Category: Comets

An artist’s impression of Giotto’s brief encounter with comet Halley. Image credit: ESA Click to enlarge
This week the European Space Agency celebrated the 20-year anniversary of the Giotto spacecraft’s encounter with Comet Halley. This was ESA’s first deep space mission, which launched on board an Ariane 1 rocket. Giotto flew for 8 months, traveling almost 150 million kilometres. It swept past the comet on March 13, 1986, getting as close as 596 km (370 miles), and delivered the best pictures ever seen of a comet’s nucleus.

Twenty years ago, in the night between 13 and 14 March 1986, ESA’s Giotto spacecraft encountered Comet Halley. It was ESA’s first deep space mission, and part of an ambitious international effort to solve the riddles surrounding this mysterious object.

The adventure began when Giotto was launched by an Ariane 1 rocket (flight V14) on 2 July 1985. After three revolutions around the Earth, the on-board motor was fired to inject it into an interplanetary orbit.

After a cruise of eight months and almost 150 million kilometres, the spacecraft’s instruments first detected hydrogen ions from Halley at a distance of 7.8 million kilometres from the comet on 12 March 1986.

Giotto encountered Comet Halley about one day later, when it crossed the bow shock of the solar wind (the region where a shock wave is created as the supersonic solar particles slow to subsonic speed). When Giotto entered the densest part of the dusty coma, the camera began tracking the brightest object (the nucleus) in its field of view.

Excitement rose at the European Space Operations Centre in Darmstadt, Germany, as the first fuzzy images and data came in. The ten experiment teams scrutinised the latest information and struggled to come up with a preliminary analysis.

The first of 12 000 dust impacts was recorded 122 minutes before closest approach. Images were transmitted as Giotto closed in to within a distance of approximately 2000 kilometres, as the rate of dust impacts rose sharply and the spacecraft passed through a jet of material that streamed away from the nucleus.

The spacecraft was travelling at a speed of 68 kilometres per second relative to the comet. At 7.6 seconds before closest approach, the spacecraft was sent spinning by an impact from a ‘large’ (one gram) particle. Monitor screens went blank as contact with Earth was temporarily lost.

TV audiences and anxious Giotto team members feared the worst but, to everyone’s amazement, occasional bursts of information began to come through. Giotto was still alive.

Over the next 32 minutes, the sturdy spacecraft’s thrusters stabilised its motion and contact was fully restored. By then, Giotto had passed within 596 kilometres of the nucleus and was heading back into interplanetary space.

The remarkably resilient little spacecraft continued to return scientific data for another 24 hours on the outward journey. The last dust impact was detected 49 minutes after closest approach. The historic encounter ended 15 March when Giotto’s experiments were turned off.

Original Source: ESA Portal

Comet. Image credit: NASA/JPL Click to enlarge
The chances of the Earth being hit by a comet from beyond Pluto ? ? la Deep Impact ? are much lower than previously thought, according to new research by an ANU astronomer.

Using computer simulations and data from an American military telescope, Dr Paul Francis, from the ANU Research School of Astronomy and Astrophysics at Mt Stromlo, has found there are seven times fewer comets in our solar system than previously thought.

?I calculate that small comets, capable of destroying a city, only hit the Earth once every 40 million years or so,? Dr Francis said. ?Big continent-busting comets, as shown in the movie Deep Impact, are rarer still, only hitting once every 150 million years or so. So I don?t lose sleep over it, but you?re still more likely to be killed by a comet than to win the Lotto jackpot.?

Previous estimates of the number of comets were based on the work of amateur astronomers, who for hundreds of years have been scanning the skies, looking for new comets.

Previously, it was believed that these amateur astronomers were only spotting three per cent of the comets passing close to the Earth: the rest were thought to be missed because they were in the wrong part of the sky or were too faint.

But Dr Francis found that the amateurs were doing better than anyone had realised ? they were actually spotting 20 per cent of comets. There are therefore far fewer undiscovered comets.

