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Moon and Companions

August 4, 2011

An impressive star system snuggles close to the Moon this evening. Spica, the brightest star of Virgo, is just above the Moon. The planet Saturn is well to their right.

Although it looks like a single point of light, Spica is really two stars. They're separated by about 10 million miles -- about a tenth of the distance from Earth to the Sun.

Each of Spica's stars is much larger, heavier, and hotter than the Sun, and thousands of times brighter.

There's no evidence of planets around the stars. If any exist, they probably orbit the pair of stars, not an individual star. And to have conditions that are comfortable for life, they'd have to be billions of miles out.

And even if such worlds did have life, it might not look all that familiar. Both of Spica's stars emit huge amounts of ultraviolet -- the form of energy that causes sunburn, skin cancers, and genetic mutations. Earth is protected from the Sun's ultraviolet by ozone in the upper atmosphere. But it's unlikely that a planet could have a thick enough ozone layer to protect it from the intense ultraviolet emitted by the stars of Spica.

So life on worlds around such stars would be different from life on Earth. Plants, for example, might not look green -- they might need different pigments to survive.

One other complication is that Spica's stars are much younger than the Sun is. So even if they have planets, it's unlikely that there's been enough time for life to evolve there.


Script by Damond Benningfield, Copyright 2011


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