In February 2017, NASA's Spitzer Space telescope discovered seven Earth-sized planets in orbit around TRAPPIST-1, an ultracool dwarf star about 40 light years away. All the seven planets in the system are closer to the host star than Mercury is to the Sun. Follow-up observations from the Kepler astronomical instrument allowed researchers to figure out how the planets maintain their orbits so close to the stars.
The orbits of the seven planets are an intricate dance, with each inner planet tugging the outer planets when the two are in a straight line with the star, this is known as a conjugation. The regular periodicity of the orbits is what led to the discovery of the planets in the first place, and researchers have even turned the TRAPPIST-1 system into a musical instrument.
The system is of scientific importance because three of the exoplanets were in orbit around the habitable zone of the star. This means that it was possible for liquid water to exist on the surface of the planets, a prerequisite for life as we know it on Earth. If the conditions were favourable, all the seven planets could have liquid water on their surface.
TRAPPIST-1 is an ultracool dwarf star, not a yellow dwarf star like the Sun. The closest sun-like star is tau Ceti, which also has four Earth-sized planets in orbit around it. Planets in orbit around Sun-like stars are better candidates for potentially harbouring life because of two reasons.
The stars are relatively tame so frequent stellar activity in the form of solar flares would not make the planets less hospitable, as is the case with TRAPPIST-1. However, fortunately for any life on the planets in the TRAPPIST-1 system, the star is quieter than others of its kind.
Additionally, the planets are tidally locked. There is no day-night cycle on the planets in the TRAPPIST-1 system, one side experience a perpetual day, the other a never ending night, with a constant twilight zone between the two regions.
Another important factor is the age of the stellar system. The longer a system has been around for, the more time there is for life to evolve from simple micro-organisms into more complex life forms. NASA researchers have now found out that the TRAPPIST-1 system is older than the solar system.
The TRAPPIST-1 system is between 5.4 billion and 9.8 billion years old. Our solar system is 4.5 billion years old. While there is plenty of time for life to evolve, the atmosphere of the planets could also be blasted away because of the increased exposure to stellar radiation over time.
However, the planets in the TRAPPIST-1 system are of a lower density than Earth, which could mean that they could have a dense atmosphere with a lot of water vapour content, which would act as effective shields against the stellar radiation.
Adam Burgasser, the lead author of the study says, "If there is life on these planets, I would speculate that it has to be hardy life, because it has to be able to survive some potentially dire scenarios for billions of years."
The upcoming James Webb Space Telescope that NASA plans to launch in 2018 will conduct follow-up observations on the TRAPPIST-1 system to identify potential signs of life. Future campaigns by NASA telescopes will study the density of the planets, as well as their atmospheres. TRAPPIST-1 remains one of the best known candidates for harbouring extraterrestrial life.
Updated Date: Aug 12, 2017 15:03 PM