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Part of Kepler's CCD array  (Source: NASA)
Kepler spacecraft will detect small planets close to the size of earth.

Humanity has wondered about the heavens above since before recorded history. Recently, the discovery of hundred of planets in other star systems has sparked extraordinary interest in determining the odds of extraterrestrial life.

The Kepler mission will seek to explain one part of the puzzle by observing the brightness of over 100,000 stars over the next forty-two months. In doing so, it will be able to track  earth-sized planets, generating future targets of interest for more advanced future space observatories like the Terrestrial Planet Finder and the Laser Interferometer Space Antenna.

Nearly all of the extrasolar planets detected thus far are giant planets the size of Jupiter or larger. Kepler will look for planets 30 to 600 times less massive, closer to the size of Earth and more likely to support life.

All planets in stable orbits transit across their star during their own unique annual cycle. This causes a dip in the star's apparent magnitude for an observer in the same plane. By timing these transits, the orbit and length of year can be calculated. The orbit of a planet can be used to determine if it lies within the "zone of life", where it is close enough to the sun to support liquid water, yet far enough that potential life is not destroyed by it.

"Kepler's mission is to determine whether Earth-size planets in the habitable zone of other stars are frequent or rare; whether life in our Milky Way galaxy is likely to be frequent or rare", said William Borucki, NASA's Principal Investigator on the Kepler Mission.

While Kepler will only focus on a small area of the sky, its results will be enough to enable accurate estimates of the number of earth-sized planets in our galaxy.

Kepler will use an array of 42 CCD (charge-coupled device) cameras, each measuring 50x25 mm. With a resolution of 1024x2200 each, Kepler has a total resolution of approximately 95 megapixels.
CCD cameras are used in most digital cameras and optical scanners. They are also used in astronomy and in night-vision devices due to their sensitivity to the ultraviolet and infrared ranges of light.

Mission operations will be conducted by NASA's Ames Research Center in Moffett Field, California, and are included as part of the $600 million total mission cost. Ames will contact the Kepler spacecraft twice a week using the X-band for command updates as well as system status updates. Scientific data is only downloaded once a month using the Ka-band, at a data rate of up to 4.33 Mb/s. To conserve bandwidth, Kepler will conduct partial analysis on board and only transmit data of interest to researchers.

The Kepler spacecraft will be launched at 2250 Eastern Standard Time from Cape Canaveral Air Force Station in Florida. It will use the Delta II multi-stage rocket, which has flown 140 missions while achieving a success rate of almost 99 percent.
Instead of a typical earth orbit, it will launch Kepler into an earth trailing orbit in order to block light from the sun and the moon. This orbit also avoids gravitational perturbations inherent in an Earth orbit, thus allowing for additional platform stability.

The Kepler Mission is named for Johannes Kepler, best known for his Laws of Planetary Motion.

Updated 3/8/2009

The Kepler spacecraft was launched successfully aboard a Delta II rocket in the D2925-10L launch configuration from pad 17B at 22:49:57 EST on Friday March 6th. The three-stage launch vehicle had nine additional solid rocket boosters, six for the first stage and three for the second stage. The third stage boosted  the Kepler payload to its heliocentric orbit trailing Earth. Two months of testing and systems verification will occur for the next two months before Kepler begins its inspiring mission.


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Kepler search for planets blooper
By jimpapadopoulos on 3/6/2009 9:52:27 AM , Rating: 1
It is reported: "All planets in stable orbits transit across their star during their own unique annual cycle. This causes a dip in the star's apparent magnitude for an observer."

That's WAY off the mark, only true for planets whose ecliptic plane includes Earth. Let me take a wild guess that far less than one thousandth of potential planets will actually be viewable by this technique.

RE: Kepler search for planets blooper
By scherzox on 3/6/2009 10:12:21 AM , Rating: 2
I was thinking the same thing. The odds of another planetary system's orbital plane being lined up with earth are very small. They will find some though, but not as many as these articles lead us to believe.

RE: Kepler search for planets blooper
By Hellfire27 on 3/6/2009 10:38:22 AM , Rating: 1
All planetary bodies in orbit around a star have a slight gravitational tug on said star. This causes the star to wobble ever so slightly, thus you would not necessarily need to be in the orbital plane to know that a planet is there. Observing the planet would be very difficult if you are not in the plane though, you would just know that something is there.

RE: Kepler search for planets blooper
By General Disturbance on 3/6/2009 12:02:36 PM , Rating: 5
This mission isn't using radial velocity variations to detect planets, which is what the wobble method is all about. For that you need very high resolution spectroscopy which can be done just fine from the ground, and has been done fruitfully.

This mission is measureming the tiny photometric changes in a star's brightness that will occur when a planet transits its disk. The posters above are obsolutely correct in that it will only be able to detect systems in which the ecplitpic plane is almost directly allong the line of sight to the star. But, I think there is actually +- a few degrees allowance given that the star is so large compared to the planet, and because the planet itself is so very much closer to the star than we are. And finally, when you look at tens of thousands of systems, statistically you will expect some fraction of them to be aligned just the way you want.

The photmetric transit method is much harder to do from the ground, simply because it is that much harder to do ultra-precision photoemtry from the ground than it is spectroscopy.

This will truly be a revolutionary mission, so here's hoping it all works out.

By jaysan on 3/12/2009 5:11:45 AM , Rating: 2
the quote from the article says "dip in the star's apparent magnitude for *an* observer."

The key word is "an". So certainly, we Earthlings aren't necessarily in the right position to observe every planetary transit out there. As you say, we'll only see a fraction of the transits -- but that fraction is 1/200. With millions of stars to look at in our sky, then the fraction of observable transits could add upto quite a lot.

This census will help us get general odds of stars in general having planets, which will help put into context our own level of uniqueness in the universe.

By mattlenda on 3/6/2009 1:34:53 PM , Rating: 3
Correct, but Kepler cannot detect star wobble. It doesn't have the resolution.

By MicahK on 3/8/2009 4:35:50 PM , Rating: 2
That and the wobble technique works great for finding bigger planets (Jupiter sized +) but they are looking for Earth sized planets, which do not create as big as a wobble, and would need extremely precise optics and instrumentation to detect.

By arrowspace90 on 3/6/2009 12:35:31 PM , Rating: 2
It is about one system in a thousand. This is no secret and is reported on NASA's own site.
But they figure that there are sufficient stars where Kepler is looking that even at that ratio, there will be significant discoveries.
Now if they can figure out some way to observe the other 999.
I think this mission is the most exciting thing since Hubble.

RE: Kepler search for planets blooper
By oab on 3/9/2009 11:51:24 AM , Rating: 3
"All planets in stable orbits transit across their star during their own unique annual cycle. This causes a dip in the star's apparent magnitude for an observer."

That statement is 100% correct. Such a planet not visible to us because the transit does not occur in the right plane for us to see it might be visible by a different observer. The observer is a theoretical one, he does not mean "visible to humans" but "visible to someone or something that observes it which is able to observe it"

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