UNVEILING THE COOL COSMOS

Space is mostly empty, but a thin gruel of gas and dust that occupies regions between stars dims and reddens light.1 Thousand-trillion- mile wide clouds containing gas and microscopic dust grains ab­sorb and attenuate visible light and reradiate it at infrared wave­lengths. NASA’s Spitzer Space Telescope has the remarkable ability to see through interstellar dust and has allowed us to look into the vast clouds in which stars are born, like those of the Orion Nebula, our nearest star-forming region. Spitzer can also peer into the dark, dust strewn plane of our Milky Way galaxy that previ­ously had been nearly impossible to penetrate. Anything that ra­diates heat, such as living bodies, and any cool object in space, such as planets or moons or even tiny silicate (rocky) and carbon (sooty) grains 1/10,000 to 1/100 of a millimeter across, emits in­frared radiation. Only an infrared telescope can image objects that glow in light waves too long for the human eye to see. The Spitzer Space Telescope can detect such light billions of light-years from Earth and has revealed this cool and invisible universe with un­precedented clarity.

With more than 850 exoplanets known as of early 2013, and another 2,700 candidate planets identified by the Kepler telescope, astronomers estimate that there are at least 50 billion exoplanets in the Milky Way galaxy. Scientists calculate that 500 million of those planets orbit in the habitable zone, the distance from their star that could allow for life.2 NASA’s Spitzer Space Telescope is helping to

detect and characterize these extrasolar worlds. In December 2010, Spitzer discovered the first carbon-rich exoplanet, named WASP- 12b, the geology of which may be comprised largely of diamond and graphite.3 Whereas rocks on Earth generally consist of silicon and oxygen in the form of quartz and feldspar, Spitzer’s observa­tions suggest that WASP-12b, about 1,200 light-years from here, has nothing like terrestrial geology. Astronomer Marc Kuchner of NASA Goddard Space Flight Center, who has helped theorize carbon-rich planets, explains that increased carbon in a planet’s composition can entirely alter its geology: “If something like this had happened on Earth, your expensive engagement ring would be made of glass, which would be rare, and the mountains would all be made of diamonds.”4 Spitzer has been instrumental in analyzing the geological makeup of exoplanets, and what astronomers are finding exceeds their wildest expectations.

At the other extreme from dim worlds in the nearby universe, Spitzer has discovered massive galaxies billions of light-years away that are forging stars at a prodigious rate. An infrared-bright, star­forming galaxy might be making thousands of stars each year compared to a couple for the Milky Way. These “starburst” galax­ies are infrared beacons from the early construction phase of the universe, during which many large galaxies were being assembled from smaller galaxy “pieces” for the first time.5 Deep within the dust-obscured hearts of distant galaxies, new worlds were being forged at a fantastic rate. A single, modest-sized telescope in space has seen directly into the center of these galaxies and provided insights on the full range of their creation stories.