Tides Have Major Impact on Planet Habitability
- From: baalke@xxxxxxxxxxxxx
- Date: Mon, 13 Oct 2008 12:33:10 -0700 (PDT)
FROM: Lori Stiles (520-626-4402; lstiles@xxxxxxxxxxxxx)
Tides Have Major Impact on Planet Habitability
University of Arizona
October 13, 2008
Astronomers searching for rocky planets that could support life in
other solar
systems should look outside, as well as within, the so-called
"habitable zone,"
University of Arizona planetary scientists say.
Planets too close to their stars are roasted. Planets too far from
their stars
are frozen. In between, research models show, there's a habitable zone
where
planet temperatures approximate Earth's. Any rocky planets in this
just-right
Goldilocks zone could be awash in liquid water, a requisite for life
as we know
it, theorists say.
New research by Brian Jackson, Rory Barnes and Richard Greenberg of
UA's Lunar
and Planetary Laboratory shows that tides can play a major role in
heating
terrestrial planets, creating hellish conditions on rocky alien worlds
that
otherwise might be livable. And just the other way, tidal heat can
also create
conditions favorable to life on planets that would otherwise be
unlivable.
Jackson presented the research Saturday at the 40th annual meeting of
the
Division of Planetary Sciences in Ithaca, N.Y. His talk is titled
"Tidal
Heating of Extrasolar Terrestrial-scale Planets and Constraints on
Habitability." The research will be published soon in the Monthly
Notices of
the Royal Astronomical Society.
Our own solar system is something of an anomaly, in that its planets
move in
relatively quiescent, circular orbits around the sun. Most extrasolar
planets
found to date have highly elongated orbits. During each orbit, the
planet is
stretched most by tides when it is near the star, and less when the
planet is
farther from its star. The resulting friction generates internal heat,
which
drives the planet's geophysical processes.
If the recently discovered "super-Earths" ? extrasolar planets only 2-
to-10
times as massive as Earth ? are indeed terrestrial, tidal heating may
be
great enough to melt them, or at least produce volcanism on par with
Jupiter's
moon, Io, "dimming their prospects for habitability," Jackson said. So
some of
the recently discovered super-Earths may be more like "super-Ios," he
said. The
lo moon is the most volcanically active body in our solar system.
"Tidal heating scales with planet mass, so we expect that most easily
detectable
super-Earths will be dominated by volcanic activity," Jackson said.
"That's one
of our first conclusions from this work, that the first Earth-like
planets
found are probably going to be strongly heated and have big volcanoes.
Even if
Earth-like planets are found within the habitable zone, they may not
be
habitable because they will be overwhelmed by this tidal heating."
Tidal heating may also create habitable conditions on planets that
otherwise are
too small or too cold to support life, Jackson said. Tidal heating can
enhance
outgassing of volatiles that contribute or replenish a planet's
atmosphere
through volcanism. Tidal heating also can generate sub-surface liquid
oceans on
water-rich rocky planets that would otherwise be frozen, just as tidal
heating
is believed to warm a sub-surface liquid water ocean on Jupiter's moon
Europa.
Also, tidal heating can drive plate tectonics, a mechanism that checks
excessive
carbon dioxide from accumulating in a planetary atmosphere, producing
the kind
of deadly greenhouse atmosphere found on Venus.
"Our study shows that tidal heating could produce enough heat to drive
plate
tectonics for billions of years, long enough for life to appear and
flourish,"
Jackson said.
SCIENCE CONTACTS:
Brian Jackson (520-626-3154; bjackson@xxxxxxxxxxxxxxx)
Rory Barnes (520-626-3154; rory@xxxxxxxxxxxxxxx)
Richard Greenberg (520-621-6950; greenberg@xxxxxxxxxxxxxxx)
.
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