Today NASA announced that the Kepler mission (NASA Discovery Mission #10), named for Johannes Kepler, a math teacher, astronomer and a big fan of Copernicus, has discovered over 400 new planet candidates.

Four of these potential new planets are less than twice the size of Earth and orbit in their sun's "habitable zone" or the region in the planetary system where liquid water might exist on the surface of a planet.

"There is no better way to kickoff the start of the Kepler extended mission than to discover more possible outposts on the frontier of potentially life bearing worlds," said Christopher Burke,  a Kepler scientist and the lead analyst based at the SETI Institute in Mountain View, California. For a succinct explanation as to what the SETI Institute does please watch this video brought to you by the finest minstrels the Internet has to offer.

The Kepler spacecraft and the 0.95-meter diameter telescope or photometer was launched in March of 2009 to answer the question: “How frequent are other Earths in our galaxy?” and to do what the Hubble Telescope can’t do: watch a place in space that contains approximately 100,000 (or more) stars like our sun that could have Earth-sized planets orbiting them.  

The Kepler space telescope identifies planet candidates by repeatedly measuring the change in brightness of more than 150,000 stars that pass in front, or "transit," their host star. The third time’s a charm for Kepler and at least three transits are needed to verify a signal as a potential planet.

After that scientists go over the data to cast out all doubt and to identify the potential candidates for planets: known spacecraft instrumentation and astrophysical false positives, phenomena that masquerade as planetary candidates.  At the beginning of last year 33 candidates in the Kepler data had been confirmed as planets. Today, there are 105.

NASA has compiled a handy table of confirmed planets and other planet data that has been gathered by Kepler the table also includes Earth’s data for comparison.

Earlier this month NASA discussed a study conducted by Caltech that used Kepler data to estimate that there is undetermined number of planets in the galaxy. The researchers analyzed the five planets that orbit a star called Kepler-32 because they think those five planets around that star are good representations of the majority of the planets in our system.

"There are at least 100 billion planets in the galaxy, just our galaxy," says John Johnson, assistant professor of planetary astronomy at Caltech and co-author of the study which can be found in the Astrophysical Journal, "That's mind-boggling."