[meteorite-list] Jupiter Drifted Towards Sun In Its Youth

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Sep 23 13:44:20 2004
Message-ID: <200409231744.KAA26084_at_zagami.jpl.nasa.gov>

http://www.newscientist.com/news/news.jsp?id=ns99996432

Jupiter drifted towards sun in its youth
Hazel Muir
New Scientist
22 September 2004
 
Jupiter, the king of planets in the solar system, drifted tens of
millions of kilometres towards the sun in its youth, a new study
suggests. Jupiter's migration could even have helped to form the Earth.

The idea that planets migrate towards their stars has received
considerable attention over the past decade, thanks to the discovery of
around a hundred planetary systems besides our own. Most contain "hot
Jupiters" - gas giants that sometimes orbit closer to their stars than
Mercury is to the Sun.

Astronomers believe these giants formed in the cold outskirts of their
systems but moved inwards as they lost angular momentum due to drag
within the dusty disc that surrounds a young star.

Clearly, such a dramatic migration did not happen in our system, where
all the giant planets like Jupiter are relatively far away from the Sun.
But now scientists say they have the first direct evidence that Jupiter
did migrate inwards, albeit to a lesser degree than the hot Jupiters.

Jupiter and the Hilda asteroids

The evidence comes from a curious group of 700 or so rocky chunks called
the Hilda asteroids, which orbit the Sun three times for every two
Jovian years. The vast majority of these have slightly elongated
elliptical orbits (see graphic, below, and animation
<http://sajri.astronomy.cz/asteroidgroups/hildaorb.gif>), whereas many
other asteroids have near-circular orbits.

According to Fred Franklin's team at the Harvard-Smithsonian Center for
Astrophysics in Cambridge, Massachusetts, a migrating Jupiter could
explain why so few Hilda asteroids have circular orbits.

Their simulations show that if a young Jupiter had orbited about 10%
farther from the Sun than it is now, and then spiralled in by about 70
million kilometres over a period of 100,000 years or more, its gravity
would have ejected any proto-Hilda asteroids with circular orbits from
the solar system. And it would have further elongated the orbits of
those that remained.

Luckily for us, Jupiter did not spiral in too far, as other hot Jupiters
apparently did, possibly because the dusty disc around the young sun was
relatively thin. "Had Jupiter migrated all the way in to, say, where
Mercury lies, it would have done some very nasty things to the Earth,"
Franklin says. "We probably wouldn't be here."

Phil Armitage who studies planet formation at the University of Colorado
in Boulder says, "This is the first clear evidence I've seen for the
migration of Jupiter." He adds that Jupiter's short trek could have
disturbed the gravity of the bodies of the inner solar system so that
they collided more frequently, spurring the formation and growth of our
own Earth.

Journal reference: The Astronomical Journal (vol 128, p 1391)

   
Received on Thu 23 Sep 2004 01:44:13 PM PDT