[meteorite-list] Hubble Finds Farthest, Faintest Solar System Objects Beyond Neptune

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:29:52 2004
Message-ID: <200309072340.QAA05354_at_zagami.jpl.nasa.gov>

http://hubblesite.org/newscenter/archive/2003/25/text

EMBARGOED FOR RELEASE: 3:00 P.M. (EDT) SEPTEMBER 6, 2003

CONTACT:
Steve Bradt
University of Pennsylvania
Phone: 215/573-6604; Pager: 215/524-6272

Donna Weaver
Space Telescope Science Institute, Baltimore, Md.
Phone: 410/338-4493; E-mail: dweaver_at_stsc.edu

PRESS RELEASE NO.: STScI-PR03-25

FARTHEST, FAINTEST SOLAR SYSTEM OBJECTS FOUND BEYOND NEPTUNE

Astronomers using NASA's Hubble
Space Telescope have discovered three
of the faintest and smallest objects ever
detected beyond Neptune. Each object
is a lump of ice and rock - roughly the
size of Philadelphia - orbiting beyond
Neptune and Pluto, where the icy bodies
may have dwelled since the formation of
the solar system 4.5 billion years ago.
They reside in a ring-shaped region called the Kuiper
Belt, which houses a swarm of icy rocks that are leftover
building blocks, or "planetesimals," from the solar
system's creation.

The results of the search were announced by a group led
by astronomer Gary Bernstein of the University of
Pennsylvania at today's meeting of the Division of
Planetary Sciences in Monterey, Calif.

The study's big surprise is that so few Kuiper Belt
members were discovered. With Hubble's exquisite
resolution, Bernstein and his co- workers expected to
find at least 60 Kuiper Belt members as small as 10
miles (15 km) in diameter - but only three were
discovered.

"Discovering many fewer Kuiper Belt objects than was
predicted makes it difficult to understand how so many
comets appear near Earth, since many comets were
thought to originate in the Kuiper Belt," Bernstein says.
"This is a sign that perhaps the smaller planetesimals
have been shattered into dust by colliding with each
other over the past few billion years."

Bernstein and his colleagues used Hubble to look for
planetesimals that are much smaller and fainter than can
be seen from ground-based telescopes. Hubble's
Advanced Camera for Surveys was pointed at a region in
the constellation Virgo over a 15-day period in January
and February 2003. A bank of 10 computers on the
ground worked for six months searching for faint-moving
spots in the Hubble images.

The search netted three small objects, named 2003
BF91, 2003 BG91, and 2003 BH91, which range in size
from 15-28 miles (25-45 km) across. They are the
smallest objects ever found beyond Neptune. At their
current locations, these icy bodies are a billion times
fainter (29th magnitude) than the dimmest objects visible
to the naked eye. But an icy body of this size that
escapes the Kuiper Belt to wander near the Sun can
become visible from Earth as a comet as the wandering
body starts to evaporate and form a surrounding cloud.

Astronomers are probing the Kuiper Belt because the
region offers a window on the early history of our solar
system. The planets formed over 4 billion years ago from
a cloud of gas and dust that surrounded the infant Sun.
Microscopic bits of ice and dust stuck together to form
lumps that grew from pebbles to boulders to city- or
continent-sized planetesimals. The known planets and
moons are the result of collisions between planetesimals.
In most of the solar system, all of the planetesimals have
either been absorbed into planets or ejected into
interstellar space, destroying the traces of the early days
of the solar system.

Around 1950, Gerard Kuiper and Kenneth Edgeworth
proposed that in the region beyond Neptune there are no
planets capable of ejecting the leftover planetesimals.
There should be a zone, the two astronomers said- now
called the Kuiper Belt - filled with small, icy bodies.
Despite many years of searching, the first such object
was not found until 1992. Since then, astronomers have
discovered nearly 1,000 from ground-based telescopes.
Most astronomers now believe that Pluto, discovered in
1930, is in fact a member of the Kuiper Belt.

Astronomers now use the Kuiper Belt to learn about the
history of the solar system, much as paleontologists use
fossils to study early life. Each event that affected the
outer solar system - such as possible gravitational
disturbances from passing stars or long-vanished
planets - is frozen into the properties of the Kuiper Belt
members that astronomers see today.

If the Hubble telescope could search the entire sky, it
would find perhaps a half million planetesimals. If
collected into a single planet, however, the resulting
object would be only a few times larger than Pluto. The
new Hubble observations, combined with the latest
ground-based Kuiper Belt surveys, reinforce the idea
that Pluto itself and its moon Charon are just large
Kuiper Belt members. Why the Kuiper Belt
planetesimals did not form a larger planet, and why there
are fewer small planetesimals than expected, are
questions that will be answered with further Kuiper Belt
studies. These studies will help astronomers understand
how planets may have formed around other stars as well.

The new Hubble results were reported by Bernstein and
David Trilling (University of Pennsylvania); Renu
Malhotra (University of Arizona); Lynne Allen
(University of British Columbia); Michael Brown
(California Institute of Technology); and Matthew
Holman (Harvard-Smithsonian Center for
Astrophysics). The results have been submitted to the
Astronomical Journal for publication, and a preliminary
report is available on the Web at

http://arxiv.org/abs/astro-ph/0308467.
Received on Sun 07 Sep 2003 07:40:48 PM PDT