Unfortunately for science fiction fans, desert worlds outside our solar system are unlikely to host life, according to new research from 91̽��. Scientists show that an Earth-sized planet needs at least 20 to 50% of the water in Earth’s oceans to maintain a critical natural cycle that keeps water on the surface.

Scientists believe that there are billions of planets outside our solar system. More than are confirmed, but only some of them are candidates for life. The search for life has focused on planets in the “,” a sweet spot that is neither too close nor too far from a central star. Planets in this zone are considered viable because they can maintain liquid surface water.

“When you are searching for life in the broad landscape of the universe with limited resources, you have to filter out some planets,” said lead author , a 91̽��doctoral student of Earth and space sciences.

Water, although essential, does not guarantee the existence of life. With this study, researchers worked to further narrow the search by investigating planets with just a small amount of water.

“We were interested in arid planets with very limited surface water inventory — far less than one Earth ocean. Many of these planets are in the habitable zone of their star, but we weren’t sure if they could actually be habitable,” White-Gianella said.

The team’s results, , show that habitability hinges on the geologic carbon cycle — a water-driven process that exchanges carbon between the atmosphere and interior over millions of years, stabilizing surface temperatures.

Carbon dioxide, which comes from volcanoes in a natural system, accumulates in the atmosphere before falling back to Earth dissolved in rainwater. Rain erodes and chemically reacts with rocks on the Earth’s surface and runoff transports carbon to the ocean, where it sinks to the seafloor. Plate tectonics drives carbon-rich oceanic plates below continental land. Millions of years later, carbon resurfaces as mountains form.

If water levels drop too low for rainfall, carbon removal — from weathering — can’t keep up with emissions from volcanic eruptions and carbon dioxide levels in the atmosphere spike, trapping water. Rising temperatures evaporate the remaining surface water, initiating runaway warming that makes the planet too hot to support life.

“So that unfortunately makes these arid planets within habitable zones unlikely to be good candidates for life,” White-Gianella said.

Although scientists have instruments that can measure surface water, rocky exoplanets are difficult to observe directly. In this study, the researchers ran a series of complex simulations to better understand how water might behave in these desert worlds.

Previous efforts to model the carbon cycle focused on cooler, perhaps wetter planets. The models factored in evaporation from sunlight, but didn’t include other drivers, such as wind. White-Gianella adapted existing models to drier planets by refining evaporation and precipitation estimates.

“These sophisticated, mechanistic models of the carbon cycle have emerged from people trying to understand how Earth’s thermostat has worked — or hasn’t — to regulate temperature through time,” said senior author , a 91̽��assistant professor of Earth and space sciences.

However, the function of the geologic carbon cycle on arid planets was largely unexplored. The results show that even planets that form with surface water could lose it, transitioning from potentially habitable to uninhabitable due to carbon cycle disruption.

One such planet exists far closer to home: Venus. The planet of love is roughly the same size as Earth, likely formed around the same time and may have started with a similar amount of water.

Yet today, the surface of Venus rivals the temperature of a wood-fired pizza oven. Standing on the surface would feel like being crushed by 10 blue whales, White-Gianella said.

Many theories attempt to explain why Earth and Venus are so different. White-Gianella and Krissanen-Totton propose that Venus, being closer to the sun, may have formed with slightly less water than Earth, which imbalanced the geologic carbon cycle. As surface temperatures rose with atmospheric carbon dioxide levels, Venus lost its water — and any life it may have hosted.

Upcoming missions to Venus will attempt to understand what happened to the planet and whether it ever hosted life. The findings could also offer insight into planets much farther away.

“It’s very unlikely that we will land something on the surface of an exoplanet in our lifetime, but Venus — our nextdoor neighbor — is arguably the best exoplanet analog,” White-Gianella said.

The researchers hope that results from future missions will help validate the results of their modeling.

“This has implications for a lot of the potentially habitable real estate out there,” Krissanen-Totton said.

This study was funded by the National Science Foundation, the NASA Astrobiology Program and the Alfred P. Sloan Foundation.

For more information, contact White-Gianella at hasktw@uw.edu or Krissanen-Totton at joshkt@uw.edu.��

The American Geophysical Union honored five 91̽�� faculty and researchers from the Earth and space sciences and atmospheric and climate science departments this week at the annual meeting in New Orleans.

Each year, the meeting draws thousands of scientists, educators and policymakers to discover emerging research, discuss hurdles and network. Prior to the meeting, AGU announces awards for individuals who have made significant contributions to Earth and space science and presents them in person during the week.

The theme is, “Where Science Connects Us,” and the 91̽��awardees were recognized for research that advances understanding of natural hazards, the history of Earth, weather and climate change.

Here are the UW’s five recipients and their respective awards:

, a 91̽��assistant professor of Earth and space sciences, studies how magmas form beneath volcanoes. She specializes in work that involves using samples from past volcanic eruptions to examine the behavior of volcanic gases like water, carbon, and sulfur, which can help researchers monitor active volcanoes. Muth received the for early career scientists who have made outstanding contributions to fields of volcanology, geochemistry, and petrology.

, a 91̽��professor of atmospheric and climate science, studies predictability, mountain meteorology and numerical weather prediction. Durran’s recent research focuses on using deep learning to change our current paradigm for numerical weather prediction, seasonal forecasting and climate modeling. He holds a joint position with NVIDIA. Durran received the award for prominent scientists who have made exceptional contributions to the understanding of weather and climate.

, a 91̽��postdoctoral researcher of atmospheric and climate science, studies the formation and evolution of aerosol particles in the atmosphere, which play a pivotal role in both air pollution and climate change. By identifying and characterizing the fundamental chemical processes governing aerosol behavior, his research supports efforts to predict current atmospheric conditions and the trajectory of air quality and climate moving forward. Kenseth received the recognizing outstanding science and accomplishments by researchers that are within three years of receiving their doctorate.

, a 91̽��assistant professor of Earth and space sciences, uses simulations to study the interactions between planetary atmospheres, interiors and biospheres to better understand the long-term evolution of Earth, Venus and rocky exoplanets. By building a holistic understanding of planetary evolution, this work will help enable scientists to search for life on other planets. Krissansen-Totton received the recognizing significant contributions to planetary science by early career researchers

, a 91̽��professor of Earth and space sciences, studies the ratio of elements and their isotopes in rocks and minerals to understand how planets form and evolve. His research introduced a new method for analysis involving isotopic “fingerprints” that allows scientists to learn about Earth’s crust, the composition of the mantle, the origins of magma and even the early solar system. Teng was inducted as a , a program that recognizes AGU members who have made exceptional contributions to Earth and space science through a breakthrough, discovery or innovation in their field.

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.��

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.