Two articles published in “The Astrophysical Journal” – you can read them here and here – describe as many researches on the possibility that at least some of the seven rocky planets of the ultra-cool dwarf star TRAPPIST-1’s system can be habitable. Two researchers from the University of Arizona’s Lunar and Planetary Laboratory examined the effects gravity of planets has on its neighbors. A team from the Center for Astrophysics (CfA) of Harvard University and Smithsonian Institution examined the effects that high-energy protons emitted by the star may have on its planets.
The TRAPPIST-1 system is really tiny, with a star that has a size similar to Jupiter’s and packed-up planets, to the point of looking more like Jupiter and its moons than the Sun and its planets. The planets of TRAPPIST-1 are tidally locked with their star and this means that they always show it the same face, like the Moon to the Earth.
Research has already been done when only the first planets were confirmed and increased considerably after the announcement in February 2017 that the number of confirmed planets rose to seven. However, the continuous addition of data from new observations led to very different and sometimes contradictory results, showing that we’re still at the beginning in the study of exoplanets. New information and the refinement of our models can greatly influence the conclusions of a research and it’s one of the reasons why this system is so interesting.
From the beginning, at least three of the planets in the TRAPPIST-1 system were considered potentially habitable because they orbit in their system’s habitable zone but there are other requirements for conditions to actually be favorable to host life forms similar to those on Earth. The solar system also has three planets in its habitable zone, as shown in green in the image with the comparison to the TRAPPIST-1 system (NASA/JPL-Caltech) but on Venus at some point a runaway greenhouse effect started that turned it into hell while Mars lost the magnetic field that protected it from solar radiation after its core cooled down and its atmosphere was stripped by solar wind.
Gravitational tidal effects were examined in particular with regard to the influence of planets on their moons, for example Jupiter on Europa and Saturn on Enceladus to better understand the underground oceans of liquid water of those moons. Hamish Hay and Isamu Matsuyama tried to study the effects that planets very close to each other can have on each other.
The two innermost planets could have effects on each other added to those of their star and this could lead to a volcanic activity capable of generating an atmosphere. Probably the two planets’ day side is too hot to be hospitable but their night side could have at least in certain zones temperatures suitable for hosting life forms similar to the Earth’s.
The planet TRAPPIST-1g, the sixth and at the outer limit of the system’s habitable zone, could have tidal effects from the other planets higher than from its star. The temperature on its surface may not be sufficient to have liquid water but if its core is heated enough by the tidal effects it could have an underground ocean just like Europa and Enceladus.
Federico Fraschetti led a team that examined the emissions of energetic protons from the star TRAPPIST-1, which is tiny but very active so its very close planets could suffer a considerable bombardment. The planet TRAPPIST-1e, the fourth and at the inner limit of the system’s habitable zone, could receive a remarkable proton flow that was estimated at a million times higher than that one suffered by the Earth. Those exoplanets should have a very strong magnetic field to be adequately protected and that’s unlikely to say the least, but that bombardment doesn’t doom the system because it could break life’s building blocks but could also provide the energy to act as a catalyst for their formation. Again, the planets’ night side could be protected enough and if there are oceans the water could act as a shield as well.
In both researches some estimates were made but the authors are well aware of the fact that precise results require data that currently are only partially known. Even the most recent studies on the TRAPPIST-1 system have many margins of approximation precisely because the study of exoplanets is still limited and at the same time very exciting precisely because new data keep on being accumulated and this system will be the target of every new astronomical instrument that can study exoplanets.
