[meteorite-list] Phoebe Moon May Be Captured Comet

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed May 4 17:42:07 2005
Message-ID: <200505042141.j44LfXO17222_at_zagami.jpl.nasa.gov>

http://news.bbc.co.uk/1/hi/sci/tech/4513379.stm

Phoebe moon may be captured comet
BBC News
May 4, 2005

Saturn's pock-marked moon Phoebe could be a comet that was captured by
the gravity of the ringed planet.

Data from the Cassini spacecraft suggests it originated in the frozen
outer Solar System region called the Kuiper Belt - a reservoir for comets.

Two studies of Phoebe are carried in this week's issue of Nature magazine.

The tiny satellite is very different in its chemical composition to
Saturn's larger moons and circles the planet in the opposite direction
to them.

"It could have been a comet," said co-author Ralf Jaumann of the German
Aerospace Center (DLR).

"Phoebe has a long journey behind it. It comes from the outer Solar
System and probably rounded the Sun a few times before it was captured
by Saturn's orbit. But we really don't know."

Phoebe and the objects that populate the Kuiper Belt are remnants of
primordial objects that served as the building blocks of planets in our
Solar System.

The saturnian satellite could itself be between 4 and 4.4 billion years
old.

Icy bodies

During the formation of the planets, gravitational interactions ejected
some so-called icy planetesimals like Phoebe into distant orbits to join
a native population of similar cosmic bodies.

This process formed the region we know today as the Kuiper Belt.

Phoebe itself must have migrated inwards and was captured by Saturn's
gravity after the ringed planet formed from its planetary nebula.

Analysis of Phoebe's surface shows that it is one of the most complex
Solar System objects yet studied.

Scientists have identified water-ice, possible clays, iron-bearing
minerals and organics such as aromatic compounds, alkanes and nitriles
on the 220km-wide Saturnian satellite. More complex organics also seem
to be there, but scientists are yet to characterise them.

The observations come from Cassini's Visual and Infrared Mapping
Spectrometer (Vims).

Dr Jaumann thinks clays could have formed through heating if Phoebe came
close to the Sun before being captured by Saturn, forcing water ice to
react with silicates.

"When we finally understand Phoebe, we will also understand the Kuiper
Belt objects," Dr Jaumann explained.

Phoebe's surface composition also suggests that chemical activity in the
first half billion years of the Solar System may have been more complex
than previously thought.

"However, we have only seen the surface and this has probably undergone
some alteration. But Phoebe has probably not had much alteration through
high pressure or heating," Dr Jaumann added.

Cassini collected data on the moon during a close flyby on 11 June 2004.
Received on Wed 04 May 2005 05:41:31 PM PDT