Posted on by Nancy Atkinson

Surprising Comet Lovejoy Now Becoming Merry and Bright

Comet Lovejoy photographed remotely with the FRAM telescope in Argentina on Dec. 17 by a Czech team of Jakub Cerny, Jan Ebr, Martin Jelinek, Petr Kubanek, Michael Prouza and Michal Ringes. Click to original image and more on the kommet.cz website.

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It was almost a pre-holiday miracle that Comet Lovejoy survived its close encounter with the Sun on Dec. 15, 2011. But now, the feisty comet is making a ‘merry and bright’ comeback, re-sprouting its tail and showing up brilliantly when seen with binoculars and in telescopic images from southern hemisphere skywatchers.

“It was a big surprise that after going through the solar atmosphere it re-emerged with a beautiful tail,” Karl Battams told Universe Today. Battams is with Naval Research Laboratory and has been detailing the Comet Lovejoy’s incredible journey on the Sungrazing Comets website. “And basically within a day it was as bright after the encounter as it was before.”

The beautiful image above was taken on Dec. 17, 2011, clearly showing two gorgeous tails on Comet Lovejoy. See more from the Czech team that took the image at their website, Kommet.cz.

As much as this comet has surprised everyone, no one is going out on a limb and predicting it will become visible with the naked eye. But who knows? The comet’s discoverer, Austrailian amateur astronomer Terry Lovejoy was able to image the comet in the day time! ” I am hopeful of a nice binocular comet low in the dawn around Christmas time,” Lovejoy said on the Ice in Space website.

Comet Lovejoy in the early morning hours of Dec. 20, 2011. Credit: Ian Musgrave, Adelaide, South Australia, Australia

“Southern hemisphere viewers can see it now early in the morning,” Battams said via phone this morning. “It is going to become increasingly easy for them to see as it moves away from the Sun. I’m not sure it will increase in brightness anymore, as it has leveled off a little bit now. Odds are stacked in the favor of a nice nighttime show for southern viewers, and gradually it will fade away.”

Of course, Comet Lovejoy isn’t the only comet that has survived a close encounter with the Sun; in fact, some comets have even brightened to naked eye visibility after surviving a scorching from the Sun. The “Great Comets” of 1843 and 1882, and Comet Ikeya-Seki of 1965 were all Kreutz sungrazers – like Comet Lovejoy — and they all became brilliant after their solar encounters, with extraordinarily long tails.

Normally these comets don’t survive and are completely obliterated by the Sun. But the few that do – only 2 or 3 a century — can be very bright.

I had asked Battams on Friday – just after the comet emerged from behind the Sun – his thoughts on Comet Lovejoy and if it might follow the example of those previous surviving sungrazers.

“All bets are off as far as I’m concerned,” he wrote via email. “We thought this was a relatively small one — maybe a hundred or two meters in diameter. Clearly it can’t be. I did not expect it to survive perihelion as anything more than a diffuse blob that would rapidly dissipate. Instead it is pretty much as bright as it was before, just with less of a tail now.”

So keep a lookout for the holiday comet of 2011, the merry and bright Comet Lovejoy!

Posted on by Nancy Atkinson

Best Look Yet of Comet Lovejoy’s Slingshot Around the Sun

There have been some great images and video of Comet Lovejoy’s close encounter with the Sun, but this video put together by Scott Wiessinger from Goddard Spaceflight Center combines and zooms in on the best views from the Solar Dynamics Observatory (SDO), which adjusted its cameras in order to watch the trajectory.

The first part of the video from SDO, (taken in 171 Angstrom wavelength, which is typically shown in yellow) was filmed on Dec 15, 2011 showing Comet Lovejoy moving in toward the Sun, with its tail “wiggling” from its interaction with the solar wind. The second part of the clip shows the comet exiting from behind the right side of the Sun, after an hour of travel through its closest approach.

No time travel with this slingshot around the Sun, but it is amazing to be able to follow this comet’s journey so closely!

