I want to believe. Or so X-files fans say, and for that matter so does Dr. Debra Fischer, an astrophysicist from San Francisco State University. And after hearing her talk about The Quest for Other Worlds and Prospects for Life on Friday night, it’s hard not to become a believer yourself.
In 1996, a year after the first planet orbiting a star outside of our own solar system was identified, Fischer and her team discovered a multi-planet system, outside our own: Upsilon Andromedae, a star very much like our own sun, was found to have three giant Jupiter-size planets orbiting it.
Before 1995, scientific consensus considered it a risky leap of faith to believe even one extra-solar planet could be found. The scientific intelligentsia still clung to Aristotelian theories that there could be no world but one: ours.
The powerful light and radiation emitted by stars makes it almost impossible to gather direct evidence of planets around them. Instead, two indirect but powerful methods are used. One is astrometry-the the tendency of stars with large planets orbiting them to wobble on their axes as they spin.
The other are the emission and absorption spectra of the stars-these are characteristic black bands that appear in the visible light spectrum of stars, due to the absorption of certain wavelengths of light by planets in the star’s system. The wobbling of the star causes the black bands of its absorption spectrum to shift in a periodic manner.
Using this Doppler shift, as it is called, the mass and characteristics of planets surrounding the star can be identified. The problem, however, is that only planets the size of Jupiter or Saturn-317 and 95 times more massive than the mass of the Earth, respectively-can be found. We have no means at this point to detect Earth-sized planets.
So if scientists were wrong about finding other planetary systems, could they also be wrong about finding life on other planets? That depends.
In their book Rare Earth, Peter Ward and David Brownlee argued that the conditions for intelligent life must mimic the conditions of Earth. The planet must be the right distance from its star; both the star and the planet must be of a certain mass.
The planet must have a massive Jupiter-like neighbour (whose gravity deflects asteroids out of the inner Solar System), a Mars-like neighbour (to possibly seed life), it must have a large moon, the right tilt, the right amount of carbon and oxygen, appropriate atmospheric properties and plate tectonics (which produces Earth’s magnetic field that shields us from solar wind). The list goes on and on.
Fischer, rebutted these arguments. Many of these conditions, she said, are unnecessary for intelligent life to form and are merely factors that reflect our biology, which is an anthropocentric view.
A large moon is not necessary, she argued; nor is a Jupiter- or Mars-like planet; planetary tilts can vary, as can the amount of carbon and oxygen. On Earth itself we are constantly surprised to find life (even simple tube worms or bacteria) in hostile acidic, cold or very hot environments.
“These extremophiles,” said Fischer, “have found other places to live than we have,” and new evidence suggests that the warm sub-crustaceous ocean of Europa, one of Jupiter’s moons, may be teeming with bacterial life. Why should we then doubt the existence of more complex life forms in less hostile environments elsewhere in the universe?
There are billions of stars in every galaxy and billions of galaxies in the universe. In the trillions of stars in the universe, is it so unlikely that other intelligent life forms exist? For now, one can either take a leap of faith or remain a skeptic.
