Is Vesta the 'smallest terrestrial planet?'

December 12, 2011 By Dauna Coulter
Like Earth and other terrestrial planets, Vesta has ancient basaltic lava flows on the surface and a large iron core. It also has tectonic features, troughs, ridges, cliffs, hills and a giant mountain. False colors in this montage denote topography, where the colors indicate heights ranging from -22 km to +19 km above a reference ellipsoid.

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 "" 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.

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3.6 / 5 (8) Dec 12, 2011
I was in favor of reclassifying Pluto, because if it's a planet, we'd have to rewrite the texts every time we found a Kuiper Belt object like it. But based on the new rules, Vesta definitely seems to qualify, even more than Pluto.
Guess we gotta rewrite the texts one more time.
2.5 / 5 (4) Dec 12, 2011
It indicates, how powerful the radioactive heating of planetoids is. We could live comfortably there inside of tunnels just a few miles beneath the surface. BTW It is estimated that about 5% of all meteorite falls on Earth originated from Vesta.
4 / 5 (8) Dec 12, 2011
Vesta does not qualify any more than Pluto does with the present definition. It has not cleared its orbit.

Zephir, that radioactive heating was due to short half life isotopes. They all completely decayed a long time ago. Uranium 238 is the main remaining isotope and it takes a much bigger body to have enough to keep the center molten. Even Mars is now gone cold in the center.

4 / 5 (4) Dec 12, 2011
Hey Ethelred, SoylentGrin was saying that Vesta qualifies as a dwarf planet even better than Pluto does. Dwarf planets don't have to clear their orbits. At least that is the way I read his/her comments.

I was in favor of reclassifying Pluto, because if it's a planet, we'd have to rewrite the texts every time we found a Kuiper Belt object like it.

... in favour of clasifying Pluto as dwarf planet.
But based on the new rules, Vesta definitely seems to qualify, even more than Pluto.

... as dwarf planet
Guess we gotta rewrite the texts one more time.

2.1 / 5 (7) Dec 12, 2011
Guess if we want our planet back, Pluto, we will have to ask Congress to pass a law defining Pluto as a planet, and make its attempted redefinition as anything else a felony. There are a lot of Pluto supporters out there. And tradition says it is a planet. WE all learned the rhymes to remember the NINE planets, and resent the dimunition of our system.
3.7 / 5 (3) Dec 13, 2011
Just another childish attempt to make Pluto a planet again.
2.3 / 5 (7) Dec 13, 2011
"We love Pluto, therefore it should be a planet".

That's their only argument. And it's a stupid one. Personally, I prefer the NEW label "Dwarf Planet", since it's more accurate.

Reasons Pluto shouldn't be a major planet:
1. It's one of the smallest objects in the solar system (even the moon is larger by comparison).
2. There are other bodies in the solar system like it (some of them are even larger, for example; Eris), and none of them are considered "planets". So what makes Pluto so special?
1.8 / 5 (5) Dec 13, 2011
Vesta could be classified as a fourth Dwarf Planet, though. I wouldn't see any problem with that. There'd be Ceres, Vesta, Pluto and Eris (probably not in that order).
4 / 5 (4) Dec 13, 2011
Hey Ethelred, SoylentGrin was saying that Vesta qualifies as a dwarf plane
OK, I didn't read it that way. Since Vesta is fairly spherical I thought of it as a dwarf planet along with Ceres. So that is why I saw it differently.

However I don't see how it qualifies more than Pluto as that has a moon and is much more massive.


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