Astronomers have found seven Earth-sized planets orbiting around the same star at a distance of 40 light-years from our planet, according to a study published on Wednesday 22nd February 2017 in the journal Nature.
Such a discovery is very rare because the planets have at the same time two important characteristics: they are similar in size to the Earth and they are all temperate. This means they could have water on their surfaces and might support life.
“This is the first time that so many planets of this kind are found around the same star” said Michaël Gillon, an astrophysicist at the University of Liège in Belgium.
The seven exoplanets were found in a tight formation around an ultracool dwarf red star (belonging to the Aquarium constellation) called TRAPPIST-1.
Basing on the estimates of their mass, the astronomers found out that they are rocky planets, not gaseous. Three of these planets (TRAPPIST-1e, f and g) are in the habitable zone of the star and may even have oceans on the surface.
The best candidate for supporting life is thought to be TRAPPIST-1f. It is a bit cooler than the Earth, but it could be suitable, with the right atmosphere and enough greenhouse gases.
The scientists say we have made a great step towards finding if there is other life in the universe. This is the very first time we have the right planets to discover it. To understand if life is really present on these planets, we will have to study their atmosphere, which could contain some gases released by living organisms.
“And as we’ve learned from studying and discovering exoplanets before, where there is one, there are more”, said Sara Seager, professor of planetary science and physics at Massachusetts Institute of Technology.
Seager is encouraged by this discovery, since it improves our chances of finding another habitable planet by knowing where to look.
The planet’s features
The planets are really close to each other and to the star: they all are in a space five times smaller than the distance from Mercury to our sun. This proximity allows the researchers to study the planets in depth.
The closest planet to the star has an orbital period of just 1.51 days. This means a year on that planet lasts only 1.51 Earth days.
The orbital periods of the other six planets are a bit longer, but they don’t last more than 20 Earth days.
If you were on one of these planets, you would receive 200 times less light than you get on the Earth, but you would still receive enough heat to keep you warm because the star is very close. You would also admire some amazing views, as the other planets would appear in the sky bigger than our moon while the star would seem even three times bigger than the sun. And because of its red nature, it is thought that the light would gain a pink hue.
Probably the planets formed together further from the star. Then, they moved into their current position.
Exactly like our moon, the planets closest to the star are tidally locked. This means they always face one way to the star. As a consequence, on one side of the planet is always night, while on the other is always day.
Moreover, the first six planets seem to orbit in synchrony (a phenomenon known as orbital resonance). For example, when TRAPPIST-1g completes four orbits around the star, TRAPPIST-1f completes three orbits, a ratio of 4:3. Also these interesting features will help us to understand the formation of these planets.
According to the first climate model, the researchers believe that the three planets closest to the star may be too warm to have liquid water, while the furthest planet, TRAPPIST-1h, is probably too distant and cold to have water on the surface. Of course we need more precise observations to obtain more accurate conclusions.
How the discovery was made
TRAPPIST-1 barely classifies as a star: it has half the temperature and a tenth the mass of the sun. It is red, not bright and only a bit larger than Jupiter. But these tiny ultracool dwarf stars, which are common in our galaxy, were largely overlooked until Gillon decided to study the space around one of them.
The researchers used a telescope called TRAPPIST (TRAnsiting Planets and Planetesimals Small Telescope) to observe the behavior of its light, such as changes in brightness. The team saw shadows, like eclipses, periodically obscuring the pattern of starlight. This phenomenon is called transiting. Of course, these shadows indicated planets, as other observations confirmed.
What will happen?
In the next future, the researchers want to study the atmosphere of each planet, determine whether they truly have liquid water on the surface and search for life.
This star system will probably be still there when our sun dies because this type of star evolves very slowly: at that time (that will occur in billions of years) TRAPPIST-1 will still be a young star and will live for another trillion years, Gillon said.
The only problem? To cover the 40 light-years distance from the Earth to TRAPPIST-1, with the space vehicles we now own, it would take millions of years.
Sources:
FRIScIence 