The Kepler Mission: The Search For Earth-like Planets
Quote:By Leonard David
Senior Space Writer
posted: 07 February 2007
06:27 am ET
BOULDER, Colorado The hunt for Earth-like worlds orbiting distant suns will get a big boost next year with the liftoff of NASAs Kepler mission. That spacecrafts job is to monitor 100,000 stars in a stellar staring contest intended to detect periodic decreases in a stars brightnessa falloff of light due to planets transiting their parent stars.
Keplers pursuit of rocky Earth-sized planets is a step forward in taking on some tough but major questions, such as: Are terrestrial planets common or rare? What are their sizes and distances?
Whats more, how often are such worlds detected in the habitable zonethe region around a star where liquid water should be available on a planet, perhaps making it a homely place for life?
Kepler is a trailblazer for other innovative searches for terrestrial planets. Future plans of planet hunting researchers were detailed here January 26-28 at a media workshop sponsored by the University of Colorados Center for Astrobiology.
Earth trailing orbit
NASA selected Kepler in late 2001 as a Discovery-class mission. But William Borucki, the missions principal investigator at NASAs Ames Research Center, Moffett Field, California, had been doggedly advocating the idea since 1992under an admittedly lackluster designation of Frequency of Earth-size Inner Planets, or FRESIP for short.
The mission was renamed after Johannes Kepler (1571-1630), the first to correctly explain planetary motion, thereby, becoming founder of celestial mechanics.
Launch date for the $500 million Kepler mission is November 2008, to be lofted into a heliocentric, Earth trailing orbit by a Delta 2 booster.
The spacecrafts operational life is four years, toting along enough life-sustaining expendables for six years, Borucki said. That two year mission extension, he said, would greatly enhance Keplers ability to spot planets smaller than Earth and reliably identify Earth-size planets in orbits corresponding to that of Mars with two year periods.
In essence, Kepler is part digital camera on steroids and part light meter. Special purpose charge coupled devices (CCDs), like those utilized in home digital camera gear, have the needed photometric attributes to take on planet hunting duties.
Keplers photometer is an array of 42 CCDs, acting as a single purpose scientific instrument. The spacecraft is outfitted with a 37-inch (0.95-meter) aperture Schmidt photometer with a 55-inch (1.4-meter) primary mirror. It features a focal plane array with more than 95 million pixels that will appraise the brightness of stars every 15 minutes.
Using precise photometry, the spacecraft can detect small decreases in stellar brightness as a planet transits its star. Three transits with a consistent period, brightness change, and duration would provide scientists the magic moment of proclaiming detection of an extrasolar planet.
The photometer will constantly gauge the brightness of 100,000 stars, searching for planets as they pass in front of their parent star. In seeing any brightness change, Kepler data can be used to determine the planets size and orbital period.
Kepler will stare at one large area of the sky in the constellation Cygnus.
Ball Aerospace here in Boulder is the prime contractor for NASAs Kepler Mission, building the photometer and spacecraft, as well as managing system integration and spacecraft testing.
Borucki reported that Kepler should detect numbers of terrestrial plants, many of them expected to be within the habitable zoneif they are common. A null result would mean Earths in the habitable zone are rare in our galaxy.
Ultimately, Borucki observed, what were asking is
what is the place of mankind in the universe? This is the first part of that answer
Of course, even if Kepler discovers that these planets are rare, it would provide valuable insight about the origin of our Earth.
However, that notion doesnt sit well with Borucki. If we dont find them we cant have Star Trek because theyll be nowhere to go.
The Kepler mission is a kind of spotter scope, an invaluable leg up for future planet searches, such as those projected for NASAs Space Interferometry Mission (SIM) and the Terrestrial Planet Finder (TPF)although both projects appear to be in a never-never land of funding support at present.
Made in the shade
Theres a new advance in the possibility for direct observation of exoplanets, reported Webster Cash, Director of the Center for Astrophysics and Space Astronomy here at the University of Colorado.
Cash has been working on an idea tagged as the New Worlds Observer, receiving early financial support and encouragement from the NASA Institute for Advanced Concepts (NIAC).
New Worlds Observer is a better way to solve the problem that the Terrestrial Planet Finder team has been struggling with, he suggested.
The proposal calls for two spacecrafta large, self-propelled, flower-shaped starshade and a conventional-quality telescope positioned far apart in space.
The key thing is that the starshade stops light from the star from ever getting into the telescope, Cash said. This is really what you want. This is the ideal goal for direct study of exoplanets.
The huge starshadeat least 100 feet (30 meters) from tip-to-tipis a space-based occulter that blocks light from a target star. If luck is with you, youll see a little cluster of tiny faint planets
an actual direct signal from the planets with no interference from the big bright star, Cash noted.
Viewed as a low-cost replacement for the Terrestrial Planet Finder, Cash said the New Worlds Observer starshade would have a price tag of some $500 million, optimized for use with about a 13-foot (4 meter) diameter telescope costing upwards of $1 billion.
Weve got all the technology to do this today, Cash added. If NASA were to fund it, we would be able to do this in seven years.
Cash has also sketched out a New Worlds Imager a much more complicated concept for the future. It involves at least five spacecraft and has the goal of taking true images of the surfaces of exoplanets, he told SPACE.com.
Avoiding wild goose chases
There is no doubt that technology, inventive approaches, theoretical work, along with ground and space-based observations are melding to yield surprising findings in the search for far-off worlds.
At the moment, some 200 extrasolar worlds have been charted, primarily huge, gas giant planets. That number will continue to grow in years to comeas the roster of detected planets shrink in size.
Margaret Turnbull, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland, said as new instruments return new data, extrasolar planet notions are sure to undergo adjustments, even abandonment
but sometimes reaffirmation.
In the case of planet formation, observations of hot Jupiters told us that our nice little theory of how to make a solar-type system of planets did not account for all possible scenarios, Turnbull told SPACE.com.
In that instance, the theory actually delayed the discovery of those hot Jupiters, Turnbull pointed out, because no one believed that they could exist. Thus, very little funding was allocated for those searches and scientists who pursued that line of research were considered fools and openly mocked. Now those researchers are winning awards for their discoveries.
Turnbull, however, strongly cautioned against criticizing theorists because we are always walking a fine line between wanting to be creative and yet not wanting to spend our limited funding on wild goose chases.