?The new data allowed us to count the number of faint and far-away comets that the amateurs had missed. And we found that they were pretty rare,? Dr Francis said.

These results apply to comets coming from beyond the orbit of Pluto, which is where most comets live. The Earth is still at risk of being hit by asteroids, and by so-called short-period comets ? ones that come past repeatedly, like Halley?s comet.

?But asteroids and short-period comets come past again and again, so if we?re clever enough we can find them all and predict which, if any, will hit the Earth,? said Dr Francis. ?If we find one on a collision course with the Earth, we would normally have hundreds of years warning in which to do something about it, like deflecting the asteroid.

?The comets coming from beyond Pluto, so called long-period comets, are nastier, as they are totally unpredictable, and if we see one on a collision course we?d have at best one or two years warning ? not long enough to do anything.?

Dr Francis? research has been accepted for publication in the Astrophysical Journal. It was based on computer simulations, published data from the Lincoln Near Earth Asteroid Research Project at White Sands Missile Range in New Mexico, and on data from amateur astronomers around the world.

Original Source: ANU News Release

Astronomers using data from Spitzer and Deep Impact are preparing a comet “soup”. Image credit: NASA Click to enlarge
When Deep Impact smashed into comet Tempel 1 on July 4, 2005, it released the ingredients of our solar system’s primordial “soup.” Now, astronomers using data from NASA’s Spitzer Space Telescope and Deep Impact have analyzed that soup and begun to come up with a recipe for what makes planets, comets and other bodies in our solar system.

“The Deep Impact experiment worked,” said Dr. Carey Lisse of Johns Hopkins University’s Applied Physics Laboratory, Laurel, Md. “We are assembling a list of comet ingredients that will be used by other scientists for years to come.” Lisse is the team leader for Spitzer’s observations of Tempel 1. He presented his findings this week at the 37th annual meeting of the Division of Planetary Sciences in Cambridge, England.

Spitzer watched the Deep Impact encounter from its lofty perch in space. It trained its infrared spectrograph on comet Tempel 1, observing closely the cloud of material that was ejected when Deep Impact’s probe plunged below the comet?s surface. Astronomers are still studying the Spitzer data, but so far they have spotted the signatures of a handful of ingredients, essentially the meat of comet soup.

These solid ingredients include many standard comet components, such as silicates, or sand. And like any good recipe, there are also surprise ingredients, such as clay and chemicals in seashells called carbonates. These compounds were unexpected because they are thought to require liquid water to form.

“How did clay and carbonates form in frozen comets?” asked Lisse. “We don’t know, but their presence may imply that the primordial solar system was thoroughly mixed together, allowing material formed near the Sun where water is liquid, and frozen material from out by Uranus and Neptune, to be included in the same body.”

Also found were chemicals never seen before in comets, such as iron-bearing compounds and aromatic hydrocarbons, found in barbecue pits and automobile exhaust on Earth.

The silicates spotted by Spitzer are crystallized grains even smaller than sand, like crushed gems. One of these silicates is a mineral called olivine, found on the glimmering shores of Hawaii’s Green Sands Beach.

Planets, comets and asteroids were all born out of a thick soup of chemicals that surrounded our young Sun about 4.5 billion years ago. Because comets formed in the outer, chilly regions of our solar system, some of this early planetary material is still frozen inside them.

Having this new grocery list of comet ingredients means theoreticians can begin testing their models of planet formation. By plugging the chemicals into their formulas, they can assess what kinds of planets come out the other end.

“Now, we can stop guessing at what’s inside comets,” said Dr. Mike A’Hearn, principal investigator for the Deep Impact mission, University of Maryland, College Park. “This information is invaluable for piecing together how our own planets as well as other distant worlds may have formed.”

NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech. The University of Maryland, College Park, conducted the overall mission management for Deep Impact, and JPL handled project management for the mission for NASA’s Science Mission Directorate.

For more graphics and more information about Spitzer, visit http://www.spitzer.caltech.edu/Media/index.shtml .

