Yahoo – AFP,
Marlowe HOOD, February 23, 2017
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| An artist's impression shows the view just above the surface of one of the planets in the TRAPPIST-1 system (AFP Photo/M. KORNMESSER) |
Paris (AFP)
- Researchers have announced the stunning discovery of seven Earth-like planets
orbiting a small star in our galaxy, opening up the most promising hunting
ground so far for life beyond the Solar System.
All seven
roughly match the size and mass of our own planet and are almost certainly
rocky, and three are perfectly perched to harbour life-nurturing oceans of
water, they reported in the journal Nature Wednesday.
Most
critically, their proximity to Earth and the dimness of their red dwarf star,
called Trappist-1, will allow astronomers to analyse each one's atmosphere in
search of chemical signatures of biological activity.
"We
have made a crucial step towards finding life out there," said co-author
Amaury Triaud, a scientist at the University of Cambridge.
"Up to
now, I don't think we have had the right planets to find out," he said in
a press briefing.
"Now
we have the right target."
The
Trappist-1 system, a mere 39 light years distant, has the largest number of
Earth-sized planets known to orbit a single star.
It also has
the most within the so-called "temperate zone" -- not so hot that
water evaporates, nor so cold that it freezes rock-solid.
The
discovery adds to growing evidence that our home galaxy, the Milky Way, may be
populated with tens of billions of worlds not unlike our own -- far more than
previously suspected.
Remarkably,
professional stargazers may simply have been looking in the wrong place.
"The
great idea of this approach was to study planets around the smallest stars of
the galaxy, and close to us," said lead author Michael Gillon, a professor
at the University of Liege in Belgium.
 |
An artist's
impression shows the view just above the surface of one of the
planets in the
TRAPPIST-1 system (AFP Photo/Simon MALFATTO, Sabrina
BLANCHARD)
|
'Ultracool' dwarf star
"That
is something nobody did before us -- most astronomers were focused on stars
like our Sun," he told journalists ahead of publication.
Gillon and
his team began to track Trappist-1 -- a so-called "ultracool" dwarf
star with less than 10 percent the mass of the Sun -- with a dedicated
telescope in 2010, and reported last year on three planets in its orbit.
They
detected the invisible exoplanets using the so-called "transit"
method: when an orbiting world passes between a star and an astronomer peering
through a telescope, it dims the starlight by a tiny but measurable amount.
But when
subsequent calculations didn't quite tally, Gillon realised that there might be
other stars that had escaped Earth-bound observation.
"So we
requested time with NASA's Spitzer Space Telescope," said co-author
Emmanuel Jehin, also at the University of Liege.
"This
allowed us to get 20 consecutive 24-hour periods of observation, which was
crucial to discovering that we had seven transiting planets."
Looking
from Earth, the astronomers could only track activity around the star at night.
"From
space, we observed continually and matched all the transits," 34 in all.
Compared to
the distance between our Sun and its planets, the Trappist-1 family is very
tightly bunched.
Indeed, the
dwarf star and its seven satellites -- with orbits ranging from 1.5 to 12 days
-- would all fit comfortably in the distance between the Sun and its closest
planet, Mercury.
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Some
artist's illustrations of how the seven planets orbiting TRAPPIST-1 might
appear — including the possible presence of water oceans — alongside some
images of the rocky planets in our Solar System (AFP Photo/Handout)
|
Like a
sunset
If Earth
were that close to the Sun, it would be a hellish ball of fire.
But because
Trappist-1 emits far less radiation, temperatures on its planets -- depending
on the atmosphere -- could be between zero and 100 degrees Celsius (32 and 212
degrees Fahrenheit), the scientists said.
Gillon and
his team have started to analyse the chemical make-up of the atmospheres.
"There
is at least one combination of molecules, if present with relative abundance,
that would tell us there is life, with 99 percent confidence," said
Gillon.
A certain
mix of methane, oxygen or ozone, and carbon dioxide, for example, could almost
certainly come only from biological sources.
"But
except for detecting a message from beyond our solar system from intelligence
out there, we will never be 100 percent sure," he added.
Someone
standing on, say, Trappist-1 D, E or F -- the three middle planets -- would
have a breathtaking panorama of the star and its system, Triaud said.
The red
dwarf -- which would loom 10 times larger than the Sun in our sky -- would be a
"deep crimson" shading into a salmon-like colour, he said.
"The
view would be beautiful -- you would have about 200 times less light that from
the Sun on Earth at midday," he added.
"It
would be like the end of a sunset."
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