Astronomers from Belgium have discovered the three
potentially habitable Earth-like exoplanets circling an ultra-cool dwarf star, called
TRAPPIST-1, nearly 40 light-years from Earth. These three planets are one of
the smallest exoplanets ever spotted, with a radius slightly larger than
Earth's, and they are the very first planets spotted around an ultra-cool dwarf
– a dim star which is not much larger than Jupiter. The research has been
published in Nature.
The most thrilling thing about this finding, made
possible by the Belgian TRAPPIST telescope as the planets traveled in front of
the star, is that these planets are close enough for us to examine. Many of the
other potentially habitable planets we've discovered are much further away and
around much perkier stars, so it is harder to observe.
Lead author Dr. Michaël Gillon from the University of
Liège told IFLScience. “These are the first planets similar in size and
temperature to Earth and Venus for which we can study the atmospheric
composition in detail, and really constrain the surface conditions and
habitability,”
At first, the system might not seem that promising. Two
of the planets, TRAPPIST- 1b and c, have years lasting about 1.5 and 2.4 Earth
days respectively, meaning they orbit very closely, while TRAPPIST-1d has a
less well determined period in the range of 4.5 to 73 days.
However, the star
has a surface temperature of only 2,550 Kelvins (2,277°C / 4,130 °F ), so they
are unlikely to be inferno worlds. Instead, they could be quite the opposite.
The closest two planets receive no more than four times
the amount of radiation received by Earth, while the furthest planet likely
receives less. This puts the planets at the edges of the star's habitable zone,
the region in which liquid water can exist. It's not certain if the planets are
solid, but TRAPPIST-1 is rich in heavy elements, which indicates a suitable
evironment for rocky planets to form.
The planets have a radius of 1.11, 1.05, and 1.16 times
that of Earth, which combined with their locations strongly indicates that
these objects possess some of the right conditions for life. The planets’
temperatures could range from slightly higher than water’s boiling point to
well below freezing.
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