Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

SOHO Watches a Comet Fading Away

29.07.2011
On Nov. 4, 2010, NASA's EPOXI spacecraft came within 450 miles of Comet Hartley 2, a small comet not even a mile in diameter, which takes about six and a half years to orbit the sun. Designated officially as 103P/Hartley 2, the comet thus became the fifth for which scientists have collected close-up images.

But the comet was also observed from another spacecraft: the Solar and Heliospheric Observer (SOHO), better known for its observations of the sun. Together, the two returned data about what appears to be an irregular comet, belching chunks of ice and losing water at a surprisingly fast pace.


On September 30, 2010, water production on Comet Hartley 2 -- as represented by the hydrogen cloud surrounding the comet seen by SOHO – jumped by a factor of two and half in a single day. (Comet and cloud size are not to scale.) Credit: NASA/Steele Hill
Inset upper right: Comet Hartley 2 as viewed by EPOXI from 435 miles away on November 4, 2010. Credit: NASA/JPL-Caltech/UMD

"By combining EPOXI's direct imaging with several months of SOHO data, we had a rare chance to see a comet in the process of shedding off large amounts of water," says Michael Combi, a space scientist at the University of Michigan in Ann Arbor, Mich., who wrote about his findings in a June 10, 2011 issue of the Astrophysical Journal Letters. "Comets always lose water as they heat up during the approach to the sun, but this was much more than usual. Something pretty dramatic happened in those weeks."

Understanding the composition and behavior of comets intrigues scientists because they are some of the first objects that formed around our sun some 4.5 billion years ago and they’ve evolved little since. These chunks of ice, rock, and frozen gas hold clues to what existed in those early days of the solar system's formation, says Combi. So he uses an instrument onboard SOHO called SWAN – for Solar Wind ANistropy – to observe how water streams off of comets.

SWAN's main job is to map the distribution of hydrogen atoms across the entire sky. This helps those who study the sun's magnetic environment by tracking how the interstellar wind of particles moves through our area of space. But the instrument also can help track comets, which are generally surrounded by an extremely thin atmosphere of water vapor. Under ultraviolet light from the sun, the hydrogen atoms fly off the water molecules at great speed and produce a huge cloud or "coma" of hydrogen. The coma absorbs sunlight and then re-emits it, making it detectable in SWAN images. Observing the clouds can then help determine how much water is being vaporized from the comet over time.

SWAN has collected data on nearly one hundred comets, so when Combi and his colleagues at Michigan learned EPOXI was destined to get a closer view of Hartley 2, they pored over old data from that comet's most recent approaches in 1997 and 2004. Unfortunately, the sun obscured SOHO's view of Hartley in 2004, but the 1997 data was accessible. They compared this to SWAN's 2010 observations from Sept. 14 to Dec. 15.

Surprisingly, the comet's water production in 1997 was three times the amount of water put out in 2010. "We've analyzed multiple comets with short periods like Hartley 2 on repeated trips around the sun," says Combi. "But none of them has shown such a drastic change from one close pass by the sun to the next."

The SWAN data captured another surprise. On Sept. 30, the hydrogen jumped by a factor of two and a half in a single day. It dropped down again some six weeks later.

Standard models of how comets behave helped Combi's team correlate the hydrogen signature to just how much of the comet's surface should be giving off water, a process known as "sublimating," because the water turns directly from ice to a vapor without passing through a liquid phase. The amount of surface area predicted didn't jibe with what EPOXI itself saw – a comet that only gave off water from one half of its shape. But EPOXI also captured images of an extended halo of icy fragments that burst off the comet, most likely flung into space by carbon dioxide emissions on the comet's surface. These ice chunks probably added sublimated water to the hydrogen cloud.

"The rate of water generation being so much higher in 1997 implies that the ice fragmentation was even more severe then," says solar physicist Joe Gurman, U.S. project scientist for SOHO at NASA's Goddard Space Flight Center in Greenbelt, Md. "To me, that means we're watching how comets eventually 'dry up' and become less active with repeated passes through the inner solar system."

Comparing EPOXI observations to SWAN's did not, however, always jibe with current understandings of comets. EPOXI measured cyanide output – an element that tends to be fairly minimal within comets but is so bright that it is easy to measure and indeed was one of the first elements identified in comets in the 1880s. Cyanide output typically correlates to water output, but in this case EPOXI saw a burst of cyanide – it increased seven times on Sept. 17 -- at a time when water production was only gently increasing.

"Analysis of all this data on Hartley 2 is just beginning," says Combi, "So it will be awhile before we figure out all that's happening. But we have here an example of an unusual comet. We don't know if this one had odd behaviors or some different kind of composition – but maybe we'll start seeing things like this, perhaps even in hindsight, in other comets."

With only five comets privy to a near spacecraft fly-by, new data points like this can help refine our understanding of comet composition. It remains an interesting scientific debate whether anomalous comets like Hartley 2 behave differently because they formed of different materials originally or because they've experienced different environments over time. As more analysis of the EPOXI and SWAN data come, the next few years should provide additional insight into these remnants from the very dawn of the solar system.

Karen C. Fox
NASA's Goddard Space Flight Center

Karen C. Fox | EurekAlert!
Further information:
http://www.nasa.gov
http://www.nasa.gov/mission_pages/soho/hartley2-fades.html

More articles from Physics and Astronomy:

nachricht DGIST develops 20 times faster biosensor
24.04.2017 | DGIST (Daegu Gyeongbuk Institute of Science and Technology)

nachricht New quantum liquid crystals may play role in future of computers
21.04.2017 | California Institute of Technology

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

DGIST develops 20 times faster biosensor

24.04.2017 | Physics and Astronomy

Nanoimprinted hyperlens array: Paving the way for practical super-resolution imaging

24.04.2017 | Materials Sciences

Atomic-level motion may drive bacteria's ability to evade immune system defenses

24.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>