Discussion and news about the modern effort to understand the nature of life on Earth, finding planets around other stars, and the search for life elsewhere in the universe

Tuesday, June 1, 2010

Star Flavors

As the effort to find new planets around stars barrels along, some intriguing characteristics are beginning to reveal themselves. We know that stars range from just about a tenth of the mass of our Sun all the way up to some crazy big balls of plasma hitting over 100 times more massive. The environment for any planets orbiting in these systems will be radically different. Small stars are dim, as much as a thousand times fainter than the Sun, with a red hue. The most massive stars are tens of thousands of times more luminous, blue-hot, barely held together by gravity, belching forth material. In  keeping with their outward appearances, low mass stars can sustain a gentle fusion burn of their core material for a trillion years. The big guys follow the live-fast-die-young business plan, and rip through their semi-stable, rock and roll, lifestyle in a mere million years or so. Pity the planets in those systems.

Some new work adds support for another layer of flavor by finding evidence for a fundamental shift in the nature of the planetary populations around stars of different masses. Stars just a little heftier than our Sun, by 50-100%, appear to play host to many more giant planets - objects larger than Jupiter - than do stars like the Sun. While we don't yet know what's going on with the smaller, more terrestrial-type, planets that may or may not exist in these systems, it suggests an acute planetary dependence on the size of the stellar parent (among other things).

Our still fledgling ideas about how planets form, out of the great disks of gas and dust that surround young stars, are more or less consistent with an upturn in the numbers of giant planets around bigger stars, but the details are hard to come by. What's really surprising is just how little a change in the type of star is needed to see a pretty dramatic shift in the numbers of giant planets - whatever is going on is a sensitive business.

This adds another lever into the machinery for trying to evaluate systems as potential harbors for life. Fast burning, massive, stars may make certain types of planets more efficiently, but what matters the most - longevity or numbers? Do we even care about these types of systems if small terrestrial-type planets get muscled out? Maybe it's the moon systems of these giant planets that are of interest?  A star twice the mass of the Sun is perhaps 5 times more likely to harbor giant planets and their moons, but will burn through its hydrogen core in a 'mere' two billion years. Is that a second class habitat or a premium one?

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