Infrared Spectra of Comet-Asteroid Transition Object 944 Hidalgo

Document Type

Conference Proceeding

Publication Date


Publication Title

American Geophysical Union


Asteroid 944 Hidalgo is suspected of being an extinct comet. Understanding the origin of this enigmatic object is relevant to several areas of planetary astronomy, and the study of its surface composition may be diagnostic of its origin. Silicates have been detected in active comets, and on Jupiter Trojans. Our team investigated Hidalgo in the 8-30 micron range to determine the mineral composition and presence of surface silicates. We chose this wavelength region because it is most diagnostic for the detection of silicates. We applied to use NASA's Spitzer Space Telescope as Hidalgo is too faint at these wavelengths for ground- based telescopes. Once the data were collected, the continuum was modeled and subtracted from the raw spectra. The result is a plot of emissivity versus wavelength that shows clear emission features from 8-13 microns, and around 20 microns; both of which have been identified with silicates. Our spectrum is compared with those of Jupiter Trojans, which are believed to be related to comets, and comet Hale-Bopp. With the project complete, we have demonstrated the presence of silicate emissions in Hidalgo and strong similarity with spectra of Jupiter Trojans and of active comets. These results argue in favor of Hidalgo having formed further from the Sun than main belt asteroids. We conclude that our findings are consistent, but not definitive, with Hidalgo being of cometary origin. Understanding the composition of this body and others like it is important for determining the origin of Earth's water.