Technology & Science

Asteroid a 'wannabe' planet, scientists say

Astronomers examining Pallas, one of the solar system's largest asteroids, with the Hubble Space Telescope have dubbed it a "protoplanet."
This artist's impression, created using a 3-D model, shows a large object crashing into Pallas. ((B. E. Schmidt and S. C. Radcliffe))

Astronomers examining one of the solar system's largest asteroids with the Hubble Space Telescope have dubbed it a "protoplanet."

Pallas, an asteroid 265 kilometres in diameter and located in the asteroid belt between Mars and Jupiter, joins two other asteroids, Ceres and Vesta, which are also considered protoplanets.

These protoplanets are planetary embryos that weren't large enough to continue to grow into planets, but still share some physical characteristics of full-grown planets.

Objects in the solar system formed from a disk of rocks and dust orbiting the sun. As gravity pulled objects together, larger clumps of rock formed. If the objects became large enough, they heated up and underwent chemical changes.

The largest clumps became planets, but some weren't big enough and remained as protoplanets.

Potential to grow

Astronomers at UCLA identified features and variations in colour on the surface of Pallas that they say indicate it had the potential to grow. They said Pallas appeared to have formed from water-rich minerals and may have undergone chemical changes, differentiating it from other asteroids.

The researchers published a 3-D model of Pallas created from the Hubble telescope data and analyzed in impact crater on Pallas. They said it suggests a large object hit the asteroid, breaking off rocks and debris.

The astronomers said this impact could have been the source of the small asteroids that orbit with Pallas in the same "family."

Ceres, the largest object in the asteroid belt, is also considered a "dwarf planet," under definitions adopted by the International Astronomical Union in 2006, while Pallas and Vesta are not.

Pallas isn't considered a dwarf planet because of the small asteroids that share its orbit. Vesta, besides also sharing its orbit with small asteroids, isn't spherical enough to quality as a dwarf planet.

Ceres, Pallas, Vesta, and one other asteroid, Juno, were all discovered in the early 19th century and were considered planets until the middle of that century, when still more asteroids were found orbiting between Mars and Jupiter.