WISE warms up to new mission phase
by Peter Stevenson
for ASTRONOMY NOW
Posted: 08 October 2010
NASA’s Wide-field Infrared Survey Explorer (WISE) may have reached the end of its infrared mapping phase, but it now embarks on a warmer mission to track nearby comets, asteroids and brown dwarfs.
December 2009 saw the launch of WISE, an Earth-orbiting infrared telescope which has been employed to map cold, dusty or distant objects which ordinary visible light telescopes cannot manage. During 2010 it has taken over 1.8 million pictures using its 16 inch telescope and four wavelength infrared detectors, managing to observe the sky over one and a half times, discovering stars, comets and over 33,500 asteroids in the process.
A WISE image of the constellation Camelopardalis. Although visible light is blocked by dust clouds, the infrared WISE image has allowed the discovery of a cluster of new stars within it (AFGL 490). Image: NASA.
Initially WISE was “chilled out” down to eight Kelvin in order to minimise infrared noise arising from the telescope itself. However, the liquid hydrogen used as coolant has now been depleted, and WISE is now in the process of heating up to a relatively Mediterranean 69 kelvin (-203 degrees celsius). Despite this, the mission will still continue, as Amy Mainzer of NASA describes: “Two of our four infrared detectors still work even at warmer temperatures, so we can use those bands to continue our hunt for asteroids and comets”. WISE will thus spend the next few months on a new project searching primarily for near Earth objects (the mission has been renamed NEO-WISE) – particularly bodies at risk for Earth collisions – as well as using re-scans of the sky to ascertain the movements, and thus distances and velocities, of previously detected objects such as brown dwarfs.
An important benefit of the vast amount of WISE data collected is in providing a widefield view of space which can be scanned to identify potentially interesting targets in which to pursue further in the future, while also providing material for the scientific community to use for decades.
Artist's concept of NASA's Wide-field Infrared Survey Explorer. Image: NASA/JPL.
A pertinent example of WISE’s ability to provide preliminary imaging is the recent pictures of Hartley 2, a comet which is the target of a more specific investigation by the EPOXI spacecraft due to rendezvous with it on 4 November. EPOXI is set to discover more about the comet’s nucleus (core) size as well as examining dust particles surrounding it, all to ascertain more about the history of the icy body. In fact, the Hartley 2 - EPOXI rendezvous is set to become the most detailed imaging of a comet in history. That being said, the WISE data is proving invaluable as the widefield images it has taken have allowed scientists to track the dusty tail of the comet as it orbits the Sun, which has increased from sputtering gas and dust ejections in the Spring to full blown jets of gas come July. “Comparing the dust early on to what we see later with EPOXI helps us understand how the activity started on Hartley 2,” describes Michael A Hearn, principle EPOXI investigator.
The wealth of data already collected has made WISE and unbridled success in terms of large scale infrared imaging and in detecting otherwise “invisible” bodies.
Astronomy Now will be reporting further on the EPOXI mission nearer the Hartley 2 rendezvous on 4 November.
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