Planets and Asteroids

What are planets?

The members of our solar system have long held humanity's fascination. Today, astronomers are still trying to understand (among other things) the nature of the solid bodies (planets, moons, asteroids, comets, meteorites) in our own celestial back yard.

In 2006 the International Astronomical Union (IAU) defined a planet as an object orbiting the Sun that is massive enough to be pulled into an essentially spherical shape by its own gravity, but not massive enough to cause thermonuclear fusion in its core (and hence be classified as a brown dwarf or a star). In addition, the object must have cleared its neighbouring region of planetesimals. Objects that fail in that last criterion - currently Pluto, Eris and Ceres - are dwarf planets. Smaller objects, such as the remainder of the asteroids are small solar system objects.

Current research areas

mm imaging of Asteroids
Peter Barnes has been looking at the surface properties of some of the large Main Belt Asteroids, such as Vesta and Metis. With Thomas Muller at the Max Planck Institute in Germany, we have discovered that, although their thermal emission properties at far-infrared and submillimetre wavelengths are well-understood, at 3 mm we learn can new things about the surface texture (grain size distribution of the "soil" or regolith) of such bodies: see figs 1 & 2. These discoveries were made using the Australia Telescope's Compact Array near Narrabri.

Observing asteroids can also have more practical benefits to other areas of astronomy. It is intended that they will be important calibrators for astronomy satellites and new ground-based facilities, such as Herschel and ALMA, and perhaps can be used to improve the Compact Array's calibration as well. Therefore we are also planning a careful comparison with ATCA of Mars, Uranus, Neptune, Ceres, and Pallas in order to understand better both our instruments and these bodies.

For more information contact Peter BARNES


"3.2 mm lightcurve observations of (4) Vesta and (9) Metis with the Australia Telescope Compact Array," Thomas Mller and Peter J. Barnes, A&A, in press, 2007 (astro-ph 0703215)


Fig. 1

Fig. 2

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