Near-Earth Objects (NEOs) represent an extinction level threat to the entire human race. The odds are extremely low that an undetected asteroid or comet will strike the Earth and cause catastrophic damage, but given a long enough period of time anything can happen. It has been hypothesized that a large asteroid impacted the Earth 65 million years ago and led to the mass extinction of the dinosaurs.
NEOs with diameters of less than 10m are typically destroyed in the upper atmosphere, but 50m NEOs can cause massive damage like the Tunguska Event in 1908. A 1km sized NEO is projected to strike the Earth every 500,000 years, while NEOs larger than 5km hit every ten million years.
The possibility of global devastation galvanized the U.S. Congress into action in 2005, mandating NASA to detect 90% of the NEOs ranging from 140m and above by 2020. There are an estimated 20,000 asteroids and comets that have orbits close to Earth, and only 6000 of them have been found so far.
The problem is that many asteroids and comets don't reflect a lot of light, making them hard to detect using conventional telescopes. NASA plans to address this with the Wide-field Infrared Survey Explorer (WISE), which will scan the entire sky in infrared light. Asteroids and comets emit infrared energy, and WISE is not only expected to detect thousands of them, but also provide data on their size, shape, and composition.
WISE is designed to detect the infrared glow of hundreds of millions of objects besides asteroids and comets. It will detect new galaxies, stars, and brown dwarfs, creating a vast catalog of millions of images. These will be used to find new targets for the Spitzer Space Telescope and the Herschel Space Observatory, two other observation missions which focus on specific infrared objects for study.
The closest known star is Proxima Centauri, a red dwarf star approximately 4.2 light-years away. Some astronomers have theorized that a failed star may lie much closer to our Solar System. Known as brown dwarfs, these objects have insufficient mass to create or maintain a nuclear fusion reaction.
Infrared technology has progressed significantly since the 1983 launch of WISE's predecessor, the Infrared Astronomical Satellite. NASA says that WISE’s sensitivity is hundreds of times greater, and will enable it to detect around 400 new NEOs by scanning four different infrared wavelengths.
WISE will detect four distinct bands of mid-infrared light with wavelengths of 3.4, 4.6, 12 and 22 microns. The only existing whole-sky survey with a wavelength of between 3 and 10 microns is from the Cosmic Background Explorer (COBE), which operated in 1989. Results from that mission led to the award of the Nobel Prize in Physics during 2006.
The primary instrument onboard WISE is a 40cm (16-inch) telescope connected to four separate infrared detectors. Each detector has a resolution of 1,032,256 pixels, much improved over the Infrared Astronomical Satellite’s total of 62 pixels. These instruments are kept cool within a tank filled with frozen hydrogen in order to prevent heat contamination during observations. Images are transmitted back to Earth via Ku-band frequencies at a rate of 100 Mb/s.
WISE was launched successfully today into a polar orbit from Vandenberg Air Force Base in California using a Delta II rocket, with an altitude of 525 km (326 miles). The Jet Propulsion Laboratory is managing the mission, and is responsible for all ground operations that track and control the spacecraft. NASA is investing approximately $320 million for the whole project, including design, development, launching, and operations.
The WISE mission is only expected to last for ten months, after which it will run out of its liquid hydrogen coolant. The completed WISE catalog will be released in 2012, and NASA expects to be studying that data for decades.
