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鈥檚 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鈥檚 conference will be held June 24-28 at the Hyatt Regency Hotel in Bellevue. It鈥檚 the biggest meeting of astrobiologists in the world and dozens of 91探花 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 91探花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 , 91探花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 91探花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 91探花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 91探花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 鈥� 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 91探花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鈥檚 focus and scientific benefit is about more than simply hunting for life, though that is the key motivator.

“It鈥檚 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 鈥� fundamental, I would say 鈥� interdisciplinary science that thrives independently of the existence of extraterrestrial life.鈥�

Aspects of an otherwise Earthlike planet鈥檚 tilt and orbital dynamics can severely affect its potential habitability 鈥� even triggering abrupt 鈥渟nowball states鈥� where oceans freeze and surface life is impossible, according to new research from astronomers at the 91探花.

The research indicates that locating a planet in its host star鈥檚 鈥渉abitable zone鈥� 鈥� that swath of space just right to allow liquid water on an orbiting rocky planet鈥檚 surface 鈥� isn鈥檛 always enough evidence to judge potential habitability.聽

, 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 鈥� a planet鈥檚 obliquity or its orbital eccentricity 鈥� 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 鈥� oval 鈥� 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 91探花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 鈥� given the same distance from its star 鈥� 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 鈥� changes in the distance between a planet and star over an orbit 鈥� 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 91探花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鈥檚 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

As telescopes of ever-greater power scan the cosmos looking for life, knowing where to look 鈥� and where not to waste time looking 鈥� will be of great value.

New research by 91探花 astronomer and co-authors describes possible planetary systems where a gravitational nudge from one planet with just the right orbital configuration and tilt could have a mild to devastating effect on the orbit and climate of another, possibly habitable world.

Their have been accepted for publication in the Astrophysical Journal.

The magnitude of the chaos can range widely, Barnes said, from planets whose orbits remain largely circular to those “whose orbits get so elongated that a planet could slam into its host star 鈥� an extreme form of climate change!”

Even if the effect isn’t that dramatic, the orbit 鈥� thus the climate, as orbit is a primary driver of climate 鈥� could still be severe enough to inhibit life, or sterilize the planet if life has already begun, Barnes said.

The particular effect they studied is called a “” and it comes into play when two planets’ orbital periods are an integer ratio of each other, such as Neptune orbiting the sun three times for every time Pluto orbits twice. A repetitive force, like a gravitational nudge, happens at the same place in the planets’ orbits around the star, the effect of which grows slowly over millions of years.

This can happen to a planet in its star’s habitable zone, the swath of space around it that’s just right to allow an orbiting rocky planet to have water in liquid form on its surface, thus giving life a chance. Barnes calls such worlds “chaotic Earths” and suggests making them lower priorities in the search for life.

Another condition for this orbital bullying is “mutual inclination,” meaning that the two planets are angled toward each other in space. Planets in our solar system all lie along the same plane in space, and are called coplanar, but not all planetary systems are like that. So Barnes and colleagues decided to “kick up” inclinations between planets in computer models and study the result.

“That was the basic idea,” he said. “What happens when you have planets that are in this resonance and with mutual inclinations?

“And what we found was that things go all haywire. Those little perturbations that keep happening at the same point cause one of the orbits to do some crazy things 鈥� even flip over entirely 鈥� and then kind of come back to where it was before. It was pretty unexpected for us.”

If the fluctuations are small, such worlds might yet retain their chance of life and be worth further study. But if they are dramatic, astronomers should probably look elsewhere.

“Planets in systems that drive orbits to near-misses with the host stars are less promising targets and should be skipped over for other candidates,” Barnes said, “even if they are found today on circular orbits in the habitable zone.”

Further computer modeling will help researchers distinguish between these two possibilities, he said.

Powerful tools such as the will come online in a few years, able to determine the atmospheres of exoplanets, or those outside the solar system. But the work will be expensive, so astronomers will need to choose their objects of study wisely, Barnes said.

Barnes is lead author of the study. Co-authors are and , 91探花astronomy professor and graduate student, respectively; Richard Greenberg of the University of Arizona and Sean Raymond of Laboratoire d’Astrophysique de Bordeaux in France.

The research was done through the , a UW-based interdisciplinary research group, and funded by NASA and the National Science Foundation.

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For more information, contact Barnes at 206-543-8979 or rory@astro.washington.edu. NASA Cooperative Agreement No. NNA13AA93A, NSF grant AST-1108882.