Victoria Meadows – 91̽��News

Five 91̽��faculty members elected as AGU Fellows, plus more honors

91̽��News staff — Tue, 19 Sep 2023 21:46:56 +0000

Another lovely day on the 91̽��’s Seattle campus.

The American Geophysical Union Sept. 13 that five 91̽�� faculty members have been elected as new fellows, representing the departments of astronomy, Earth and space sciences, oceanography, global health, and environmental and occupational health sciences.

The Fellows program recognizes AGU members who have made exceptional contributions to Earth and space sciences through a breakthrough, discovery or innovation in their field. The five 91̽��honorees are among 54 people from around the world in the 2023 Class of Fellows. AGU, the world’s largest Earth and space sciences association, annually recognizes a select number of individuals nominated by their peers for its highest honors. Since 1962, the AGU Union Fellows Committee has selected less than 0.1% of members as new fellows.

Also honored by AGU this year are three 91̽��faculty members, from the departments of Earth and space sciences and atmospheric sciences, who have received other awards.

Here are the UW’s five new AGU Fellows:

, professor of Earth and space sciences, studies which characteristics of Earth help this planet support life, and whether life might be found on other planets. His work spans astronomy, biology and geology, on planetary environments including Earth, Mars, Venus and icy moons, as well as planets outside this solar system. He is the author of “Astrobiology: A Very Short Introduction” for the layperson and “Atmospheric Evolution on Inhabited and Lifeless Worlds” for researchers.

, who holds the Karl M. Banse Endowed Professorship in oceanography, explores the limits and ecological contributions of microbial life in deep ocean and polar regions, focusing in recent years on how microbes adapt to the extreme conditions of Arctic sea ice. In addition to a research and teaching career, Deming founded what is now the 91̽��Center for Environmental Genomics and helped establish the nation’s first graduate training program in astrobiology.

, professor of global health and of environmental and occupational health sciences, has been conducting research on the health risks of climate variability and change for nearly 30 years. She focuses on estimating current and future health risks of climate change, designing adaptation policies and measures to reduce risks in multi-stressor environments, and estimating the health co-benefits of mitigation policies. Ebi is also founding director of the 91̽��, or CHanGE.

, professor of astronomy, is an astrobiologist and planetary astronomer whose research focuses on predicting, acquiring and analyzing observations of planetary atmospheres and surfaces. In addition to studying planets within our solar system, she is interested in exoplanets — those outside the solar system — and how they might reveal the presence of life. With the UW’s Virtual Planetary Laboratory, she uses models of planets and planet-star interactions to generate plausible planetary environments and spectra for extrasolar terrestrial planets and the early Earth.

, professor and chair of Earth and space sciences, is a geochemist and glaciologist whose research focuses on polar climate and ice sheets in the Arctic and in Antarctica. He is best known for his analyses of Antarctic ice cores using measurements of oxygen and hydrogen in the ice to better understand how climate has varied in the past, over hundreds to thousands of years.

In addition to the newly elected fellows, 91̽��faculty members are also recognized in several subject-specific awards and lectures:

, professor of atmospheric sciences, will deliver the in December at the AGU’s fall meeting. Alexander studies the relationship between climate change and the chemical composition of the atmosphere. She looks at the pathways by which atmospheric pollutants form, how those chemical pathways can vary, and what that means both for present-day air quality and for the future of climate change.

, research assistant professor of Earth and space sciences, has received the for his research modeling natural disasters using geodesy, or the shape of the Earth’s surface, and seismology. Crowell pioneered ways to use GPS and related data in earthquake and tsunami early warning systems. He is currently using this data to better understand natural disasters as they unfold and develop a risk-mitigation framework for coastal hazards such as tsunamis.

, research assistant professor of Earth and space sciences, has received the . Journaux uses modeling and experiments to explore the conditions in extreme environments on other planets, and how that might affect their ability to harbor life. He is a member of the science team for NASA’s upcoming Dragonfly mission, which will characterize the chemistry and habitability of Saturn’s largest moon, Titan.

, a researcher at the Pacific Northwest National Laboratory with an affiliate 91̽��faculty position in oceanography, has received the .

All honorees will be recognized in December at the AGU’s fall meeting in San Francisco.

20 91̽��researchers elected to the Washington State Academy of Sciences for 2021

James Urton — Fri, 16 Jul 2021 22:51:44 +0000

A spring day on the 91̽�� campus. Photo: Dennis Wise

Twenty scientists and engineers at the 91̽�� are among the 38 new members elected to the Washington State Academy of Sciences for 2021, according to a July 15 . New members were chosen for “their outstanding record of scientific and technical achievement, and their willingness to work on behalf of the Academy to bring the best available science to bear on issues within the state of Washington.”

Current academy members selected 29 of the new members. An additional nine were elected by virtue of joining one of the National Academies.

New 91̽��members who were elected by current academy members are:

