[meteorite-list] Is Vesta the 'Smallest Terrestrial Planet?'

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 12 Dec 2011 10:44:29 -0800 (PST)
Message-ID: <201112121844.pBCIiTBE021130_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/science-news/science-at-nasa/2011/09dec_vestaplanet/

Is Vesta the "Smallest Terrestrial Planet?"
NASA Science News
December 9, 2011

NASA's Dawn spacecraft spent the last four years voyaging to asteroid
Vesta - and may have found a planet.

Vesta was discovered over two hundred years ago but, until Dawn, has
been seen only as an indistinct blur and considered little more than a
large, rocky body. Now the spacecraft's instruments are revealing the
true complexity of this ancient world.

"We're seeing enormous mountains, valleys, hills, cliffs, troughs,
ridges, craters of all sizes, and plains," says Chris Russell, Dawn
principal investigator from UCLA. "Vesta is not a simple ball of rock.
This is a world with a rich geochemical history. It has quite a story to
tell!"

In fact, the asteroid is so complex that Russell and members of his team
are calling it the "smallest terrestrial planet."

Vesta has an iron core, notes Russell, and its surface features indicate
that the asteroid is "differentiated" like the terrestrial planets
Earth, Mercury, Mars, and Venus.

Differentiation is what happens when the interior of an active planet
gets hot enough to melt, separating its materials into layers. The light
material floats to the top while the heavy elements, such as iron and
nickel, sink to the center of the planet.

Researchers believe this process also happened to Vesta.

The story begins about 4.57 billion years ago, when the planets of the
Solar System started forming from the primordial solar nebula. As
Jupiter gathered itself together, its powerful gravity stirred up the
material in the asteroid belt so objects there could no longer coalesce.
Vesta was in the process of growing into a full-fledged planet when
Jupiter interrupted the process.

Although Vesta's growth was stunted, it is still differentiated like a
true planet.

"We believe that the Solar System received an extra slug of radioactive
aluminum and iron from a nearby supernova explosion at the time Vesta
was forming," explains Russell. "These materials decay and give off
heat. As the asteroid was gathering material up into a big ball of rock,
it was also trapping the heat inside itself."

As Vesta's core melted, lighter materials rose to the surface, forming
volcanoes and mountains and lava flows.

"We think Vesta had volcanoes and flowing lava at one time, although
we've not yet found any ancient volcanoes there," says Russell. "We're
still looking. Vesta's plains seem similar to Hawaii's surface, which is
basaltic lava solidified after flowing onto the surface.

Vesta has so much in common with the terrestrial planets, should it be
formally reclassified from "asteroid" to "dwarf planet"?

"That's up to the International Astronomical Union, but at least on the
inside, Vesta is doing all the things a planet does."

If anyone asks Russell, he knows how he would vote.

Author: Dauna Coulter
Editor: Dr. Tony Phillips
Credit: Science at NASA
Received on Mon 12 Dec 2011 01:44:29 PM PST