Posted on by Nancy Atkinson

Feisty Comet Lovejoy Survives Close Encounter with the Sun

An image received on Dec. 16th from the Solar and Heliospheric Observatory confirm that Comet Lovejoy survived perihelion and is now receding from the Sun. Credit: NASA, notations by Karl Battams.

It’s the morning after for the sungrazing Comet Lovejoy, and this feisty comet has scientists shaking their heads in disbelief. “I don’t know where to begin,” wrote Karl Battams, from the Naval Research Laboratory, who curates the Sun-grazing comets webpage. “What an extraordinary 24hrs! I suppose the first thing to say is this: I was wrong. Wrong, wrong, wrong. And I have never been so happy to be wrong!”

Many experts were predicting Comet Lovejoy would not survive perihelion, where it came within about 120,000 km from the Sun. But some extraordinary videos by NASA’s Solar Dynamics Observatory showed the comet entering and then surprisingly exiting the Sun’s atmosphere. Battams said he envisioned that if the comet survived at all, what would be left would be just a very diffuse component that would endure maybe a few hours after its close encounter with the Sun. But somehow it survived, even after enduring the several million-degree solar corona for nearly an hour. However, Comet Lovejoy appears to have lost its tail, as you can see in the image below.

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The comet is now in the view of other spacecraft, which will continue monitoring the object. It will likely grow a “new” tail as outgassing of dust, gas and debris will continue. It is not known yet how much of Comet Lovejoy’s core remains — which was 200 meters in diameter earlier this week — or how long it will continue to stay together after its close brush with the Sun.

But we’ll keep you posted!

See more videos of Lovejoy’s survival below:

Posted on by Nancy Atkinson

Watch as Comet Lovejoy Takes a Death-Dive Into the Sun

A comet discovered on Dec. 2, 2011 is now on a near collision course with the Sun, and likely won’t survive such a close encounter. The best part is that you can follow along and watch as it happens! Comet C/2011 W3 Lovejoy will pass behind the sun at around 24:00 UTC (7 pm EST) on Thursday, Dec. 15, 2011 and probably won’t be seen again. In the video above, processed images from the STEREO A spacecraft shows Comet Lovejoy blazing towards the Sun, with the comet’s tail wiggling as it interacts with the solar wind.

The Solar Dynamics Observatory website has a special page where they will be uploading the latest images of the comet as it meets its fiery fate. As Comet Lovejoy moves toward perihelion, the SDO team will point SDO a little to the left of the Sun to try and see the tail of the comet with their instruments. This website will allow you to see those images as quickly as they can download them from the spacecraft.

Science live and in action!

Astronomers and various spacecraft have been keeping an eye on Comet Lovejoy the past few days as this Kreutz-group comet headed towards the Sun. Just today (Thursday) the images from the SOHO spacecraft showed the comet sprouting a bulbous head. This is occurring because the comet is getting so bright, it is overwhelming the detectors on the SOHO satellite. “The photons are ‘bleeding’ out to form that cross-like pattern,” said Dan Pendick on the Geeked On Goddard website.

Pendick also quoted solar scientist Jack Ireland from Goddard, who noted that at times two tails can be seen on the comet. “The thick white tail is primarily dust breaking away from the comet nucleus,” Ireland said, as the Sun’s radiation and solar wind that knocks material off the comet nucleus. But to the left is a tail of charged particles (ions) being deflected to the side by the magnetic field carried by the solar wind.

At its closest approach, Comet Lovejoy will pass just 120,000 km above the solar surface. At that distance, the icy comet is not expected to survive the Sun’s fierce heat. But the comet could actually disintegrate at any moment. Kreutz comets have a tendency to evaporate as they approach, or pass close to the Sun.

If the comet does stay the course and stay visible until it goes around the Sun, we likely won’t be able to see its demise because its closest approach will take place on the far side of the Sun.

But this is a great chance to watch this event as it is about to happen.

“We have here an exceptionally rare opportunity to observe the complete vaporization of a relatively large comet, and we have approximately 18 instruments on five different satellites that are trying to do just that,” wrote Karl Battams, from the Naval Research Laboratory, who curates the Sun-grazing comets webpage, and has been documenting Lovejoy’s journey.

