Yahoo – AFP,
5 February 2018
 |
| The European Southern Observatory shows the TRAPPIST-1 system in order of increasing distance from their host star, surfaces portrayed with an artist’s impression of potential surface features, including water -- whose presence might make them "habitable |
Seven
planets recently spotted orbiting a dim star in our Milky Way galaxy are rocky,
seem to have water, and are potentially "habitable", researchers
studying the distant system said Monday.
Though much
remains unknown about the planets' surfaces and atmospheres, the new
measurements have not ruled out the possibility that they may harbour even
rudimentary life, the scientists reported.
"So
far, no sign allows us to say that they are not habitable," said
University of Birmingham astronomer Amaury Triaud, the co-author of a study on
the subject.
"All
the traffic lights we have passed so far are green."
Research
teams gleaned more information about the dwarf star at the centre of the
Trappist-1 system, as well as improved measurements of the size and mass of
each planet, and the composition of their atmospheres.
All seven
are mostly made of rock, with up to five percent of their mass in water --
though it may be in the form of gas or ice, or trapped deep inside the rocky
orbs, researchers said.
On Earth,
the oceans account for about 0.02 percent of our planet's mass.
A year ago,
researchers announced the discovery of the seven Earth-like planets orbiting
Trappist-1, an "ultracool" red dwarf star some 39 light years from
our home.
As for the
odds of the planets hosting organic life forms, "we cannot say at this
stage, as they are vastly different from the only planet we know to harbour
life (Earth)," Triaud told AFP.
"But
they have suitable characteristics and are to date the best place beyond the
edge of our (Solar) system to search."
The
presence of liquid water is considered essential for life to exist anywhere.
Astronomers
used the Hubble Space Telescope to learn more about the Trappist system by
studying the planets' atmospheres as they passed in front of their star,
appearing as a dark, travelling dot from the observer's point of view.
Findings
were published Monday in two papers in the journals Nature Astronomy, and
Astronomy and Astrophysics.
Cooler
than the Sun
All seven
planets were considered potential candidates for harbouring water, but the
chances to find it in liquid form are highest in the temperate
"Goldilocks" zone -- not too far from the star for it to be frozen,
nor too close to evaporate.
The
Trappist-1 system is considered the current best hope for finding evidence of
alien life.
"When
we combine our new masses with our improved radii measurements, and our
improved knowledge of the star, we obtain precise densities for each of the
seven worlds, and reach information on their internal composition," said
Triaud.
"All
seven planets remarkably resemble Mercury, Venus, our Earth, it's Moon, and
Mars."
 |
| An artist’s impression shows an imagined view from the surface of a planet orbiting an ultracool dwarf star 40 light-years from Earth discovered using the TRAPPIST telescope at ESO’s La Silla Observatory in Chile |
According
to study co-author Simon Grimm from the University of Bern, the third and
fourth planets from the star are "the most likely" to host some form
of life.
"The
more we learn about these planets, the more habitable they seem to be,"
Grimm told AFP by email.
Compared to
our Solar System, the Trappist-1 family is very tightly-knit. With orbits
ranging from 1.5 to 12 days, the planets would have fit comfortably in the
distance between the Sun and its closest planet, Mercury.
Trappist-1
has a mass less than 10 percent the mass of our Sun and is much cooler, which
explains why its planets can orbit so nearby.
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