, professor and Port of Tacoma Chair in Environmental Science at 91̽��Tacoma, director of the and science director of the , “for foundational work on the environmental fate, behavior and toxicity of PCBs.”
, professor of psychology, “for contributions in research on racial and gender inequality that has influenced practices in education, government, and business” and “for shifting the explanation for inequality away from individual deficiencies and examining how societal stereotypes and structures cause inequalities.”
, professor of chemistry and member faculty at the , “for leadership in the innovative synthesis and chemical modification of nanoscale materials for application in light emission and catalysis.”
, professor of global health and of environmental and occupational health sciences, and founding director of the , “for work on the health impacts of climate change, on climate impact forecasting, on adaptation to climate change and on climate policy to protect health.”
, professor of environmental and forest sciences and dean emeritus of the College of the Environment, “for foundational studies of regional paleoenvironmental history and sustained excellence in academic leadership to catalyze and sustain transformative research and educational initiatives.” Graumlich is also president-elect of the American Geophysical Union.
Dr. , the Joseph W. Eschbach Endowed Chair in Kidney Research and co-director of the , “for pioneering contributions and outstanding achievements in the development of the novel wearable artificial kidney, as well as numerous investigator-initiated clinical trials and multi-center collaborative studies.”
, professor of environmental chemistry and chair of the Physical Sciences Division at 91̽��Bothell, “for leadership in monitoring and understanding the global transport of atmospheric pollutants from energy production, wildfire, and other sources, as well as science communication and service that has informed citizens and enhanced public policy.”
, professor and chair of psychology, “for contributions demonstrating how psychological science can inform long-standing issues about racial and gender discrimination” and “for research that has deep and penetrating implications for the law and societal efforts to remedy social inequities with evidence-based programs and actions.”
, the Leon C. Johnson Professor of Chemistry, member faculty at the and chair of the Department of Chemistry, “for developing new spectroscopy tools for measuring energy flow in molecules and materials with high spatial and temporal resolution.”
, professor of astronomy, “for founding the and leading the decades-long development of the interdisciplinary modeling framework and community needed to establish the science of exoplanet astrobiology” and “for training the next generation of interdisciplinary scientists who will search for life beyond Earth.”
, professor and chair of aeronautics and astronautics, “for leadership and significant advances in nonlinear methods for integrated sensing and control in engineered, bioinspired and biological flight systems” and “for leadership in cross-disciplinary aerospace workforce development.”
, associate professor of chemistry and member faculty with the Molecular Engineering and Sciences Institute, “for exceptional contributions to the development of synthetic polymers and nanomaterials for self-assembly and advanced manufacturing with application in sustainability, medicine and microelectronics.”
Dr. , Associate Dean of Medical Technology Innovation in the College of Engineering and the School of Medicine, the Graham and Brenda Siddall Endowed Chair in Cornea Research, and medical director of the 91̽��Eye Institute, “for developing and providing first class clinical treatment of severe corneal blindness to hundreds of people, for establishing the world premier artificial cornea program in Washington, and for leading collaborative research to translate innovative engineering technologies into creative clinical solution.”
Dr. , professor of medicine and director of the , “for global recognition as an authority on drug and vaccine development for viral and parasitic diseases through work as an infectious disease physician and immunologist.”
Dr. , professor of pediatrics and of anesthesiology and pain medicine, and director of the , “for outstanding leadership in pediatric anesthesiology and in the care of children with traumatic brain injury” and “for internationally recognized expertise in traumatic brain injury and direction of the Harborview Injury Prevention and Research Center for the last decade as an exceptional mentor and visionary leader.”

91̽��members who will join the Washington State Academy of Sciences by virtue of their election to one of the National Academies are:

, professor of biostatistics, “for the development of novel statistical models for longitudinal data to better diagnose disease, track its trajectory, and predict its outcomes” and “for revolutionizing how dynamic predictors are judged by their discrimination and calibration and has significantly advanced methods for randomized controlled trials.” Heagerty was elected to the National Academy of Medicine in 2021.
, the Bill and Melinda Gates Chair in Computer Science and Engineering, “for foundational contributions to the mathematics of computer systems and of the internet, as well as to the design and probabilistic analysis of algorithms, especially on-line algorithms, and algorithmic mechanism design and game theory.” Karlin was elected to the National Academy of Sciences in 2021.
, professor emeritus of applied mathematics and data science fellow at the , “for inventing key algorithms for hyperbolic conservation laws and transforming them into powerful numerical technologies” and “for creating the Clawpack package, which underpins a wide range of application codes in everyday use, such as for hazard assessment due to tsunamis and other geophysical phenomena.” LeVeque was elected to the National Academy of Sciences in 2021.
, the Benjamin D. Hall Endowed Chair in Basic Life Sciences and an investigator with the Howard Hughes Medical Institute, “for advancing our physical understanding of cell motility and growth in animals and bacteria” and “for discovering how the pathogen Listeria uses actin polymerization to move inside human cells, how crawling animal cells coordinate actomyosin dynamics and the mechanical basis of size control and daughter cell separation in bacteria.” Theriot was elected to the National Academy of Sciences in 2021.
, professor and chair of biological structure, “for elucidating cellular transformations through which neurons pattern their dendrites, and the interplay of activity-dependent and -independent mechanisms leading to assembly of stereotyped circuits” and “for revelations regarding the fundamental principles of neuronal development through the application of an elegant combination of in vivo imaging, physiology, ultrastructure and genetics to the vertebrate retina.” Wong was elected to the National Academy of Sciences in 2021.

New members to the Washington State Academy of Sciences are scheduled to be inducted at a meeting in September.

Purported phosphine on Venus more likely to be ordinary sulfur dioxide, new study shows

James Urton — Wed, 27 Jan 2021 16:57:28 +0000

An image of Venus compiled using data from the Mariner 10 spacecraft in 1974. Photo:

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.

This image, which shows the night side of Venus glowing in thermal infrared, was captured by Japan’s Akatsuki spacecraft. Photo:

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.

Earth’s cousins: Upcoming missions to look for ‘biosignatures’ in the atmospheres of nearby worlds

James Urton — Sat, 15 Feb 2020 00:05:43 +0000

Artist’s depiction of the TRAPPIST-1 star and its seven worlds. Photo: NASA/JPL-Caltech/R. Hurt (IPAC)

Scientists have discovered thousands of , including dozens of terrestrial — or rocky — worlds in the around their parent stars. A promising approach to search for signs of life on these worlds is to probe exoplanet atmospheres for “biosignatures” — quirks in chemical composition that are telltale signs of life. For example, thanks to photosynthesis, our atmosphere is nearly 21% oxygen, a much higher level than expected given Earth’s composition, orbit and parent star.

Finding biosignatures is no straightforward task. Scientists use data about how exoplanet atmospheres interact with light from their parent star to learn about their atmospheres. But the information, or spectra, that they can gather using today’s ground- and space-based telescopes is too limited to measure atmospheres directly or detect biosignatures.