Amateur astronomers have been trying to capture this event as well, with everyone wondering how bright the comet will get. For updates from amateur astronomers, check out the Yahoo Groups comet observers forum.

Comet C/2011 W3 Lovejoy was actually discovered by an amateur, Australian astronomer Terry Lovejoy (hence the comet’s name.) This is the first Kreutz comet found from a ground-based observer since 1970, and it was spotted with a modest 8″ telescope too! You can read Lovejoy’s tale of his discovery here.

On average, new Kreutz-group comets are discovered every few days by spacecraft like SOHO, but from the ground they are much rarer to see and harder to discover.

“This is the first ground-based discovery of a Kreutz-group comet in 40 years, so we really can’t be sure just how bright it will get,” said Battams. “However, I do think that it will be the brightest Kreutz-group comet SOHO has ever seen.”

Comet Lovejoy’s spectacular progress can also be monitored via the web at SOHO’s LASCO instrument page.

For the SDO special webpage, images from SDO take about 30 minutes to move from the spacecraft until they are available on the website. The SOD team plans to off-point the spacecraft at 23:30 UTC (6:30 pm ET) and return to normal solar observing at 12/16 00:30 UTC (7:30 pm ET). Images should start arriving by 24:00 UTC (7 pm EST.)

Posted on by Nancy Atkinson

Latest Images of Comet Elenin: Not Much to See

Screenshot of a video of images from the GRAS telescopes in Mayhill Station, New Mexico on Oct. 21, 2011, showing what might be a diffuse blob of material, all that's left of Comet Elenin. Credit: Ernesto Guido, Giovanni Sostero and Nick Howes.

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A series of images of Comet Elenin taken on October 21, 2011 might show an “extremely faint and diffuse blob of light,” according to Ernesto Guido, Giovanni Sostero and Nick Howes, who used two remote telescopes in New Mexico to image again the field of view where Comet Elenin should be. Their first observing session with a 10” reflector showed no obvious moving object in the telescope’s field of view, while the second session a 0.1 meter refractor showed a hint of something moving in the background when images taken 2 hours apart were “blinked,” but interference from moonlight hasn’t been ruled out.

The trio of astronomers encourage other observers to confirm or refute this view with additional observations/images. “We suggest the use of wide-field, fast focal ratio scopes, possibly under very good sky conditions,” they said.

You can see more at the Remanzacco Observatory website, including a video of the “blinking.”

Posted on by Nancy Atkinson

Evidence of a Late Heavy Bombardment Occuring in Another Solar System

This artist's conception illustrates a storm of comets around a star near our own, called Eta Corvi. Evidence for this barrage comes from NASA's Spitzer Space Telescope, whose infrared detectors picked up indications that one or more comets was recently torn to shreds after colliding with a rocky body. Image credit: NASA/JPL-Caltech

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Planetary scientists have not been able to agree that a turbulent period in our solar system’s history called the Late Heavy Bombardment actually occurred. But now, using observations from the Spitzer Space Telescope, scientists have detected activity resembling a similar type of event where icy bodies from the outer solar system are possibly pummeling rocky worlds closer to the star. This is the first time such activity has been seen in another planetary system.

“Where the comets are hitting the rocky bodies is in the habitable zone around this star, so not only are life-forming materials possibly being delivered to rocky worlds, but also in the right place for life as we know it to grow,” said Carey Lisse, senior research scientist at the Johns Hopkins University Applied Physics Laboratory. “This is similar to what happened to our own solar system during the Late Heavy Bombardment.”

Lisse spoke to journalists in a conference call from the Signposts of Planets meeting taking place at Goddard Space Flight Center this week.

Spitzer observations showed a band of dust around the nearby, naked-eye-visible star called Eta Corvi, located in the constellation Corvus in northern sky. Within the band of warm dust, Spitzer’s infrared detectors saw the chemical fingerprints of water ice, organics and rock, which strongly matches the contents of an obliterated giant comet, suggesting a collision took place between a planet and one or more comets. Also detected was evidence for flash-frozen rocks, nanodiamonds and amorphous silica.