Original source: NASA News Release

Comet Tempel 1. Image credit: NASA/JPL Click to enlarge
Painting by the numbers is a good description of how scientists create pictures of everything from atoms in our bodies to asteroids and comets in our solar system. Researchers involved in NASA’s Deep Impact mission have been doing this kind of work since the mission’s July 4th collision with comet Tempel 1.

“Prior to our Deep Impact experiment, scientists had a lot of questions and untested ideas about the structure and composition of the nucleus, or solid body of a comet, but we had almost no real knowledge,” said Deep Impact principal investigator Dr. Michael A’Hearn, a professor of astronomy at the University of Maryland, College Park. “Our analysis of data produced by Deep Impact is revealing a great deal, much of it rather surprising.”

For example, comet Tempel 1 has a very fluffy structure that is weaker than a bank of powder snow. The fine dust of the comet is held together by gravity. However, that gravity is so weak, if you could stand on the bank and jump, you would launch yourself into space.

Another surprise for A’Hearn and his colleagues was the evidence of what appears to be impact craters on the surface of the comet. Previously, two other comets had their nuclei closely observed and neither showed evidence of impact craters.

“The nucleus of Tempel 1 has distinct layers shown in topographic relief ranging from very smooth areas to areas with features that satisfy all the criteria for impact craters, including varying size,” A’Hearn said. “The problem in stating with certainty that these are impact craters is that we don’t know of a mechanism by which some comets would collide with the flotsam and jetsam in our solar system, while others would not.?

According to A’Hearn, one of the more interesting findings may be the huge increase in carbon-containing molecules detected in spectral analysis of the ejection plume. This finding indicates comets contain a substantial amount of organic material, so they could have brought such material to Earth early in the planet’s history when strikes by asteroids and meteors were common.

Another finding is the comet interior is well shielded from the solar heating experienced by the surface of the comet nucleus. Mission data indicate the nucleus of Tempel 1 is extremely porous. Its porosity allows the surface of the nucleus to heat up and cool down almost instantly in response to sunlight. This suggests heat is not easily conducted to the interior and the ice and other material deep inside the nucleus may be pristine and unchanged from the early days of the solar system, just as many scientists had suggested.

“The infrared spectrometer gave us the first temperature map of a comet, allowing us to measure the surface’s thermal inertia, or ability to conduct heat to the interior,” said Dr. Olivier Groussin, the University of Maryland research scientist who generated the map.

It is this diligent and time consuming analysis of spectral data that is providing much of the “color” with which Deep Impact scientists are painting the first ever detailed picture of a comet. For example, researchers recently saw emission bands for water vaporized by the heat of the impact, followed a few seconds later by absorption bands from ice particles ejected from below the surface and not melted or vaporized.

“In a couple of seconds the fast, hot moving plume containing water vapor left the view of the spectrometer, and we are suddenly seeing the excavation of sub-surface ice and dust,” said Deep Impact co-investigator Dr. Jessica Sunshine, with Science Applications International Corporation, Chantilly, Va. “It is the most dramatic spectral change I’ve ever seen.”

These findings are published in the September 9 issue of the journal Science, and were presented this week at the Division for Planetary Sciences meeting in Cambridge, England. Mission scientists are filling in important new portions of a cometary picture that is still far from finished.

The University of Maryland is responsible for overall Deep Impact mission science, and project management is handled by JPL. The spacecraft was built for NASA by Ball Aerospace & Technologies Corporation, Boulder, Colo. JPL is a division of the California Institute of Technology, Pasadena, Calif.

For more information about the Deep Impact mission on the Internet, visit: http://www.nasa.gov/deepimpact .

original Source: NASA News Release

999th and 1000th comets identified in SOHO images. Image credit: ESA/NASA Click to enlarge
On 5 August 2005, the ESA/NASA SOHO spacecraft achieved an incredible milestone – the discovery of its 1000th comet!

