June 25, 2009
The Space Telescope Science Institute (STScI) in Baltimore is partnering on a historic search for Earth-size planets around other stars. STScI is the data archive center for NASA's Kepler mission, a spacecraft that is undertaking a survey for Earth-size planets in our region of the galaxy. The spacecraft sent its first raw science data to STScI June 19.
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The institute was the logical choice for storing the anticipated flood of data because its scientists have processed enough observations from NASA's Hubble Space Telescope over the past 19 years to fill almost two collections of material in the U.S. Library of Congress.
The institute's role is to convert the raw science data into files that can be analyzed by Kepler researchers and to store the files every 3 months in an archive.
"We are part of this mission because of our experience with Hubble data processing and archiving," said David Taylor, project manager for the development of Kepler's Data Management Center (DMC) at the institute. "NASA's Ames Research Center — the home of Kepler's science operations — had not done a science mission like this one. Building the data management center from scratch would have been more costly, and it would have taken longer to get up to speed."
Launched March 6 on a Delta II rocket from Cape Canaveral, Florida, the Kepler spacecraft will spend the next 3.5 years searching for habitable planets by staring nonstop at more than 100,000 Sun-like stars out of about 4.5 million cataloged stars in the spacecraft's field-of-view — in the summer constellations Cygnus and Lyra.
The spacecraft simultaneously measures the variations in brightness of the more than 100,000 stars every 30 minutes, searching for periodic dips in a star's brightness that happen when an orbiting planet crosses in front of it and partially blocks the light. These fluctuations are tiny compared with the brightness of the star. For an Earth-size planet transiting a solar-type star, the change in brightness is less than 1/100 of 1 percent. This event is similar to the dimming one might see if a flea were to crawl across a car's headlight viewed from several miles away.
When the mission is completed in several years, the survey should tell astronomers how common Earth-size planets are around stars.
Once a month, the Kepler spacecraft will send its science data, about 50 gigabytes, back to Kepler's Mission Operations Center at the Laboratory for Atmospheric and Space Physics at the University of Colorado. Raw science data will then be relayed to the institute's DMC. DMC Operations will convert the information into Flexible Image Transport System (FITS) files, a digital file format used to store, transmit, and manipulate scientific information.
The FITS files will be sent to the Kepler Scientific Operations Center (SOC) at Ames Research Center in Mountain View, California, where the science data analysis will be carried out.
Kepler mission scientists will turn the data into 30-minute snapshots of light from each of the 100,000 or more stars. From these snapshots, the scientists will construct a light curve for each star, which details any brightness fluctuations. They will review the light curves to look for any periodic decrease in brightness, an indication of a possible transiting planet.
The mission scientists also will use the light curves to study the stars and their interiors. Because of the quality of the Kepler data and the large number of stars the spacecraft will observe, scientists hope to improve their understanding of stellar evolution.
"The mission's main purpose is to find planets that are the same distance from its solar-type star as Earth is from the Sun," said Daryl Swade, who directed the systems engineering development of Kepler's Data Management Center at the institute. "So that means that the planet would cross in front of its star every year. We would need three or four of these transits to confirm the detection, which will take about three or four years."
A planet at an earthlike distance from its star would be in the star's "habitable zone," where temperatures are just right for liquid oceans to exist on the surface without freezing over or evaporating away. On Earth, a liquid ocean was needed to nurture the chemical processes that led to the appearance of life. This is considered an important prerequisite for life as we know it to appear elsewhere in the galaxy.
Kepler's science data also will be archived at the institute. Every three months the SOC at Ames will ship FITS files in a 500-gigabyte computer hard drive to the institute for storage in the Multimission Archive. The archive houses data from about 14 missions, including Hubble, the Far Ultraviolet Spectroscopic Explorer (FUSE), and the Galaxy Evolution Explorer (GALEX).
Based on its strong track record in processing and archiving data, the nstitute could earn a role in many future missions.
"Partnering with other institutions to share the duties of a mission may be a trend for future missions," Taylor said.