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Laboratoire d’Astrophysique de Bordeaux in France. Selsis and his colleagues
have proposed that two other Gliese-orbiting planets might be habitable.
Recent studies, Selsis said, show that the
habitability zone of Gliese 581 extends
farther than originally thought, placing
planet Gliese 581d, which flanks Gliese
581g on the side farther from the star, in
the habitability zone, too. More extensive
modeling of Gliese 581d suggests that its
bigger mass (about 7. 1 times more massive
than Earth) could have accumulated an
atmosphere large enough to keep the
planet warm, making liquid water a possibility there too.
A surface temperature that allows liq-
uid water is considered necessary for life.
“At this point, we can’t say anything about
the physical conditions on the planet,”
Butler said of Gliese 581g. “We can’t say
anything for sure about the atmosphere.
We can’t say anything sure about water.”
Vogt points out that water is abundant
in the galaxy, so it is hard to imagine that
Gliese 581g wouldn’t have any. “Given
the ubiquity and propensity of life to
flourish wherever it can ... my own per-
sonal feeling is that the chances of life on
this planet are 100 percent,” Vogt said. “I
have almost no doubt about it.”
But Selsis cautions that being in
the all-important “habitability zone”
where temperatures are right for life as
we know it is “necessary, but certainly
not sufficient.” The planet could have
formed without any water. It could be
regularly bombarded with objects capa-
ble of wiping out any life that develops.
Or it could have such a heavy atmosphere
that its surface would be extremely hot.
Gliese
581g
Gliese
581
f
e cb
d
Earth
Venus
Mercury
Sun
on the small side all but one of
Gliese 581’s planets (top) hug the parent star
closer than mercury orbits the sun (bottom).
but Gliese 581 is substantially dimmer than the
sun, so planet g could still have liquid water on
its surface — considered a requisite for life.
Auriga
Perseus
Capella
Pollux
Alnath
Taurus
Aldebaran
Betelgeuse
Orion
Procyon
Sirius
Rigel
Triangulum
Aries
Sun
Cetus
Rigel Kentaurus A
From Gliese 581g, you could see the earth’s sun, about
20 light-years distant, and many of the stars (blue labels)
and constellations (orange labels) visible from earth.
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eternal sunshine the rocky
planet is tidally locked to its
star, so one side is perpetually
sunny and the other is always
dark and cold. there wouldn’t
be time-dependent seasons,
and a person sitting at a given
longitude would experience the
same temperature and weather
patterns year-round.
what would it be like to live on Gliese 581g?
Gliese 581g, however, would probably appear whitish.
Visible planets the three inner
planets in the Gliese system
would be visible with the naked
eye from the surface, and they
would have phases, similar to the
progression of the moon cycle as
seen from earth.
Weighed down the gravity of the
planet is estimated to be slightly
stronger than that of earth. a
130-pound earth woman would
weigh between 143 and 221
pounds on Gliese 581g.
howdy neighbor a person on
Gliese 581g could see earth’s
sun with the naked eye. but red
dwarfs don’t burn as brightly, so
earthlings must use a telescope
to see Gliese 581.
Big orange ball Gliese 581g’s
parent star would appear about
twice as large as the sun appears
to an earth observer, and, depending on the atmosphere, the star
might appear orange. the quality of the light on the surface of
Time to burn red dwarfs can
persist for hundreds of billions of
years — a life span much longer
than other types of stars, including the sun. that means that any
life on Gliese 581g will have a
very long time to evolve.
