Asteroid and Comet Census from WISE

This animation demonstrates how the Wide-field Infrared Survey Explorer, or WISE, surveyed asteroids and comets in the Solar System. The project to hunt for asteroids and comets -- including near-Earth objects, or NEOs -- using the WISE data is called NEOWISE.

The perspective shown here is looking down from high above Earth’s North Pole, a kind of bird's eye view of the Solar System out to Jupiter. The planets are shown as blue dots, and their orbits are the dashed lines. Earth is the third blue dot from the Sun. The big mass of black dots consists of asteroids in the main belt, between Mars and Jupiter.

The green dots show the previously known near-Earth objects - both asteroids and comets - that NEOWISE spotted during its mission. The near-Earth objects that were discovered by WISE are shown as red dots. The turquoise squares are previously known comets observed by the mission, and the yellow squares are the WISE-discovered comets.

There are various places in the orbit where there is a decrease in the number of objects that WISE surveyed. The first gap is due to the fact that the NEOWISE project did a test-run before the WISE survey officially got under way. The small black slice of objects that appears at the beginning of the video is the test-run, followed by a short gap with no observations, followed by the official start of the survey. The second gap/reduction (about 19 seconds into the video) shows when WISE was scanning through the center of the Milky Way. The overwhelming number of stars made it especially difficult for the NEOWISE software to find moving objects in those images.

The next big reduction (about 55 seconds in) was caused when the WISE satellite began to run out of coolant. As planned, shortly after the completion of the all-sky survey (1/2 of an orbit), WISE’s longest wavelength detector (22 microns) began to warm up and could no longer produce reliable data. Then, about two months later (when the red line appears), all of the coolant was gone and the second longest wavelength detector (12 microns) also became unusable. These two longer wavelength bands were much more sensitive to finding cooler objects than the remaining two bands, hence the drastic drop in the number of objects detected. The 3.4 and 4.6 micron bands continued to operate perfectly after the coolant ran out and up until WISE was put into hibernation mode at the end of January 2011.

The animation covers the period from early January 2010 through January 19, 2011. As of January, 2011, the project has observed more than 153,000 main belt asteroids and discovered more than 33,000. It has observed hundreds of near-Earth objects and discovered 134 near-Earth objects. It has also observed over 100 comets and discovered 20 comets.

Image credit: NASA/JPL-Caltech/WISE team

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