If the Light's on, Somebody May be Home

The recent discovery of three planets orbiting a sun-like star once again raises one of mankind's favorite questions: can life exist on other planets?

Someday, the aurora might help find an answer, according to Syun-Ichi Akasofu, director of both the Geophysical Institute and the International Arctic Research Center at the University of Alaska Fairbanks. Akasofu has studied the aurora since 1957, and he thinks other planets' auroras could be used to detect life elsewhere in the universe.

The idea was inspired by the discovery of three planets circling a sun that's much like ours, though a bit bigger. The star, Upsilon Andromedea, is 44 light years away, which means a spacecraft moving at the speed of light would take 44 years to get there. Still, it's not too far away by astronomical standards (the diameter of the Milky Way is about 100,000 light years).

The most significant part of the discovery is that it shows our solar system is not unique: maybe there's a planet out there just like Earth, providing a home for people or dinosaurs or beetles or bacteria or something we can't even imagine.

The possible connection between extraterrestrial life and aurora first came to Akasofu when he spoke to an Elderhostel group. Akasofu fielded a question from a man who wanted to know if the aurora would change color if humans polluted the atmosphere enough to change the concentration of its gases. The question is valid because gases create the colors of the aurora. Green is the most common color in the aurora because Earth has a lot of oxygen in its atmosphere. This oxygen, exhaled by plants and animals, finds its way to the upper reaches of the atmosphere. When oxygen molecules and atoms floating about 60 miles above Earth are struck by particles from the sun, they glow green, and people lucky enough to live near the poles see aurora.

Earth has aurora because it meets the two required conditions; it has a magnetic field (shaped like the one surrounding a bar magnet) and that magnetic field is struck by the solar wind, a stream of particles and gas from the sun. The interaction between the magnetic field and the solar wind creates the magnetosphere, an invisible, comet-like structure around Earth.

In the early days of space physics research, there were hints that other planets had auroras, too. In 1955, scientists discovered that Jupiter was giving off radio emissions, which suggested the planet might have a magnetic field. In 1974, the Pioneer-10 spacecraft had instruments aboard that detected a magnetosphere on Jupiter. Five years later, the spacecraft Voyager captured the first image of Jupiter's aurora.

Since that time, scientists found aurora on Saturn. The Hubble Space Telescope allowed scientists to see that both Jupiter and Saturn have auroras colored pink from hydrogen in those planets' atmospheres. Neither planet has green auroras because neither planet has oxygen, and oxygen, as far as we know, is only given off by living organisms.

If life in the forms we're familiar with exists on some other planet, that planet will have oxygen in the upper reaches of its atmosphere. If that planet has the magnetism to support an aurora, it should at least occasionally be green. And a green aurora 100 light years away will be much easier to detect than a wandering stegosaurus at the same distance.