Comet Tails Becoming Trend for Asteroids

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Comet tails seem to be trending in the asteroid belt the last few years, as scientists have discovered yet another new instance of a known common asteroid becoming active and ejecting trailing streams of rock and ice. Traditionally, the difference between a comet and an asteroid was clear. However, the sudden change in appearance of a known Hygiea asteroid in the Main Belt has scientists rethinking what they know about the rocky bodies orbiting between Mars and Jupiter. The newest example is the first in its family to display a tail.

Classic descriptions of comets portray them as bodies made of ice and rock that sublimate when they approach the sun’s heat, emitting the dust and vapor blown by solar winds in a long stream that gives comets their characteristic tail and a coma or thin layer of atmosphere around the nucleus. On the other hand, asteroids have been generally understood to be static hunks of space rock. Hygiea Asteroid 62412 joins a dozen other regular asteroids that have begun to resemble comets in the last few years.

The increasing frequency of asteroid transformations calls for further research to explain the phenomenon of the new interstellar trend. Scientists are not sure what is instigating the sudden changes in stable and well-known asteroids. One theory speculates that ices on the asteroids may be suddenly exposed to the sun causing an eruption of vapor. Another theory hypothesizes that the comet tails could be the result of asteroid-to-asteroid collisions. In any case, scientists are becoming aware through new and improved observational methods that the celestial objects’ activity levels can fluctuate over time rather than remain static and stable as previously believed.

Scott Sheppard, faculty member at the Carnegie Institute in Washington, D.C. and Chadwick Trujillo, an astronomer at the Gemini North Observatory, who discovered the change in Asteroid 62412, are stepping up to the plate with additional surveys to better understand the nature and life cycles of comets and asteroids. The Hygiea family of asteroids resulted from a collision that broke up the massive 250-mile wide 10 Hygiea asteroid. It was the fourth largest asteroid in the Main Belt and its offshoots makeup up about one percent of the objects in the asteroid belt. Sheppard and Trujillo’s discovery prompts them to estimate that about 100 similar hybrid asteroid-comet objects exist in the Main Belt. They expect their astronomical surveys to reveal many more.

Sheppard acknowledges that their understanding of the space bodies is changing as they have seen that, much like volcanoes, asteroids have dormant and active phases. They will be conducting a deep survey of spatial objects not easily visible to the general public with the goal of discovering the mechanisms that activate some asteroids comet-like qualities but not others. The researchers have found that 62412 rotates rapidly, possibly creating an ejection of water vapor, another potential factor in explaining the unforeseen appearance of the tail.

Researchers have also ascertained that the newest member of the comet-tailed asteroid company has a density consistent with primitive asteroids rather than resembling the lower-density comets, deepening the mystery surrounding the trend. They presented their work to the American Astronomical Society’s Division of Planetary Sciences on Nov. 11, 2014 and plan to publish their study in The Astrophysical Journal. Puzzling comet tail and all, Asteroid 62412 has become the newest celestial object of interest, gaining scientific watchmen eager to understand the source of its latest activity.

by Tamara Christine Van Hooser


Carnegie Institution of Washington Science

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Photo courtesy of Kevin Dooley – Flickr License

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