The Kepler mission will be the first serious attempt to discover Earth-like
planets around other stars in our Milky Way galaxy. Designed as an
orbiting space telescope, Kepler is the eighth and most recently approved
mission of NASA's ambitious Discovery Program. The final price tag of the
mission will be around $299 million, which is the cap for missions in the
Discovery Program.
Transit method
Astronomers have discovered 80 or so large gas planets around other
stars, however a small, solid terrestrial planet has yet to be discovered. This
is partly because current ground-based and space-based telescopes, including
Hubble, do not have the sensitivity to detect them. To discover extrasolar
planets, scientists use the transit method. When a planet moves in front
of the star it is orbiting, it blocks some of the star's light. This
decrease in luminosity can be detected and used to compute the size and orbit of
the planet. Until now, we have only been able to discover large gaseous
planets such as our sun's Jupiter. The Kepler mission will utilize a telescope
so powerful that it can detect changes in the light of a star of 1/100th of a
percent. It will stare at the same point in the constellation Cygnus and
track up to 100,000 stars simultaneously. In order to avoid statistical
bias, no star in this region will be discounted from observation, even if it is
considered too large or too small to host Earth-like planets. Most current
theories of planet formation suggest the stars with the highest probability of
possessing solid, inner terrestrial planets are about the size of our sun.
Many believe large gas planets are a critical part in the formation of small
planets in a solar system small, as they may act as a shield for the inner
sanctum by gravitationally taking care of comets, asteroids, and other
planet-busting intruders. Scientists predict that most sun-like stars have
one to two inner planets, and they expect to find hundreds of these worlds
during its five year long data collection period.
Habitable zones
In 1993, Kasting, Whitmore, and Reynolds proposed the boundaries of
a so-called habitable zone around a given star where liquid water is most
likely to exist. The Kepler mission will focus on discovering planets
within this zone. The calculation of this zone is tailored for an
individual star's size and intensity. Still, theorists are not certain
that water is critical for the formation of life. Based on the number of planets
found in habitable zones, researchers will be able to refine the infamous Drake
equation. Currently, there is no evidence of how common terrestrial,
habitable planets are in the universe, or even the galaxy. This number is
a critical part of the Drake equation, which seeks to predict the number of
intelligent civilizations in the universe.
Onboard instrumentation
Encircling the globe in an Earth-trailing heliocentric orbit, the Kepler mission will
employ an enormous 95 centimeter photometer incorporating a primary mirror
with a diameter of 1.5 meters. This allows the planet-seeking contraption
a constant field of view of about 10 degrees by 10 degrees, resulting in a
100 degree "square of sky." To block the blinding
intrusion of the sun, Kepler will sport a movable sun shield. Data
collected are sent back instantaneously to Earth via a High-Gain antenna to be
analyzed by ground computers. The mathematical examination of
this information should result in frequent discoveries of extrasolar planets
over the mission's five year life span.
Johannes Kepler
NASA has always been quite fond of naming missions and their spacecraft after
historical figures in the field of astronomy and mathematics. (See: Galileo probe, Hubble Space Telescope, Cassini probe,
Huygens probe) The Kepler mission is named after Johannes Kepler,
the famous 17th century astronomer credited with discovering the three laws of
planetary motion, first published in 1609 and 1619. You might remember from
grade school his famous edict that planets "sweep out equal areas in equal
times." Interestingly, Kepler was reluctant to give up his vision of a
perfect and crystalline universal
geometry for the uneven and oblong reality of the solar system, perhaps in
much the same way many will have to one day grudgingly admit that other beings
inhabit other earths around other suns.
Critical Mission Dates
Habitable Zones around Main Sequence Stars, JF Kasting, DP Whitmire,
RT Reynolds, Icarus, 101, 108-128 (1993)
www.kepler.arc.nasa.gov
discovery.nasa.gov/kepler.html
Other NASA Discovery Program Missions
·NEAR·
·Mars Pathfinder·
·Lunar Prospector·
·Stardust·
·Genesis·
·CONTOUR·
·Deep Impact·
·Messenger·
·Dawn·
·ASPERA-3·