[meteorite-list] Closest Planetary System Hosts Two Asteroid Belts (Spitzer)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 27 Oct 2008 16:30:09 -0700 (PDT)
Message-ID: <200810272330.QAA29860_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2008-197

Closest Planetary System Hosts Two Asteroid Belts
Jet Propulsion Laboratory
October 27, 2008

New observations from NASA's Spitzer Space Telescope indicate that the
nearest planetary system to our own has two asteroid belts. Our own
solar system has just one.

The star at the center of the nearby system, called Epsilon Eridani, is
a younger, slightly cooler and fainter version of the sun. Previously,
astronomers had uncovered evidence for two possible planets in the
system, and for a broad, outer ring of icy comets similar to our own
Kuiper Belt.

Now, Spitzer has discovered that the system also has dual asteroid
belts. One sits at approximately the same position as the one in our
solar system. The second, denser belt, most likely also populated by
asteroids, lies between the first belt and the comet ring. The presence
of the asteroid belts implies additional planets in the Epsilon Eridani
system.

"This system probably looks a lot like ours did when life first took
root on Earth," said Dana Backman, an astronomer at the SETI Institute,
in Mountain View, Calif., and outreach director for NASA's Sofia
mission. "The main difference we know of so far is that it has an
additional ring of leftover planet construction material." Backman is
lead author of a paper about the findings to appear Jan. 10 in the
Astrophysical Journal.

Asteroid belts are rocky and metallic debris left over from the early
stages of planet formation. Their presence around other stars signals
that rocky planets like Earth could be orbiting in the system's inner
regions, with massive gas planets circling near the belts' rims. In our
own solar system, for example, there is evidence that Jupiter, which
lies just beyond our asteroid belt, caused the asteroid belt to form
long ago by stirring up material that would have otherwise coalesced
into a planet. Nowadays, Jupiter helps keep our asteroid belt confined
to a ring.

Astronomers have detected stars with signs of multiple belts of material
before, but Epsilon Eridani is closer to Earth and more like our sun
overall. It is 10 light-years away, slightly less massive than the sun,
and roughly 800 million years old, or one-fifth the age of the sun.

Because the star is so close and similar to the sun, it is a popular
locale in science fiction. The television series Star Trek and Babylon 5
referenced Epsilon Eridani, and it has been featured in novels by Issac
Asimov and Frank Herbert, among others.

The popular star was also one of the first to be searched for signs of
advanced alien civilizations using radio telescopes in 1960. At that
time, astronomers did not know of the star's young age.

Spitzer observed Epsilon Eridani with both of its infrared cameras and
its infrared spectrometer. When asteroid and comets collide or
evaporate, they release tiny particles of dust that give off heat, which
Spitzer can see. "Because the system is so close to us, Spitzer can
really pick out details in the dust, giving us a good look at the
system's architecture," said co-author Karl Stapelfeldt of NASA's Jet
Propulsion Laboratory, Pasadena, Calif.

The asteroid belts detected by Spitzer orbit at distances of
approximately 3 and 20 astronomical units from the star (an astronomical
unit is the average distance between Earth and the sun). For reference,
our own asteroid belt lies at about 3 astronomical units from the sun,
and Uranus is roughly 19 astronomical units away.

One of the two possible planets previously identified around Epsilon
Eridani, called Epsilon Eridani b, was discovered in 2000. The planet is
thought to orbit at an average distance of 3.4 astronomical units from
the star -- just outside the innermost asteroid belt identified by
Spitzer. This is the first time that an asteroid belt and a planet
beyond our solar system have been found in a similar arrangement as our
asteroid belt and Jupiter.

Some researchers had reported that Epsilon Eridani b orbits in an
exaggerated ellipse ranging between 1 and 5 astronomical units, but this
means the planet would cross, and quickly disrupt, the newfound asteroid
belt. Instead, Backman and colleagues argue that this planet must have a
more circular orbit that keeps it just outside the belt.

The other candidate planet was first proposed in 1998 to explain
lumpiness observed in the star's outer comet ring. It is thought to lie
near the inner edge of the ring, which orbits between 35 and 90
astronomical units from Epsilon Eridani.

The intermediate belt detected by Spitzer suggests that a third planet
could be responsible for creating and shepherding its material. This
planet would orbit at approximately 20 astronomical units and lie
between the other two planets. "Detailed studies of the dust belts in
other planetary systems are telling us a great deal about their complex
structure," said Michael Werner, co-author of the study and project
scientist for Spitzer at JPL. "It seems that no two planetary systems
are alike."

JPL manages the Spitzer mission for NASA's Science Mission Directorate,
Washington. Science operations are conducted at the Spitzer Science
Center at the California Institute of Technology in Pasadena. Caltech
manages JPL for NASA. More information about Spitzer is at
http://www.spitzer.caltech.edu/spitzer and http://www.nasa.gov/spitzer .
More information about extrasolar planets and NASA's planet-finding
program is at http://planetquest.jpl.nasa.gov .

Media contact: Whitney Clavin 818-354-4673
Jet Propulsion Laboratory
whitney.clavin at jpl.nasa.gov

2008-197
Received on Mon 27 Oct 2008 07:30:09 PM PDT