Exoplanet researchers such as , a professor of astronomy at the 91̽��, are focused on what forthcoming observatories, like the , or JWST, could measure in exoplanet atmospheres. On Feb. 15 at the in Seattle, Meadows, a principal investigator of the UW’s , will deliver a talk to summarize what kind of data these new observatories can collect and what they can reveal about the atmospheres of terrestrial, Earth-like exoplanets. Meadows sat down with 91̽��News to discuss the promise of these new missions to help us view exoplanets in a new light.

Victoria Meadows, a professor of astronomy at the 91̽�� and director of the Virtual Planetary Laboratory. Photo: Ron Hasler

What changes are coming to the field of exoplanet research?

In the next five to 10 years, we’ll potentially get our first chance to observe the atmospheres of terrestrial exoplanets. This is because new observatories are set to come online, including the James Webb Space Telescope and ground-based observatories like the . A lot of our recent work at the Virtual Planetary Laboratory, as well as by colleagues at other institutions, has focused on simulating what Earth-like exoplanets will “look” like to the JWST and ground-based telescopes. That allows us to understand the spectra that these telescopes will pick up, and what those data will and won’t tell us about those exoplanet atmospheres.

What types of exoplanet atmospheres will the JWST and other missions be able to characterize?

Our targets are actually a select group of exoplanets that are nearby — within 40 light years — and orbit very small, cool stars. For reference, the Kepler mission identified exoplanets around stars that are more than 1,000 light years away. The smaller host stars also help us get better signals on what the planetary atmospheres are made of because the thin layer of planetary atmosphere can block more of a smaller star’s light.

So there are a handful of exoplanets we’re focusing on to look for signs of habitability and life. All were identified by ground-based surveys like and its successor, — both run by the University of Liège — as well as the run by Harvard. The most well-known exoplanets in this group are probably the seven terrestrial planets orbiting . TRAPPIST-1 is an M-dwarf star — one of the smallest you can have and still be a star — and its seven exoplanets span interior to and beyond the habitable zone, with three in the habitable zone.

We’ve identified TRAPPIST-1 as the best system to study because this star is so small that we can get fairly large and informative signals off of the atmospheres of these worlds. These are all cousins to Earth, but with a very different parent star, so it will be very interesting to see what their atmospheres are like.

What have you learned so far about the atmospheres of the TRAPPIST-1 exoplanets?

The astronomy community has taken observations of the TRAPPIST-1 system, but we haven’t seen anything but “non-detections.” That can still tell us a lot. For example, observations and models suggest that these exoplanet atmospheres are less likely to be dominated by hydrogen, the lightest element. That means they either don’t have atmospheres at all, or they have relatively high-density atmospheres like Earth.

No atmospheres at all? What would cause that?

M-dwarf stars have a very different history than our own sun. After their infancy, sun-like stars brighten over time as they undergo fusion.

M-dwarfs start out big and bright, as they gravitationally collapse to the size they will then have for most of their lifetimes. So, M-dwarf planets could be subjected to long periods of time — perhaps as along as a billion years — of high-intensity luminosity. That could strip a planet of its atmosphere, but volcanic activity can also replenish atmospheres. Based on their densities, we know that many of the TRAPPIST-1 worlds are likely to have reservoirs of compounds — at much higher levels than Earth, actually — that could replenish the atmosphere. The first significant JWST results for TRAPPIST-1 will be: Which worlds retained atmospheres? And what types of atmospheres are they?

I’m quietly optimistic that they do have atmospheres because of those reservoirs, which we’re still detecting. But I’m willing to be surprised by the data.

What types of signals will the JWST and other observatories look for in the atmospheres of TRAPPIST-1 exoplanets?

Probably the easiest signal to look for will be the presence of carbon dioxide.

Is CO2 a biosignature?

Not on its own, and not just from a single signal. I always tell my students — look right, look left. Both Venus and Mars have atmospheres with high levels of CO2, but no life.

In Earth’s atmosphere, CO2 levels adjust with our seasons. In spring, levels draw down as plants grow and take CO2 out of the atmosphere. In autumn, plants break down and CO2 rises. So if you see seasonal cycling, that might be a biosignature. But seasonal observations are very unlikely with JWST.

Instead, JWST can look for another potential biosignature, methane gas in the presence of CO2. Methane should normally have a short lifetime with CO2. So if we detect both together, something is probably actively producing methane. On Earth, most of the methane in our atmosphere is produced by life.

What about detecting oxygen?

Oxygen alone is not a biosignature. It depends on its levels and what else is in the atmosphere. You could have an oxygen-rich atmosphere from the loss of an ocean, for example: Light splits water molecules into hydrogen and oxygen. Hydrogen escapes into space, and oxygen builds up into the atmosphere.

The JWST likely won’t directly pick up oxygen from — the biosphere we’re used to now. The Extremely Large Telescope and related observatories might be able to, because they’ll be looking at a different wavelength than the JWST, where they will have a better chance of seeing oxygen. The JWST will be better for detecting biospheres similar to what we had on Earth billions of years ago, and for differentiating between different types of atmospheres.

What are some of the different types of atmospheres that TRAPPIST-1 exoplanets might possess?

The M-dwarf’s high-luminosity phase might drive a planet toward an atmosphere with a runaway greenhouse effect, like Venus. As I said earlier, you could lose an ocean and have an oxygen-rich atmosphere. A third possibility is to have something more Earth-like.

Let’s talk about that second possibility. How could JWST reveal an oxygen-rich atmosphere if it can’t detect oxygen directly?

The beauty of the JWST is that it can pick up processes happening in an exoplanet’s atmosphere. It will pick up the signatures of collisions between oxygen molecules, which will happen more often in an oxygen-rich atmosphere. So we likely can’t see oxygen amounts associated with a photosynthetic biosphere. But if a much larger amount of oxygen was left behind from ocean loss, we can probably see the collisions of oxygen in the spectrum, and that’s probably a sign that the exoplanet has lost an ocean.

So, JWST is unlikely to give us conclusive proof of biosignatures but may provide some tantalizing hints, which require further follow-up and — moving forward — thinking about new missions beyond the JWST. NASA is already considering new missions. What would we like their capabilities to be?

