Given that there’s so much free lunch available, what’s the greatest amount that life could be eating to still leave behind the amount we see? How much life would that support?”

Thanks to Cassini, he said, we know about Enceladus’ ocean and the types of gases, salts and organic compounds that are present there. Studying how the plume composition changes can teach us yet more about this ocean and everything in it.

“Future spacecraft missions will sample the plumes looking for signs of life, many of which will be affected just by the eruption process,” Fifer said. “So, understanding the difference between the ocean and the plume now will be a huge help down the road.”

###

For more information, contact Fifer at lufifer@uw.edu.

On July 6, proposed a new type of mission to crack some of the universe’s most intriguing mysteries and search for life on distant worlds. 91̽�� professor co-chaired the committee from , or AURA. The group unveiled what Dalcanton described as a “call to arms,” a detailed proposal for a deep-space telescope to peer far into the cosmos. Members see this ambitious mission as a worthy successor to the – NASA’s Earth-orbiting observatory that revolutionized our knowledge of the universe since its launch in 1990 – and upcoming missions like the , launching in 2018, and the , launching in the mid-2020s.

Given the decades spent planning the Hubble and the James Webb space telescopes, Dalcanton believes this is the ideal time to consider the future.

“If we think about what we want in the sky after the James Webb Space Telescope, we need to start thinking about it now,” she said. “These are decades-long projects. No mission happens accidentally. AURA thought that it was time to start looking ahead to find a path forward that is scientifically transformative but also technologically possible.”

Dalcanton and her colleagues propose the , or HDST. This observatory would sit more than 1 million miles from Earth — far beyond the orbit of the moon — where it could search for Earth-like planets around distant stars. The telescope would employ its nearly-40-foot-wide mirror to detect light from faint planets, after suppressing the light from the much brighter stars they orbit. Scientists on Earth can analyze the light signatures from those planets to determine the composition of the planets’ atmospheres and look for chemical signatures similar to Earth’s.

“The goal is not just to find watery planets with rocky cores,” stressed Dalcanton. “We want to find atmospheres that have been shaped by the presence of life.”

An alien astronomer measuring Earth’s chemical signatures, for example, would probably be stunned to find that our atmosphere is over 20 percent oxygen gas and contains significant amounts of methane. That would be an unexpected combination for a lifeless planet, and a sign that Earth is no ordinary world.

“If you leave an atmosphere up to its own devices, it wouldn’t have both oxygen and methane,” said Dalcanton. “The only reason we have both is because life is shaping the atmosphere.”

The committee proposes that HDST survey approximately 50 Earth-like worlds to look for multiple unusual signatures that could be signs of life. This would involve an extensive search for potentially habitable planets around hundreds of stars, as well as detailed measurements of their atmospheres. These observations would help planetary scientists understand how Earth-like worlds form and when life might arise and evolve on distant globes.

HDST’s giant mirror and other technological advances would give this space telescope greater sensitivity than any of its predecessors. It will be able to see planets whose reflected light rays are 10 billion times fainter than the stars they orbit. HDST’s resolving capacity would also be 25 times greater than the Hubble Space Telescope’s, producing sharper and more detailed images. The telescope would be 100 times more sensitive than Hubble to ultraviolet radiation, which will allow scientists to observe how galaxies recycle cosmic gas, dust and other materials in a billions-year cycle of star birth and death.

HDST is part of the next-generation vision for advances in astronomy, said Dalcanton. Through proposals and rigorous advocacy for the Hubble Space Telescope and other missions, her predecessors sowed seeds for today’s discoveries. Upcoming missions like the James Webb Space Telescope will fuel discoveries over the next decade. But Dalcanton said she and her co-authors want to think far into the future.

“Hubble launched 25 years ago when I started grad school, and at lot of us in my generation realize that we have to pay this success forward,” she said. “I would like to see the High-Definition Space Telescope in the sky because there will be another astronomy graduate student who’s going to have a fantastic career of discovery using it.”

