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Deep Impact Blasted Comet

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WHAT'S NEXT FOR DEEP IMPACT? »

NASA artist concept of Deep Impact encountering the comet
Deep Impact fires projectile into Comet Tempel 1
click to enlarge nasa artist concept
NASA's Deep Impact robot explorer arrived at the nucleus of Comet Tempel 1 as scheduled on July 4, 2005, and promptly blasted a hole in the face of that small black body.

The spacecraft, about the size of a small car, accomplished its main assignment as it flew past the comet by sending a hefty 820-lb. copper-clad projectile smashing into the surface of the dirty snowball at 22,680 miles per hour. That speed is about the equivalent of traveling all the way across the United States in less than eight minutes.

The crash probably created a spectacular crater the size of a football field and more than 65 feet deep. Material was seen spewing out at impact.

Photography. As the 1,325-lb. main spacecraft flew by, it monitored the impact from a distance of about 5,000 miles with a high-resolution telephoto camera focused on the crater and a medium-resolution wide-angle camera recording the broader view. The impactor had a medium-resolution camera that recorded images as late as three seconds before the probe collided with the comet.

The impact was the first ever attempt to peer beneath the surface of a comet to see freshly exposed pristine interior ice and mud. Scientists hoped the new information about the internal composition and structure of a comet would reveal clues to the early formation of our Solar System.

Big splash. The impactor was about the size of a washing machine. It flew in and positioned itself in front of the comet, a hulking black object traveling through space at 6.3 miles per second. That's about 22,680 mph.

The 3.7-mile-wide comet ran into the impactor creating a huge explosion that was said to be equivalent to five tons of TNT. The crash created an impact crater in the comet's surface the length of a football stadium and from 2 to 14 stories deep. The heat produced briefly by the crash was several thousand degrees.

The comet was described variously as shaped like a potato or a pickle.
What is a comet?

Comets are odd-shaped chunks of dust and ice that were born along with the Solar System and now orbit the Sun. When a mammoth cloud of gas and dust condensed 4.5 billion years ago to form the Sun and planets, comets were formed from the left overs.

Today, we see comets as small astronomical objects, typically about the size of a mountain on Earth and something like an asteroid, but composed largely of ice rather than rock.

Comets are mostly frozen carbon dioxide, methane, water, dust and minerals.

Those dirty snowballs are believed to hold dust samples from the earliest history of our Solar System. Comets have been seen and reported since antiquity.

They travel highly elongated orbits around the Sun. Comets are too small to be seen from Earth when they are in the far outer regions of the Solar System.

When a comet nears the Sun, heat vaporizes some of the ice producing a cloud, or coma, of gas around the nucleus. As the nucleus melts, it drags behind it a tail of dust and gas. The solar wind drives ice away from the comet creating a tail. Sometimes a coma bloats out a million miles from the nucleus and the tail is millions of miles long.

Comets become visible to us on Earth when they approach the Sun and some melting occurs.

Scientists think comets probably contain matter left over from the birth of the Sun, planets and the Solar System because most comets seem to have formed at the same as the Solar System – an estimated 4.6 billion year ago. During those eons, comets have preserved their interior materials as if they were in a deep freeze.
Astronomers watched. A comet is a small astronomical object consisting mostly of frozen gases, water and dust. They are too small to be seen when they are in the outer regions of the Solar System. However, when a comet nears the Sun, heat vaporizes some of the ice producing a cloud around the the nucleus and a long tail of dust and gas. They sometimes then become visible to us on Earth.

At 83 million miles from Earth, Comet Tempel 1 was near the Sun, but still 100 times too dim to be seen with the naked eye on Earth. However, the cone-shaped plume of debris sprayed into space as the impactor crashed into it made the comet more visible from Earth with small telescopes. It became six times brighter as seen on Earth in the moments after the crash.

News reports from around the world indicated more than 100 professional astronomers at 60 observatories and a great many amateur astronomers peered through their telescopes at the action on Tempel 1.

Space telescopes. While orbiting in space around Earth, the Hubble, Chandra, Spitzer, Galex and SWAS space telescopes turned to observe the event. The European interplanetary probe Rosetta, on its way to explore another comet, also turned an eye toward the event.

Observations by telescopes on Earth and in orbit complimented the data sent home by the Deep Impact main spacecraft.

Tempel 1 was Discovered in 1867. It revolves around the Sun in an elliptical orbit between Mars and Jupiter completing a trip in about six years.

The flight out from Earth. Deep Impact was one of NASA's discovery mission spacecraft sent 83 million miles across the Solar System to explore the interior of the nucleus of the comet. It was launched January 12, 2005, aboard a Delta 2 rocket from pad 17-B at Cape Canaveral Air Force Station, Florida.

A different spacecraft, Stardust, had taken pictures of the nucleus of comet Wild 2 during a fly-by in January 2004. The difference here was the projectile fired by Deep Impact actually dug a hole in the heart of Comet Tempel 1 so scientists could see some of the small body's interior.

At the end of the six-month trip to the comet, the impactor was released from the main spacecraft 24 hours before the impact on Tempel 1. The battery-powered impactor first tumbled in free flight, then maneuvered by autopilot into the path of the comet during its final two hours of flight. It fired thrusters to keep it on course as it headed toward a bright spot on the comet nucleus.

Tough target. Rick Grammier, Deep Impact project manager, told news media at NASA's Jet Propulsion Lab (JPL) that it was like "a bullet trying to hit a second bullet with the third bullet."

Lots of public interest in the event was reported. For instance, some 10,000 persons crammed Hawaii's Waikiki Beach to see video of the impact projected on a big movie screen.

