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Moon and Spica

An impressive star system snuggles close to the Moon tonight. Spica, the brightest star of Virgo, is to the lower left of the Moon as night falls, and they move even closer later on.

Although it looks like a single point of light, Spica is really two stars. They’re separated by just a few million miles. Each of them is much bigger, 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 a single star.

To have conditions that are comfortable for life, the planets would have to be billions of miles out — a hundred times farther than Earth is from the Sun.

Even if such worlds had life, it might not look familiar. That’s because the 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 atmosphere. But it’s unlikely that a planet could have enough ozone to protect it from the intense ultraviolet from the stars of Spica. So if there were life, it would have to adapt to the radiation, so it probably would be very different from anything on Earth.

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 stars.

Tomorrow: mismatched planets at dawn.

Script by Damond Benningfield


Today's program was made possible by Mercer Caverns, in Calaveras County in California's historic Gold Country.

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