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Origin of asteroid trail revealed

Spanish researchers have shed light on the birth of asteroid trail, suggesting that internal rupture or collision with another asteroid might be behind it.

Washington: Spanish researchers have shed light on the birth of asteroid trail, suggesting that internal rupture or collision with another asteroid might be behind it.

Ten asteroids have been located to date that at least at one moment have displayed a trail like that of comets. They are named main-belt comets (MBC) as they have a typical asteroidal orbit but display a trail at the same time. This means that their dust (and possibly gas) emission activity is like comets.

One of these objects, baptized as P/2012 F5 (Gibbs), was discovered in March 2012 from the Mount Lemmon Observatory in Arizona (USA). In May and June of that year, Spanish astrophysicists from the Gran Telescopio Canarias tracked it and have discovered when the trail was born using mathematic calculations.

"Our models indicate that it was caused by an impulsive short-lived event lasting just a few hours around the 1st July, 2011, with an uncertainty of 20 days," as explained to SINC by Fernando Moreno, researcher at the Astrophysics Institute of Andalusia (CSIC).

They collaborated with other colleagues from the Astrophysics Institute of the Canary Islands and the University of La Laguna to conduct the study.

The telescope images reveal "a fine and elongated dust structure that coincides exactly with the synchrone of that day," said Moreno.

For a given observation date, a synchrone is the position in the sky of the particles emitted from these types of objects with zero speed in an instant of time. In this case the synchrone of the 1st July, 2011 is the best adapted to the fine trail.

The width and varying brightness of the head to the end of the trail allowed for the researchers to deduce the physical properties of the particles and proportions of their different sizes.

As for the maximum size and speed values of the liberated particles, the team has calculated that the asteroid should have a radius of between 100 m and 150 m and the dust mass emitted should be about half a million tons.

The researchers juggled two possible theories for the origin of the P/2012 F5 trail: "It could have arisen from collision with another asteroid or rather a rotational rupture." The second mechanism consists of material gradually breaking free after partial fragmentation of the asteroid.

In turn, the rapid spinning of the asteroid, "like an accelerating carousel" causes pieces to break off. The rotation speed of small asteroids can increase over time due to the Yarkovsky effect (YORP effect for short). This can induce acceleration due to the thermal differences of the different surface regions of the asteroid, eventually leading to rupture.

Moreno indicates that, from the brightness distribution of the trail, "we have verified that the dependence of the speed of particle ejection on size is very weak, in accordance with what we already obtained for the other asteroid of this group: 596 Scheila, which probably suffered a collision."

MBCs are main-belt asteroids situated at a distance of between 2 and 3.2 astronomical units, where 1 a.u. is the average distance between the Earth and the Sun. For some reason they become active and emit dust. For now they have not been found to generate gas but this could be due to the fact that they are weak at the very moment of observation.

The study has been published in the `The Astrophysical Journal Letters`.


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