Posted on December 4, 2012 by Laura
December 04, 2012
“Alien Solar Systems May Prove to be More Habitable than Ours”
Scattered around the Milky Way are stars that resemble our own
sun—but a new study is finding that any planets orbiting those stars may
very well be hotter and more dynamic than Earth because the interiors
of terrestrial planets in these systems are likely warmer than Earth by
up to 25 percent, which would make them more geologically active and
more likely to retain enough liquid water to support life, at least in
its microbial form. The finding comes from geologists and astronomers at
Ohio State University who have teamed up to search for alien life in a
The Ohio State team studied eight “solar twins”
of our sun—stars that very closely match the sun in size, age, and
overall composition—in order to measure the amounts of radioactive
elements they contain. Those stars came from a dataset recorded by the High Accuracy Radial Velocity Planet Searcher spectrometer at the European Southern Observatory
in Chile (image above). They searched the solar twins for elements such
as thorium and uranium, which are essential to Earth’s plate tectonics
because they warm our planet’s interior. Plate tectonics helps maintain
water on the surface of the Earth, so the existence of plate tectonics
is sometimes taken as an indicator of a planet’s hospitality to life.
Of the eight solar twins they’ve studied so far, seven appear to
contain much more thorium than our sun—which suggests that any planets
orbiting those stars probably contain more thorium, too. That, in turn,
means that the interior of the planets are probably warmer than ours.
One star in the survey contains 2.5 times more thorium than our sun,
said Ohio State doctoral student Cayman Unterborn. According to his
measurements, terrestrial planets that formed around that star probably
generate 25 percent more internal heat than Earth does, allowing for
plate tectonics to persist longer through a planet’s history, giving
more time for live to arise.
“If it turns out that these planets are warmer than we previously
thought, then we can effectively increase the size of the habitable zone
around these stars by pushing the habitable zone farther from the host
star, and consider more of those planets hospitable to microbial life,”
said Unterborn, who presented the results at the American Geophysical
Union meeting in San Francisco this week. “If it turns out that these
planets are warmer than we previously thought, then we can effectively
increase the size of the habitable zone around these stars…”
“At this point, all we can say for sure is that there is some natural
variation in the amount of radioactive elements inside stars like
ours,” he added. “With only nine samples including the sun, we can’t say
much about the full extent of that variation throughout the galaxy. But
from what we know about planet formation, we do know that the planets
around those stars probably exhibit the same variation, which has
implications for the possibility of life.”
Wendy Panero, associate professor in the School of Earth Sciences at
Ohio State, explained that radioactive elements such as thorium,
uranium, and potassium are present within Earth’s mantle. These elements heat the planet from the inside, in a way that is completely separate from the heat emanating from Earth’s core.
“The core is hot because it started out hot,” Panero said. “But the
core isn’t our only heat source. A comparable contributor is the slow
radioactive decay of elements that were here when the Earth formed.
Without radioactivity, there wouldn’t be enough heat to drive the plate
tectonics that maintains surface oceans on Earth.”
The relationship between plate tectonics and surface water is complex
and not completely understood. Panero called it “one of the great
mysteries in the geosciences.” But researchers are beginning to suspect
that the same forces of heat convection in the mantle that move Earth’s crust somehow regulate the amount of water in the oceans, too.
“It seems that if a planet is to retain an ocean over geologic
timescales, it needs some kind of crust ‘recycling system,’ and for us
that’s mantle convection,” Unterborn said.
In particular, microbial life on Earth benefits from subsurface heat.
Scores of microbes known as archaea do not rely on the sun for energy,
but instead live directly off of heat arising from deep inside the
Earth, where most of the heat from radioactive decay comes from uranium.
Planets rich in thorium, which is more energetic than uranium and has a
longer half-life, would “run” hotter and remain hot longer, he said,
which gives them more time to develop life.
“It all starts with supernovae. The elements created in a supernova
determine the materials that are available for new stars and planets to
form. The solar twins we studied are scattered around the galaxy, so
they all formed from different supernovae. It just so happens that they
had more thorium available when they formed than we did.”
Jennifer Johnson, associate professor of astronomy at Ohio State and
co-author of the study, cautioned that the results are preliminary. “All
signs are pointing to yes—that there is a difference in the abundance
of radioactive elements in these stars, but we need to see how robust
the result is,” she said.
Next, Unterborn wants to do a detailed statistical analysis of noise
in the HARPS data to improve the accuracy of his computer models. Then
he will seek telescope time to look for more solar twins.
The Daily Galaxy via http://researchnews.osu.edu
“Alien Solar Systems May Prove to be More Habitable than Ours”.
Thanks to: http://2012indyinfo.com