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Moon and Spica

March 24, 2016

An impressive star system snuggles close to the Moon tonight. Spica, the brightest star of Virgo, is to the lower right of the Moon as they climb into good view in late evening.

Although it looks like a single pinpoint 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 both stars, not an individual star.

To have conditions that are comfortable for life, planets would have to be billions of miles out. And even if such worlds did have life, it might not look familiar. That’s because Spica’s stars emit huge amounts of ultraviolet radiation — the form of energy that causes sunburn and skin cancers. Earth is protected from the Sun’s ultraviolet energy by ozone in the upper atmosphere. But it’s unlikely that a planet could have enough ozone 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 around these bright, deadly stars.

Script by Damond Benningfield

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