It was bound to happen sooner or later: The European Space Agency's Herschel Space Telescope has run out of the liquid helium it uses to keep cool. With the temperatures of all instruments on board spiking, the spacecraft's mission has ended. It will be propelled to an orbit around the sun, where, the ESA says, "it will remain indefinitely."
Herschel launched four years ago from French Guiana with 2,300 liters of the helium, thought to be enough to keep the instruments cool for a bit more than three years. During its career, it captured the infrared light emanating from some of the coolest regions of the universe. Below are some of the highlights from the mission, all of which have been adjusted so that they appear in light humans can see (because they would be quite dull otherwise):
The W3 Nebula
6,200 light years away from Earth in one of our spiral galaxy's main arms is this massive star-forming region known as W3. Discovered originally in 2006, Herschel took this image of it just last month. The tiny yellow dots are low-mass protostars; the violet regions contain giant stars, with eight times more mass than our sun.
The Cygnus X Region
Another star-forming region, Cygnus X, is a bit closer than W3, at 4,500 light years. The image captures how the formation of stars, many of which are very young and very huge, results in the development of related structures -- filaments, clouds, etc. -- throughout the entire region.
The Orion Nebula
This image was created by combining observations from Herschel and Spitzer, another infrared space telescope. Herschel's observations (from the far-infrared part of the spectrum) appear in red and green, showing younger protostars. Spitzer's (mid-infrared) appear in blue, showing older stars. The Orion nebula is even closer yet, at about 1,344 light years away.
The Andromeda Galaxy
This is a really cool way to see how the work of different telescopes can come together to make something much more information-heavy (not to mention beautiful) than they can alone. Because the Andromeda Galaxy is our closest spiral neighbor, scientists look to it for clues to understanding our own spiral galaxy. In the above image, Herschel's observations alone are shown in the upper right corner, XMM-Newton's in the bottom right, and an astrophotographer's in the top left. All three are combined in the bottom left composite image.
This survey image captures a portion of the sky eight times the width of the moon, located in the direction of the constellation Hydra. There are more than 6,000 *galaxies* in the image, some of whose light is reaching us billions of years after it was generated. Many of them appear just as single dots.