[meteorite-list] Lessons from an Odd Kuiper Belt Object (2003 EL61)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Apr 21 23:29:49 2006
Message-ID: <200604211653.JAA10817_at_zagami.jpl.nasa.gov>

http://skyandtelescope.com/news/article_1716_1.asp

Lessons from an Odd Kuiper Belt Object
By David Tytell
Sky & Telescope
April 20, 2006

To date astronomers have found more than 1,000 Kuiper
Belt objects (KBOs) beyond Neptune, and the strangest one of all might
just be the key to understanding how the largest of these distant
ice-rock bodies acquire their moons.

Last July, 2003 EL61 entered the KBO lexicon just days before the "10th
planet," 2003 UB313. But follow-up observations of 2003 EL61 left astronomers
scratching their heads. Its spin period is just 3.9 hours, making 2003
EL61 the fastest rotating known body in our solar system larger than 100
kilometers (60 miles) across.

As for its shape, picture a squashed American football. Models suggest
that 2003 EL61's long dimension could exceed both Pluto's and 2003
UB313's diameters. The body also has two small satellites: an inner moon
with a 34.7-day non-circular orbit and a brighter, outer companion with
a 49.1-day circular orbit.

Observations of the primary body made by Chadwick Trujillo (Gemini
Observatory) and his colleagues reveal the strong spectral signature of
crystalline water ice. This is odd because crystalline ice forms at
temperatures above 110 kelvins (-163?C) whereas the ambient temperature
of space around 2003 EL61 is less than 50 K. Moreover, crystalline water
ice typically lasts only 10 million years before it's destroyed, which
points to possible resurfacing, perhaps by micrometeorite impacts
converting existing surface ices to crystalline form by flash-heating.

Spectra of the outer satellite obtained by Kristina Barkume, Michael
Brown, and Emily Schaller (Caltech) reveal the signature of almost pure
water ice. While the observations were too low in resolution to
distinguish the type of water ice, it seems that nearly all of the moon
is coated in frost.

Putting the pieces together, 2003 EL61 strongly suggests that the moons
of the largest KBOs differ in origin from those of ordinary KBOs. The
satellite systems of the larger objects formed from the remains of
violent impacts instead of by delicate gravitational capture. According
to Brown, "[2003 EL61] itself is rapidly rotating and thus elongated - a
predicted consequence of a giant impact which forms a small satellite."
Moreover, he adds, other astronomers have predicted that "small
satellites, which form from disks, will be made almost entirely of water
ice, which is precisely what we see." Impact is already a favored
formation mechanism for another large KBO system - Pluto and its three
moons.
Received on Fri 21 Apr 2006 12:53:25 PM PDT