[meteorite-list] Where the ETs are hiding

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Tue, 13 Oct 2009 16:41:12 -0500
Message-ID: <hss9d5p717l2v818nof3cofjd28ooi378n_at_4ax.com>

Hopefully, they aren't wild things.

http://www.scientificamerican.com/blog/post.cfm?id=what-do-we-really-know-about-the-ku-2009-10-13

What do we really know about the Kuiper Belt? Fifth dispatch from the annual
planets meeting

By George Musser

FAJARDO, Puerto Rico?It smacked of a cunning plan. The organizers of last week's
planets conference put one of the best talks in the very last session of the
very last day. Most scientists had either left for the airport or the beach. I
almost didn't make it myself?the room and time got switched at the last minute.

If the speaker, Wesley Fraser of the California Institute of Technology, is
right, planetary scientists are going to have to rethink the Kuiper Belt?the
vast band of smallish planets that orbit beyond Neptune. Using the Hubble Space
Telescope, Fraser and his colleague Mike Brown observed one of the largest of
these objects, Quaoar, and its little moonlet, Weywoot, to refine estimates of
its size and mass. They found that Quaoar is smaller than previously thought,
only 900 kilometers in diameter. Consequently, it must be denser?about four
grams per cubic centimeter. This makes it by far the densest Kuiper Belt object
(KBO). It outdoes even a fairly dense asteroid such as Vesta.

Planetary scientists typically explain dense KBOs by imagining that they started
off larger and less dense; they then collided with one another, stripping off
lighter material such as ice and leaving behind mostly rock. Yet by the new
estimate Quaoar is denser even than rock, so even completely stripping its ice
wouldn't be enough. Moreover, astronomers detect ice on its surface. It makes no
sense. "It's confusing, to say the least," Fraser says.

That's only half of it. Most KBO moonlets have circular orbits. That is thought
to be a consequence of coalescing from collisional debris: debris rings
naturally settle into a circular shape. Yet Weywoot's orbit is distinctly
oblong. "We have to completely rewrite the book," Fraser concludes.

One radical idea is that Quaoar is a refugee from the asteroid belt between Mars
and Jupiter. Asteroids tend to be denser than KBOs, and Jupiter might
conceivably flick one to the farthest reaches of the solar system. But the
hapless exile would tend to wind up on a highly elliptical orbit around the sun,
whereas Quaoar's orbit is nearly circular.

Erik Asphaug of the University of California, Santa Cruz, offered another
explanation based on work he presented earlier in the week. Perhaps Quaoar
collided with a much bigger body?something approaching the proportions of Mars.
Like a Mini blindsided by a Hummer, Quaoar would have gotten seriously banged up
by such a collision, maybe enough to give it an anomalously high density. If so,
Quaoar might be living proof that substantial planets used to orbit in the
distant solar system and may still lurk out there.

Clearly this is one of those "more data are needed" situations, and Fraser has
applied for additional telescope time. One thing is sure, though. People
typically call KBOs icy bodies, like giant comets. But they can also be rocky,
like small Earths.
Received on Tue 13 Oct 2009 05:41:12 PM PDT