The 1000th comet was a Kreutz-group comet spotted in images from the C3 coronagraph on SOHO’s LASCO instrument by Toni Scarmato, from Calabria, Italy.
Just five minutes prior to discovering SOHO’s 1000th comet, Toni had also spotted SOHO’s 999th comet! These comets take Toni’s personal number of SOHO discoveries to 15.

Many SOHO comet discoveries have been by amateurs using SOHO images on the internet, and SOHO comet hunters come from all over the world. Toni Scarmato, a high school teacher and astrophysics graduate of the University of Bologna, said: ?I am very happy for this special experience that is possible thanks to the SOHO satellite and NASA-ESA collaboration.

“I want to dedicate the SOHO 1000th comet to my wife Rosy and my son Kevin to compensate for the time that I have taken from them to search for SOHO comets.”

The SOHO team also held a contest over the internet to guess the time when the 1000th comet would be discovered. The contest winner is Andrew Dolgopolov of Dublin, Ireland, who guessed the time of the comet?s closest approach to the Sun (perihelion time) within 22 minutes.

SOHO, the Solar and Heliospheric Observatory , is a joint effort between NASA and ESA and is now in its tenth year of operation. Although it was originally planned as a solar and heliospheric mission, it was optimistically hoped that LASCO might observe at least a handful of ?sungrazer? comets, based on the success of the SOLWIND coronagraph in the late 1970s and 1980s, which discovered a small number of very bright Kreutz-group comets.
It was not long after SOHO began sending down a steady stream of data in 1996 that SOHO scientists spotted a Kreutz-group comet in LASCO images. Soon, several more comets had been found and word started to spread of SOHO?s potential as a comet discoverer.

In 2000, amateur astronomer Mike Oates started to search the SOHO images, which had recently became available via the internet. He soon revealed just how much potential SOHO had by quickly spotting over 100 comets in LASCO images.

Almost all SOHO’s comets are discovered using images from its LASCO instrument, the Large Angle and Spectrometric Coronagraph. LASCO is used to observe the faint, multimillion-degree outer atmosphere of the Sun, called the corona. A disk in the instrument is used to make an artificial eclipse, blocking direct light from the Sun so the much fainter corona can be seen. Sungrazing comets are discovered when they enter LASCO’s field of view as they pass close by the Sun.

As time passed, more professional astronomers, as well as amateur enthusiasts from all over the world, joined the search for SOHO comets. In August 2002, Rainer Kracht (now the leading SOHO comet discoverer, with over 150 SOHO comets) spotted SOHO?s 500th comet. This in itself was an achievement that none of the SOHO/LASCO scientists ever imagined would, or could, happen.

However, just three years later, SOHO, with 1000 comet discoveries, is responsible for almost half of all officially recorded comets in history! Add to this the fact that the SOHO mission has completely revolutionised solar physics and the understanding of the Sun, and it shows just how truly amazing the SOHO spacecraft is!

Original Source: ESA Portal

The huge plume of material shooting out of Comet Tempel 1. Image credit: NASA/JPL. Click to enlarge.
Data from Deep Impact’s instruments indicate an immense cloud of fine powdery material was released when the probe slammed into the nucleus of comet Tempel 1 at about 10 kilometers per second (6.3 miles per second or 23,000 miles per hour). The cloud indicated the comet is covered in the powdery stuff. The Deep Impact science team continues to wade through gigabytes of data collected during the July 4 encounter with the comet measuring 5-kilometers-wide by 11-kilometers-long (about 3-miles-wide by 7-miles-long).

“The major surprise was the opacity of the plume the impactor created and the light it gave off,” said Deep Impact Principal Investigator Dr. Michael A’Hearn of the University of Maryland, College Park. “That suggests the dust excavated from the comet’s surface was extremely fine, more like talcum powder than beach sand. And the surface is definitely not what most people think of when they think of comets — an ice cube.”

How can a comet hurtling through our solar system be made of a substance with less strength than snow or even talcum powder?

