Star Flares May Obstruct Search for Life in Promising Star Systems

Investigating the atmosphere surrounding the TRAPPIST-1 star system, one of the most promising locations in the galaxy, may prove even more challenging for astronomers than previously anticipated due to sporadic radiation bursts emitted by the stars.

First identified in 2016, TRAPPIST-1 is a diminutive red star located about 40 light years from Earth and is known to orbit at least seven planets. Several of these planets are situated within habitable zones that could support liquid water, making them prime candidates for astronomers searching for signs of extraterrestrial life.

For life to be sustainable, these planets must retain an atmosphere. Up to now, extensive observations from the James Webb Space Telescope have shown no signs of atmospheres on any of the planets.

Now, Julien DeWitt from the Massachusetts Institute of Technology and his team have detected minor bursts emanating from TRAPPIST-1 for several minutes each hour. These radiation surges seem to complicate the planets’ capacity to capture light filtering through their atmospheres — if they exist — which is essential for determining the chemical makeup of any atmosphere.

Using the Hubble Space Telescope, DeWitt and his team searched for specific ultraviolet wavelengths from TRAPPIST-1 that would be absorbed by hydrogen. If a planet detected this light more than anticipated while transiting in front of the star, it could suggest that hydrogen was escaping from its atmosphere.

Although they found no definitive evidence, significant variabilities in different observations hint that extra light is being emitted at certain times. Hubble data can be divided into 5-minute increments, showing that this additional light is fleeting. DeWitt and his team deduce that these must be microflares — akin to solar flares from our sun, but occurring more frequently.

TRAPPIST-1 is quite faint, requiring astronomers to observe for extended periods to gather enough light. “Furthermore, there’s this flaring activity, which coincides with the timing of the transiting planets,” DeWitt states. “It’s particularly difficult to draw any conclusive insights regarding the existence of [atmospheres on the exoplanets],” he adds.

DeWitt and his colleagues also assessed whether these flares could impede a planet’s ability to retain its atmosphere. They found that one planet, TRAPPIST-1b, which the James Webb Space Telescope had already failed to detect atmospheric evidence for, could lose an equivalent of 1,000 times the hydrogen found in Earth’s oceans every million years. However, it’s often challenging to pinpoint which of these flares actually impact the planet. DeWitt suggests many uncertainties and various scenarios still need exploration.

Such stars can exhibit varying activity levels, but TRAPPIST-1 appears to be experiencing a more active phase, states Ekaterina Ilin from the Dutch Institute of Radio Astronomy. “This outcome isn’t completely unexpected or otherworldly; it’s just unfortunate. It’s more active than we had hoped,” she remarks. “In a way, it adds new layers to interpreting these flares, especially if you consider them.”