Dalcanton, co-chair from the Massachusetts Institute of Technology and their team discussed HDST with a July 6 at the in New York. The event coincided with the release of for the High-Definition Space Telescope. Dalcanton hopes this report will guide and influence astronomers, engineers and policymakers as they decide which major projects to pursue in the decades to come.

“This is a chance to get people excited about something that could be their children’s Hubble,” Dalcanton concluded.

In addition to Dalcanton and Seager, co-authors include 15 astronomers and technology experts from U.S. universities and research institutions. AURA commissioned the report and the organized the announcement and panel discussion.

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For more information, contact Dalcanton at 206-685-2155 or jd@astro.washington.edu.

To find life in the universe, it helps to know what it might look like. If there are organisms on other planets that do not rely wholly on photosynthesis — as some on Earth do not — how might those worlds appear from light-years away?

That’s among the questions 91̽�� doctoral student and astronomer of the UW-based, interdisciplinary sought to answer in research in May in the journal Astrobiology.

Using computer simulations, the researchers found that if organisms with nonphotosynthetic pigments — those that process light for tasks other than energy production — cover enough of a distant planet’s surface, their spectral signal could be strong enough to be detected by powerful future telescopes now being designed. The knowledge could add a new perspective to the hunt for life beyond Earth.

Such organisms “will produce reflectance, or brightness, signatures different than those of land vegetation like trees,” said lead author Schwieterman. “This could push us to broaden our conception of what surface biosignatures might look like” on an exoplanet, or world beyond our solar system.

He said the research grew from a meeting with co-author of the UK Centre for Astrobiology in 2012. Schwieterman sought a topic for a research rotation in the 91̽�� in which students do work outside their main field of study.

“I was interested in doing biology in the lab and linking it to remotely detectable biosignatures, which are indications there is life on a planet based on observations that could be made from a space-based telescope or large ground-based telescope,” Schwieterman said.

There had already been literature about looking for something akin to Earth’s vegetation “red edge” as a possible biosignature on exoplanets, he said. The red edge — caused by oxygen-producing organisms such as trees — is the increase in brightness when you move from the visible wavelength range to the infrared, or light too red to see. It’s why foliage looks bright in infrared photography and is often used to map vegetation cover by Earth-observing satellites.

Schwieterman and Cockell, a University of Edinburgh astrobiologist, decided to look further, and measure the reflectance of Earthly organisms with different kinds of pigments. They included those that do not rely on photosynthesis to see what biosignatures they produce and how those might differ from photosynthetic organisms — or indeed from nonliving surface features like rocks and minerals.

Pigments that absorb light are helpful to Earthly organisms in ways other than just producing energy. Some protect against the sun’s radiation or have antioxidants to help the organism survive extreme environments such as salt concentrations, high temperatures or acidity. There are even photosynthetic pigments that do not produce oxygen at all.

Schwieterman and Meadows then plugged their results Virtual Planetary Laboratory spectral models — which include the effects of the atmosphere and clouds — to simulate hypothetical planets with surfaces covered to varying degrees with such organisms.

“With those models we could determine the potential detectability of those signatures,” he said.

Exoplanets are much too far away to observe in any detail; even near-future telescopes will deliver light from such distant targets condensed to a single pixel. So even a strong signal of nonphotosynthetic pigments would be seen at best only in the “disk average,” or average planetary brightness in the electromagnetic spectrum, Schwieterman said.

“This broader perspective might allow us to pick up on something we might have missed or offer an additional piece of evidence, in conjunction with a gaseous biosignature like oxygen, for example, that a planet is inhabited,” Schwieterman said.

The UW-based planetary lab has a of spectra and pigments of nonphotosynthetic organisms and more that is available to the public, and to which data from this project have been added.

Schwieterman said much work remains to catalog the range of spectral features that life on Earth produces and also to quantify how much of a planetary surface could conceivably be covered with pigmented organisms of any type.

“We also need to think about what kinds of adaptations might exist on other worlds that don’t exist on Earth — and what that means for the interaction of those possible extraterrestrial organisms with their light environments.”

