Solar System

The SDSS colors of main belt asteroids. The dots show the distribution of 33,000 asteroids observed by Sloan Digital Sky Survey (SDSS). The x- and y-axes are the semi-major axis and proper inclination (roughly speaking, the distance from the Sun and the height above the orbital plane) computed by Milani and Knezević, and listed in ASTORB file compiled by Bowell. The dots are colored according to their measured SDSS colors. A striking feature of this figure is the color homogeneity and distinctiveness displayed by asteroid families, which are seen as clumps. Their distinctive optical colors indicate that the variations in chemical composition within a family are much smaller than the compositional differences between families, and strongly support earlier suggestions that asteroids belonging to a particular family have a common origin. For more details, please see a paper Color Confirmation of Asteroid Families by Ivezić et al. (2002).

The small bodies of the Solar System offer a unique insight into its early stages and evolution. Only a few locations still exist where samples of the original solid materials of the solar nebula remain: the main Asteroid Belt, the Trojan populations of the giant planets, the Kuiper Belt just outside the orbit of Neptune, and, far beyond the planets, the objects in the Oort Cloud. Today these populations can be studied as asteroids and comets. Understanding these populations, both physically and in their number and size distributions, is a key element in testing various theories of Solar System formation and the evolution of our planetary system.

My interest in asteroids originated with the early analysis of SDSS data. Asteroids are “contaminants” when using imaging data to select candidate quasars for spectroscopic observations. In order to mitigate this problem, Robert Lupton (Princeton University) designed a simple but poweful algorithm for recognizing moving objects. An initial promising analysis of these data received a crucial boost when Mario Jurić, at the time an undergraduate student from Croatia, joined our team and helped us cross-correlate SDSS data with the catalog of known asteroids maintained by the Minor Planet Center. This project yielded what is still the largest catalog of accurate multi-color asteroid photometry, the SDSS Moving Object Catalog. A nice summary and visualization of the improvement in our knowledge of asteroid colors enabled by this catalog is available here (roll your mouse over the image).

The SDSS Moving Object Catalog enabled a number of publications, from the initial catalog description by Ivezić et al. (2001) to solving a puzzle in the relationship between meteors and asteroids by Jedicke et al. (2004) and to a beautiful study of asteroid families and their size distribution by Parker et al. (2008). Here is a cross-section of the main asteroid belt with families labeled and color-coded by their SDSS colors.

With the SDSS naming rights for many hundreds of asteroids, it was fun and great pleasure to name one after each SDSS collaborator, including my favorite asteroid.

SDSS also discovered many comets, as discussed in Solontoi et al. (2010).

I am looking forward to new asteroid data expected from LSST, that will include millions of asteroids. If you are interested, please take a look at Chapter 5 in the LSST Science Book.