The findings are helping astronomers better understand near-Earth objects as a whole -- a population whose physical properties are not well known. The study is also important to astrobiologists because asteroid impacts may have played an important role in the origin and evolution of life. Impacts with our planet could have delivered materials essential for the origin of the first living cells. Major impacts may also alter the course of evolution by causing wide-spread extinction events.
After nearly six years of operation, in May 2009, Spitzer used up the liquid coolant needed to chill its infrared detectors. It is now operating in a so-called "warm" mode (the actual temperature is still quite cold at 30 Kelvin, or minus 406 degrees Fahrenheit). Two of Spitzer's infrared channels, the shortest-wavelength detectors on the observatory, are working perfectly.
One of the mission's new "warm" programs is to survey about 700 near-Earth objects, cataloguing their individual traits. By observing in infrared, Spitzer is helping to gather more accurate estimates of asteroids' compositions and sizes than what is possible with visible light alone. Visible-light observations of an asteroid won't differentiate between an asteroid that is big and dark, or small and light. Both rocks would reflect the same amount of visible sunlight. Infrared data provide a read on the object's temperature, which then tells an astronomer more about the actual size and composition. A big, dark rock has a higher temperature than a small, light one because it absorbs more sunlight.
"Very little is known about the physical characteristics of the near-Earth population," said Trilling. "Our data will tell us more about the population, and how it changes from one object to the next. This information could be used to help plan possible future space missions to study a near-Earth object."
The data show that some of the smaller objects have surprisingly high albedos (an albedo is a measurement of how much sunlight an object reflects). Since asteroid surfaces become darker with time due to exposure to solar radiation, the presence of lighter, brighter surfaces for some asteroids may indicate that they are relatively young. This is evidence for the continuing evolution of the near-Earth object population.
The research complements that of NASA's Wide-field Infrared Survey Explorer, or WISE, an all-sky infrared survey mission also up in space now. WISE has already observed more than 430 near-Earth objects -- of these, more than 110 are newly discovered.
In the future, both Spitzer and WISE will tell us even more about the "flavors" of near-Earth objects. This could reveal new clues about how the cosmic objects might have dotted our young planet with water and organics -- ingredients needed to kick-start life.
Join Dr. David Grinspoon, astrobiology curator at the Denver Museum of Nature & Science, as he investigates a giant impact crater. In this podcast, Grinspoon explains what the crater might indicate about the history of life on Earth and the possibility for life elsewhere in the solar system.