 Billions Of Galaxies Neighbor Earth
|
Sept. 25, 2003 — The chances of Earth being alone in the universe just got a whole lot smaller, as astronomers have dramatically raised the estimate on how many planets are out there.
The new estimate is based on calculations carried out by Charles Lineweaver and Daniel Grether at the University of New South Wales. Their findings, soon to be published in the Astrophysical Journal, estimate that at least 25 percent of Sun-like stars have planets.
"This means there are at least 100 billion stars with planets in our Galaxy," Lineweaver said. "With about 100 billion galaxies in the observable universe, our result suggests that there are at least 10 trillion planetary systems in the Universe."
|
 
 |
|||||||
This is an astounding number when you consider that the first extrasolar planet or 'exoplanet' — a planet outside of our own solar system — was only detected in 1996 by observing a wobble in the star it orbited. Since then, astronomers have been carefully monitoring the motion of 2,000 nearby stars for the presence of orbiting extrasolar planets.
"To date, they've detected a hundred or so extrasolar planets, meaning the fraction of stars with extrasolar planets was around 5 percent," Lineweaver said.
"But most planets are too small or take too long to orbit their host stars to be detected. For example, say our Sun was one of the stars being monitored: We wouldn't have detected any planets around it using the techniques and technology available to us at the moment."
However, the longer astronomers observe individual stars and the better our technology becomes for making these observations, the more planets are found.
"By combining the world's exoplanet data and correcting for these factors," Lineweaver said, "we obtain a larger fraction of stars with planets around them: 25 percent, compared to the 5-15 percent found in previous analyses."
"We are not saying that 25 percent of all stars have planets: only the Sun-like stars — stars similar to our own Sun. However, it could be that close to 100 percent of stars have planets. With current data we just can't tell but our estimate of 'at least 25 percent of Sun-like stars' is better than previous estimates. This means that there are at least 100 billion stars with planets in our Galaxy alone."
And how many of those planets might support life?
"Earth-like planets are still too small to detect so we haven't found any," Lineweaver said. "However, the rapidity with which life arose on Earth suggests that more than 10 percent of terrestrial planets have life. We're not talking about trees and animals; we're talking about any kind of life. The smart money is on the idea that bacteria [are] all over the Universe. What it has evolved into is anybody's guess."
< news main
