[LINK] "In Praise of K-class Stars"

[rfmcdonald]

Centauri Dreams has an interesting post up suggesting that Class K stars, less massive hence less bright than our Sol, might be very suitable hosts for Earth-like planets.

Recently we’ve been kicking around the subject of K-class stars in the comments to various posts here, and with K stars we really can start talking about planets much more like our own. Here I fall back to the IAU meeting, where Jean-Mathias Grießmeier (ASTRON, The Netherlands) looked at the role of magnetic fields in determining how likely life is to develop. Such fields provide a shield against incoming charged particles from stellar mass ejections as well as pervasive solar winds. They also offer protection against high-energy cosmic rays.

And here’s the quote from Grießmeier that resonates with me. He’s looking at the kind of stars we might expect to find life around, and concludes that our Sun probably wouldn’t top a list of such stars as compiled by the average extraterrestrial astronomer:

“The Sun does not seem like the perfect star for a system where life might arise. Although it is hard to argue with the Sun’s ’success’ as it so far is the only star known to host a planet with life, our studies indicate that the ideal stars to support planets suitable for life for tens of billions of years may be a smaller slower burning ‘orange dwarf’ with a longer lifetime than the Sun ― about 20-40 billion years. These stars, also called K stars, are stable stars with a habitable zone that remains in the same place for tens of billions of years. They are 10 times more numerous than the Sun, and may provide the best potential habitat for life in the long run.”

K stars — now we’re talking! A stable habitable zone that offers a long period for life’s development, and a population that far outnumbers G-class stars like the Sun. It’s nice to speculate about the closest such star, the K-dwarf Alpha Centauri B, but of course we still have to resolve the question of planetary formation in binary systems like this one. We should have some answers fairly quickly, what with two ongoing attempts to find planets in the Alpha Centauri system, and may well know about Centauri planets before we start getting hard returns from Kepler.

Some of the K-class stars in our stellar neighbourhood include Alpha Centauri B, Epsilon Eridani, and the famous 40 Eridani A.