New findings from NEOWISE, the asteroid- and comet-hunting portion of NASA's Wide-field Infrared Survey Explorer mission, show that comet Hartley 2 leaves a pebbly trail as it laps the sun, dotted with grains as big as golf balls.
Previously, NASA's EPOXI mission, which flew by the comet on Nov. 4, 2010, found golf ball- to basketball-sized fluffy ice particles streaming off comet Hartley 2. NEOWISE data show that the golf ball-sized chunks survive farther away from the comet than previously known, winding up in Hartley 2's trail of debris. The NEOWISE team determined the size of these particles by looking at how far they deviated from the trail. Larger particles are less likely to be pushed away from the trail by radiation pressure from the sun.
The observations also show that the comet is still actively ejecting carbon dioxide gas at a distance of 2.3 astronomical units from the sun, which is farther away from the sun than where EPOXI detected carbon dioxide jets streaming from the comet. An astronomical unit is the average distance between Earth and the sun.
"We were surprised that carbon dioxide plays a significant role in comet Hartley 2's activity when it's farther away from the sun," said James Bauer, the lead author of a new paper on the result in the Astrophysical Journal. An abstract of the scientific paper is online at http://arxiv.org/abs/1107.2637, with the option of downloading a full PDF.
JPL manages and operates the Wide-field Infrared Survey Explorer for NASA's Science Mission Directorate, Washington. The principal investigator, Edward Wright, is at UCLA. The mission was competitively selected under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory, Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp., Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.