“You have to think of it in the context of its environment,” said Dr. Pete Schultz, Deep Impact scientist from Brown University, Providence, R.I. “This city-sized object is floating around in a vacuum. The only time it gets bothered is when the Sun cooks it a little or someone slams an 820-pound wakeup call at it at 23,000 miles per hour.”

The data review process is not overlooking a single frame of approximately 4,500 images from the spacecraft’s three imaging cameras taken during the encounter.

“We are looking at everything from the last moments of the impactor to the final look-back images taken hours later, and everything in between,” added A’Hearn. “Watching the last moments of the impactor’s life is remarkable. We can pick up such fine surface detail that objects that are only four meters in diameter can be made out. That is nearly a factor of 10 better than any previous comet mission.”

The final moments of the impactor’s life were important, because they set the stage for all subsequent scientific findings. Knowing the location and angle the impactor slammed into the comet’s surface is the best place to start. Engineers have established the impactor took two not unexpected coma particle hits prior to impact. The impacts slewed the spacecraft’s camera for a few moments before the attitude control system could get it back on track. The penetrator hit at an approximately 25 degree oblique angle relative to the comet’s surface. That’s when the fireworks began.

The fireball of vaporized impactor and comet material shot skyward. It expanded rapidly above the impact site at approximately 5 kilometers per second (3.1 miles per second). The crater was just beginning to form. Scientists are still analyzing the data to determine the exact size of the crater. Scientists say the crater was at the large end of original expectations, which was from 50 to 250 meters (165 to 820 feet) wide.

Expectations for Deep Impact’s flyby spacecraft were exceeded during its close brush with the comet. The craft is more than 3.5 million kilometers (2.2 million miles) from Tempel 1 and opening the distance at approximately 37,000 kilometers per hour (23,000 miles per hour). The flyby spacecraft is undergoing a thorough checkout, and all systems appear to be in excellent operating condition.

The Deep Impact mission was implemented to provide a glimpse beneath the surface of a comet, where material from the solar system’s formation remains relatively unchanged. Mission scientists hoped the project would answer basic questions about the formation of the solar system by providing an in-depth picture of the nature and composition of comets.

The University of Maryland is responsible for overall Deep Impact mission science, and project management is handled by JPL. The spacecraft was built for NASA by Ball Aerospace & Technologies Corporation, Boulder, Colo. JPL is a division of the California Institute of Technology, Pasadena, Calif.

Original Source: NASA News Release

X-ray detections from Tempel 1 after Deep Impact collision. Image credit: Swift. Click to enlarge.
Here come the X-rays, on cue. Scientists studying the Deep Impact collision using NASA’s Swift satellite report that comet Tempel 1 is getting brighter and brighter in X-ray light with each passing day.

The X-rays provide a direct measurement of how much material was kicked up in the impact. This is because the X-rays are created by the newly liberated material lifted into the comet’s thin atmosphere and illuminated by the high-energy solar wind from the Sun. The more material liberated, the more X-rays are produced.

Swift data of the water evaporation on comet Tempel 1 also may provide new insights into how solar wind can strip water from planets such as Mars.

“Prior to its rendezvous with the Deep Impact probe, the comet was a rather dim X-ray source,” said Dr. Paul O’Brien of the Swift team at the University of Leicester. “How things change when you ram a comet with a copper probe traveling over 20,000 miles per hour. Most of the X-ray light we detect now is generated by debris created by the collision. We can get a solid measurement of the amount of material released.”

“It takes several days after an impact for surface and sub-surface material to reach the comet’s upper atmosphere, or coma,” said Dr. Dick Willingale, also of the University of Leicester. “We expect the X-ray production to peak this weekend. Then we will be able to assess how much comet material was released from the impact.”

Based on preliminary X-ray analysis, O’Brien estimates that several tens of thousands of tons of material were released, enough to bury Penn State’s football field under 30 feet of comet dust. Observations and analysis are ongoing at the Swift Mission Operations Center at Penn State University as well as in Italy and the United Kingdom.

