TRAPPIST-1e Likely Doesn’t Have What It Takes To Be a Habitable Planet — Here’s Why
Are we alone in the universe? It’s a question that has sparked curiosity in astronomers for generations. There are at least 6,000 known planets outside our Solar System (also known as exoplanets), but only a handful are thought to offer conditions suitable for life, according to NASA.
One of those is TRAPPIST-1e — the fourth of seven exoplanets to orbit TRAPPIST-1, a red dwarf star in the constellation Aquarius, 39 light-years from Earth.
This is because TRAPPIST-1e is a rocky planet that exists within the “Goldilocks zone,” whereby its distance from its star means it is possible, at least in theory, for there to be water on the surface. But this is only true if the planet has an atmosphere — and it is on this point we should exercise some caution, say researchers writing in a study published in the Astrophysical Journal of Letters.
“The basic thesis for TRAPPIST-1e is this: If it has an atmosphere, it’s habitable,” Sukrit Ranjan, an assistant professor at the University of Arizona’s Lunar and Planetary Laboratory, said in a statement. “But right now, the first-order question must be, ‘Does an atmosphere even exist?'”
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TRAPPIST-1e’s Atmosphere
Publishing their results in twin studies in the Astrophysical Journal of Letters, the team collected data using the James Webb Space Telescope (JWST), aiming it at TRAPPIST-1e as it passed TRAPPIST-1 four times.
The results suggested hints of methane, which could indicate the existence of an atmosphere. Only later research suggests it is unlikely that the source of the methane is TRAPPIST-1e itself. In fact, “the previously reported tentative hint of an atmosphere is more likely to be ‘noise’ from the host star,” said Ranjan.
Ranjan and his fellow researchers came to this conclusion after simulating various scenarios in which the planet TRAPPIST-1e has an atmosphere rich in methane, calculating the probability of each.
Through this, the team was able to rule out the possibility of a cloudy H2-dominated atmosphere. While still possible, the research also “weakly disfavors” both a thin atmosphere rich in carbon dioxide (like Mars) and a thick atmosphere rich in carbon dioxide (like Venus).
According to the results, the most likely scenario is that TRAPPIST-1e has a methane-rich atmosphere similar to Titan, Saturn’s largest moon, and the only satellite of any planet to boast a thick atmosphere, according to NASA. Even this, the researchers concluded, appears improbable. Hence, the likelihood of any methane is simply “noise.”
Because TRAPPIST-1’s temperature is significantly cooler than that of our sun (a yellow dwarf), gas molecules can be found in its atmosphere. This makes it difficult to determine whether the methane hints detected belong to the star or the planet.
While the research puts a damper on the idea that TRAPPIST-1e has a methane-rich atmosphere that can sustain water and, therefore, possibly host life, it should not rule it out either — “we just need more data,” said Ranjan.
Searching For A Habitable Planet
There are billions of planets in the Milky Way, but only a select few with the ingredients required to host life. The TRAPPIST-1 system is of intense interest to astronomers because all seven planets that orbit the star are made of rock, similar in size and mass to Earth, and temperate.
While the entire system can fit within Mercury’s orbit, it is TRAPPIST-1e that is situated in the habitable (or “Goldilocks”) zone and is most likely to boast conditions that enable life to thrive.
The team hopes that future research will help confirm whether or not TRAPPIST-1e has an atmosphere.
“With 15 additional JWST transits of TRAPPIST-1 e on the horizon, we stand on the precipice of revealing an atmosphere, or its absence, on one of the most compelling rocky exoplanets,” the study’s authors wrote.
Read More: James Webb Space Telescope Captures Smallest Exoplanet Ever Seen in Historic First
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