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Mars projected to collide with Earth

Billion-year alert

Forget sending astronauts to Mars, the planet may come crashing right here to Earth if gravitational interactions substantially agitate its now-stable orbit.

A new study in the June 11 issue of Nature predicts there's a real, albeit slim possibility of a planetary smash-up inside the inner solar system, largely thanks to Mercury's distinctly lopsided orbit.

Boffins Jacques Laskar and Mickael Gastineau of the Paris Observatory say results of a new computer model show a roughly one per cent chance within the next five billion years that such a planetary apocalypse will occur.

The researchers simulated the most current data available on the interactions of solar system's eight planets (with the addition of Pluto and Earth's moon) over the course of five billion years - a point in which the Sun is expected to swell into a red giant, swallow the inner planets, and leave astronomers out of work regardless.

Out of 2,501 scenarios sequentially nudging Mercury's orbit by only .38 millimeters, 25 lead to a large enough increase in the planet's orbital eccentricity to allow collisions with Venus or the Sun.

In one simulation, Mercury smashes into Venus about 1.76 billion years from now. In three others, Mercury falls into the Sun.

In yet another, Mercury's gravitational tug yanks Mars within 800 kilometers (497 miles) of Earth 3.34 billion years from now, causing the red planet to rip apart and shower Earth with debris.

Mercury is a particular nuisance to the stability of the solar system because its orbit is a slightly elongated ellipse, leaving it more vulnerable to being swayed by gravity of the large outer planets like Jupiter.

Astronomers believe the solar system is about 4.6 billion years old - so Earth's about half way to retirement with only a few dents on her. Let's just hope Mercury has insurance. ®

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