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IIlustration showing radiation from a star slamming into planets with and without magnetic fields. (Credit: Aurora Simonnet/Sonoma State University)

Scientists on a new project led by CU Boulder will develop “worlds in a box” to study the conditions that might make far away planets habitable.

Visualization showing the escape of ions from Mars' atmosphere. (Credit: NASA Goddard Space Flight Center)

Artist's depiction of what Mars looks like today, left, and how it may have appeared billions of years ago, right, when water covered the planet's surface. (NASA Goddard Space Flight Center)

The research is part of NASA’s (ICAR) program. Recently, the space agency to pursue explorations in the realm of astrobiology, the study of life beyond Earth.

David Brain, professor in the (LASP) and Department of Astrophysical and Planetary Sciences (APS), will lead one of those teams. The $5 million effort will investigate over five years the phenomenon of atmospheric escape—how some planets, like Earth, hold onto their atmospheres while others, like Mars, don’t. 

“I have been interested in atmospheric escape from Mars for a very long time as a potential explanation for the evidence that liquid water once resided on the surface of that planet,” Brain said. “It was possible billions of years ago, but it’s not possible today.”

He explained that billions of years ago, vast oceans of water likely covered much of the surface of Mars. Today, liquid water can’t exist on the planet’s surface, largely because its modern-day atmosphere is more than 100 times thinner than Earth’s. Recent research points to an explanation: Data from NASA’s (MAVEN) spacecraft, which was designed and built at LASP, have shown that radiation from the sun is slowly stripping away Mars’ atmosphere. 

Brain and his colleagues want to learn more about why that might happen to some planets and not others. In the new project, he and his colleagues will use computer simulations, or models, to create a motley crew of digital worlds—then test how their atmospheres behave around a series of different stars. He hopes that the team’s research will help astrophysicists identify worlds light-years from Earth that could, potentially, support thriving communities of living organisms.

“Our models are kind of like worlds in a box,” Brain said. “We can put a telescope in that box and figure out what we might see if we were observing that planet from far away.”

Planets galore

The research builds on decades of study delving into the impacts of stars on planetary atmospheres, said Daniel Baker, director of LASP.

“Comparative planetary studies have been a great strength of LASP for decades,” he said. “This exciting new interdisciplinary research will help scientists understand why some planets keep their atmospheres, increasing the likelihood that they could be habitable.”

David Brain

For Brain and his colleagues, one of the biggest question marks surrounding atmospheric escape may be magnetic fields.

He explained that scientists have long assumed that planets need strong magnetic fields to be able to maintain thick atmospheres. Earth, for example, harbors such a magnetic field, which is what makes the needles on compasses point north. This field also creates a sort of protective shell around the planet, called a “magnetosphere,” that may help to prevent Earth’s nitrogen-rich atmosphere from flying off into space. Mars, meanwhile, doesn’t have the same protection. 

“Do habitable worlds require magnetic fields? It's something that we all blindly assumed 25 years ago when I was in graduate school,” Brain said. “But recently that’s been called into question.”

The new project aims to find out. The researchers will use models to build a planetary toy box of sorts. They will draw on a complex series of equations to represent different kinds of planets, capturing the physics of their upper atmospheres. Then the team will place those possible worlds into orbit around an equally diverse set of suns. What would happen to Mars, for example, if it orbited a small but volatile red dwarf star like the nearby Proxima Centauri? How would Earth fare around a supergiant star like Betelgeuse? 

For now, Brain isn’t sure what the team will find. He suspects that whether a planet can hang onto its atmosphere hinges on a wide range of factors—the presence of a magnetic field, yes, but also a planet’s size and whether its atmosphere is dominated by carbon dioxide, like on Mars, or hydrogen, like on Jupiter.

“I think the answer is going to be: It depends,” he said.