CIS: Tail discovered on long-known asteroid

[bystander]

Tail discovered on long-known asteroid
Carnegie Institution for Science | 2014 Nov 11

[i]The faint tail can be seen in active asteroid 62412. [b](Credit: Scott Sheppard)[/b][/i]

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A two-person team of Carnegie's Scott Sheppard and Chadwick Trujillo of the Gemini Observatory has discovered a new active asteroid, called 62412, in the Solar System's main asteroid belt between Mars and Jupiter. It is the first comet-like object seen in the Hygiea family of asteroids. Sheppard will present his team's findings at the American Astronomical Society's Division of Planetary Sciences meeting and participate today in a press conference organized by the society.

Active asteroids are a newly recognized phenomenon. 62412 is only the 13th known active asteroid in the main asteroid belt. Sheppard and Trujillo estimate that there are likely about 100 of them in the main asteroid belt, based on their discovery.

Active asteroids have stable orbits between Mars and Jupiter like other asteroids. However, unlike other asteroids, they sometimes have the appearance of comets, when dust or gas is ejected from their surfaces to create a sporadic tail effect. Sheppard and Trujillo discovered an unexpected tail on 62412, an object which had been known as a typical asteroid for over a decade. Their findings reclassify it as an active asteroid. The reasons for this loss of material and subsequent tail in active asteroids are unknown, although there are several theories such as recent impacts or sublimation from solid to gas of exposed ices.

"Until about ten years ago, it was pretty obvious what a comet was and what a comet wasn't, but that is all changing as we realize that not all of these objects show activity all of the time," Sheppard said.

In the past, asteroids were thought to be mostly unchanging objects, but an improved ability to observe them has allowed scientists to discover tails and comas, which are the thin envelope of an atmosphere that surrounds a comet's nucleus. ...

Discovery and Characteristics of the Rapidly Rotating Active Asteroid (62412) 2000 SY178 in the Main Belt - Scott Sheppard, Chadwick Trujillo

• arXiv.org > astro-ph > arXiv:1410.1528 > 06 Oct 2014

[BDanielMayfield]

This statement by the reporter struck me as odd ...

The reasons for this loss of material and subsequent tail in active asteroids are unknown, although there are several theories such as recent impacts or sublimation from solid to gas of exposed ices.

... because the very title of the finding he or she is reporting about gives the reason material is flying off this rock:

Discovery and Characteristics of the Rapidly Rotating Active Asteroid <a href="tel:(62412) 2000">(62412) 2000</a> SY178 in the Main Belt - Scott Sheppard, Chadwick Trujillo

• arXiv.org > astro-ph > arXiv:1410.1528 > 06 Oct 2014

You just need to read the paper's abstract to see that this is the case.

[geckzilla]

It says it is rapidly rotating but does it say that the material is flying off due to this rotation?

[BDanielMayfield]

Well, here's the abstract, with rotational expressions red-shifted for emphasis:

We report a new active asteroid in the main belt of asteroids between Mars and Jupiter. Object (62412) 2000 SY178 exhibited a tail in images collected during our survey for objects beyond the Kuiper Belt using the Dark Energy Camera (DECam) on the CTIO 4 meter telescope. We obtained broad-band colors of 62412 at the Magellan telescope, which along with 62412's low albedo suggest it is a C-type asteroid. 62412's orbital dynamics and color strongly correlate with the Hygiea family in the outer main belt, making it the first active asteroid known in this heavily populated family. We also find 62412 to have a very short rotation period of 3.33+-0.01 hours from a double-peaked light curve with a maximum peak-to-peak amplitude of 0.45+-0.01 magnitudes. We identify 62412 as the fastest known rotator of the Hygiea family and the nearby Themis family of similar composition, which contains several known main belt comets. The activity on 62412 was seen over 1 year after perihelion passage in its 5.6 year orbit. 62412 has the highest perihelion and one of the most circular orbits known for any active asteroid. The observed activity is probably linked to 62412's rapid rotation, which is near the critical period for break-up. The fast spin rate may also change the shape and shift material around 62412's surface, possibly exposing buried ice. Assuming 62412 is a strengthless rubble pile, we find the density of 62412 to be around 2200 kg/m3.

Even without my color coding the reason dust is flying off this asteroid seems readily apparent. If it wasn't rapidly spinning it wouldn't be active, and it would be just another asteroid. The spin is what makes this object special.