Swift is providing the only simultaneous multi-wavelength observation of this rare event, with a suite of instruments capable of detecting visible light, ultraviolet light, X-rays, and gamma rays. Different wavelengths reveal different secrets about the comet.

The Swift team hopes to compare the satellite’s ultraviolet data, collected hours after the collision, with the X-ray data. The ultraviolet light was created by material entering into the lower region of the comet’s atmosphere; the X-rays come from the upper regions. Swift is a nearly ideal observatory for making these comet studies, as it combines both a rapidly responsive scheduling system with both X-ray and optical/UV instruments in the same satellite.

“For the first time, we can see how material liberated from a comet’s surface migrates to the upper reaches of its atmosphere,” said Prof. John Nousek, Director of Mission Operations at Penn State. “This will provide fascinating information about a comet’s atmosphere and how it interacts with the solar wind. This is all virgin territory.”

Nousek said Deep Impact’s collision with comet Tempel 1 is like a controlled laboratory experiment of the type of slow evaporation process from solar wind that took place on Mars. The Earth has a magnetic field that shields us from solar wind, a particle wind composed mostly of protons and electrons moving at nearly light speed. Mars lost its magnetic field billions of years ago, and the solar wind stripped the planet of water.

Comets, like Mars and Venus, have no magnetic fields. Comets become visible largely because ice is evaporated from their surface with each close passage around the Sun. Water is dissociated into its component atoms by the bright sunlight and swept away by the fast-moving and energetic solar wind. Scientists hope to learn about this evaporation process on Tempel 1 now occurring quickly — over the course of a few weeks instead of a billion years — as the result of a planned, human intervention.

Swift’s “day job” is detecting distant, natural explosions called gamma-ray bursts and creating a map of X-ray sources in the universe. Swift’s extraordinary speed and agility enable scientists to follow Tempel 1 day by day to see the full effect from the Deep Impact collision.

The Deep Impact mission is managed by NASA’s Jet Propulsion Laboratory, Pasadena, California. Swift is a medium-class NASA explorer mission in partnership with the Italian Space Agency and the Particle Physics and Astronomy Research Council in the United Kingdom, and is managed by NASA Goddard. Penn State controls science and flight operations from the Mission Operations Center in University Park, Pennsylvania. The spacecraft was built in collaboration with national laboratories, universities and international partners, including Penn State University; Los Alamos National Laboratory, New Mexico; Sonoma State University, Rohnert Park, Calif.; Mullard Space Science Laboratory in Dorking, Surrey, England; the University of Leicester, England; Brera Observatory in Milan; and ASI Science Data Center in Frascati, Italy.

Original Source: PSU News Release

False colour image of Tempel 1 taken by Gemini North. Image credit: Gemini. Click to enlarge.
The Gemini North telescope on Mauna Kea successfully captured the dramatic fireworks display produced by the collision of NASA’s Deep Impact probe with Comet 9P/Tempel 1. Researchers in two control rooms on Hawaii?s Big Island (on Mauna Kea and in Hilo) were able to keep enough composure amid an almost giddy excitement to perform a preliminary analysis of the data. They concluded from the mid-infrared spectroscopic observations that there was strong evidence for silicates or rocky material exposed by the impact. Little doubt remains that the unprecedented quality of the Gemini data will keep astronomers busy for years.

?The properties of the mid-infrared light were completely transformed after impact,? said David Harker of the University of San Diego, co-investigator for the research team. ?In addition to brightening by a factor of about 4, the characteristics of the mid-infrared light was like a chameleon and within five minutes of the collision it looked like an entirely new object.? Harker?s research partner Chick Woodward of the University of Minnesota speculated further, ?We are possibly seeing crystalline silicates which might even be similar to the beach sand here in Hawaii! This data will keep us busy trying to figure out the size and composition of these grains to better understand the similarities and differences between the material contained within comets and other bodies in the solar system.?

In addition to the spectroscopic observations, before-and-after images were also obtained by the Gemini telescope in thermal infrared light and can be seen in Figure 1. Gemini monitored the comet for several weeks prior to the impact and will continue to watch it through the end of July.

