Weekly Science Update

Wednesday, December 13, 2006
The Shape of the Solar System
One of the primary reasons why astronomers study planets around other stars is to learn whether our own Earth and solar system are typical or unusual, and to unravel new details about how they formed and evolved. One outstanding current puzzle is the striking alignment between the planes of the planetary orbits of the solar system and the equator of the Sun: the orbital planes the eight planets are within a few degrees of one another and the Sun's spin axis (Pluto, now considered a minor planet, has a more extreme orbital inclination).

SAO astronomer Matt Holman is a member of a team of twelve astronomers that has measured the orbital alignment of the giant planet in the stellar system HD 189733. Using careful techniques of optical spectroscopy on the Keck telescope, along with some meticulous analysis, the team was able to determine the angle between the orbital plane of the planet in this system and its star's equator: only about one degree, with a one degree uncertainty. This makes HD 189733 the third known, exoplanetary system with such a measured angle, and the third where that angle is small, as it is in our own solar system. Since otherwise all three solar systems are quite different from our own -- the giant planet lies closer to its star than Mercury does to our Sun, for example -- the result implies that whatever mechanism(s) cause a solar system to align in this way is quite robust.


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