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For instance, Mercury's orbital eccentricity (eccentricity is a measure of how stretched and noncircular an orbit is) may "increase to the point at which it intersects the orbit of Venus, setting the stage for catastrophe," notes Laughlin.

In what Laughlin calls a "small but disturbing subset of possible future trajectories, Mercury becomes trapped in a 'secular resonance' with Jupiter, a state of affairs in which the elliptical figure of Mercury's orbit rotates in synchrony with Jupiter's orbital precession."If this happens, one scenario finds, Mars and Earth come within 500 miles of one another in 3.3 billion years, putting little green men practically within hailing distance and proving "disastrous for life on the Earth," write the Paris astronomers.

(What that life will be, 3 billion years on, is anyone's guess.) In five cases, Mars is ejected from the solar system.

(Biographical details in this post are drawn from my article on Copernicus in Macmillan's .) In 1491 he matriculated in the famous Jagiellonian University of Cracow, an institution strong in mathematics and proud of its endowed chair of astronomy dating from 1410.

Copernicus’ study of the theories of such luminaries as Ptolemy, Euclid, Sacrobosco and Regiomontanus was complemented by his own observation in Cracow of the comets of 14, and of four lunar and solar eclipses during the next two years.

But the chances of orbits changing with less-than-catastrophic results are greater, notes Laughlin: "the planetary orbits will indeed become chaotic," with "the time required for chaos to significantly degrade the predictability of a system [on] the order of 5 million years." For a 4.5 billion-year-old solar system, that's practically tomorrow.

So while the odds of any one of these violent scenarios coming to pass are about 1 percent, notes Laughlin, that small but nonzero probability is enough to bring astronomers "a vicarious thrill of danger." Whatever turns you on.

Copernicus, Even though he probably accepted a fairly young cosmos—the only option available in the 16th century—Nicolaus Copernicus was far too sophisticated a thinker to have been a friend of 21st century biblical literalists.

Were he alive today, the Roman Catholic astronomer would no doubt give short shrift to any fundamentalist who insisted on constraining science by the prescientific dictates of the Bible.

There’s always a good reason to visit the bustling streets of Fez, Morocco, but with the newly reopened library at al-Qarawiyyin University, there’s another great reason to make the trip.

It isn't every day that you read an astronomy paper that talks about the "grisly" details of changes in planets' orbits, triggering a tongue-in-cheek warning: "suffice it to say here that Earth does not fare well in the resulting interplanetary melee." But a pair of papers in today’s issue of Nature are not your everyday offerings.

Copernicus completed his life’s work— initiated a profound process of revision of the cosmos that continues today.