The Gemini observations were part of a coordinated effort between the W.M. Keck, Subaru and Gemini Observatories so that each could concentrate on different observations and provide a complete, complementary ?picture? of the impact. Astronomers anticipate that the data gathered from the largest and most sophisticated set of telescopes positioned to see the impact will add considerably to our understanding of comets as dynamic probes of our solar system?s early evolution some 4.5-5 billion years ago.

The Gemini observations were made using Michelle, the facility mid-infrared imager/spectrograph built at the Royal Observatory of Edinburgh (ROE) in the UK. The instrument has unique capabilities in the mid-infrared especially at Gemini which uses protected silver coatings on main mirrors to provide exceptional performance in the ?thermal? or mid-infrared part of the spectrum.

Original Source: Gemini Observatory News Release

Swift’s view of Comet Tempel 1. Image credit: PSU. Click to enlarge.
Scientists using the Swift satellite witnessed a tale of fire and ice today, as NASA’s Deep Impact probe slammed into the frozen comet Tempel 1. The collision briefly lit the dim comet’s surface and exposed, for the first time, a section of ancient and virgin material from the comet’s interior.

Swift is providing the only simultaneous multi-wavelength observation of this rare event, with a suite of instruments capable of detecting optical light, ultraviolet, X-rays and gamma rays. Different wavelengths reveal different secrets about the comet.

So far, after a set of eight observations each lasting about 50 minutes, Swift scientists have seen a quick and dramatic rise in ultraviolet light, evidence that the Deep Impact probe struck a hard surface, as opposed to a softer, snowy surface.

More observations and analysis are expected in the coming days from teams at NASA and Penn State and in Italy and the United Kingdom.

“We have now observed this comet before, during, and after the collision,” said Dr. Sally Hunsberger of the Swift Mission Operation Center at Penn State. “The comparison of observations at different times — that is, what was seen, when and at what wavelength — should prove to be quite interesting.”

Most of the debris observed in ultraviolet light likely came from once-icy surface material heated to 2,000 degrees by the impact. X-rays have not been detected yet but analysis will continue throughout the week. X-rays are expected to be emitted from newly liberated sub-surface material lifted into the comet’s coma, which is then illuminated by the high-energy solar wind from the Sun. It takes about a day, however, for the material to reach the coma.

“Some called it fireworks today, but it really was more like ‘iceworks,'” said Prof. Keith Mason, Director of Mullard Space Science Laboratory at University College London, who organized the Swift observations. “Much of the comet is ice. It’s the other stuff deep inside we’re most interested in — pristine material from the formation of the solar system locked safely below the comet’s frozen surface. We don’t know exactly what we kicked up yet.”

Swift’s “day job” is detecting distant, natural explosions called gamma-ray bursts and creating a map of X-ray sources in the universe, far more energetic “fireworks.” Indeed, since beginning this Deep Impact campaign on July 1 — in addition to seeing comet Tempel 1 — Swift has seen a gamma-ray burst and a supernova and has discovered a black hole in the Milky Way galaxy. The satellite’s speed and agility, however, provides an important complement to the dozens of other world-class observatories in space and on Earth observing the Deep Impact experiment. Swift will continue to monitor the comet this week.

Comets are small astronomical objects usually in highly elliptical orbits around the sun. They are made primarily of frozen water, methane and carbon dioxide with a small amount of minerals. They likely originate in the Oort Cloud in the outskirts of the solar system. Comet Tempel 1 is about the size of Washington, D.C. Some scientists say that comets crashing into Earth billions of years ago brought water to our planet.

A comet becomes visible when radiation from the Sun evaporates its outer layers, creating a coma, the thin atmosphere. Solar wind impacts the coma to form the comet’s tail of dust and gas, which always points away from the Sun. Comets are best visible when they enter the inner solar system, closer to the Sun.

