The giant asteroid Vesta. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Vesta in View
Jul 04, 2011

The Dawn spacecraft is set to begin its investigation of Asteroid Vesta.

There are three classes of "substellar objects" defined by the International Astronomical Union (IAU):

Planet: In orbit around the Sun; massive enough to possess a rounded shape; and with little (if any) remnant debris from its formation left in orbit. Based on that definition, there are eight planets in the Solar System: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Dwarf Planet: In orbit around the Sun; massive enough to possess a rounded shape, but its orbital environment is not clear and it is not a moon. The dwarf planet Ceres resides in the Asteroid Belt. Pluto (voted by the IAU to be a dwarf planet in August 2006) and Eris are located in the Kuiper Belt, with Sedna farther out in the hypothetical Oort Cloud. Pluto is also considered to be the first of a new celestial body classification, "trans-Neptunian objects (TNO)."

Small Solar System Bodies (SSSB): Refers to all other objects in orbit around the Sun, such as asteroids, comets, and moons.

NASA launched the Dawn spacecraft on September 27, 2007. Its scientific mission is scheduled to begin on July 17, 2011, when it enters orbit around the largest asteroid in the Solar System, Vesta. Vesta is now the largest asteroid, comparable in size to Saturn's moon Enceladus, because Ceres was moved into the dwarf planet category. Heinrich Wilhelm Olbers discovered Vesta in 1807.

Ceres was the first asteroid discovered by Guiseppe Piazzi in 1801 and was the largest known until its promotion. Ceres has a diameter of 950 kilometers, but since no spacecraft has visited Ceres its size is an estimate derived from combining various telescope observations. Ceres is about as large as Saturn's moons Tethys and Dione. Dawn will visit Ceres in February 2015, after spending a year circling Vesta.

Vesta appears to have experienced violent collisions at some time in the past, since several large craters mar its surface. One crater is 460 kilometers in diameter, making it more than 80% as large as the asteroid itself. Whatever formed the crater gouged out a hole 13 kilometers below the asteroid's mean elevation. The rolled rim is about 6 kilometers higher than the mean. In the center is an 18 kilometer high peak. As has been asked many times in these pages: Why did an impact that removed more than 1% of the asteroid's mass not blow it to bits?

Planetary scientists ignore electrical explanations because they know almost nothing about plasma and electric currents in space. The "rubble pile" theory of asteroid composition was created to help explain the mass anomalies that have been seen in asteroid crater studies. It is the only available explanation in a gravity-based model. Asteroids are supposed to be "loosely compacted," so it is presumed that they act like big sand piles and absorb impacts without shattering. Asteroids therefore have no hard crust, according to consensus viewpoints, so they do not fracture despite repeated pounding.

In an Electric Universe, it is unnecessary for one object to crash into another for craters to exist. Electric arcs can gouge surfaces and scoop out material, accelerating it into space, leaving clean, deep pits. Based on laboratory analysis, plasma discharges probably eroded Vesta (and other asteroids and moons with large, deep craters).

Stephen Smith