This dust is located 3 AU away from Eta Corvi, which is the “habitable zone” around that star, and is close enough to the star that Earth-like worlds could exist. Lisse said although it hasn’t been confirmed, researchers think there is a Neptune-like world and at least two other planets in this system. A bright, icy Kuiper Belt-like region located 3-4 times farther out than our own Kuiper Belt was discovered around Eta Corvi in 2005.

“This is very possibly a planet-rich system,” Lisse said.

The light signature emitted by the dust around Eta Corvi also resembles meteorites found on Earth. “We see a match between dust around Eta Corvi and the Almahata Sitta meteorites, which fell to Earth in Sudan in 2008,” Llisse said. “We can argue that the material around Eta Covi is rich in carbon and water, things that help life grow on Earth.”

The Eta Corvi system is approximately one billion years old, which the research team considers about the right age for such a bombardment.

No asteroidal dust was found in the disk around Eta Corvi.

“Asteroidal dust would look like it had been heated, and chemically and physically altered, and most of the water and carbon would be gone,” Lisse said. “This dust is very rich in water and carbon and the rocky components are very primitive and un-altered.”

Most planetary formation theories can’t account for such an intense period of bombardment in our own solar system so late in its history, but the Nice Model proposed in 2005 suggests the Late Heavy Bombardment was triggered when the giant planets in our solar system— which formed in a more compact configuration – rapidly migrated away from each other (and their orbital separations all increased), and a disk of small asteroids and comets that lay outside the orbits of the planets was destabilized, causing a sudden massive delivery of asteroids and comets to the inner solar system. The barrage scarred the Moon and produced large amounts of dust.

“We can see the process of this happening at Eta Corvi and can learn more about our own solar system, since we can’t go back in time,” Lisse said. “It’s very possible that the rain of comets and Kuiper Belt Objects brought life to Earth.”

Lisse and his team are not sure if one big comet or lots of smaller comets are pummeling the inner solar system. “It is probably many bodies, but we only see the effects of the largest ones,” he said.

Could this be an indication that a Late Heavy Bombardment happens in many solar systems? “It’s not clear whether this is an atypical system, but we do know of one other possible system where it could be happening,” Lisse said in response to the question posed by Universe Today. “I think this is a rare event, which might mean that life is rare if you need a Late Heavy Bombardment for life to happen.”

Lisse said the reason they studied this star was the earlier detection of the Kuiper Belt-like region around Eta Corvi. “We knew it was an exceptional system from previous infrared sky surveys and the large bright Kuiper Belt was just the tip of the iceberg,” Lisse said. “This system was shouting, ‘I’m something extraordinary, come figure out my mystery!”

Paper: Spitzer Evidence for a Late Heavy Bombardment and the Formation of Urelites in Eta Corvi at ~1 Gyr

Source: Signposts of Planets conference call, JPL Press release

Posted on by Nancy Atkinson

Where’s My Doomsday? Remnants of Comet Elenin Pass by Earth Without Incident

Image taken with the 2m Faulkes North Telescope of the region of sky where Comet Elenin should have been. . Field of view 10 arcmins Stack of up to 13 Bessel R band filtered images (20s) Limiting Magnitude 20.5 Image (c) Nick Howes, Ernesto Guido, Giovanni Sostero/LCOGT/Faulkes Telescope Project. Used by permission

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If you were waiting for Comet Elenin to wreak havoc on Earth so that you didn’t have to pay off your credit card debt or go into work today, I’m sorry to inform you that doomsday didn’t happen. All that remained of Comet Elenin, — which wasn’t much — made its closest pass by Earth yesterday (Oct. 16, 2011) without causing any earthquakes, tsunamis, or high tides and it didn’t collide with Earth, either. Moreover, there was no brown dwarf or Mothership hidden in the comet’s coma. And in case you didn’t notice, this comet did not cause three days of darkness around September 26, 2011.

“I don’t know why fearmongers chose my comet,” the comet’s discoverer Leonid Elenin told Universe Today. “I received many letters from scared people. But if they believe in conspiracy theories I can’t help them.”

