Asteroid Imposters

Article written: 3 Sep , 2008
Updated: 24 Dec , 2015


A frequent plot device in the old “Mission: Impossible” television show was the special masks the IMF team used so they could impersonate anyone. Viewers were often surprised to find out who ended up being an imposter. Similarly, astronomers and planetary scientists are considering that a fair amount of Near Earth Objects (NEOs) aren’t what they appear: they could be comets impersonating asteroids. Paul Abell, from the Planetary Science Institute says between five and ten percent of NEOs could be comets that are being mistaken for asteroids, and Abell is working on ways to make unmasking them a mission that’s possible.

Some NEOs could be dying comets, those that have lost most of the volatile materials that create their characteristic tails. Others could be dormant and might again display comet-like features after colliding with another object, said Abell. He is using NASA’s Infrared Telescope Facility at the Mauna Kea Observatories in Hawaii and the MMT telescope on Mount Hopkins, south of Tucson, Ariz., to uncover observational signatures that separate extinct/dormant comets from near-Earth asteroids.

This is important for a couple of reasons. First, dormant comets in near-Earth space could become supply depots to support future exploration activities with water and other materials. Second, like other NEOs, they could pose a threat to Earth if they are on a collision course with our planet. Third, they can provide data on the composition and early evolution of the solar system because they are thought to contain unmodified remnants of the primordial materials that formed the solar system.
Comet Tempel 1.  Credit:  NASA/U of Maryland
Unlike rocky asteroids that blast out craters when they slam into Earth, comets are structurally weak and likely to break up as they enter the atmosphere, leading to a heat and shockwave blast that would be much more devastating than the impact from an asteroid of the same size.

Low-activity, near-earth comets flashed onto the planetary-science radar screen in 2001, when NEO 2001 OG108 was discovered by the Lowell Observatory Near Earth Asteroid Search telescope. It had an orbit similar to comets coming in from the Oort Cloud, but had no cometary tail. But in early 2002 when it came closer to the sun, the heat vaporized some of the comet’s ice to create the clouds of dust and gas that make up the comet’s coma and tail. It was then reclassified as a comet.

“That’s what started me on this line of reasoning and scientific investigation,” Abell said.
By combining orbital data with spectra and the albedos (brightness) of these objects, Abell hopes to identify which are low-activity comets and where they are coming from.
“Are all these comets made of the same type of material or are they different?” Abell asked. “If they’re composed of different materials, they may have different spectral signatures, and our preliminary work on Jupiter-family comets and Halley-type comets shows that this may be true. Why is that? Is it something to do with the initial conditions of their formation regions? Or is it due to the different environments in which they spend most of their time?”

“All this is important to understanding their internal makeup, which will give us data on the material composition and evolution of the early solar system,” he added.

Source: PSI Press Release

9 Responses

  1. Jorge says

    I increasingly dislike the separation between comets and asteroids in small body taxonomy. What’s the difference between a “dying comet that has lost most of the volatile materials that create their characteristic tails” and, say, a rubble pile asteroid? For all practical purposes, there is none. It’s just an asteroid by another name, especially if it lost them a long time ago. And a comet with all the volatiles intact that never wonders into the inner system is also simply an asteroid by another name. Judging by the ice-rich outer system moons, they are likely visually and structurally very similar to ice-poor asteroids and their properties are probably pretty much the same, with rock-hard ices working mostly just as rock-hard… er… rocks do in inner system asteroids. Only if and when they get kicked inwards they start to erupt and really become comets.

    Besides, a “common” asteroid that wonders close enough to a star also begins to erupt, comet-like. Iron, for instance, boils at 3000 K, and you get much higher temperatures than that in star coronae. Why isn’t it called a comet, then?

    This is another astronomical designation that comes from the times of old and seems to me to be losing grip on reality as the knowledge improves, becoming in increasingly dire ned of redefinition.

    I’d go for scrapping it alltogether. Instead I’d prefer talking about objects that exhibit cometary behavior. At most, I’d designate by “comet” the objects that exhibit periodic cometary behavior (since it does change their surfaces and probably their internal structure). Everything else would simply be asteroids, regardless of their composition.

  2. Member
    Gerald, Walnut Creek, CA says

    Perhaps an appropriate name for asteroids that are really dormant comets would be: “dwarf asteroids.” Or maybe: “dwarf comets.” How about “cometinos” or “asterinos?” I think the IAU needs to get on this right away.

  3. watchful stone guardian says

    How about “cometoids”? 😉

  4. neoguru says

    Words, words, words. A comet by any other name is still a comet, etc. What’cha call ’em is irrelevant. It’s what they ARE that counts and I believe it important that we differentiate beween the types and call ’em whatever applies.

  5. Jorge says

    Sure. But then what’s the point of trying to differentiate a “dying comet that has lost most of the volatile materials that create their characteristic tails” from an “asteroid proper”, if they are basically the same thing?

    (I don’t even like the term “volatile materials”, btw: all materials are volatile, in the proper temperature range, which is basically the point I’m trying to make here)

  6. Aodhhan says

    Unfortunately the world doesn’t support your point. As humans we tend to classify everything into as many different areas as possible.

    Relatively speaking, we are still pretty ignorant on the composition of both asteroids and comets. Its likely, as we become smarter on these celestial bodies, we will find there are not only many different types of asteroids, comets etc, but many different stages, periods of evolution and ways they are created.

    In short, it is only going to get worse!

    …nothing is ever so bad, that it cannot get worse.

  7. Jorge says

    Wanna bet that that’s precisely why this question of nomenclature will end up surfacing sooner or later? The complexity, I mean.

    Then, we’ll see some (myself included) wanting to set one umbrella category for all the smallish things going around stars (or not… we’ll see) and subdivide from there, and others just stating that old categories just became “meaningless” and so on and so forth…

    If only the IAU stayed out of it, it might even be constructive, interesting and educational. But the IAU will not stay out of it, so it’ll be a noisy mess, filled with silly definitions nobody agrees with. You’ll see. 😉

  8. Todd says

    I’m with Jorge.

    Human beings often feel secure classifying an object as one thing or another.

    In reality comets and asteroids are the same type of body, differentiated only because of how they differ as seen from the Earth.

    Modern genetics has linked animals more accurately than gross morphology.

    I think it’s inevitable that small solar system bodies will be scientifically classified on a system that includes specific gravity (rubble pile, solid, or in between) and geochemical composition (ices, metals, silicates, or some combination). From the surface of planet Earth (or some other body) lay people will long refer to comets, asteroids, and meteor showers. Scientists now describe them more accurately.

  9. Aodhhan says

    I totally understand your frustration with the IAU. Unfortunately, we really do need this organization (well… one which provides their function). I just wished they operated a bit friendlier.
    I don’t think I’m the only one who believes they come off a bit eliteist, staunchy, pompus, arrogant, condescending, narrow minded, narcissistic, bone-headed, stubborn, irritating etc.

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