That also brings me to a very important point: Exoplanet science is massively interdisciplinary. Understanding the environment of these worlds requires considering orbit, composition, history and host star — and requires the input of astronomers, geologists, atmospheric scientists, stellar scientists. It really takes a village to understand a planet.

For more information, contact Meadows at meadows@uw.edu.

Introducing VPLanet: A virtual planet simulator for modeling distant worlds across time

Peter Kelley — Thu, 19 Sep 2019 18:06:32 +0000

91̽�� astrobiologist Rory Barnes and co-authors have created VPLanet, a software package that simulates multiple aspects of planetary evolution across billions of years, with an eye toward finding and studying potentially habitable worlds. Photo: PHL@UPR Arecibo / ESA/Hubble, NASA

91̽�� astrobiologist has created software that simulates multiple aspects of planetary evolution across billions of years, with an eye toward finding and studying potentially habitable worlds.

Barnes, a 91̽��assistant professor of astrobiology, astronomy and data science, released the first version of VPLanet, his virtual planet simulator, in August. He and his co-authors described it in a accepted for publication in the Publications of the Astronomical Society of the Pacific.

“It links different physical processes together in a coherent manner,” he said, “so that effects or phenomena that occur in some part of a planetary system are tracked throughout the entire system. And ultimately the hope is, of course, to determine if a planet is able to support life or not.”

VPLanet’s mission is three-fold, Barnes and co-authors write. The software can:

simulate newly discovered exoplanets to assess their potential to possess surface liquid water, which is a key to life on Earth and indicates the world is a viable target in the search for life beyond Earth
model diverse planetary and star systems regardless of potential habitability, to learn about their properties and history, and
enable transparent and open science that contributes to the search for life in the universe

The first version includes modules for the internal and magnetic evolution of terrestrial planets, climate, atmospheric escape, tidal forces, orbital evolution, rotational effects, stellar evolution, planets orbiting binary stars and the gravitational perturbations from passing stars.

It’s designed for easy growth. Fellow researchers can write new physical modules “and almost plug and play them right in,” Barnes said. VPLanet can also be used to complement more sophisticated tools such as machine learning algorithms.

An important part of the process, he said, is validation, or checking physics models against actual previous observations or past results, to confirm that they are working properly as the system expands.

“Then we basically connect the modules in a central area in the code that can model all members of a planetary system for its entire history,” Barnes said.

And though the search for potentially habitable planets is of central importance, VPLanet can be used for more general inquiries about planetary systems.

“We observe planets today, but they are billions of years old,” he said. This is a tool that allows us to ask: ‘How do various properties of a planetary system evolve over time?’”

The project’s history dates back almost a decade to a Seattle meeting of astronomers called “Revisiting the Habitable Zone” convened by , principal investigator of the UW-based , with Barnes. The habitable zone is the swath of space around a star that allows for orbiting rocky planets to be temperate enough to have liquid water at their surface, giving life a chance.

They recognized at the time, Barnes said, that knowing if a planet is within its star’s habitable zone simply isn’t enough information: “So from this meeting we identified a whole host of physical processes that can impact a planet’s ability to support and retain water.”

Barnes discussed VPLanet and presented a tutorial on its use at the recent AbSciCon19 worldwide astrobiology conference, held in Seattle.

The research was done through the Virtual Planetary Laboratory and the source code is available .

Barnes’s other faculty co-authors are astronomy professor ; , professor of atmospheric sciences; and research scientist . Other 91̽��co-authors are doctoral students , , and ; and undergraduate researchers Caitlyn Wilhelm, Benjamin Guyer and Diego McDonald.

Other co-authors are of the Carnegie Institution for Science; of the Flatiron Institute, of the Max Planck Institute for Astronomy in Heidelberg, Germany, of the University of Bern, of the NASA Goddard Space Flight Center and of Weber State University.

The research was funded by a grant from the NASA Astrobiology Program’s Virtual Planetary Laboratory team, as part of the research coordination network, or NExSS.

###

For more information, contact Barnes at 206-543-8979 or rkb9@uw.edu.

Grant numbers

VPL under cooperative agreement #NNA13AA93A

NASA grants #NNX15AN35G, #13-13-NA17 0024, and #80NSSC18K0829

NASA Earth and Space Science Fellowship Program grant #80NSSC17K0482

James Webb Space Telescope could begin learning about TRAPPIST-1 atmospheres in a single year, study indicates

Peter Kelley — Tue, 13 Aug 2019 20:01:58 +0000

New research from 91̽��astronomers models how telescopes such as the James Webb Space Telescope will be able to study the planets of the intriguing TRAPPIST-1 system. Photo: NASA

New research from astronomers at the 91̽�� uses the intriguing TRAPPIST-1 planetary system as a kind of laboratory to model not the planets themselves, but how the coming might detect and study their atmospheres, on the path toward looking for life beyond Earth.

The study, led by , a 91̽��doctoral student in astronomy, finds that the James Webb telescope, set to launch in 2021, might be able to learn key information about the atmospheres of the TRAPPIST-1 worlds even in its first year of operation, unless — as an old song goes — clouds get in the way.

“The Webb telescope has been built, and we have an idea how it will operate,” said Lustig-Yaeger. “We used computer modeling to determine the most efficient way to use the telescope to answer the most basic question we’ll want to ask, which is: Are there even atmospheres on these planets, or not?”

His paper, “The Detectability and Characterization of the TRAPPIST-1 Exoplanet Atmospheres with JWST,” was in June in the Astronomical Journal.

The TRAPPIST-1 system, 39 light-years — or about 235 trillion miles — away in the constellation of Aquarius, interests astronomers because of its seven orbiting rocky, or Earth-like, planets. Three of these worlds are in the star’s habitable zone — that swath of space around a star that is just right to allow liquid water on the surface of a rocky planet, thus giving life a chance.

The star, TRAPPIST-1, was much hotter when it formed than it is now, which would have subjected all seven planets to ocean, ice and atmospheric loss in the past.

“There is a big question in the field right now whether these planets even have atmospheres, especially the innermost planets,” Lustig-Yaeger said. “Once we have confirmed that there are atmospheres, then what can we learn about each planet’s atmosphere — the molecules that make it up?”

