For all the hope and expectation, it is
sobering to recall that, despite the best
efforts of scientists and engineers, there is
still no evidence that life exists anywhere
beyond our own planet.
There are, however, some planetary
prime suspects. Here are the five places
astronomers and astrobiologists think are
the best chances for harbouring ET.
LHS 1140b
News of this planet, a
“rocky super-earth”, was announced in the journal Nature in April. Orbiting a red
dwarf 39 light-years from Earth, the planet
sits in its star’s habitable zone and has an
estimated mass almost seven times that of
our own planet, leading to the assumption
that it comprises rock encasing a solid
iron core.
According to Jason Dittmann of
the Harvard Smithsonian Centre for
Astrophysics in Massachusetts, US, LHS
1140b’s density means it might have
survived the runaway global warming
thought to denude many red dwarf
planets. If so, it might now boast a stable
atmosphere and liquid water.
“This is the most exciting exoplanet
I’ve seen in the past decade,” he said.
“We could hardly hope for a better target
to perform one of the biggest quests in
science – searching for evidence of life
beyond Earth.”
Enceladus
Thanks to data from
NASA’s Cassini spacecraft, Saturn’s
moon Enceladus has emerged as every
ET-hunter’s favourite target – mainly due
to the strong likelihood that it features a
subterranean ocean.
In April this year, a team of scientists
from the South West Research Institute
(SWRI) in Texas, US, revealed a plume of hydrogen erupting from the moon’s surface. The plume may well be evidence
of hydrothermal vents in the subsurface
ocean – the same type of vents that
support extremophile life on earth.
“The discovery of hydrogen gas and
the evidence for ongoing hydrothermal
activity offer a tantalising suggestion that
habitable conditions could exist beneath
the moon’s icy crust,” says principal
investigator Hunter Waite.
Titan
Another of Saturn’s 53 moons,
Titan is known to have permanent
hydrocarbon lakes, a nitrogen-heavy
atmosphere, and possibly a subsurface
ocean beneath a salty crust. It is a possible host for either water-dependent or methane-dependent life.
Proxima-b
This planet, discovered
in August 2016, orbits the star Proxima
Centauri, 4.2 light-years away
from our sun, and is the nearest candidate
beyond the solar system for hosting ET.
Research in May’s Astronomy &
Astrophysics journal found the chances of life existing on the planet may hinge on its orbital speed.
Astrophysicists at the University of
Exeter calculated that if Proxima-b rotates
on its axis three times for every two times
it orbits its sun, then the chances of it
being habitable are substantially
improved.
Trappist-1
The announcement of the Trappist-1 system in February, with seven
rocky planets orbiting an ultracool dwarf
star, sent ripples of excitement through
astrobiologists everywhere. At least three
of the planets looked like they were within
the star’s habitable zone.
The latest analysis, by Eric Wolf from
the Laboratory for Atmospheric and Space
Physics at the University of Colorado,
Boulder, US, has somewhat dampened expectations, suggesting that only one of
the group has life-sustaining potential.
But never mind: one chance in seven is still
better than no chance at all.
