Making a short list in the hunt for E.T.

No... not Entertainment Tonight. A scientist named Margaret Turnbull of the Carnegie Institute has come up with a short list of the five most likely stars where we could find intelligent, extraterrestrial life. The criteria she used in her analysis certainly seem to make sense.

Age: The star needs to be at least 3 billion years old. That's how long it should take for advanced life to arise on a planet.

Iron content: The star's iron content needs to be at least 1/2 that of our sun. Without the heavy metals, "rocky" interior planets like Earth would likely not form.

Size: Stars which are more than 1.5 times the mass of the sun will have significantly shorter life spans and will probably not produce "habitable zones" for Earth-like planets before they expire.

Stability: No stars are being considered if they have frequent, violent flares which could destroy primitive biospheres.

No Companions: Binaries, or other multiple star systems would be very unlikely to produce inner, rocky worlds with stable orbits where life could develop.

So with that in mind, given, as Dr. Turnbull puts it, "bazillions of stars" to pick from, which stars made the list?

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• Beta CVn: a Sun-like star 26 light-years away in the constellation Canes Venatici (the hound dogs)
• HD 10307: has almost the same mass, temperature and iron content of the Sun
• HD 211 415: has about half the metal content of the Sun and is a bit cooler
• 18 Sco: a near match for the Sun in the constellation Scorpio
• 51 Pegasus: a Jupiter-like planet has been found here; may also host planets like Earth
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One factor not called out in this article, which I think should have been, is distance. It's not that stars will be less likely to produce planets, etc. if they are further away, but we need to consider what use they would be to us if the distances are too vast. Beta CVn, the top candidate, is already fairly distant at 26 light-years. Even if we train all of our instruments on that system and detect some sort of radio signals, assuming we decide to fire off a high energy communications stream at them for a couple of years in hopes of getting their attention, it would take over a quarter of a century for the signal to reach them, and another 26 years for them to respond, assuming they decide to do so. Some of the other candidates are much further away, so communications would be complicated even further.

Still, this is exciting news. This has been a dream (or nightmare, if you prefer) of man since we first began looking up at the heavens. To think that it might become a reality in our lifetimes is simply staggering. We're getting pretty close to knocking on somebody else's door. The questions are, will they answer? And do we really want them to?