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Researchers say galaxy may swarm with 'nomad planets' (Forwarded)
Andy Freeberg, SLAC
Dan Stober, Stanford News Service
February 23, 2012
Researchers say galaxy may swarm with 'nomad planets'
Nomad planets don't circle stars, but may carry bacterial life, say
researchers from Kavli Institute.
By Andy Freeberg
Our galaxy may be awash in homeless planets, wandering through space instead
of orbiting a star.
In fact, there may be 100,000 times more "nomad planets" in the Milky Way
than stars, according to a new study by researchers at the Kavli Institute
for Particle Astrophysics and Cosmology (KIPAC), a joint institute of
Stanford University and the SLAC National Accelerator Laboratory.
If observations confirm the estimate, this new class of celestial objects
will affect current theories of planet formation and could change our
understanding of the origin and abundance of life.
"If any of these nomad planets are big enough to have a thick atmosphere,
they could have trapped enough heat for bacterial life to exist," said Louis
Strigari, leader of the team that reported the result in a paper submitted
to the Monthly Notices of the Royal Astronomical Society. Although nomad
planets don't bask in the warmth of a star, they may generate heat through
internal radioactive decay and tectonic activity.
Searches over the past two decades have identified more than 500 planets
outside our solar system, almost all of which orbit stars. Last year,
researchers detected about a dozen nomad planets, using a technique called
gravitational microlensing, which looks for stars whose light is momentarily
refocused by the gravity of passing planets.
The research produced evidence that roughly two nomads exist for every
typical, so-called main-sequence star in our galaxy. The new study estimates
that nomads may be up to 50,000 times more common than that.
To arrive at what Strigari himself called "an astronomical number," the
KIPAC team took into account the known gravitational pull of the Milky Way
galaxy, the amount of matter available to make such objects and how that
matter might divvy itself up into objects ranging from the size of Pluto to
larger than Jupiter. Not an easy task, considering no one is quite sure how
these bodies form. According to Strigari, some were probably ejected from
solar systems, but research indicates that not all of them could have formed
in that fashion.
"To paraphrase Dorothy from The Wizard of Oz, if correct, this extrapolation
implies that we are not in Kansas anymore, and in fact we never were in
Kansas," said Alan Boss of the Carnegie Institution for Science, author of
The Crowded Universe: The Search for Living Planets, who was not involved in
the research. "The universe is riddled with unseen planetary-mass objects
that we are just now able to detect."
A good count, especially of the smaller objects, will have to wait for the
next generation of big survey telescopes, especially the space-based
Wide-Field Infrared Survey Telescope and the ground-based Large Synoptic
Survey Telescope, both set to begin operation in the early 2020s.
A confirmation of the estimate could lend credence to another possibility
mentioned in the paper -- that as nomad planets roam their starry pastures,
collisions could scatter their microbial flocks to seed life elsewhere.
"Few areas of science have excited as much popular and professional interest
in recent times as the prevalence of life in the universe," said co-author
and KIPAC Director Roger Blandford. "What is wonderful is that we can now
start to address this question quantitatively by seeking more of these
erstwhile planets and asteroids wandering through interstellar space, and
then speculate about hitchhiking bugs."
Additional authors included KIPAC member Matteo Barnaband affiliate KIPAC
member Philip Marshall of Oxford University. The research was supported by
NASA, the National Science Foundation and the Royal Astronomical Society.
This image is an artistic rendition of a nomad object wandering the
interstellar medium. The object is intentionally blurry to represent
uncertainty about whether it has an atmosphere. A nomadic object may be an
icy body akin to an object found in the outer solar system, a more rocky
material akin to am asteroid or even a gas giant similar in composition to
the most massive solar system planets and exoplanets. (Photo: Greg Stewart /
SLAC National Accelerator Laboratory)
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