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Wednesday, June 19, 2024 | Back issues
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Stellar Flares Can Reduce Planet Habitability

An artist's conception of HD 209458 b, an exoplanet whose atmosphere is being torn off at more than 35,000 km/hour by the radiation of its close-by parent star. This hot Jupiter was the first alien world discovered via the transit method, and the first planet to have its atmosphere studied. (NASA/European Space Agency/Alfred Vidal-Madjar (Institut d'Astrophysique de Paris, CNRS))

(CN) — Learning more about stellar flares could be key to determining the habitability of exoplanets, researches said in a study released Sunday.

Scientists at the Center for Space Science at NYU Abu Dhabi in the United Arab Emirates calculated erosion rates of planetary atmospheres using stellar flare emission data from NASA's Transiting Exoplanet Survey Satellite (TESS) observatory.

Launched in April 2018 aboard a SpaceX Falcon 9 rocket, TESS is a survey mission of the 200,000 brightest stars near the sun to discover exoplanets, which are planets that orbit stars outside of our solar system. The TESS satellite is composed of four identical cameras with seven lenses, sensors and electronics attached to a special plate enclosed by a sunshade to prevent stray light from distorting the image of nearby stars, according to NASA.

Research scientist Dimitra Atri and graduate student Shane Carberry Mogan found that more frequent, lower energy flares — radiation emissions from stars that form what’s known as “space weather” — had a greater impact on an exoplanet's atmosphere than less frequent, higher energy flares. These emissions consist of extreme ultraviolet photons and charged particles that can alter an exoplanet’s upper atmosphere.

While many stellar flares are invisible to the naked eye, they are powerful enough to disrupt radio communications. Their frequency can be several times per day or a few times a week.

“Given the close proximity of exoplanets to host stars, it is vital to understand how space weather events tied to those stars can affect the habitability of the exoplanet,” said Atri. 

The scientists’ findings were explained in a paper titled “Stellar flares versus luminosity: XUV-induced atmospheric escape and planetary habitability” published in the journal Monthly Notices of Royal Astronomical Society: Letters.

Defined by a planet's ability to sustain liquid water on its surface, planetary habitability is an essential concept in exoplanet science. Sustaining an atmosphere is one of the most important requirements for a habitable planet. 

Stellar flares are less understood than solar flares, which emit directly from the sun. But they can be more powerful.

In July 2020, astronomers observed massive stellar flares on the red dwarf star AD Leonis, including a superflare 20 times more powerful than common flares from the sun. That is believed to be the first time such a phenomenon had ever been observed.

Atri and his colleague also determined how different types of stars emit extreme ultraviolet radiation through stellar flares, and how nearby planets are affected.

Atri’s research provides new insights into the habitability of exoplanets since the effects of stellar activity are not well understood. The study also highlights the need for “better numerical modeling of atmospheric escape — how planets release atmospheric gases into space,” which can erode the atmosphere and diminish a planet's habitability. “The next research step would be to expand our data set to analyze stellar flares from a larger variety of stars to see the long-term effects of stellar activity, and to identify more potentially habitable exoplanets,” Atri stated.

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