Robust stellar flames may not impede life on exoplanets, may make it easier to detect

Although violent and unpredictable, the stellar flames emitted by the host star of a planet do not necessarily prevent the formation of life, according to a new study by Northwestern University.

Emitted by stars, stellar flames are sudden flashes of magnetic images. On Earth, rockets sometimes damage satellites and disrupt radio communications. Elsewhere in the universe, stellar rockets also have the ability to deplete and destroy atmospheric gases, such as ozone. Without ozone, harmful levels of ultraviolet (UV) radiation can enter the planet’s atmosphere, thus reducing its chances of sheltering surface life.

Combining 3-D atmospheric chemistry and climate modeling with observed data from distant star flames, a team led by the Northwest discovered that stellar flames could play an important role in the long-term evolution of a planet’s atmosphere and habitability.

“We compared the atmospheric chemistry of planets that experience frequent eruptions with flameless planets. The long-term atmospheric chemistry is very different,” said Howard Chen of Northwestern, the study’s lead author. “Continuous flames actually lead the atmospheric composition of a planet into a new chemical equilibrium.”

“We found that stellar burns may not prevent the existence of life,” added Daniel Horton, lead author of the study. “In some cases, the flare does not erode all atmospheric ozone. Surface life could still have a chance to fight.”

The study will be published in the journal on December 21 Nature Astronomy. It is a joint effort between researchers at Northwestern, the University of Colorado at Boulder, the University of Chicago, the Massachusetts Institute of Technology and NASA’s Nexus for Exoplanet System Science (NExSS).

Horton is an assistant professor of Earth and planetary sciences at Weinberg College of Arts and Sciences in Northwestern. Chen is a PhD candidate in the Horton Climate Change Research Group and a future NASA investigator.

The importance of missiles

All stars – including our own sun – light up or randomly release stored energy. Fortunately for earthlings, the flames of the sun usually have a minimal impact on the planet.

“Our sun is more of a gentle giant,” said Allison Youngblood, an astronomer at the University of Colorado and co-author of the study. “It is older and not as active as younger and smaller stars. The earth also has a strong magnetic field that deflects the sun’s harmful winds.”

Unfortunately, most potentially habitable exoplanets are not as lucky. For planets to be able to shelter life, they must be close enough to a star that their water does not freeze – but not close enough for water to vaporize.

“We studied planets orbiting the dwarf stars M and K – the most common stars in the universe,” Horton said. “The habitable zones around these stars are narrower because the stars are smaller and less powerful than stars like our sun. On the other hand, dwarf stars M and K are thought to have more frequent flaring activity than our sun, and their blocked planets are unlikely to have magnetic fields that help deflect their stellar winds. “

Chen and Horton previously conducted a study of the long-term climatic environments of dwarf M star systems. However, missiles appear over long periods of hours or days. Although these short periods of time can be difficult to simulate, the incorporation of flame effects is important to form a more complete picture of the exoplanet’s atmospheres. The researchers achieved this by incorporating flare data from the Transiting Exoplanet Satellite, launched in 2018, in their model simulations.

Using missiles to detect life

If there is life on these dwarf exoplanets M and K, previous work hypothesizes that stellar flames could make it easier to detect. For example, stellar flames can increase the abundance of life-indicating gases (such as nitrogen dioxide, nitric oxide, and nitric acid) from imperceptible to detectable levels.

“Space weather events are usually seen as detrimental to the home,” Chen said. “But our study shows quantitatively that some space times can actually help us detect important gas signatures that could mean biological processes.”

This study involved researchers from a wide range of backgrounds and expertise, including climate scientists, exoplanet scientists, astronomers, theorists and observers.

“This project was the result of the team’s fantastic collective effort,” said Eric T. Wolf, a planetary scientist at CU Boulder and co-author of the study. Our paper highlights the benefits of interdisciplinary efforts when investigating conditions on extrasolar planets.