[meteorite-list] New Study Suggests More Planets Lurk in Kuiper Belt

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Feb 14 11:37:32 2006
Message-ID: <200602141635.k1EGZ8p04974_at_zagami.jpl.nasa.gov>


New study suggests more planets lurk in Kuiper belt
by Dan Vergano
USA Today
February 12, 2006

The cold, quiet outer reaches of our solar system appear to have once
been a shooting gallery, astronomers report, in which giant comets
smacked into each other with surprising frequency and formed planets. Maybe.
This artist's concept shows the planet catalogued as 2003UB313 at the
lonely outer fringes of our solar system. This artist's concept shows
the planet catalogued as 2003UB313 at the lonely outer fringes of our
solar system.

Beyond Neptune's orbit, about four billion miles from the sun in the
vicinity of Pluto, lies the Kuiper belt, a ring of comets circling our
solar system. Discovery of oversized rivals to Pluto, essentially giant
comets, have shaken up our ideas about the Kuiper belt in the last
decade. Most recently, the confirmation in a recent Nature study that
one of these jumbo icebergs is bigger than Pluto has threatened to
expand our solar system's planetary ranks, a subject of heated debate
among astronomers.

Now, a study in The Astrophysical Journal finds that the "10th planet,"
discovered last year and named UB313, has a moon, just like Pluto. But
that study, led by UB313 discoverer Mike Brown of the California
Institute of Technology, also took a look at more moons in the Kuiper
Belt. And it suggests that the whoppers of the comet ring formed
differently than regular comets.

Brown and colleagues looked for moons around the four brightest, and
likely the biggest, objects in the Kuiper belt. Pluto has three moons,
UB313 has one and another, EL61, has two. The fourth giant, 2005 FY9,
doesn't have any.

In the Kuiper Belt, objects are thought to have gently captured their
moons through gravitational tides. They gently pull on one another over
long periods of time, finally circling each other in an elongated,
delicate dance. Pluto, in contrast, plainly had captured its big moon,
Charon, in an impact, based on the way the two orbit one another.

But the moons of UB313 and EL61 are too small to have exerted much tidal
pull on anything, says Brown's team. And the two giant comets appear to
be spinning quickly, a sign that something sizeable smacked into them at
some point. Based on the shape of their moons' orbits, it appears more
likely that big impacts between comets spread a ring of debris around
those two, and their moons coalesced from that wreckage.

"While once Pluto appeared unique in the outer solar system in terms of
size and satellite formation mechanism, it now appears to be one of a
family of similar-sized objects with perhaps similar collisional
histories," Brown's team concludes.

In other words, don't pretend UB313 isn't a planet on the grounds that
it formed differently than Pluto, Brown is saying. Because that may not
be the case.

Interestingly, Earth's moon likely formed from a similar collision 4.5
billion years ago, when something bigger than Mars collided with the
planet's northern half. And the moon is actually bigger at 2,160 miles
diameter, than Pluto or UB313. But at least our planet has something in
common with the maybe-planets of the Kuiper Belt.
Received on Tue 14 Feb 2006 11:35:08 AM PST

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