For some reason, conspiracy and doomsday theorists chose this small little comet — one that was to come no closer to Earth than 34 million km (21 million miles) during its closest approach on October 16th – to be the harbinger of doom.

But here we are, just fine.

Well, except for wars, terrorism, global warming and other things that the human race inflicts on itself. There are enough bad things going on here on planet Earth that conspiracy theorists shouldn’t fabricate doomsday predictions just to needlessly scare people for fun and profit.

So why didn’t Comet Elenin cause doomsday?

1. It couldn’t have hit Earth, or affected Earth’s orbit. The comet was predicted to come 34 million km (21 million miles) away at its closest approach. Just in case you can’t figure that out, one object can’t hit another at that distance. Plus, the gravity exerted by a small object won’t affect Earth either. To put this in perspective, this distance is only a little closer than the closest approach of Venus to Earth, and roughly 100 times the distance from the Earth to the Moon. Nothing happens to Earth when Venus is at closest approach, and Venus is 12,000 kilometers in diameter, while Elenin was 3-5 kilometers across. When the comet was intact it had less than a billionth of the tidal force of the Moon.

Where Comet Elenin should have been in the sky on October 16, 2011 shows nothing left of the the distinegrated comet, and all that is visible are star trails. Credit: Ian Musgrave, using the Global Rent-a-Scope.

2. Comet Elenin fell apart. Sometimes, long period comets that originate from the outer parts of our solar system begin to dissipate as they get closer to the Sun. But Elenin was hit by solar flares from the Sun on August 19 and began disintegrating. When it reached its closest point to the Sun on September 10, it basically was toast. Just recently the location of where the comet should be has become visible in the night sky, out of the Sun’s glare. Several images from different amateur astronomers show absolutely nothing. The comet has completely disintegrated and fallen apart.

Earlier today, astronomer Nick Howes and his colleagues using the 2 meter Faulkes telescope took 30 minutes worth of exposures and saw nothing of Comet Elenin in the sky (top image). “We observed objects at magnitude 20.5, but saw no trace at all of Comet Elenin,” Howes told Universe Today. “If it had stayed together, it should have been almost visible with the naked eye now.”

3. What is left of the comet won’t cause problems, either. The average density of a comet’s coma is about the same as the density of the atmosphere on the Moon, and any rocks or debris that might be left over from the comet are small enough that they would burn up in Earth’s atmosphere if Earth does go through the wake of the coma or debris from the comet. And remember, several times a year Earth goes through the debris from comets and all that happens is we get beautiful meteor showers to enjoy.

And after this, don’t worry about Comet Elenin or its leftovers. Earth won’t pass through it again for another 12,000 years.

So move along, folks, nothing here. Comet Elenin is just another doomsday that didn’t happen, just like NASA, Leonid Elenin, and many other people said.

And if you proudly claim you aren’t a sheeple and are now just waiting and searching for the next doomsday theory to hang your every hope upon, why don’t you try expending your energy on this: Enjoy every day on this beautiful planet and live your life in its fullest. Use real science and learn to think critically. And perhaps you could be a person who could help come up with solutions to some of the real problems on planet Earth.

(And by the way, don’t worry about Oct. 21, 2011 (Harold Camping makes another prediction) or Dec. 21, 2012 (Mayan calendar) either. Same story.)

Second image source: Astroblog by Ian Musgrave

Posted on by Jon Voisey

Was the “First Photographed UFO” a Comet?

First photograph of a UFO sighting, taken 12 August 1883 by Jose Bonilla.
First photograph of a UFO sighting, taken 12 August 1883 by Jose Bonilla.

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On August 12th, 1883, Mexican astronomer José Bonilla was preparing to study the Sun at the recently opened Zacatecas Observatory. However, the Sun’s surface was marred by numerous objects quickly travelling across its disk. Over the course of the day and the next, Bonilla exposed several wet plates to take images of the 447 objects he would observe. They weren’t released publicly until January 1st, 1886 when they were published in the magazine L’Astronomie. Since then, UFOlogists have crowed these photographs as the first photographic evidence of UFOs. The chief editor of L’Astronomie passed the observations off as migrating animals, but a new study proposes the observation was due to the breakup of a comet that nearly hit us.

