Would Mars be More Habitable if it Orbited a Red Dwarf?

Thanks to the explosion in discoveries made in the last decade, the study of extrasolar planets have entered a new phase. With 4,884 confirmed discoveries in 3,659 systems (and another 7,958 candidates awaiting confirmation), scientists are shifting their focus from discovery to characterization. This means examining known exoplanets more closely to determine if they possess the necessary conditions for life, as well as “biomarkers” that could indicate the presence of life.

A key consideration is how the type of star may impact a planet’s chances of developing the right conditions for habitability. Consider red dwarf stars, the most common stellar class in the Universe and a great place to find “Earth-like,” rocky planets. According to a new study by an international team of scientists, a lifeless planet in our own backyard (Mars) might have evolved differently had it orbited a red dwarf instead of the Sun.

The research was conducted by an international, multi-disciplinary research team consisting of modelers, observational scientists and space physics, planetary science, and astrophysics theoreticians led by David Brain and fellow researchers from the Laboratory for Atmospheric and Space Physics (LASP) at the CU Boulder. Brain is also the leader of the Magnetic fields, Atmosphere, and the Connection to Habitability (MACH) NASA DRIVE Science Center, a NASA integrated multi-agency initiative located at the NASA Marshall Space Flight Center in Huntsville, Alabama.

Stellar flares could threaten life on planets that orbit red dwarfs. Credit: NASA/ESA/D. Player (STScI)

Brain and his colleagues from LASP and CU Boulder were joined by researchers from the NASA Goddard Space Flight Center, the Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), the California-based SRI International, the Swedish Institute for Space Physics (IRF), and universities from across the U.S., the University of Leiden in the Netherlands, and the University of Tokyo and Tohoku University in Japan.

Their findings were recently shared in a series of presentations at the 2021 American Geographical Union (AGU) Fall Meeting, held this week in New Orleans. As they explained, by applying our current understanding of Mars to rocky exoplanets, scientists will be able to characterize and identify habitable, Earth-like planets in other solar systems. As their results showed, the answer hinges on an exoplanets’ atmospheres and what it takes for each planet to retain its atmosphere.

For the sake of their research, the team examined the case of “Exoplanet Mars,” a Mars-sized rocky planet orbiting an M-type red dwarf star. Consistent with the dimmer and cooler nature of red dwarfs, this star would be only 4% as bright as our Sun and have an effective temperature of 2770 K (2,500 °C; 4532 °F) – about 3000 K cooler than our Sun. It would also be more variable than our Sun, meaning that it would be prone to flare-ups, which would impact Exoplanet Mars’ atmosphere.

The challenge, according to Brain, was to assemble the necessary expertise, observations, and modeling to understand the relative importance of each property and how they contribute to habitability over time. Interestingly enough, language was not a barrier to this international team, but its multi-disciplinary nature presented some problems. Because of how scientific disciplines and methodology have diverged in recent decades, there was a “language barrier” of sorts.

Artist’s rendering of a solar storm hitting Mars and stripping ions from the planet’s upper atmosphere. Credits: NASA/GSFC

As a result, the multi-disciplinary team needed to develop a more effective means of communication that bridged the disciplines and their particular methods. This, said Brain, is where the MACH Drive Service Center (DSC) played an especially-important role:

“Our center has brought together experts from many scientific disciplines to collaboratively address big-picture questions like the habitability of alien planets. Together we are figuring out which physics are important to include and how to link models together, while making sure team members feel heard and are inclusive in the process.

The preliminary results indicate that Exoplanet Mars would have lost its atmosphere at a greater rate than the real Mars if it were orbiting a red dwarf star. This is consistent with what astronomers have observed from nearby red dwarf systems, many of which emit flares that are powerful enough to strip Earth’s atmosphere. At the same time, recent research has shown that these flares may be emitted from the poles, thus sparing any planets.

Regardless, the true significance of this research is how it will help scientists characterize and identify habitable, Earth-like planets in other solar systems. As we move into the next phase of searching for habitable planets in the cosmos, knowing what stars and planetary systems are likely to provide the best results is essential.

Further Reading: LASP