by Nola Taylor Redd
September 20, 2012
Artist's rendition of
the "super Earth" Gliese 163c,
which may be
capable of supporting microbial life
A newly discovered alien planet may be
one of the top contenders to support life beyond Earth, researchers
The newfound world, a "super Earth"
Gliese 163c, lies at the edge of its star's
habitable zone - that just-right range of distances where liquid
water could exist.
"There are a wide range of
structures and compositions that allow Gliese 163c to be a
habitable planet," Xavier Bonfils, of France's Joseph
Fourier University-Grenoble, told SPACE.com by email.
He went on to caution that several
possible uninhabitable combinations exist as well.
The Top 5
...Potentially Habitable Alien
July 24, 2012
Astronomers have found more than 700 planets beyond our solar
system, and thousands more await confirmation by follow-up
Many of these alien worlds are too
hot or too cold to support life as we know it, but researchers
have found a few that appear to be much more hospitable.
On July 19, scientists at the University of Puerto Rico at
Arecibo’s Planetary Habitability Laboratory released a list of
the top five potentially habitable exoplanets.
Here's a brief rundown of the PHL's
1. Gliese 581g
This rocky world was
announced in September 2010 and has been controversial ever
since, with some researchers casting doubt on its existence
and its discoverers remaining firmly behind their find.
Gliese 581g, which is located just 20 light-years away, is
likely two to three times as massive as Earth and zips
around its parent star every 30 days or so.
This orbit places the planet
squarely in its star's "habitable zone" - that just-right
range of distances where liquid water, and perhaps life as
we know it, could exist.
This artist's conception shows the inner four
planets of the Gliese 581 system and their host star.
The large planet in the foreground is Gliese
which is in the middle of the star's
habitable zone and is only two to three times as massive as
Some researchers aren't convinced Gliese 581g
Credit: Lynette Cook
2. Gliese 667Cc
Gliese 667Cc, which was
discovered in February 2012 by the same core team that
spotted Gliese 581g, orbits a red dwarf 22 light-years away,
in the constellation Scorpius (The Scorpion).
The alien world is a so-called "super Earth" that's at least
4.5 times as massive as our planet, and it completes an
orbit every 28 days.
At least one other planet
circles the star Gliese 667C, which is part of a triple-star
conception of the alien planet GJ 667Cc,
located in the habitable zone of its parent star.
Credit: Carnegie Institution for Science
Kepler-22b was spotted by
NASA's planet-hunting Kepler space telescope in December
It's a super Earth about 2.4
times as wide as our planet. If the greenhouse effect
operates on Kepler-22b like it does on Earth, the alien
world would have an average surface temperature of 72
degrees Fahrenheit (22 degrees Celsius), researchers have
Kepler-22b is found about 600 light-years away, and it
orbits a star very much like our own sun.
conception illustrates Kepler-22b,
known to comfortably circle in the habitable zone of a
4. HD 85512b
HD 85512b is another
super Earth, one that's thought to be 3.6 times as massive
as our planet. The alien world is found about 35 light-years
from us, in the direction of the constellation Vela (The
Astronomers announced the discovery of HD 85512b in
September 2011. The planet's estimated surface temperature
is 77 degrees Fahrenheit (25 degrees Celsius).
artist’s impression shows the planet HD 85512b
Sun-like star HD 85512 about 35 light-years from Earth.
is about 3.6 times as massive as the Earth
the edge of the habitable zone around the star,
water, and perhaps even life, could potentially exist.
Credit: ESO/M. Kornmesser
5. Gliese 581d
This world, which is
about seven times as massive as Earth, orbits a bit farther
out than its planetary sibling Gliese 581g. When 581d was
first discovered in 2007, many scientists regarded it as too
cold to be potentially habitable.
In the years since, however,
atmospheric-modeling studies have suggested that the planet
may indeed be able to support life as we know it - provided
581d is warmed by a greenhouse effect.
impression of Gliese 581d,
discovered by the Kepler spacecraft that
is thought to
be in its star's habitable zone, and a speculative moon.
Credit: Debivort | Wikimedia Commons
A newfound super
Bonfils and an international team of
astronomers studied nearly 400
red dwarf stars with the High Accuracy Radial Velocity Planet
Searcher (HARPS), a spectograph on the 3.6-meter telescope at the
European Southern Observatory's La Silla Observatory in Chile.
Gliese 163c was one of two
alien planets found orbiting the star Gliese 163, which lies
about 50 light-years from Earth in the Dorado constellation The team
found indications of a third planet as well but cannot confirm it at
Weighing in at about seven times the
mass of Earth, Gliese 163c could be a rocky planet, or it could be a
dwarfed gas giant, researchers said.
"We do not know for sure that it is
a terrestrial planet," Bonfils said. "Planets of that mass
regime can be terrestrial, ocean, or Neptune-like planets."
Orbiting at the inner edge of the
habitable zone, Gliese 163c takes 26 days to zip around its parent
star, which is considerably dimmer than our sun.
The second planet, Gliese 163b, has an
orbital period of only nine days, while the third unconfirmed planet
circles from a distance.
Bonfils pointed out that there is about
a 2 percent chance that Gliese 163c might pass between its star and
the sun from Earth's perspective. If so, scientists may be able to
glean more information about the distant planet by watching it cross
the face of its host star.
The research has been submitted for
review and publication.
A good candidate
The Planetary Habitability Laboratory
(PHL) at the University of Puerto Rico at Arecibo keeps a catalog of
the alien worlds it considers good candidates to host life.
The newly discovered Gliese 163c ranks
fifth on the list.
"We are finding more potentially
habitable planets now than before," PHL's Abel Mendez, who was
not part of the Gliese 163c discovery team, told SPACE.com by
Out of the six planets on PHL's list,
four have been found in the last year alone -- Kepler-22b, Gliese
667Cc, HD 85512b, and, of course, Gliese 163c.
"Most of these are relatively close,
so we can expect to find better and closer ones as our
technological sensitivity to
Earth-size planets improves," Mendez said.
To rank habitable planets, Mendez and
his colleagues at PHL compare them with the only planet known to
host life. They rank the worlds according to how similarly their
masses, diameters and temperatures match up with those of Earth.
Temperatures of alien planets are tough
for researchers to estimate. Temperature is heavily influenced by
atmospheric characteristics, and scientists don't know much about
most exoplanets' atmospheres.
Mendez suggested that one scenario for
Gliese 163c might include a balmy ocean with an atmosphere 10 times
as dense as Earth's. The global ocean might slosh beneath a pink,
cloud-covered sky. At around 140 degrees Fahrenheit (60 degrees
Celsius), the temperature would be too hot for prolonged human
exposure or complex plants or animals, but some microbes could
But it's also possible that Gliese 163c
is too hot for even those hardy lifeforms to exist.
In the meantime, Bonfils and his team
intend to use HARPS to continue their search for planets that could
be ripe for life, hoping to find one that may allow astronomers to
study it today rather than tomorrow.
"Although it is nice to build the
sample of possibly habitable planets that will be observed with
the next generation of telescopes, it would be even better if we
could find a planet one could characterize with today's
observatories," Bonfils said.