SLIDE 9.
Four-point-two
billion years after the brief cosmic eyeblink of Earthly
intelligence, the game is up. The dead Earth orbits alone, its moon
a separate planet wandering in increasingly unstable ellipses
around the sun. Glowing dull red beneath an atmosphere of carbon
dioxide baked from its rocks, there will be no sign that this world
ever harbored life. The sun it circles, a sullen-faced ruddy ogre,
is nearing the end of its hydrogen reserves. Soon it will expand,
engulfing the inner planets.
But events on a
larger scale are going to spare the Earth this fate. For billions
of years, the galaxy in which this star orbits has been converging
with another large starswarm, the M-31 Andromeda galaxy. Now the
spiraling clouds of stars are interpenetrating and falling through
each other, and the sun is in for a bumpy ride as galaxies
collide.
A binary system of
red dwarfs is closing with the solar system at almost five hundred
kilometers per second. They are going to pass within half a billion
kilometers of the sun, a hairbreadth miss in cosmic terms: in the
process they will wreak havoc on the tidy layout of the solar
system. Jupiter, dragged a few million kilometers sunward, will
enter an unstable elliptical orbit, and over the course of a few
thousand years it will destabilize all the other planets. Luna
departs first, catapulted out of the plane of the ecliptic; Earth,
most massive of all, will spend almost five million years wobbling
between the former orbits of Venus and Saturn before it finally
caroms past Jupiter and drifts off into the eternal night, the
tattered remnants of its atmosphere condensing and freezing in a
shroud of dry ice.