“The Deep Impact collision was the most watched astronomical event of the year,” said Dr. Neil Gehrels, Swift Principal Investigator at NASA Goddard Space Flight Center in Greenbelt, Md. “All the ‘big-guns’ observatories tracked it. In the next few days, as material continues to fly off the comet from newly created vents, we will see whether Swift can offer new insight into comets by virtue of the high-energy light we are seeing.”

Prof. Mason and Prof. Alan Wells of the University of Leicester in England are at the Swift Mission Operation Center to help with the observation.

The Deep Impact mission is managed by NASA’s Jet Propulsion Laboratory, Pasadena, California. Swift is a medium-class NASA explorer mission in partnership with the Italian Space Agency and the Particle Physics and Astronomy Research Council in the United Kingdom, and is managed by NASA Goddard. Penn State controls science and flight operations from the Mission Operations Center in University Park, Pennsylvania. The spacecraft was built in collaboration with national laboratories, universities and international partners, including Penn State University; Los Alamos National Laboratory, New Mexico; Sonoma State University, Rohnert Park, Calif.; Mullard Space Science Laboratory in Dorking, Surrey, England; the University of Leicester, England; Brera Observatory in Milan; and ASI Science Data Center in Frascati, Italy.

Original Source: PSU News Release

The brilliant flash of light created by Deep Impact as it smashed into Tempel 1. Image credit: NASA/JPL. Click to enlarge.
The hyper-speed demise of NASA’s Deep Impact probe generated an immense flash of light, which provided an excellent light source for the two cameras on the Deep Impact mothership. Deep Impact scientists theorize the 820-pound impactor vaporized deep below the comet’s surface when the two collided at 1:52 am July 4, at a speed of about 10 kilometers per second (6.3 miles per second or 23,000 miles per hour).

“You can not help but get a big flash when objects meet at 23,000 miles per hour,” said Deep Impact co-investigator Dr. Pete Schultz of Brown University, Providence, R.I. “The heat produced by impact was at least several thousand degrees Kelvin and at that extreme temperature just about any material begins to glow. Essentially, we generated our own incandescent photo flash for less than a second.”

“They say a picture can speak a thousand words,” said Deep Impact Project Manager Rick Grammier of NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “But when you take a look at some of the ones we captured in the early morning hours of July 4, 2005 I think you can write a whole encyclopedia.”

At a news conference held later on July 4, Deep Impact team members displayed a movie depicting the final moments of the impactor’s life. The final image from the impactor was transmitted from the short-lived probe three seconds before it met its fiery end.

“The final image was taken from a distance of about 30 kilometers (18.6 miles) from the comet’s surface,” said Deep Impact Principal Investigator Dr. Michael A’Hearn of the University of Maryland, College Park. “From that close distance we can resolve features on the surface that are less than 4 meters (about 13 feet) across. When I signed on for this mission I wanted to get a close-up look at a comet, but this is ridiculous? in a great way.”

The Deep Impact scientists are not the only ones taking a close look at their collected data. The mission’s flight controller team is analyzing the impactor’s final hours of flight. When the real-time telemetry came in after the impactor’s first rocket firing, it showed the impactor moving away from the comet’s path.

“It is fair to say we were monitoring the flight path of the impactor pretty closely,” said Deep Impact navigator Shyam Bhaskaran of JPL. “Due to the flight software program, this initial maneuver moved us seven kilometers off course. This was not unexpected but at the same time not something we hoped to see. But then the second and third maneuvers put us right where we wanted to be.”

The Deep Impact mission was implemented to provide a glimpse beneath the surface of a comet, where material from the solar system’s formation remains relatively unchanged. Mission scientists hoped the project would answer basic questions about how the solar system formed, by providing an in-depth picture of the nature and composition of the frozen celestial travelers known as comets. The University of Maryland is responsible for overall Deep Impact mission science, and project management is handled by JPL. The spacecraft was built for NASA by Ball Aerospace & Technologies Corporation, Boulder, Colo.

For information about Deep Impact on the Internet, visit http://www.nasa.gov/deepimpact.

Original Source: NASA News Release