Given the way he suggests the James Webb Space Telescope might search, it could learn a lot in fairly short time, this paper finds.

Astronomers detect exoplanets when they pass in front of or “transit” their host star, resulting in a measurable dimming of starlight. Planets closer to their star transit more frequently and so are somewhat easier to study. When a planet transits its star, a bit of the star’s light passes through the planet’s atmosphere, with which astronomers can learn about the molecular composition of the atmosphere.

Lustig-Yaeger said astronomers can see tiny differences in the planet’s size when they look in different colors, or wavelengths, of light.

“This happens because the gases in the planet’s atmosphere absorb light only at very specific colors. Since each gas has a unique ‘spectral fingerprint,’ we can identify them and begin to piece together the composition of the exoplanet’s atmosphere.”

Lustig-Yaeger said the team’s modeling indicates that the James Webb telescope, using a versatile onboard tool called the Near-Infrared Spectrograph, could detect the atmospheres of all seven TRAPPIST-1 planets in 10 or fewer transits — if they have cloud-free atmospheres. And of course we don’t know whether or not they have clouds.

If the TRAPPIST-1 planets have thick, globally enshrouding clouds like Venus does, detecting atmospheres might take up to 30 transits.

“But that is still an achievable goal,” he said. “It means that even in the case of realistic high-altitude clouds, the James Webb telescope will still be capable of detecting the presence of atmospheres — which before our paper was not known.”

Many rocky exoplanets have been discovered in recent years, but astronomers have not yet detected their atmospheres. The modeling in this study, Lustig-Yaeger said, “demonstrates that, for this TRAPPIST-1 system, detecting terrestrial exoplanet atmospheres is on the horizon with the James Webb Space Telescope — perhaps well within its primary five-year mission.”

The team found that the Webb telescope may be able to detect signs that the TRAPPIST-1 planets lost large amounts of water in the past, when the star was much hotter. This could leave instances where abiotically produced oxygen — not representative of life — fills an exoplanet atmosphere, which could give a sort of “false positive” for life. If this is the case with TRAPPIST-1 planets, the Webb telescope may be able to detect those as well.

Lustig-Yaeger’s co-authors, both with the UW, are astronomy professor , who is also principal investigator for the UW-based ; and astronomy doctoral student . The work follows, in part, on previous work by Lincowski modeling possible climates for the seven TRAPPIST-1 worlds.

“By doing this study, we have looked at: What are the best-case scenarios for the James Webb Space Telescope? What is it going to be capable of doing? Because there are definitely going to be more Earth-sized planets found before it launches in 2021.”

The research was funded by a grant from the NASA Astrobiology Program’s Virtual Planetary Laboratory team, as part of the Nexus for Exoplanet System Science (NExSS) research coordination network.

Lustig-Yaeger added: “It’s hard to conceive in theory of a planetary system better suited for James Webb than TRAPPIST-1.”

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For more information, contact Lustig-Yaeger at jlustigy@uw.edu.

Looking for life: 91̽��researchers, presentations abound at 2019 astrobiology conference in Bellevue

Peter Kelley — Thu, 20 Jun 2019 21:35:53 +0000

What are ocean worlds like? Is life possible inside a planet? What might a faraway technological civilization look like from here? Which planets warrant closer study, and why? And above all: Are we alone?

is the study of life in the universe and of the terrestrial environments and planetary and stellar processes that support it. To study astrobiology is to ask questions that cut across multiple disciplines and could take lifetimes to answer. The field gathers expertise from a host of other disciplines including biology, chemistry, geology, oceanography, atmospheric and Earth science, aeronautical engineering and of course astronomy itself.

These questions also include: What can Earth’s own species, and its chemical past, tell us about how to spot life elsewhere? How did the first cells arise? Can we map the surfaces of exoplanets? How can we motivate students to be curious about space?

Every two years, researchers gather from around the world to share and discuss their latest findings in a weeklong conference. Called for short, this year’s conference will be held June 24-28 at the Hyatt Regency Hotel in Bellevue. It’s the biggest meeting of astrobiologists in the world and dozens of 91̽�� researchers will attend and participate.

Public attitudes have warmed greatly toward astrobiology in the 21^st century, prompted by exoplanet discoveries and exploration of other worlds in the solar system. Study of extraterrestrial life remains a hopeful science wryly aware that, as an old joke goes, it has yet to prove that its very subject matter exists.

The 91̽��founded its own program in 1999, involving roughly 30 faculty and about as many students a year. “The program is a leader in both training the next generation of astrobiologists and in fundamental astrobiology research,” said , 91̽��professor of astronomy and principal investigator for the UW-based , which explores computer models of planetary environments and will be the subject of a .

“The Astrobiology Science Conference is the biggest meeting of astrobiologists in the world, and this year, members of the 91̽��Astrobiology Program are playing a major role in conference organization, as well as presenting our research at the meeting,” said Meadows, who chaired the science committee for AcSciCon2019.

Here are several 91̽��presentations and papers scheduled for the weeklong conference. Though the lead presenter is listed here only, most projects involve the work of several colleagues.

