An article published in the journal “Nature” reports a study on the exoplanet TRAPPIST-1 c which indicates that its atmosphere is very thin or non-existent. A team of researchers used the James Webb space telescope to examine one of the seven planets of the TRAPPIST-1 system and the results allow to rule out the hypothesis that it’s similar to Venus. Thermal emissions indicate a temperature on its surface’s day-side of about 107° Celsius. According to the researchers, this indicates that this exoplanet may have formed with little water.
The TRAPPIST-1 exoplanet c is one of the first exoplanets detected in the TRAPPIST-1 system. This system has become famous for the presence of seven rocky planets but already in May 2016, the verification of some of them was announced. TRAPPIST-1 c is just larger than Earth its mass is about 30% greater than the Earth’s. Due to its distance from its star, it receives a similar amount of heat to that which Venus receives from the Sun, therefore one of the hypotheses was that this exoplanet also had a very thick atmosphere composed almost entirely of carbon dioxide.
The TRAPPIST-1 system is very interesting because its seven planets are at such distances from their star that conditions on their surfaces can vary greatly. They’re all tidally locked to their star, to which they always show the same face, and astronomers want to understand the consequences. Attempts were made in previous years to figure out if they had an atmosphere but the results were inaccurate. The beginning of the James Webb Space Telescope’s mission started changing that.
The new studies of the TRAPPIST-1 system began with its innermost planet, TRAPPIST-1 b, which appears to lack an atmosphere according to results published last March. Certainties will come from further observations but it’s normal for a planet very close to its star to lose its primordial atmosphere. Meanwhile, the James Webb Space Telescope observed the next planet, TRAPPIST-1 c.
MIRI (Webb’s Mid-Infrared Instrument) is the one that was specifically used on four different occasions during the so-called secondary eclipses, meaning when the planet passed behind its star. On those occasions, the planet’s thermal emissions are no longer detected and then return at the end of the eclipse.
The analysis of the collected data indicates that TRAPPIST-1 c doesn’t have an atmosphere or at least it’s very thin and cloudless. The temperature on its surface’s day-side is about 107° Celsius. This suggests that it formed with a limited amount of water and is consequently uninhabitable by Earth-like life forms.
These results may be disappointing for those who hoped that the innermost planets of the TRAPPIST-1 system had atmospheres. However, ultra-cool dwarf stars like TRAPPIST-1 can be active with superflares that sweep away the atmospheres of very-close planets, so the results can’t be that surprising.
The researchers plan to continue with their targeted studies of the exoplanets TRAPPIST-1 b and TRAPPIST-1 c to obtain more data, especially on their night side. The new results will offer greater certainty about their possible atmospheres and will also concern the temperature differences between their day and night sides.
The innermost planets of the TRAPPIST-1 system offer an excellent possibility to calibrate the observations conducted with the James Webb Space Telescope by measuring with great precision the star’s brightness detected by its instruments. It’s a crucial step to obtain results by exploiting its planets’ eclipses, which are very frequent given that the year of the outermost planet lasts less than 19 Earth days.
Now astronomers hope that at least the planets in the most favorable positions in terms of habitability potential have an atmosphere. Hopes and prudence mix in the studies of the TRAPPIST-1 system and finally, the James Webb Space Telescope could offer definitive answers.
