Mercurial Menace

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The elusive planet Mercury -- the closest planet to the Sun -- is tough to see, because it's small and it huddles close to the Sun. But you have a chance to glimpse it the next few evenings, in the western sky after sunset. It looks like a fairly bright star, but it's so low in the sky that you'll need binoculars to pick it out.

Two new studies -- one from France, the other from California -- have concluded that in the distant future, Earth might get a far better view of Mercury. In fact, it might be too good -- there's a tiny chance that the planet could crash into Earth.

Both studies used computers to simulate how the planets orbit the Sun. They found that the gravity of Jupiter, the largest planet in the solar system, could stretch Mercury's orbit.

Mercury's orbit around the Sun is already pretty stretched out. But in the far future, Jupiter's gravitational influence could cause Mercury to cross the orbit of Venus, the next planet out from the Sun. At that point, Mercury might get ejected from the solar system. Or it might crash into the Sun or Venus. Or in the worst case, it might even crash into Earth.

Such an impact would kill all life on Earth. Fortunately, though, the chance that Mercury will spiral out of its present orbit is small. There's only a one percent chance it will happen in the billions of years before the Sun begins to die and solves the problem -- by expanding enough to engulf its closest planet.

Script by Ken Croswell, Copyright 2008

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