The research was funded by a grant from the NASA Astrobiology Institute.

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For more information, contact Schwieterman at eschwiet@uw.edu, or 206-616-1505.
Cooperative agreement number NNA13AA93A.

Planets with volcanic activity are considered better candidates for life than worlds without such heated internal goings-on.

Now, graduate students at the 91̽�� have found a way to detect volcanic activity in the atmospheres of exoplanets, or those outside our solar system, when they transit, or pass in front of their host stars.

Their , published in the June issue of the journal , could aid the process of choosing worlds to study for possible life and even one day help determine not only that a world is habitable, but in fact inhabited.

Volcanism is a key element in planetary habitability. That’s because volcanic outgassing helps a planet maintain moderate, life-inviting temperatures, regulating the atmosphere by cycling gases such as carbon dioxide between the atmosphere and the mantle.

Lead author , who has since graduated with a doctorate, said the project started in a 91̽��astrobiology graduate seminar when a professor asked how one might detect — the grinding together and apart of huge slabs of a planet’s surface — on faraway worlds.

Plate tectonics is considered an aid to the origin of life because it allows for the recycling of materials from the atmosphere to the planetary interior. Some scientists have even proposed that life on Earth began at sites created by tectonic plates.

The students studied various models trying to predict whether an exoplanet might have plate tectonics, but found little in scientific literature on how to directly detect tectonic plates. So they started brainstorming.

“I came up with the idea of looking at explosive volcanic eruptions as a proxy, or stand-in, for plate tectonics,” Misra said. “I had done some work modeling aerosols produced by volcanic eruptions for other projects, so I started looking into how we might detect an eruption and what it would tell us.”

So the team used data from volcanic eruptions on Earth to predict what an Earth-like exoplanet might look like during such eruptions. The thinking, Misra said, was that explosive volcanic eruptions usually happen at the edges of tectonic plates, making them a good proxy indeed.

Gases released from smaller, nonexplosive volcanic eruptions tend to return quickly to the planet’s surface. Explosive eruptions, however, can send volcanic gases up into the stratosphere, where they “greatly affect the spectrum of the planet,” Misra said. The optical signature of the gases might be detectable by powerful telescopes such as the James Webb Space Telescope, scheduled for launch in 2018.

Co-authors are , and , all graduate students in the UW’s Department of Earth and Space Sciences and affiliated with the 91̽��astrobiology program.

But while the connection between volcanic eruptions and tectonic plates is true on Earth, Misra said the team cannot say with certainty that the same is true throughout the cosmos. Still, he said, “An explosive eruption can probably be tied to volcanism if false positives such as dust storms can be ruled out.”

“These long-lasting, high-up aerosols can have a huge signal for an exoplanet, which is the key result for the paper,” Misra said. “What this means is that if we can detect a volcanic eruption on a planet, and if it meets other criteria like being in the habitable zone, that planet should move up our list of potential targets to search for life.”

The work may also someday help astronomers infer that a planet not only might have life, but actually does. Misra explained that while oxygen is thought an indicator of life, it’s also possible for oxygen to be produced abiotically, or by something other than biology.

Volcanism, Misra said, may help distinguish between oxygen that is produced by life or other planetary processes by helping astronomers better understand the planet’s environment.

“Volcanic gases often react with and destroy oxygen, and a detection of both oxygen and volcanism suggests that there is a source of oxygen in the planetary environment, which could be life,” Misra said.

The research was done through the , a UW-based interdisciplinary research group, and funded through the NASA Astrobiology Institute.

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For more information, contact Misra at 440-554-6514 or amit0@astro.washington.edu. Cooperative agreement number NNA13AA93A.

With its thick, hazy atmosphere and surface rivers, mountains, lakes and dunes, , Saturn’s largest moon, is one of the most Earthlike places in the solar system.

As the examines Titan over many years, its discoveries bring new mysteries. One of those involves the seemingly wind-created sand dunes spotted by Cassini near the moon’s equator, and the contrary winds just above.

