Claims of 100 Earth-Like Planets Not True
An artist's interpretation of the Kepler observatory in space.
Credit: NASA.

Despite overzealous news headlines this week, NASA's Kepler spacecraft has not indentified more than 100 Earth-like planets in the galaxy.

The planet-hunting telescope, launched in April 2009, has so far confirmed only five alien planets beyond the solar system, mission scientists told SPACE.com.

The erroneous reports of new planets were generated in response to a recent videotaped speech Kepler co-investigator Dimitar Sasselov gave at a TED (Technology Entertainment and Design) conference in July.

"More than 100 'Earth-like' planets discovered in past few weeks," read the headline of a Wednesday article in the U.K.'s Daily Mail newspaper. The Observer, another U.K. paper, also reported the finding.

However, Sasselov was referencing only possible planets among the Kepler data, scientists said.

"What Dimitar presented was 'candidates,'" said David Koch, the mission's deputy principal investigator at NASA's Ames Research Center in Moffett Field, Calif. "These have the apparent signature we are looking for, but then we must perform extensive follow-up observations to eliminate false positives, such as background eclipsing binaries. This requires substantial amounts of ground-based observing which is done primarily in the summer observing season."

In June the Kepler team announced the discovery of 706 planet candidates ? objects that preliminarily have the right signature to be alien worlds.

The telescope looks for stars whose light appears to dim periodically, representing the time when a planet passes in front of the star and temporarily blocks some of its light. These findings were detailed in a scientific paper by Kepler's science principal investigator William Borucki, also of NASA Ames.

"In my TED talk I was simply repeating what was already announced by the Kepler team back [on] June 15, 2010 and is in the Borucki et al., paper," Sasselov told SPACE.com.

"So, no new news here ? but more to come later in the year!" he said.

Koch confirmed that Kepler's official planet tally is still much lower. "Other than the 5 planets previously published, we have not announced anything else," he said.

However, Sasselov did say that what Kepler has learned so far about extrasolar planets offers tantalizing hints that our planet may not be unusual.

Among the hundreds of candidate planets, a large percentage of them appear to be Earth-like ? that is, small and rocky, rather than large and gassy, like Jupiter.

"Even before we have confirmed the planets among these hundreds of candidates, we can see statistically that the smaller-sized planets will be more common than the large-sized (Jupiter- and Saturn-like ones) in the sample," Sasselov explained.

That's good news for scientists who hope to one day detect life on another planet. Since life as we know it is thought to require water and Earth-like conditions, planets that look a lot like ours could be habitable.

To date, using a variety of methods, astronomers have confirmed almost 500 planets beyond our solar system, Sasselov said. So far, most of these definitive planet finds have been of the gas giant variety, but that's because they're easier to spot than planets like Earth. [The strangest alien planets]

As telescopes and planet-hunting techniques improve, and as researchers follow-up on Kepler's observations, the tally for siblings to Earth should go up, he said.