January 3, 2013
Our Galaxy Abounds With Planets Say Caltech Astronomers
Lee Rannals for redOrbit.com - Your Universe Online
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The team provided more evidence that planetary systems are a more normal occurrence with stars than previously suspected. They made their estimate while analyzing planets orbiting a star called Kepler 32, which serves as an example of a vast majority of stars in the galaxy.
"There's at least 100 billion planets in the galaxy — just our galaxy," John Johnson, assistant professor of planetary astronomy at Caltech and coauthor of the study, said in a press release.
Jonathan Swift, a postdoc at Caltech and lead author of the paper, points out that it is "a staggering number, if you think about it."
Kepler 32 was detected by NASA's Kepler space telescope, which helped determine that the planetary system was made up of five planets. Two of the planets in this system have been confirmed by other astronomers, while the Caltech team confirmed the remaining three.
The planets orbit an M-dwarf, a type of star that accounts for about three-quarters of all the stars in the Milky Way. The five planets, which are similar in size to Earth and orbit closer to their star, are typical of the class of planets that the telescope has discovered orbiting other M dwarfs.
While the system may not be unique, it is set apart from others by its coincidental orientation: the orbits of the planets lie in a plane that is positioned so that Kepler views the system edge-on. This orientation means that each planet blocks Kepler-32's starlight as it passes between the star and the Kepler telescope.
The astronomers determined the planets´ characteristics by analyzing the changes in the star's brightness as they passed by. This orientation provided an opportunity for scientists to study the system in great detail.
"I usually try not to call things 'Rosetta stones,' but this is as close to a Rosetta stone as anything I've seen," said Johnson. "It's like unlocking a language that we're trying to understand–the language of planet formation."
One fundamental question remaining is how many planets are out there. Other astronomers have estimated that there may be approximately one planet per star, but Caltech is the first team to have made an estimate by studying M-dwarf systems.
M-dwarf systems are different than our solar system in that the stars are cooler and much smaller than the sun. Kepler-32 has half the mass of the sun and half its radius. The whole planetary system fits within just over a tenth of an astronomical unit.
The fact that M-dwarf systems vastly outnumber other kinds of systems carries a profound implication. The Caltech astronomers believe that the planets on Kepler-32 must have started their orbits farther away from the star before moving inward over time and settling into their current configuration.
"You look in detail at the architecture of this very special planetary system, and you're forced into saying these planets formed farther out and moved in," Johnson explained.
The team says that the fact that the galaxy may be filled with undiscovered planets has far-reaching implications for the field of astronomy. "It's really fundamental from an origins standpoint," says Swift, who also pointed out that M dwarfs are invisible to the naked eye since the light that they emit falls in the infrared spectrum.
"Kepler has enabled us to look up at the sky and know that there are more planets out there than stars we can see."