Seven rocky planets confirmed in the TRAPPIST-1 system

Artistic concept of the planets in the TRAPPIST-1 system (Image NASA/JPL-Caltech)
Artistic concept of the planets in the TRAPPIST-1 system (Image NASA/JPL-Caltech)

NASA held a press conference to communicate new discoveries in the research on the TRAPPIST-1 star system. These results have also been described in an article published in the journal “Nature”. Using data collected by NASA’s Spitzer Telescope, a team of researchers led by Michaël Gillon of the STAR Institute confirmed the existence of 7 planets in this system, all rocky. Potentially, at least in some region of all those planets there could be liquid water.

Since the announcement in May 2016 of the detection of exoplanets orbiting the tiny star TRAPPIST-1 there was a lot of enthusiasm from researchers for the possibilities that were opening. That team of researchers was also led to Michaël Gillon and together with his collaborators announced the discovery of three potentially habitable rocky planets. However, there was the possibility that other planets existed in that system and the most optimistic predictions have come true.

After the first discoveries, many other observations of the TRAPPIST-1 system started to understand how many planets there were and possibly figure out their sizes and masses. To do this the system was observed by a number of telescopes, several ground-based ones but also the Spitzer Space Telescope, obtaining a large amount of data that allowed to better understand how many planets are orbiting the star.

The Spitzer Space Telescope has an excellent position to observe the planets passing in front of the TRAPPIST-1 star. This wasn’t part of Spitzer’s original mission but after the exhaustion of the liquid helium that cooled part of its instruments at NASA they found ways to tweak the instruments used for this type of observations. In this case 500 almost continuous hours of observations were carried out.

TRAPPIST-1 is an ultra-cool dwarf whose system looks more like Jupiter and its moons than the solar system. The star has a size slightly greater than that of Jupiter even if its mass is over 80 times that of the gas giant planet. The 7 planets now confirmed are all rocky and similar in size, at least comparable to that of the Earth and in a few cases very similar.

The seven planets are very close to the star TRAPPIST-1, so much that even the one farthest away is much closer to it than Mercury is to the Sun. However, this tiny star’s light is so faint that at those short distances the planets receive an amount of energy that could be suitable to maintain water liquid on at least part of their surface in the presence of an atmosphere comparable to that of the Earth.

Basically, there are 7 potentially habitable planets even though there are so many question marks for which there are many hypotheses but right now no certainty. The closest planets might be more similar to Venus, the more distant ones more like Mars. If some didn’t have an atmosphere they’d be more similar to Mercury. In short, there are many reasons to be excited about this discovery but there are also many reasons to be cautious.

The 7 planets are relatively close together and their orbital periods are between 1.5 and 12.4 Earth days so there are conjunctions all the time. For this reason if life forms had risen on one of them and and some species had spores it would be relatively easy for them to migrate to the other planets, fertilising those where the conditions are favorable enough. A mind-blowing hypothesis is that there’s a biosphere that includes all the planets.

This new discovery will lead to further intensify the research on the TRAPPIST-1 system and to look for other exoplanets around small stars with the TRAPPIST telescope but also with other instruments. The TRAPPIST-1 system is already a candidate for new observations to be carried out when the James Webb Space Telescope will be launched and when ESO activates its E-ELT (European Extremely Large Telescope) telescope to collect more precise information on those exoplanets.

Artistic concept of the view from the TRAPPIST-1e planet (Image NASA/JPL-Caltech)
Artistic concept of the view from the TRAPPIST-1e planet (Image NASA/JPL-Caltech)

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