A study of water vapor and ice particles emitting from the plume on Saturn’s moon Enceladus, leading to a better understanding of the moon’s subsurface ocean. With Earth and space sciences doctoral student and colleagues. ()
An examination of whether the coming James Webb Space Telescope will be able to detect atmospheres for all worlds in the intriguing, seven-planet system TRAPPIST-1, and finding that clouds and water vapor in the planets’ atmospheres might make such study more challenging. With astronomy and astrobiology doctoral student and colleagues. ()
Description of a new open-source computer software package called VPLanet that simulates a wide range of planetary systems across billions of years, simulating atmospheres, orbits and stellar phenomena that can affect a planet’s ability to sustain liquid water on its surface, which is key to life. With Rory Barnes and colleagues. ()
An exploration of how viruses and hosts co-evolved, enabling microbial life in extremely cold brines. With oceanography professor ().
Modeling Earth’s atmosphere 2.7 billion years ago and the effect of iron-rich micrometeorites that rained down, melted and interacted with the surrounding gases, leading to a better understanding of carbon dioxide levels at that time. With Earth and space sciences graduate student and colleagues. ()
A presentation on the 91̽��Astronomy Department’s successful outreach to students through its that visits K-12 schools, enabling them to create shows of their own. With astronomy research assistant professor and several colleagues. and .)
An exploration of how to determine if oxygen detected on an exoplanet is really produced by life, using high-resolution planetary spectra from ground-based telescopes. With , an astronomy doctoral student, and colleagues. ()
A discussion of how studying a giant Pacific Octopus might help us learn more about different forms of cognition and better know and understand life beyond Earth — if we ever find it. With , a doctoral student in psychology. ()
A study of microbial life in extremely cold brines within unfrozen subsurface areas of permafrost, and their possible relevance to similar environments on Mars or icy moons in the solar system. With , a doctoral student in biological oceanography, and colleagues. (.)

Many other 91̽��faculty members will participate, either with reports on their own research or in support of colleagues or graduate students. These include ESS professors , , , , , astronomy professors , and , among others.

Astrobiologists such as Sullivan point out that the field’s focus and scientific benefit is about more than simply hunting for life, though that is the key motivator.

“It’s about thinking about life in a cosmic context. And about the origin and evolution of life,” Sullivan said.

“Even if you only care about Earth life, astrobiology is a viable — fundamental, I would say — interdisciplinary science that thrives independently of the existence of extraterrestrial life.”

Study brings new climate models of small star TRAPPIST 1’s seven intriguing worlds

Peter Kelley — Tue, 20 Nov 2018 18:00:20 +0000

The small, cool M dwarf star TRAPPIST-1 and its seven worlds. New research from the 91̽�� speculates on possible climates of these worlds and how they may have evolved. Photo: NASA

Not all stars are like the sun, so not all planetary systems can be studied with the same expectations. New research from a 91̽��-led team of astronomers gives updated climate models for the seven planets around the star TRAPPIST-1.

The work also could help astronomers more effectively study planets around stars unlike our sun, and better use the limited, expensive resources of the , now expected to launch in 2021.

“We are modeling unfamiliar atmospheres, not just assuming that the things we see in the solar system will look the same way around another star,” said , 91̽��doctoral student and lead author of a published Nov. 1 in Astrophysical Journal. “We conducted this research to show what these different types of atmospheres could look like.”

The team found, briefly put, that due to an extremely hot, bright early stellar phase, all seven of the star’s worlds may have evolved like Venus, with any early oceans they may have had evaporating and leaving dense, uninhabitable atmospheres. However, one planet, TRAPPIST-1 e, could be an Earthlike ocean world worth further study, as previous research also has indicated.

TRAPPIST-1, 39 light-years or about 235 trillion miles away, is about as small as a star can be and still be a star. A relatively cool “M dwarf” star — the most common type in the universe — it has about 9 percent the mass of the sun and about 12 percent its radius. TRAPPIST-1 has a radius only a little bigger than the planet Jupiter, though it is much greater in mass.

All seven of TRAPPIST-1’s planets are about the size of Earth and three of them — planets labeled e, f and g — are believed to be in its habitable zone, that swath of space around a star where a rocky planet could have liquid water on its surface, thus giving life a chance. TRAPPIST-1 d rides the inner edge of the habitable zone, while farther out, TRAPPIST-1 h, orbits just past that zone’s outer edge.

“This is a whole sequence of planets that can give us insight into the evolution of planets, in particular around a star that’s very different from ours, with different light coming off of it,” said Lincowski. “It’s just a gold mine.”

Previous papers have modeled TRAPPIST-1 worlds, Lincowski said, but he and this research team “tried to do the most rigorous physical modeling that we could in terms of radiation and chemistry — trying to get the physics and chemistry as right as possible.”

The team’s radiation and chemistry models create spectral, or wavelength, signatures for each possible atmospheric gas, enabling observers to better predict where to look for such gases in exoplanet atmospheres. Lincowski said when traces of gases are actually detected by the Webb telescope, or others, some day, “astronomers will use the observed bumps and wiggles in the spectra to infer which gases are present — and compare that to work like ours to say something about the planet’s composition, environment and perhaps its evolutionary history.”

He said people are used to thinking about the habitability of a planet around stars similar to the sun. “But M dwarf stars are very different, so you really have to think about the chemical effects on the atmosphere(s) and how that chemistry affects the climate.”

Combining terrestrial climate modeling with photochemistry models, the researchers simulated environmental states for each of TRAPPIST-1’s worlds.

Their modeling indicates that:

TRAPPIST-1 b, the closest to the star, is a blazing world too hot even for clouds of sulfuric acid, as on Venus, to form.
Planets c and d receive slightly more energy from their star than Venus and Earth do from the sun and could be Venus-like, with a dense, uninhabitable atmosphere.
TRAPPIST-1 e is the most likely of the seven to host liquid water on a temperate surface, and would be an excellent choice for further study with habitability in mind.
The outer planets f, g and h could be Venus-like or could be frozen, depending on how much water formed on the planet during its evolution.

Lincowski said that in actuality, any or all of TRAPPIST-1’s planets could be Venus-like, with any water or oceans long burned away. He explained that when water evaporates from a planet’s surface, ultraviolet light from the star breaks apart the water molecules, releasing hydrogen, which is the lightest element and can escape a planet’s gravity. This could leave behind a lot of oxygen, which could remain in the atmosphere and irreversibly remove water from the planet. Such a planet may have a thick oxygen atmosphere — but not one generated by life, and different from anything yet observed.

“This may be possible if these planets had more water initially than Earth, Venus or Mars,” he said. “If planet TRAPPIST-1 e did not lose all of its water during this phase, today it could be a water world, completely covered by a global ocean. In this case, it could have a climate similar to Earth.”

Lincowski said this research was done more with an eye on climate evolution than to judge the planets’ habitability. He plans future research focusing more directly on modeling water planets and their chances for life.

