NASA declares End of Deep Impact Comet Hunter Mission

September 21, 2013

NASA has officially ended the Deep Impact Comet Research Mission after being unable to communicate with the spacecraft for over a month, bringing a nearly nine-year mission of discovery to a close.

Deep Impact performed a successful deployment of an impactor and a flyby of comet Tempel 1 and an additional flyby of comet Hartley 2 returning hundreds of thousands of photos and unprecedented scientific data. Launched on January 12, 2005 atop a Delta II Rocket from Cape Canaveral, Deep Impact set out to answer fundamental questions about comets - their composition, formation and origin.

Image: NASA/JPL/Caltech

After 174 days of cruising through space, the 3.2 by 1.7 by 2.3-meter Deep Impact spacecraft reached Tempel 1 and deployed its impactor - a 370-Kilogram copper projectile equipped with navigation systems and thrusters that was sent on its way for a high-speed collision with the comet.

Image: NASA/JPL/Caltech/UMD

Image: NASA/JPL/Caltech/UMD

On July 4, 2005 at 5:45 UTC, the impact occurred at a relative speed of 10.3 kilometers per second creating a 30-meter deep and 100-meter wide crater that was discovered years after the impact.

The event was heavily studied from a number of vantage points - the instrumented impactor returned close-up images until about three seconds before impact while the Flyby spacecraft had its instruments pointed at the comet to gather data during the impact - obtaining visible and infrared imagery and spectra to provide data on the composition of the impact ejecta and comet nucleus as the vehicle passed within 500 Kilometers of the comet. Additionally, many earth-based and space-based observatories were used to take images and spectroscopic data.

NASA's Swift X-Ray Telescope continued watching the comet after the impact and concluded that outgassing continued for a total of 13 days and a total of 10 to 25 Million Kilograms of dust and 5 Million Kilograms of water were lost from the impact. This result was surprising because it showed that the comet contained much more dust and less water than expected by the science community.

The flash created by the impact as the coffee-table-sized impactor was atomized was much fainter than anticipated which indicated that the comet has a thin surface layer of high porosity with 75% empty space which stood in contrast with existing theories of comets having a solid crust that impeded outgassing.

It was also revealed that Tempel 1 contains clays, carbonates, silicates and sodium which is rather uncommon in space. Based on its interior chemistry, Tempel 1 likely formed in the Uranus and Neptune region of the Oort Cloud, scientists concluded.

"Six months after launch, this spacecraft had already completed its planned mission to study comet Tempel 1," said Tim Larson, project manager of Deep Impact at JPL. "But the science team kept finding interesting things to do, and through the ingenuity of our mission team and navigators and support of NASA’s Discovery Program, this spacecraft kept it up for more than eight years, producing amazing results all along the way."

Image: NASA/JPL/Caltech/UMD

Image: NASA/JPL/Caltech/UMD

Following its Flyby of Tempel 1, Deep Impact was put on a trajectory for a close encounter with Earth in order to alter its course for a Flyby of Comet Boethin to use its spectrometer and imagers to study the composition of that comet, but as the Earth Flyby approached, the target comet likely broke up into pieces, becoming impossible to track. Mission Controllers quickly had to switch to a new target which became Comet Hartley 2, requiring an extra two-years of transit time for the spacecraft.

Along the way, Deep Impact studied a number of object including six stars to confirm the motion of Exoplanets around them. Deep Impact also provided data of Earth, the Moon and Mars. From a distance of 50 Million Kilometers to Earth, Deep Impact returned breath-taking images of the Moon passing in front of the planet. The images show remarkable detail including oceans, continents and clouds as the Moon passed the planet Deep Impact once launched from.

Photo: NASA Goddard, Donald J. Lindler, Sigma Space Corporation, UMD

Finally, on November 4, 2010, the spacecraft flew past Comet Hartley 2 coming within 700 Kilometers of its nucleus to acquire detailed photographs and data.

A number of bright jets were observed and high resolution imagery of the comet's surroundings revealed the presence of icy grains in the coma that are driven out of the nucleus by the outgassing of carbon dioxide. These grains explained why many comets produced more water vapor than should be possible by sublimation of water ice from the nucleus - a question that had been puzzling scientists for years.

Observations of Hartley 2 showed the importance of the relation of carbon dioxide and carbon monoxide that was different for short period comets and long-period comets. This difference confirmed that short-period comets formed closer to the sun than their long-period companions - contrary to the common belief that short-period comets formed in the Kuiper belt beyond Neptune, while the long-period comets formed in the vicinity of the giant planets.

Combining data of Tempel 1 and Hartley 2 pointed to a great chemical diversity in a comet's composition as the emission of water and carbon dioxide showed local variations across the two comet nuclei.

Image: NASA/JPL/Caltech/UMD

Image: NASA/JPL/Caltech/UMD

Image: NASA/JPL/Caltech/UMD

Image: NASA/JPL/Caltech/UMD

Image: NASA/JPL/Caltech/UMD

Emissions & Outgassing of Hartley 2

Comet Garradd was observed by Deep Impact in 2012 showing that its outgassing varied on a 10.4 hour period corresponding to its rotation period. Also, dry ice content of the comet was measured to be about ten percent of its water ice content.

In 2013 one of Deep Impacts last activities were a set of observations of comet ISON - returning infrared data, and light curves to assess to comets rotation rate in addition to visible-light images. Although ISON was still in the outer solar system, it already showed a tail of 64,400 Kilometers.

After a journey of 7.6 Billion Kilometers, Deep Impact made its final communication with Earth on August 8, 2013. Teams tried to send commands to the spacecraft for about four weeks to try and re-activate is systems, attempting to recover from an apparent computer problem that caused the spacecraft to lose control of its orientation in space.

Without attitude control, Deep Impact was no longer pointing its antennas at Earth and solar arrays toward the sun, making power generation and communications difficult. As a result, onboard equipment was likely ruined due to extreme thermal environments.

In September, attempts to communicate with Deep Impact were ceased and the mission's end was declared - concluding a mission that exceeded all expectations.

Image: NASA/JPL/Caltech/UMD

M11 - Wild Duck cluster

“Despite this unexpected final curtain call, Deep Impact already achieved much more than ever was envisioned," said Lindley Johnson, the Program Executive for the Deep Impact mission since a year before it launched. "Deep Impact has completely overturned what we thought we knew about comets and also provided a treasure trove of additional planetary science that will be the source data of research for years to come.”

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