BY DR EMILY BALDWIN
Posted: 12 June, 2009
WISE will provide the most detailed survey of the sky in infrared yet, revealing hundreds of millions of objects from galaxies and stars to dark and potentially hazardous asteroids. “Most of the sky has never been imaged at these infrared wavelengths with this kind of sensitivity,” says Edward Wright, the mission’s principal investigator at UCLA. “We are sure to find many surprises.”
The near-infrared sky, with the Milky Way at centre, as constructed from millions of galaxies and stars in the 2MASS catalogue. WISE will add to this view of the infrared sky in greater detail than ever.
The mission’s science instrument – which comprises a 40- centimetre telescope with four infrared cameras – was attached to the spacecraft last month and will undergo a series of rigorous tests to simulate the effects of launch in the coming weeks. A cryostat will use frozen hydrogen to chill the sensitive megapixel infrared detectors down to seven Kelvin.
WISE is expected to reveal thousands of asteroids that have previously gone undetected, in both the Asteroid Belt and in the Earth’s local neighbourhood. These will be asteroids that don’t reflect much visible light, but WISE will be sensitive to their glow in infrared light. By cataloguing these objects, the mission will provide better estimates of their sizes, a critical step for assessing the risk associated with those that might impact Earth.
“We know that asteroids occasionally hit Earth, and we’d like to have a better idea of how many there are and their sizes,” says Amy Mainzer of NASA’s Jet Propulsion Laboratory and the mission’s deputy project scientist. “Whether they are dark or shiny, they all emit infrared light. They can’t hide from WISE.”
The central region of the Milky Way Galaxy as seen in infrared light by the MSX satellite and 2MASS survey. WISE images will be of similar quality.
The mission is also expected to uncover the coldest stars – brown dwarfs. These dull orbs are too small to have ignited like our own fuel-burning Sun, and as a result are often too faint to be seen in visible light. Scattered across the Galaxy, WISE is expected to reveal around one thousand brown dwarfs, possibly even some that are closer to us than the current nearest known star, Proxima Centauri, at a distance of just four light years.
“We’ve been learning that brown dwarfs may have planets, so it’s possible we’ll find the closest planetary systems,” says Peter Eisenhardt, the mission’s project scientist. “We should also find many hundreds of brown dwarfs colder than 480 degrees Celsius, a group that as of now has only nine known members.”
WISE is also geared up to shed light on the Universe’s most luminous galaxies seen long ago in the dusty throes of their formation, and the discs of planet-forming material around stars. The catalogue of cosmic treasures created by WISE will then act as a check list for other infrared telescopes, such as Spitzer, Herschel and the James Web Space Telescope, to follow up.
Currently, 1 November is earmarked for WISE’s launch from Vandenberg Air Force Base in California, onboard a United Launch Alliance Delta II rocket. After in-space instrument calibration, WISE will set to work mapping the entire sky in infrared in just six months. It is envisaged that WISE will have enough coolant to allow its instruments to map the sky a second time, to search for any changes in the infrared sky.