The only piece of evidence the authors, led by Hector Manterola at the Universidad Nacional Autónoma de México, use to suggest that this was a comet in the process of breaking up, was the descriptions of the objects as being “fuzzy” in nature and leaving dark trails behind them. Assuming this were the case, the authors consider how close the object would have been. Since astronomers at observatories in Mexico City, or Puebla had not reported the objects, this would imply that they did not cross the disc of the Sun from these locations due to parallax. As such, the maximum distance the object could have been is roughly 80,000 km, roughly 1/5th the distance to the moon.

But the team suggests the fragments may have passed even closer. By the time comets reach the inner solar system, they have a significant velocity of some tens of kilometers per second. In such a case, to transverse the disc of the Sun in the time reported by Bonilla (a third to a full second), the object would have been, at most, at a distance of ~8,000km.

At such distances, the overall size of the fragments would be in rough agreement of sizes of other fragmented comets such as 73P/Schwassmann-Wachmann 3, which gave off several fragments in 2006. Based on the number of fragments, estimated sizes, and density of an average comet, the authors estimate that the mass may be anywhere between 2 x 1012 and 8 x 1015 kg. While this is a very large range (three orders of magnitude), it roughly brackets the range of known comets, again making it plausible. The upper range of this mass estimate is on par with Mars’ moon Deimos, which is generally held to be similar in mass to the progenitor of the impact that killed the dinosaurs.

One oddity is that one would likely expect such a close breakup to result in a meteor storm. The timing of these events is just before the annual Perseid meteor shower, but reports for that year, such as this one, do not depict it as being exceptional, or having a different radiant than should be expected. Instead, it notes that 157 of the 186 meteors observed on the 11th were definitively Perseids, and that the “year’s display cannot be reckoned as a fine one by any means.” Meanwhile, the Leonid meteor shower (peaking in November), was exceptional that year, generating an estimated 1,000 meteors an hour, but again, no records seem to indicate an unusual origin.

In total, I find the characterization of Bonilla’s observation as a comet plausible, but generally unconvincing. However, if it were a fragmented comet, we’re very lucky it wasn’t any closer.

Posted on by Nancy Atkinson

Best Evidence Yet That Comets Delivered Water for Earth’s Oceans

New measurements from the Herschel Space Observatory have discovered water with the same chemical signature as our oceans in a comet called Hartley 2 (pictured at right). Image credit: NASA/JPL-Caltech

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The idea isn’t new that Earth’s oceans originated from comets bombarding our planet back in its early days. But astronomers have now found the best evidence yet for this scenario. The Herschel infrared space observatory detected that comet Hartley 2, which originates from the distant Kuiper Belt, contains water with the same chemical signature as Earth’s oceans.

“Our results with Herschel suggest that comets could have played a major role in bringing vast amounts of water to an early Earth,” said Dariusz Lis, senior research associate in physics at the California Institute of Technology in Pasadena and co-author of a new paper in the journal Nature, published online on Oct. 5. “This finding substantially expands the reservoir of Earth ocean-like water in the solar system to now include icy bodies originating in the Kuiper Belt.”

Previous looks at various other comets showed water content different from Earth, with deuterium levels around twice that of Earth’s oceans, but those comets came from the Oort Cloud. Scientists theorized that if comets of this kind had collided with Earth, they could not have contributed more than a few percent of Earth’s water.

The Deep Impact spacecraft successfully flew past Comet Hartley 2 in November 2010 and is an example of the type of comet that the UCLA scientists describe in their research. Image: UPI/NASA/JPL-Caltech/UMD.

But Herschel’s observations of Hartley 2 are the first in-depth look at water in a comet from the Kuiper Belt — home of icy, rocky bodies that includes dwarf planets and innumerable comets — and it showed a surprising difference.

