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Planetoid, protoplanet- Vesta

Don't think for a moment that icy, distant Pluto is alone in the ongoing astronomical game to redefine well-know bodies inside our solar system. Some astronomers classify Pluto as a dwarf planet rather than as the ninth major planet-fine, but other researchers still cling to Pluto's discoverer Clyde Tombaugh's identification of this distant world as the real McCoy, a planet. No matter, it's likely that this reclassification revolution, so near-and-dear to astronomers, will continue for years to come.

Now there's a new naming battle brewing: some astronomers are wondering how to reclassify Vesta, the solar system's largest asteroid or planetoid.

According to Dr. Tony Phillips of NASA, astronomers consider Vesta to be an asteroid because it is within the main asteroid belt-between the planets Mars and Jupiter. Yet there's something very weird about it.

Unlike its tumbling neighbors in the main belt, Vesta is no lightweight asteroid. And unlike its rocky pals (most only 100 kilometers wide and smaller), Vesta is big-530 kilometers in diameter.

That's almost planet sized or rather dwarf-planet sized.

"On March 29, 1807, German astronomer Heinrich Wilhelm Olbers spotted Vesta as a pinprick of light in the sky. Two hundred and four years later, as NASA's Dawn spacecraft prepares to begin orbiting this intriguing world, scientists now know how special this world is, even if there has been some debate on how to classify it," Dr. Phillips told Seeing Stars.

While Dr. Phillips doesn't take sides in NASA's emerging Vesta debate, Dr. Tom McCord, a NASA Dawn co-investigator, most definitely does.

"I don't think Vesta should be called an asteroid," said Dr. McCord.

"Not only is Vesta so much larger, but it's an evolved object, unlike most things we call asteroids."

Dr. McCord points to Vesta's layered structure (with a core, mantle and crust) as the reason why it's more aligned with the terrestrial planets-Mercury, Earth, Venus and Mars-than the lumpy asteroids.

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