An alternate title for this post could be “When a Comet Might Not Be a Comet”.
On the night of Jan 6, the LINEAR (Lincoln Near Earth Asteroid Research) survey detected a previously unknown comet. This is LINEAR’s 193rd comet discovery with only the space-based SOHO spacecraft has found more comets. Most of their comets are called Comet LINEAR so this one should be more specifically referred to as comet P/2010 A2 (LINEAR).
So what’s so special about this comet? First let’s take a look at image below taken by Bob McMillian (University of Arizona) with the Spacewatch 1.8-m telescope on Kitt Peak.
At first glance this looks like a normal comet with most of the expected characteristics of a comet. Fuzzy appearance, check. Tail (though not all comets have tails, tails are a sign of cometary activity), check.
One characteristic shown in the image above is odd. Many early observers of this comet have commented on its lack of an obvious bright center in the coma, what is termed its central condensation. Comets are due to dust and gas outgassing from an ice-rich rocky nucleus (like an asteroid but with a large fraction of volatile ices). As a result, the coma should have a relatively sharp bright center in the vicinity of the nucleus. Instead Comet LINEAR’s coma appears sheared tailward with no definite sign of an active nucleus.
As odd as its appearance may be, we have seen this before. It is possible the comet has just experienced a short lived outburst. Just like smoke dissipating after an explosion, the coma and tail we see are remnants of an outburst slowly being blown away by the solar wind. Alternately, the nucleus may have just disintegrated with the remnants again being dispersed by the solar wind. As last week’s SOHO comet showed, the disintegration of comets are not rare events.
Up to now all of the signs point towards this object being a comet, albeit one that is acting a little strange. That is until you look at its orbit. With a perihelion distance of 1.87 AU, an aphelion of 2.62 AU and a semi-major axis of 2.25 AU, P/2010 A2 is on a very un-comet-like orbit. The orbit more closely resembles the orbit of a Flora family asteroid of the inner Main Belt. Though a few asteroids in the Main Belt have been observed to occasionally show cometary activity (the so called Main Belt Comets), these objects have all been located in the outer Main Belt and are volatile-rich carbonaceous asteroids. The inner Main Belt, and the Flora family especially, is dominated by stoney asteroids with few, if any, carbonaceous objects.
In summary, we have an object that looks like a comet orbiting where no volatile-rich object should be. So what might be happening?
- Comet LINEAR is a rare carbonaceous asteroid located in the inner Main Belt that has just experienced a recent episode of cometary activity. This is exciting because it may mean that there are more volatile-rich asteroids in the inner Main Belt and closer to Earth.
- Comet LINEAR really is just a “boring” stoney asteroid, but it recently was impacted by another smaller asteroid and the cometary appearance we see is the result of this collision. If so this would be our first imaged asteroid impact.
Images like the one above will allow astronomers to model the dust in the coma and tail. A quick inspection of the above image and a few others I’ve seen show the tail to be made of large particles trailing the comet along its orbit. There may be some evidence of a much shorter and fainter tail stretching to the SE which is consistent with the direction expected for a normal anti-solar tail of small dust particles being blown back by the solar wind.
Just as forensic scientists can reconstruct a crime scene well after the fact from evidence left behind, past dust activity can be reconstructed from the morphology of a comet’s coma and tail. Evidence of a single dust producing event may suggest an asteroid impact, while evidence of continuous activity points towards a volatile-rich asteroid.
I’m sure there will be much more to this object’s story in the weeks ahead…
[Note added later by editor: I forgot to add that the comet is faint at a magnitude of 18-19. You will need a CCD camera on a moderate sized telescope to image this comet. It is definitely too faint to be seen with out optical and digital imaging aid.]
The Transient Sky - Comets, Asteroids, Meteors 
hi . I saw something steaking in the sky yellow with greenish tail ? direction was from mt soledad la jolla towards Del Mar . was very bright & short lived . first thought someone was shhoting a roman candle
I just came from a thread about a strange comment, and I was wondering if the Electric Universe theory could shed any light on both topics?
About the object P/2010 A2:
I just saw today’s image on the APOD site and then checked several links. If
the most likely interpretation is a recent asteroid-asteroid collision, how
recent is “recent”? Ie: How long should such an object be spewing out dust
like this before becoming ‘quiet’ again? Are we talking years, decades,
centuries, or even longer?
Maybe your asking the wrong question people… Do you not see that this may have a very basic exsplination…. X shaped, from the same family that wiped out the dinosaurs, very unlikely behavaviour, read “uncensored” for something a little more believeable than what main stream science is trying to feed you all. open your minds.
just a thought what if p/2010 a2 is actually planet x which is supposed to hit on the 21/dec/2012 it resembles the same characteristics as planet x i.e p/2010 a2 apparantly is remnents of what killed the dinosaurs 65 million years ago it has gone pretty close to the asteroid belt just as planet x did 65 million years ago with planet x astronomers apparantly dont know if it is an asteroid a comet or a planet and with p/2010 a2 they dony know if it is a comety or a meteor or an asteroid and why call planet x planet x is it because it leaves an x pattern in the sky just like p/2010 a2 did
What if an asteroid was on a trajectory to strike some alien installation on Mars or wherever, and the aliens sent a ship to destroy or deflect the thing? After a few shots, it might be a debris field that strings out along the course of its travel, and it might look like this. Complicated speculation, but that’s all the ‘scientists’ are doing, and their theories don’t account for a debris tail that is organized into a streak. Solar wind pressure is minute, and a collision would form an irregular patch of debris. Not this.
I am very glad that it is not the Planet X or Nibiru. Earth will surviwe!
(ASV) And there shall be signs in sun and moon and stars; and upon the earth distress of nations, in perplexity for the roaring of the sea and the billows; Luk 21:25 – By me, all we can see last nowdays inform us, that the Kingdom of Jesus Christ is at hand. It is coming to earth and for all people living on one as a grant from God
Are there any updates on this object yet?
Hi Chris,
Sorry for the late response on your question.
Recently two papers have been released on P/2010 A2 (LINEAR).
http://arxiv.org/abs/1006.5832
http://arxiv.org/abs/1010.2575
Both groups agree that activity (or dust release) occurred in March of 2009. After that the two groups disagree on the cause of the dust release. One group claims it is due to normal cometary activity due to water (or some other) ice. The other group claims it is due to the impact of a small (few meters across) asteroid impacting the P/2010 A2 (~200 meters across).
Since these are the same two possible explanations that were considered at the time of discovery, the papers, unfortunately, don’t help clarify what caused the release of its dust. With the our ability to scan more and more of the sky to fainter and fainter levels, we will undoubtedly find more objects like P/2010 A2. Hopefully then we’ll be able to solve the ‘mystery’ of P/2010 A2.
Thanks for writing,
– Carl
Im sorry, but P 2010/A2 Elenin appears to be symetrically mechanical in nature. It almost appears to be shaped by nature or whatever to do just one thing, sail true as influenced and split objects in its path. From a layman, it looks basically obvious. A solid – benign inactive dark core material with no thermal properties and nothing but residual dust and debris streaming from its ‘cow-catcher’ front end after last impact.