WISE Opens Its Eyes and Gives Us a New Window on the Universe

On December 29, 2009, the world got a new window on the cosmos. That was the day that NASA’s WISE (Wide-field Infrared Survey Explorer), in orbit around Earth, shed its protective cover and began its mission: compiling the most complete and accurate map of the sky at mid-range infrared wavelengths to date. WISE will be able to detect objects that are too dark to emit visible light, but which do emit heat. This will include everything from galaxies billions of lightyears away, to near-earth objects (NEOs) such as asteroids and comets. In addition to adding enormously to our scientific knowledge, some of this information may be of vital interest, since it will be our best survey of NEOs so far. If one of these objects is heading for Earth, WISE will probably be the instrument that detects it.

WISE was launched on a Delta rocket on December 14, and after a few weeks of prepping the satellite, NASA jettisoned the cover that had kept the sensitive instrument cold. Since WISE sees in the infrared, it could pick up its own heat, which would ruin the data being collected. To guard against this, it was cooled with frozen hydrogen and sealed in a vacuum container similar in principal to a Thermos bottle. Now that it is in orbit and without its cover, the vacuum of space will serve the same purpose, but even better. At the moment, the instruments on the satellite are being calibrated, and observations will begin shortly. WISE will spend eighteen months surveying the sky, at which time it should have exhausted its supply of internal coolant. At that time, the mission will be over.

What are some of the things that WISE might find? Scientists have high expectations. This mission will build on the findings of two earlier infrared missions, COBE and IRAS. To get an idea of how big an improvement WISE is over its predecessors, consider this: while IRAS, which went up in the 1980′s, had only 62 pixels in its cameras, each of WISE’s four cameras has over a million. With eyes like that, it should be able to see a lot.

You can get an idea of the kind of science that will be done with WISE by considering the things it can see. The wavelengths that the satellite can detect fall into four bands:

Band 1: 3.4 microns- This is a broad filter to detect stars and galaxies.

Band 2: 4.6 microns- This is radiation from things that are too cool to be stars, but have some internal heat- in other words, brown dwarfs.

Band 3: 12 microns- This is the wavelength at which asteroids radiate in the infrared.

Band 4: 22 microns- At this wavelength, relatively cold things will be revealed, such as the dust of star-forming regions.

WISE will orbit Earth from pole to pole, surveying strips of the sky with each passage. This will allow each spot in the sky to be imaged many times, and by comparing the images, NASA scientists will be able to detect any that show visible movement over a short period of time. By doing, this, they will identify asteroids within the solar system, most of which are in the main asteroid belt between Mars and Jupiter. This will give us our first really accurate map of the asteroids in our system.

In addition to these nearer objects, WISE will be able to pick up the faint warmth of brown dwarfs. As stated above, these are bodies that are almost massive enough to become stars, but not quite. They never achieve nuclear fusion, the fundamental characteristic of stars, but they do emit some infrared radiation. It is possible that one or more brown dwarfs exist close to the solar system, but have remained undetected before now. WISE will find these objects, if they’re out there, and should even be able to pick up the glow from any planets that orbit them. (There is no reason why a brown dwarf should not have planets, though it is unclear whether they could support life.)

It is also hoped that WISE will show us the brightest galaxies in the universe. In addition to the faint objects that it will detect, the telescope will pick up infrared radiation from brighter sources, such as galaxies bursting with the heat of trillions of suns. These ultraluminous infrared galaxies, or ULIRGs, are almost undetectable in visible light surveys, and may not have been found before.

Other things that WISE is expected to see include young stars and the discs of planetary debris that surround them, clusters of galaxies in the distant, early universe, and a detailed view of our own Milky Way galaxy. In doing this, it will give the best view yet of the evolution of stars, protoplanetary discs, galaxies and clusters of galaxies- in other words, the universe from the bottom up.

The WISE mission promises to be a gold mine, providing enough data to keep the worthy scientists of NASA working for years. Unfortunately, we will have to wait a little while to see any results. The WISE data will be released in two stages. A preliminary release is scheduled to take place six months after the end of the mission, or about 16 months after launch, and a final release is scheduled for 17 months after mission’s end, or about 27 months after launch.

Watch for future articles about WISE at this website.

Sources:

WISE mission page at NASA website: wise.ssl.berkeley.edu/

Ten Things You Should Know About WISE at website of the Jet Propulsion Laboratory: jpl.nasa.gov/wise/facts.cfm

WISE Overview at website of the Jet Propulsion Laboratory: jpl.nasa.gov/wise/overview.cfm

WISE public website: astro.ucla.edu/~wright/WISE/

Lakdawalla, Emily: WISE Guys, at the Planetary Society Blog, August 27, 2009: planetary.org/blog/article/00002070/