Using HIFI, a highly sensitive infrared spectrometer, Herschel peered into the comet’s coma, or thin, gaseous atmosphere, and found that Hartley 2 possessed half as much “heavy water” as other comets analyzed to date. In heavy water, one of the two normal hydrogen atoms has been replaced by the heavy hydrogen isotope known as deuterium. The ratio between heavy water and light, or regular, water in Hartley 2 is the same as the water on Earth’s surface.

“Comet Hartley’s deuterium-to-hydrogen ratio is almost exactly the same as the water in Earth’s oceans,” says Paul Hartogh, Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany, who led the international team of astronomers in this study.

The amount of heavy water in a comet is related to the environment where the comet formed, and by comparing the deuterium to hydrogen ratio found in the water in Earth’s oceans with that in extraterrestrial objects, astronomers were hoping to identify the origin of our water.

Astronomers know Hartley 2 comes from the Kuiper Belt, since they can track its path as it swoops into Earth’s neighborhood in the inner solar system every six-and-a-`half years. The five comets besides Hartley 2 whose heavy-water-to-regular-water ratios have been obtained all came from the Oort Cloud, an even more distant region in the solar system. This region is 10,000 times farther away than the Kuiper Belt, and is home to the most documented comets.

The team is now using Herschel to look at other Kuiper Belt comets to see whether they, too, carry the same type of water.

“Thanks to this detection made possible by Herschel, an old, very interesting discussion will be revived and invigorated,” said Göran Pilbratt, ESA Herschel Project Scientist. “It will be exciting to see where this discovery will take us.”

Paper: “Ocean-like Water in the Jupiter-family Comet 103P Hartley”

Sources: JPL, ESA

Posted on by Gemma Lavender

Puzzling Comet Composition Solved?

How Are Comets Formed?
The Deep Impact spacecraft successfully flew past Comet Hartley 2 in November 2010 and is an example of the type of comet that the UCLA scientists describe in their research. Image: UPI/NASA/JPL-Caltech/UMD.

For years comets have mystified scientists with their compositions that appear to have formed in both warm and cold environments, rather than in one location of a uniform temperature. But new research shows that the reason some comets feature patches of differing surface composition is not because they are made from material that formed in different parts of the Solar System, but because some parts of their surface absorb heat at varying rates. This leads to localized heat sinks and cold traps, according to a new model constructed by David Jewitt and Aurelie Guilbert-Lepoutre from the University of California, Los Angeles (UCLA). Their model shows that the chemical composition of a comet can evolve in the ten million year period during which a comet is classed as a Centaur, migrating from the Kuiper Belt to the inner Solar System.

“The Centaurs are objects which have escaped from the Kuiper belt and are drifting amongst the giant planets,” says Jewitt. “Their lifetimes in these orbits are limited to about 10 million years because they are gravitationally perturbed by the planets to other orbits. At least half are ejected from the Solar System to the interstellar medium. Some are kicked inside the orbit of Jupiter, where the ice begins to sublimate and we call them comets.”

The key is variances in the surface – thermal conductivity, reflectivity (albedo), obliquity (tilt) and even topography such as craters or hilly terrain. This leads to the creation of ‘thermal shadows’.

“Just as it is cooler in the shadow of a building than standing in the full Sun, the region beneath a bright spot or a boulder on the surface of a comet will remain cooler than the surroundings,” says Jewitt. The higher the albedo, the more sunlight is reflected away, keeping that particular patch of the comet 20 to 30 degrees Celsius cooler than its surroundings. The thermal shadows can be maintained “We have calculated the way the cool spot extends down into the interior of the comet, and examined how deep and how long-lived this cool shadow region can be for objects moving on a variety of different orbits.”

Being colder, the thermal shadows attract volatile materials such as water-ice and carbon dioxide from elsewhere on the comet, enhancing the composition there. Consequently the composition of the comet becomes strongly non-uniform, as does the activity on the comet, manifest in jets of the kind seen, for example, by the Deep impact spacecraft on the Comet Hartley 2 in November 2010.

The paper can be found on the astro-ph archive and can be read here.