Postcards sent home. Deep Impact had started sending pictures to Earth two months prior to arrival at Comet Tempel 1. It took its first photograph of Tempel 1 from 40 million miles away in April 2005. Then, while still 20 million miles out in June 2005, Deep Impact snapped an image of the comet's solid core for the first time.

Later, after it was released and on its way in to intersect with the comet, the impactor also record images and gathered data. It sent images until just three seconds before it was run over by the comet. The last picture, snapped just 18.6 miles above the comet's surface, showed features as small 10 feet wide.

During its close-observation flyby, the main spacecraft traveled as close as 310 miles from the comet. It observed the impact, the ejected matter, and the composition and structure of the comet interior. The time from the impact to the end of the flyby was about 800 seconds.

Real-time data. Data returned to Earth in real time included optical images from the impactor and the main spacecraft as well as spectral measurements by the main spacecraft. The rest of the data was stored during the flyby and radioed to Earth afterward. The main spacecraft sent pictures for 24 hours after the impact.

Because Deep Impact was such a great distance away, radio signals took 7.5 minutes to travel from spacecraft to Earth. Of course, radio commands from Earth to the spacecraft took the same length of time, 7.5 minutes. The speed of a radio signal is the same as the speed of light – about 186,500 miles per second.

Deep Impact Events
Launch 2005
Jan 12
Comet Temple photography begins 60 days before impact. 2005
May
The 820-lb. copper impactor released 24 hours before impact. 2005
July 3
Spacecraft flyby deflection maneuver. 2005
July 3
Deep Impact observes the impact crater for 14 minutes as it flies over the comet. 2005
July 4
Deep Impact waits five minutes as it passes debris in the comet tail, then turns to observe the departing comet for 24 hours. 2005
July 5
Data is sent to NASA's 210-ft. Deep Space Network antennas during impact and to 112-ft. antennas for one more week. 2005
July 11
Deep Impact science. The objectives of the Deep Impact project scientists were: What had astronomers expected to see after the projectile plowed into the four-mile-wide comet? Scientists had said that it was not very likely the impact could have created such a huge shockwave that the comet would have broken apart.

Did it move the comet? Could the impact have knocked the comet off its path and sent it toward Earth? No, NASA said there was no measurable change in the comet's orbit and no threat to distant Earth.

The space agency said the collision between the impactor and comet was like a pebble hitting a semi-truck traveling the freeway. There was a physical effect, but not enough force to knock the truck off the road or divert it from its path.

Is this mission really a test to see how to blow up a comet or to give the military information for their work? No, NASA said. The mission was funded as a science project. Its objectives were to study the inside of a comet to gain more knowledge about the structure and composition. New information from this mission was combined with data from other missions to give us a better overall understanding of comets. This mission was funded solely for the purpose of gaining new science knowledge, the space agency said.

NASA artist concept of Deep Impact encountering the comet
Deep Impact approaches Comet Tempel 1. The flyby spacecraft in the foreground has just released the impactor, seen in this NASA artist concept as a yellow object in the middle distance. The comet is the white object with tail in the background.
click to enlarge
Of course, it would be valuable to know what might push away a comet or asteroid heading toward Earth. Such a doomsday rock, as these near-Earth objects have been called, could cause catastrophic damage to parts of our planet if one were to hit Earth.

Scientists wonder if there are hard-to-see dormant comets moving through space as dark near-Earth objects.

What are we after? With spacecraft such as Deep Impact, Stardust and Rosetta, scientists are looking for answers to questions about comets: Discovery missions. The Deep Impact project was a partnership of NASA's Jet Propulsion Laboratory (JPL), the University of Maryland, and Ball Aerospace. The university was responsible for the science instruments. The project was managed by JPL. The spacecraft was built by Ball Aerospace & Technologies Corporation, Boulder, Colorado.

Deep Impact was NASA's eighth Discovery Program spacecraft. The program prepares and operates low-budget science missions. The Deep Impact project cost $330 million.

Other Discovery spacecraft have included Near-Shoemaker that landed on asteroid Eros, the Mars Pathfinder lander with Sojourner rover, and the solar wind collection spacecraft Genesis, which crashed into the Earth when its parachutes failed to open on descent.

Stardust flew within 147 miles of Comet Wild 2 and will return to Earth with interstellar dust samples in January 2006.


What's Next for Deep Impact?

While NASA has not approved a specific future mission, the space agency has given JPL scientists the go-ahead to bring the interplanetary probe closer to Earth's orbit and plan for some future explorations.

JPL found Deep Impact's main spacecraft in good condition despite being sandblasted by debris from the impactor collision with Comet Tempel 1.

Controllers fired Deep Impact's thrusters on July 20, 2005, to change to a course that will bring it back near Earth by 2008. The spacecraft will fly in a mode designed to conserve energy until it receives orders for a second mission.

Comet 85P/Boethin. Deep Impact might be steered toward Comet 85P/Boethin, which was discovered in 1975 and circles around the Sun every 11 years.

The spacecraft does not have another impactor, but it would be able to use its science instruments to collect date on a second comet and radio the information back to Earth.

Where the original Deep Impact mission cost $333 million, an extension might cost only an additional $32 million.

When the July 4, 2005, impactor collision took place 83 million miles from Earth, two flashes of bright light were seen and a crater was carved into the potato-shaped comet. A larger-than-expected debris cloud extended thousands of miles into space, and has prevented scientists from peering into the comet's interior.

The impactor vaporized as it crashed on the comet's sunlit side, but the mothership survived unharmed. After the collision, the main spacecraft flew within 310 miles of Tempel 1 and took pictures of the comet as it flew away.

Learn more:
NASA:
European Space Agency: 		University of Maryland: Space Today Online: Reports from other observers:

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