Here’s the problem: Climate simulations indicate that Titan’s near-surface winds — like Earth’s trade winds — blow toward the west. So why do the surface dunes, reaching a hundred yards high and many miles long, point to the east?

The direction of the dunes has at times been attributed to the effects of Saturn’s gravitational tides or various land features or wind dynamics, but none quite explained their eastward slant.

Violent methane storms high in Titan’s dense atmosphere, where winds do blow toward the east, might be the answer, according to new research by 91̽�� astronomer and co-authors in a published today in the journal Nature Geoscience.

Using computer models, Charnay, a 91̽��post-doctoral researcher, and co-authors hypothesize that the attitude of Titan’s sand dunes results from rare methane storms that produce eastward gusts much stronger than the usual westward surface winds.

“These fast eastward gusts dominate the sand transport, and thus dunes propagate eastward,” Charnay said.

The storm winds reach up to 10 meters a second (22 mph), about 10 times faster than Titan’s gentler near-surface winds. And though the storms happen only when Titan is in equinox and its days and nights are of equal length — about every 14.75 years — they are of sufficient power to realign Titan’s dunes. Titan was last in equinox in August 2009.

It probably helps that, according to Cassini’s observations, Titan’s atmosphere is in “super-rotation” above about 5 miles, meaning that it rotates a lot faster than the surface itself. Their model, Charnay said, suggests that these methane storms “produce strong downdrafts, flowing eastward when they reach the surface,” thus rearranging the dunes.

Charnay said he tried first, without success, to solve the problem with a global climate model that didn’t factor in methane clouds, then realized that it was impossible, hinting that methane could be part of the solution.

“It was a kind of detective game, as often is the case in planetary sciences, where we have many mysteries and a few clues to solve them,” he said.

The dunes in question, which are linear and run parallel to Titan’s equator, are probably not composed of silicates like Earth sand, Charnay said, but of hydrocarbon polymers — a kind of soot resulting from the decomposition of methane in the atmosphere.

Charnay noted a December reported in Nature showing that it would take winds of at least 3.2 mph to lift and transport sand across Titan’s surface — that’s 40 percent to 50 percent stronger wind than previous estimates.

The measurement of such a high wind speed threshold was a pleasant surprise, Charnay said: “That means that only fast winds transport Titan’s sand, compatible with our hypothesis of strong storm gusts controlling the orientation and propagation of dunes.”

Titan, discovered in 1655 by Christiaan Huygens, has long intrigued astronomers. Its atmosphere is 98.4 percent nitrogen and most of the rest is methane, and a bit of hydrogen. Its gravity is one-sixth that of Earth’s and its air density is four- to five-times higher, meaning that flight will be relatively easy for visiting spacecraft. The European Space Agency’s Huygens probe, which rode along on Cassini, on Titan in 2005 and sent back of the moon’s stone-strewn surface.

Charnay said direct observation by Cassini would be the way to confirm his hypothesis. Unfortunately, the Cassini mission will end in 2017 and Titan’s next equinox is not until 2023.

“But there will be other missions,” he said. “There are still a lot of mysteries about Titan. We still don’t know how a thick nitrogen atmosphere formed, where the methane comes from nor how Titan’s sand forms.

“And it is not completely excluded that , perhaps in its . So Titan really is a fascinating and evolving world, which has to be understood as a whole.”

Charnay’s co-authors are Erika Barth and Scot Rafkin of the Southwest Research Institute in Boulder, Colorado; Sébastien Lebonnois of the Laboratory of Dynamic Meteorology; and Sylvain Courrech du Pont, Clément Narteau, Sebastian Rodriguez and Antoine Lucas of Paris Diderot University.

The research was done in part through the , a UW-based interdisciplinary research group, and funded by the NASA Postdoctoral Program and the French National Research Agency.

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��For more information, contact Charnay at bcharnay@uw.edu or benjamin.charnay@lmd.jussieu.fr. Grant #ANR-12-BS05-001-03/EXO-DUNES.

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