“Before we knew of this planetary system, estimates for the detectability of atmospheres for Earth-sized planets were looking much more difficult,” said co-author , a 91̽��astronomy doctoral student.

The star being so small, he said, will make the signatures of gases (like carbon dioxide) in the planet’s atmospheres more pronounced in telescope data.

“Our work informs the scientific community of what we might expect to see for the TRAPPIST-1 planets with the upcoming James Webb Space Telescope.”

Lincowski’s other 91̽��co-author is , professor of astronomy and director of the UW’s . Meadows is also principal investigator for the NASA Astrobiology Institute’s , based at the UW. All of the authors were affiliates of that research laboratory.

“The processes that shape the evolution of a terrestrial planet are critical to whether or not it can be habitable, as well as our ability to interpret possible signs of life,” Meadows said. “This paper suggests that we may soon be able to search for potentially detectable signs of these processes on alien worlds.”

TRAPPIST-1, in the Aquarius constellation, is named after the ground-based , the facility that first found evidence of planets around it in 2015.

Other co-authors are David Crisp of the Jet Propulsion Laboratory at the California Institute of Technology; Tyler Robinson of Northern Arizona University; Rodrigo Luger of the Flatiron Institute in New York City; and Giada Arney of the NASA/Goddard Space Flight Center in Greenbelt, Maryland. Robinson, Luger and Arney earned their doctoral degrees from the 91̽��and were members of the 91̽��Astrobiology Program.

The team used storage and networking infrastructure provided by the Hyak supercomputer system at the UW, funded by the UW’s Student Technology Fee. The research was funded by the NASA Astrobiology Institute; Lincowski also received support from NASA under its Earth and Space Science Fellowship Program. The work benefited from researchers’ participation in the NASA Nexus for Exoplanet System Science (NExSS) research coordination network.

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For more information, contact Lincowski at alinc@uw.edu, Lustig-Yeager at jlustigy@uw.edu or Meadows at vsm@astro.washington.edu.

NASA Astrobiology Institute Cooperative agreement #NNA13AA93A
Lincowski fellowship through grant #80NSSC17K0468

91̽��part of NASA network coordinating search for life on exoplanets

Peter Kelley — Mon, 25 Jun 2018 19:43:53 +0000

An artist’s conception of what life could look like on the surface of a distant planet. Photo: NASA

Researchers with the 91̽��-led are central to a group of published by NASA researchers in the journal Astrobiology outlining the history — and suggesting the future — of the search for life on exoplanets, or those orbiting stars other than the sun.

The research effort is coordinated by NASA’s Nexus for Exoplanet Systems Science, or NExSS, a worldwide network dedicated to finding new ways to study the age-old question: “Are we alone?”

A theme through the research and the discussions behind it is the need to consider planets in an integrated way, involving multiple disciplines and perspectives.

“For life to be detectable on a distant world it needs to strongly modify its planet in a way that we can detect,” said 91̽��astronomy professor , lead author of one of the papers and principle investigator of the Virtual Planetary Laboratory, or VPL for short. “But for us to correctly recognize life’s impact, we also need to understand the planet and star — that environmental context is key.”

Work done by NExSS researchers will help identify the measurements and instruments needed to search for life using future NASA flagship missions. The detection of atmospheric signatures of a few potentially habitable planets may possibly come before 2030, although whether the planets are truly habitable or have life will require more in-depth study.

The papers result from two years of effort by some of the world’s leading researchers in astrobiology, planetary science, Earth science, , astrophysics, chemistry and biology, including several from the 91̽��and the Virtual Planetary Laboratory, or VPL. The coordinated work was born of online meetings and an in-person workshop held in Seattle in July of 2016.

The pace of exoplanet discoveries has been rapid, with over 3,700 detected since 1992. NASA formed the international NExSS network to focus a variety of disciplines on understanding how we can characterize and eventually search for signs of life, called biosignatures, on exoplanets.

The NExSS network has furthered the field of exoplanet biosignatures and “fostered communication between researchers searching for signs of life on solar system bodies with those searching for signs of life on exoplanets,” said Niki Parenteau, an astrobiologist and microbiologist at NASA’s Ames Research Center, Moffett Field, California, and a VPL team member. “This has allowed for sharing of ‘lessons learned’ by both communities.”

The first of the papers reviews types of signatures astrobiologists have proposed as ways to identify life on an exoplanet. Scientists plan to look for two major types of signals: One is in the form of gases that life produces, such as oxygen made by plants or photosynthetic microbes. The other could come from the light reflected by life itself, such as the color of leaves or pigments.

Such signatures can be seen on Earth from orbit, and astronomers are studying designs of telescope concepts that may be able to detect them on planets around nearby stars. Meadows is a co-author, and lead author is , a VPL team member who earned his doctorate in astronomy and astrobiology from the 91̽��and is now a post-doctoral researcher at the University of California, Riverside.

Meadows is lead author of the second review paper, which discusses recent research on “false positives” and “false negatives” for biosignatures, or ways nature could “trick” scientists into thinking a planet without life was alive, or vice versa.

In this paper, Meadows and co-authors review ways that a planet could make oxygen abiotically, or without the presence of life, and how planets with life may not have the signature of oxygen that is abundant on modern-day Earth.

The paper’s purpose, Meadows said, was to discuss these changes in our understanding of biosignatures and suggest “a more comprehensive” treatment. She said: “There are lots of things in the universe that could potentially put two oxygen atoms together, not just photosynthesis — let’s try to figure out what they are. Under what conditions are they are more likely to happen, and how can we avoid getting fooled?”

Schwieterman is a co-author on this paper, as well as 91̽��doctoral students , and .

With such advance thinking, scientists are now better prepared to distinguish false positives from planets that truly do host life.

Two more papers show how scientists try to formalize the lessons we have learned from Earth, and expand them to the wide diversity of worlds we have yet to discover.

, 91̽��professor of Earth and space sciences, is lead author on a paper that proposes a framework for assessing exoplanet biosignatures, considering such variables as the chemicals in the planet’s atmosphere, the presence of oceans and continents and the world’s overall climate. Doctoral student is a co-author.

