LOPSIDED LOBES: The smaller lobe of Comet Hartley 2 appears to be primarily responsible for its release of volatiles.
Image: NASA/JPL-Caltech/UMD
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NANTES, France—The shape of Comet Hartley 2 has inspired a number of colorful descriptors—it's been called a pickle, a peanut, a dog bone and a bowling pin.
But none of those shape analogues shares what may be a defining characteristic of Hartley 2—its two lobes now appear to be made of different material. The end pieces of the comet may have formed separately before merging to create the odd-shaped object, researchers ventured here this week at a joint meeting of the American Astronomical Society Division for Planetary Sciences and the European Planetary Science Congress. [Read more news from the meeting here.]
The analysis comes from data gathered by NASA's Deep Impact/EPOXI spacecraft, which buzzed Comet Hartley 2 in November 2010. At that time the comet was near Earth and about as close to the sun as it gets on its elliptical orbit, which carries it out past the orbit of Jupiter. During its flyby, EPOXI photographed volatile compounds such as water and carbon dioxide sublimating from ice to vapor and streaming off the sunlit, smaller end of the comet (the top of the bowling pin, if you will). But 8.5 hours later, when the Hartley 2 had rotated so that its larger end aimed sunward, the comet's activity did not shift accordingly. "Where the larger lobe is pointed toward the sun, we do not see the carbon dioxide turned on or much water outflow," said mission scientist Lori Feaga of the University of Maryland, College Park. "The outgassing is definitely coming from the small lobe and not from the larger lobe."
The implication is that the smaller end of the comet is rich in volatiles, which escape when the comet draws near the sun, whereas the larger end is relatively volatile-poor, at least near the surface. "We have a very heterogeneous nucleus," Feaga said. "The lobes are different."
One explanation is that the two ends developed independently and then joined in a sort of protoplanetary merger. "I think you get two different compositions in two different parts by forming gradually," said Michael A'Hearn, also of U.M. and principal investigator for Deep Impact's extended EPOXI mission. (The spacecraft's original mission, to slam an impactor into another comet, known as Tempel 1, was completed in 2005.) "Bringing the two ends together gently, almost like a contact binary [star], gives you a natural way," he added.
Such a merger is "perfectly possible," noted Paul Weissman, a senior research scientist at the NASA Jet Propulsion Laboratory in Pasadena, Calif., during a question-and-answer period following Feaga's presentation. But the details are not straightforward. After the talk, Weissman mused that getting two different compositions out of the comet-spawning Kuiper Belt might be tricky, because the belt is expected to have been fairly homogenous. (It is thought that most short-period comets originated in this broad orbital band, located beyond the orbit of Neptune.) "How you'd get what looks like a volatile-rich object linked up to a volatile-poor object is a bit of a puzzle," he said.
Shapely considerations aside, Hartley 2 seems to be unique in at least one other way, Hal Weaver of the Johns Hopkins University Applied Physics Laboratory reported at the meeting. Weaver and his colleagues used a spectrograph on the Hubble Space Telescope to measure the comet's carbon monoxide (CO) abundance. Carbon monoxide varies widely from comet to comet, but Hartley 2's reserves are puny. The Hubble data revealed "the lowest CO abundance of any comet measured to date," Weaver said.
One explanation could be that Hartley 2's frequent passes through the inner solar system—it completes an orbit which brings it close to the sun every 6.4 years—have stripped it of highly volatile carbon monoxide. But the comet retains other volatiles, such as water and carbon dioxide, and Weaver points out that the comet became an inner solar system regular only following an 1875 encounter with Jupiter, so it has not had much time to shed its volatiles. And some comets on much longer orbits still display low abundances of carbon monoxide, although their encounters with the sun are relatively rare.
"I favor the primordial effect that this particular comet formed from material…depleted in carbon monoxide," Weaver said. Perhaps Hartley 2 formed in a part of the solar system where carbon monoxide was rare, for instance, or where it was too warm for the compound to solidify into ice.
Either way, Hartley 2's volatile activity today may reflect the conditions that brought it into being billions of years ago, just as its asymmetric release of gases points to an ancient merger. It seems planetary scientists have much to learn from the odd-shaped comet—whatever colorful descriptor they prefer for it.
