With Coolant To Spare, WISE Team Pushes for Extended Mission

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SAN FRANCISCO — As scientists pore through hundreds of thousands of images captured by the Wide-field Infrared Survey Explorer (WISE) since its mid-December launch, a senior NASA review panel is evaluating a proposal to keep the space telescope in service through January 2011 — three months longer than initially planned. That extension would allow WISE to conduct a second complete pass of the sky and would lead to the discovery of additional stars, asteroids and comets, NASA officials said.

All systems onboard the WISE spacecraft built by Ball Aerospace & Technologies Corp. of Boulder, Colo., and the infrared telescope built by the Space Dynamics Laboratory of Logan, Utah, are in excellent condition, according to Bill Irace, WISE project manager at the Jet Propulsion Laboratory in Pasadena, Calif. Prior to its Dec. 14 launch, NASA officials expected WISE to remain in operation for 10 months before depleting its stock of hydrogen needed to cool the spacecraft’s telescope and detectors. Based on current hydrogen supplies, WISE mission officials now expect the hydrogen to last into November, or about a month longer than originally estimated. WISE is able to detect the faint glow of distant stars, comets and asteroids because its instruments have been chilled to the point where they produce no detectable infrared light.

WISE produces approximately 7,500 images a day in each of four wavelengths of infrared light, surveying the entire sky in six months. During the initial 10-month mission, scientists planned to completely map the sky one-and-a-half times. The science campaign began one month after launch when mission managers confirmed that all onboard systems were functioning properly.

Ned Wright, WISE principal investigator, has proposed a three-month extension of the space telescope’s mission to complete a second complete survey of the sky, according to NASA spokesman J.D. Harrington. Although the hydrogen is expected to be exhausted by early November, the WISE instrument still would be able to capture imagery in two of its four infrared wavelengths. “Once the instrument warms up, there will be too much noise for the two longer wavelength filters to get data with the required level of sensitivity,” Harrington added.

The proposal for the extended mission was submitted to NASA’s Astrophysics 2010 Senior Review team during its meeting in early April. A decision on the plan is expected to be released within the next few weeks, Harrington wrote in an e-mail.

WISE mission officials say additional data gathered during the three-month extended mission would confirm initial findings and lead to new discoveries. “During a second coverage of the sky, WISE will be scanning in the opposite direction so image artifacts will be in different positions, increasing the reliability of the WISE catalog,” according to Wright, who is also a professor at the University of California, Los Angeles. That additional imagery also would lead to the detection of ever fainter light sources, he said.

Even if the extended mission is limited to data gathering in two infrared bands, that information would improve the reliability for all objects in that part of the sky that are visible in those wavelengths. It also could help astronomers track the movement of objects, including some of the failed stars known as brown dwarfs, which mission officials already have observed, according to Irace. Scientists use data on the location of stars and planets at different times to determine their distance from Earth.

The WISE spacecraft employs four infrared cameras to capture imagery every 11 seconds, revealing objects that are too cold or too far away to be easily detected by optical telescopes, including asteroids, comets, brown dwarfs and luminous galaxies that are billions of light-years away. NASA’s previous sky survey in the infrared spectrum was conducted in 1983 by a 62-pixel camera on the Infrared Astronomical Satellite. In contrast, the detectors on WISE offer images in 4 million pixels.

During its first three months, WISE has revealed more than 50 near-Earth objects, including comets, asteroids and centaurs, objects that orbit the sun but include characteristics of both comets and asteroids, according to the Jet Propulsion Laboratory’s Near-Earth Object program website. One of the goals of the WISE mission is to determine the size and distribution of asteroids in the solar system and the likelihood of a potentially hazardous impact with Earth.

The $320 million WISE mission was selected competitively as part of the space agency’s Explorer program, managed by NASA’s Goddard Space Flight Center in Greenbelt, Md. The proposed three-month extended WISE mission would cost an additional $6.5 million. WISE mission officials also have proposed spending an additional $8 million on the WISE Extended Source Catalog, Harrington said.

While the WISE Source Catalog will contain accurate position and infrared brightness information for objects that appear as compact points of light in the images such as asteroids, stars and distant galaxies, the WISE Extended Source Catalog would provide measurements for other objects such as clusters of stars, clouds of gas and dust in the Milky Way and nearby galaxies.