By combining all this information in systematic ways, scientists can analyze whether data from a planet can be better explained statistically by the presence of life, or its absence.

“If future data from an exoplanet perhaps suggest life, what approach can distinguish whether the existence of life is a near-certainty or whether the planet is really as dead as a doornail?” said Catling. “Basically, NASA asked us to work out how to assign a probability to the presence of exoplanet life, such as a 10, 50 or 90 percent chance. Our paper presents a general method to do this.”

The data that astronomers collect on exoplanets will be sparse. They will not have samples from these distant worlds, and in many cases will study the planet as a single point of light. By analyzing these fingerprints of atmospheric gases and surfaces embedded in that light, they will discern as much as possible about the properties of that exoplanet.

“Because life, planet, and parent star change with time together, a biosignature is no longer a single target but a suite of system traits,” said , a biometeorologist at NASA’s Goddard Institute for Space Studies in New York and a VPL team member. She said more biologists and geologists will be needed to interpret observations “where life processes will be adapted to the particular environmental context.”

The final article discusses the ground-based and space-based telescopes that astronomers will use to search for life beyond the solar system. This includes a variety of observatories, from those in operation today to ones that will be built decades in the future.

Taken together, this cluster of papers explains how the exoplanet community will evolve from their current assessments of the sizes and orbits of these faraway worlds, to thorough analysis of their chemical composition and eventually whether they harbor life.

“I’m excited to see how this research progresses over the coming decades,” said , an astrobiologist at NASA’s Goddard Space Flight Center, Greenbelt, Maryland, and a VPL team member. He is also a co-author on four of the five papers.

“NExSS has created a diverse network of scientists. That network will allow the community to more rigorously assess planets for biosignatures than would have otherwise been possible.”

NExSS is an interdisciplinary, cross-divisional NASA research coordination network.

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Based on a . For more information, contact Meadows at vsm@astro.washington.edu or Catling at dcatling@uw.edu.

Orbital variations can trigger ‘snowball’ states in habitable zones around sunlike stars

Peter Kelley — Mon, 14 May 2018 21:23:46 +0000

A NASA artist’s impression of Earth as a frigid “‘snowball” planet. New research from the 91̽�� indicates that aspects of an otherwise habitable-seeming exoplanet planet’s axial tilt or orbit could trigger such a snowball state, where oceans freeze and surface life is impossible. Photo: NASA

Aspects of an otherwise Earthlike planet’s tilt and orbital dynamics can severely affect its potential habitability — even triggering abrupt “snowball states” where oceans freeze and surface life is impossible, according to new research from astronomers at the 91̽��.

The research indicates that locating a planet in its host star’s “habitable zone” — that swath of space just right to allow liquid water on an orbiting rocky planet’s surface — isn’t always enough evidence to judge potential habitability.

, lead author of a paper to be published in the Astronomical Journal, said he and co-authors set out to learn, through computer modeling, how two features — a planet’s obliquity or its orbital eccentricity — might affect its potential for life. They limited their study to planets orbiting in the habitable zones of “G dwarf” stars, or those like the sun.

A planet’s is its tilt relative to the orbital axis, which controls a planet’s seasons; is the shape, and how circular or elliptical — oval — the orbit is. With elliptical orbits, the distance to the host star changes as the planet comes closer to, then travels away from, its host star.

Deitrick, who did the work while with the UW, is at the University of Bern. His 91̽��co-authors are atmospheric sciences professor , astronomy professors , and and graduate student , with help from undergraduate researcher Caitlyn Wilhelm.

The Earth hosts life successfully enough as it circles the sun at an axial tilt of about 23.5 degrees, wiggling only a very little over the millennia. But, Deitrick and co-authors asked in their modeling, what if those wiggles were greater on an Earthlike planet orbiting a similar star?

Previous research indicated that a more severe axial tilt, or a tilting orbit, for a planet in a sunlike star’s habitable zone — given the same distance from its star — would make a world warmer. So Deitrick and team were surprised to find, through their modeling, that the opposite reaction appears true.

“We found that planets in the habitable zone could abruptly enter ‘snowball’ states if the eccentricity or the semi-major axis variations — changes in the distance between a planet and star over an orbit — were large or if the planet’s obliquity increased beyond 35 degrees,” Deitrick said.

The new study helps sort out conflicting ideas proposed in the past. It used a sophisticated treatment of ice sheet growth and retreat in the planetary modeling, which is a significant improvement over several previous studies, co-author Barnes said.

“While past investigations found that high obliquity and obliquity variations tended to warm planets, using this new approach, the team finds that large obliquity variations are more likely to freeze the planetary surface,” he said. “Only a fraction of the time can the obliquity cycles increase habitable planet temperatures.”

Barnes said Deitrick “has essentially shown that ice ages on exoplanets can be much more severe than on Earth, that orbital dynamics can be a major driver of habitability and that the habitable zone is insufficient to characterize a planet’s habitability.” The research also indicates, he added, “that the Earth may be a relatively calm planet, climate-wise.”

This kind of modeling can help astronomers decide which planets are worthy of precious telescope time, Deitrick said: “If we have a planet that looks like it might be Earth-like, for example, but modeling shows that its orbit and obliquity oscillate like crazy, another planet might be better for follow-up” with telescopes of the future.”

The main takeaway of the research, he added, is that “We shouldn’t neglect orbital dynamics in habitability studies.”

Other co-authors are , a former 91̽��post-doctoral researcher now with the LESIA Observatoire de Paris; and John Armstrong of Weber State University, who earned his doctorate at the UW.

The research used storage and networking infrastructure provided by the Hyak supercomputer system at the UW, funded by the UW’s Student Technology Fee. The work was funded by the NASA Astrobiology Institute through the UW-based .

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For more information, contact Deitrick at deitrr@astro.washington.edu or russell.deitrick@csh.unibe.ch; or Barnes at rory@astro.washington.edu.

Agreement number: NNA13AA93A