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10 Comments
Add Comment"Disparate" seems to be the go-to word for journalists who want to sound profound. Unfortunately, they rarely use it correctly. (It refers to things which are so unlike that they can't be compared, e.g., acceleration and mitochondria.) Ironically, the entire article then compares the two parts of the conjoined comet, which negates the use of the cool sounding word. I'd expect a little better from Scientific American.
Reply | Report Abuse | Link to thisCould the composition problem be simply explained as the result of the concatenation of a body which had an orbit that took it near the sun long time (hence why it volatile poor), with another Kuiper Belt object that had remained in its primordial unwarmed orbit. This would not conflict with the idea that the Kuiper belt objects began with a uniform composition.
Reply | Report Abuse | Link to thisI am of the belief that the water material to form this comet, came from the earths oceans and not the other way around. The many asteroids that bombarded the earth sheared off most of Mars atmosphere, and some of Earths atmosphere. This resulted in Water, and CO2 being flung into space, where it immediately froze and later formed comets.
Reply | Report Abuse | Link to this"..it's been called a pickle, a peanut, a dog bone and a bowling pin."
Reply | Report Abuse | Link to thisWhy not call it like it is? - A strongly negatively charged lump of planetary ROCK! As are all 'asteroids' and 'comets'. The only sensible explanation in the highly electrical situation of inner space.
About time somebody pointed out that the sun's positive anode voltage is the main driving force within our solar system. Nobody can dispute that our star's heliosphere is full of the highly conductive medium of ionised hydrogen, eg the solar wind. These objects whizzing from more negative outer regions will show classical plasma discharge tendencies as they approach and leave the sun's influence.
Comas, jets and neat craters all indicate plasma discharge.
"..volatile compounds such as water and carbon dioxide sublimating from ice to vapor"
'Water' is inferred from hydroxyl molecule [OH] also present in comet comas. The sputtering action of plasma discharge strips and lofts -ve oxygen (etc) ions from surface materials. These combine with hydrogen protons in the solar wind, to form OH radicals, neutral H2O and H2O+. Other particles in the dust form CO, etc.
Why is one end of Hartley2 preferential to discharge? Maybe it's thinner and a better discharge point. At least this science is lab based. Amalgamating dust-based bodies needs a bit of fairy dust I think!
Gosh! Is this "The Onion"? If Hartley2 is an asteroid, so is the Rock of Gibraltar in Spain. ... Do not see the artificial illumination, nor the POOL OF WATER in front of it? Do you not notice there are NO STARS around its base? I have an idea. Why don't you look at it again; you might see something different this time. (I'm not kidding.) I have re-rendered EVERY SINGLE NASA PHOTO of this hunk, and it's not even an asteroid. (Sheesh!)
Reply | Report Abuse | Link to thisThere is another possible explanation for comet Hartley 2. Is the object basically cylindrical? Is it rotating around it's long axis? Might the cylinder be an artificial construct? Might it be an alien probe? Have aliens attempted to disguise a probe as a comet? Might the differences in gas emission be indicative of an ability to use outgassing as a means of propelling the object along it's orbit?
Reply | Report Abuse | Link to thisThe object is attached to something, okay? I have re-rendered every single NASA photo of this object, and I can point to a lot of other stuff "IN THE DARK" that merely isn't illuminated. I think I'll shut up now. ~EEWC
Reply | Report Abuse | Link to this"All matter" continually produces and secretes, "as AURA", the phenomenon known as H2O and yes this includes the dark matter of outer space. Dark matter particals are so small as to not interact with the phenomenon COLD.
Reply | Report Abuse | Link to thiscomments: http://www.cbc.ca/news/canada/story/2009/01/14/f-windchill.html
It takes reaction to turn stone to gas, then it takes reaction to turn gas to water and again reaction to turn water to gas, reaction then turns gas back into rock. (comet, astroid earth etc.
A reaction of Earthquake turns rock to water (have you ever wondered where water really comes from!) just because things appear in the sky does not mean that is where they originate.
Earthquake liquefaction has been sorely misunderstood.
i am reminded of another "peanut shaped"comet i think it was comet haily in 86 , is this shape some result of sublimation prosess?
Reply | Report Abuse | Link to thisQuark, the bar keep, had lopsided lobes. So?
Reply | Report Abuse | Link to this.