Artist impression of the Herschel spacecraft, which will an unprecedented view of the cold universe, bridging the gap between what can be observed in the infrared from the ground and earlier space missions of this kind.
Credit: ESA – D. Ducros, 2009
When the Herschel Space Observatory reaches its orbital perch, it will be set to boldly look where no telescope has looked before.
Infrared light is better known to most of us as heat. But heat isn?t emitted just by the hottest objects ? even an ice cube gives off infrared energy.
Celestial objects with surface temperatures of about 3600 degrees Fahrenheit (2,000 Celsius) ? cold compared to the Sun which has a surface temperature of about 9900 F (5,500 C) ? actually radiate most of their energy at infrared wavelengths. Aging stars, planets and dust are all objects in the universe best observed in the infrared, appearing as dark blobs in the visible spectrum, but until Herschel, infrared observations of these objects have been incomplete.
For one thing, ground-based telescopes are not as effective at these observations because infrared light is largely blocked by water in Earth?s atmosphere. Other space-based missions have only looked in particular infrared wavelengths. Herschel will offer a more comprehensive look from the clear window of space.
"Instead of looking out through a dirty window, you?re going to get a clean view,' said Paul Goldsmith, the NASA project scientist for Herschel at the Jet Propulsion Laboratory in Pasadena, Calif., which provided some of the key technology for the telescopes..
With its 11.5-foot (3.5-meter) mirror (the largest ever sent into space and almost 1.5 times larger than the Hubble Space Telescope), Herschel will be able to explore more in the far-infrared than any other mission, both within and outside our own galaxy. Herschel will collect almost 20 times more light than any previous infrared space telescope.
The telescope (named for the astronomer William Herschel who discovered infrared light 200 years ago) will detect light from objects as cold as minus -440 degrees F (-263 C).
With the telescope, astronomers will be able "to really get a good view of the universe in the far-infrared," Goldsmith said.
New infrared views
Within our solar system, Herschel will examine asteroids, Kuiper belt objects and comets, which are fossils of the early solar system that could hold clues to the raw ingredients that formed the planets, including Earth. One ingredient of particular interest is water.
"One of the most interesting targets for Herschel is the same water that blocks our view of the universe," Goldsmith told SPACE.com.
Some astronomers think that comets, which are sometimes thought of as "icy snowballs," could have supplied the Earth?s water. As comets near the sun in their orbit, their ice melts into water ? Herschel can detect the water?s signature, Goldsmith explained.
Herschel will also look for signs of water in interstellar clouds and compare it to the water signatures in our own solar system, to "see how we?re connected," Goldsmith said.
Astronomers will also be looking for another molecule familiar to us earthlings ? oxygen. It is predicted to be abundant in the interstellar medium, but so far no instrument has definitively detected it.
In the Milky Way, Herschel will study star-forming regions to get a first glimpse at the stages of early star formation and some of the galaxy?s youngest stars.? Baby stars are enshrouded in wombs of cold gas and dust.
"You just can't see what's going on inside until the star is actually born," Goldsmith explained. But Herschel should be able to see through the clouds to see the infant stars beyond.
"We'll get some quite beautiful images, we think, of star-forming regions," Goldsmith said.
Signs of planets
Astronomers also hope to use Herschel to peer into the dusty debris discs that encircle stars, where planets are thought to be formed.
Herschel will also investigate star formation outside our own galaxy. Astronomers know that star and galaxy formation got started fairly quickly after the Big Bang and that star formation was much more intense in the younger universe. The young galaxies that churned out stars then would have shone brightly in the infrared, making Herschel an ideal telescope to observe them and better understand the stellar baby boom in the early universe and how it might have differed from star formation today.
"We hope to unravel that a little bit," Goldsmith said.
The galaxies are thought to make up a diffuse infrared cosmic background. The Spitzer Space Telescope can just barely resolve these galaxies, but Herschel, with its sharper focus, should be able to "nail down" the source of the background, Goldsmith said.
Once Herschel reaches its final destination at the L2 Lagrangian point of the sun-Earth system ? a gravitational stability point in space about 1 million miles (1.5 million kilometers) from Earth in the opposite direction of the sun ? it needs a couple months to get up and running. But once it is, it will have 3.5 years to get the "first really in-depth looks" at the hidden infrared folds of the universe, Goldsmith said.
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