[meteorite-list] The Edge of Our Solar System

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:44:39 2004
Message-ID: <200103131902.LAA14550_at_zagami.jpl.nasa.gov>


The Edge of Our Solar System
by Venessa Thomas
March 13, 2001

A report from this year's Lunar and Planetary Science Conference in Houston:
Astronomers search Pluto's neighborhood for signs of Kuiper Belt Objects

Even if you are not a follower of planetary science, you have probably heard
about the debate over Pluto's status as a planet. The smallest and most
distant "planet" in our solar system, Pluto has been accused of simply being
just the largest member of a neighborhood gang of icy bodies called Kuiper
Belt Objects (KBOs). More than 300 KBOs have been found beyond the orbit of
Neptune, between about 30 and 55 AU from the sun, since the first was
discovered in 1992. Planetary scientists suspect that the majority of KBOs
lie undiscovered beyond 55 AU, but have so far found only one.

A "medium-wide, medium-deep" hunt for more distant KBOs was taken on by a
group of U.S. researchers from the University of Arizona, the Lunar and
Planetary Science Institute, and the University of Michigan. From the Cerro
Tololo Inter-American Observatory (CTIO) in Chile, the team examined a 1.5
square-degree region of the sky near the ecliptic for several nights in May
of 1998 and 1999. Assuming KBOs reflect about 4 percent of the sunlight
hitting them (typical of comets believed to originate in the Kuiper Belt),
the astronomers expected their search to detect objects larger than about
100 miles (160 kilometers) wide at 65 AU from the sun. They call it a
"medium-wide, medium-deep" study because most searches typically cover more
area and less "depth" (fainter magnitudes), but telescopes such as the Keck
can conduct deeper searches in smaller fields. The CTIO search covered
several times more area than any previous study at its depth.

At the Lunar and Planetary Science Conference in Houston on Monday, the team
reported its discovery of 24 new objects. To the team's disappointment, none
of the 24 is more than 53 AU from the sun.

Planetary scientists have suspected that most KBOs lie in a "safe zone"
beyond 55 AU where the gravitational influence of the Neptune and the giant
planets cannot affect their orbits. Why then can no more objects be found in
this outer region?

The CTIO team suggested a few possibilities on Monday for why its search
failed to uncover any KBOs beyond 53 AU. Perhaps KBOs in the outer belt are
fainter than expected, lead scientist Renu Malhotra proposed. The albedo of
KBOs in the outer belt could be lower, or maybe they are smaller than the
CTIO search could detect. Perhaps the outer region of the Kuiper Belt is
extremely thin and inclined (tilted with respect to the ecliptic). The team
says the belt would have to be much less than 1 degree thick for it to
escape their search.

Malhotra and her colleagues also admit that their search might indicate that
the Kuiper Belt simply does not extend beyond 55 AU. Perhaps an encounter
with another star during the solar system's formation depleted the outer
Kuiper Belt. Or, the team suggests, KBOs may have just never existed that
far from the sun. The single KBO discovered beyond 55 AU has a highly
eccentric (elongated) orbit and may have been perturbed by one of the giant
planets into such an odd path around the sun.

Additional searches may be the key to solving this mystery. Until then,
planetary scientists will keep wondering: Are there more distant KBOs still
hidden from view or does the edge of our solar system's disk lie at 55 AU?
Received on Tue 13 Mar 2001 02:02:46 PM PST

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