Mission controllers from the University of Maryland-led EPOXI mission celebrated last week as NASA's Deep Impact space probe flew close by the Hartley 2 comet, sending back rare and valuable data about the comet. This is only the fifth time that a comet core has been viewed from such a near distance by a space probe, and it is hoped that by understanding comets better we can learn more about the origin and history of our solar system.
On November 4th at 10am EDT the spacecraft passed within 700 kilometers (435 miles) of the Hartley 2 comet, and within twenty minutes the first images of the encounter were being viewed 37 million kilometers (23 million miles) away on Earth. The initial images provided new information about the comet's volume – the peanut-shaped Hartley 2 comet is the smallest so far to be examined at such proximity – and showed jets of CO2 gas gushing from its surface in plumes.
“Early observations of the comet show that, for the first time, we may be able to connect activity to individual features on the nucleus. We certainly have our hands full," said Michael A'Hearn, University of Maryland astronomer. "The images are full of great cometary data, and that's what we hoped for.” A'Hearn is one of the originators of, and science team leader for, both the Deep Impact mission and its follow-on mission EPOXI.
"There'll be enough data downloaded to keep researchers busy for the next five, 10, 15 years probably. It's proving to be very interesting," said Malcolm Hartley, the man who discovered the comet in 1986.
Comets are believed to be made up of leftover debris material that didn't get incorporated into the planets at the birth of the solar system, and remain gravitationally bound to the sun. As they are thought to be composed of unchanged primitive material, they are extremely interesting to scientists who wish to learn about conditions during the early stages of the solar system.
Hartley 2 is the fifth comet nucleus visited by any spacecraft and the second one visited by the Deep Impact spacecraft. Launched in January 2005, Deep Impact found widespread fame when it slammed a probe into the Tempel 1 comet on July 4th that year. It was this successful mission that won approval for the spacecraft to study a second comet.
The name EPOXI is itself a combination of the names for two extended missions; the extrasolar planet observations, known as Extrasolar Planet Observations and Characterization (EPOCh), and the flyby of comet Hartley 2, known as the Deep Impact Extended Investigation (DIXI). During the EPOCh phase of EPOXI, the Deep Impact spacecraft provided information on possible extrasolar planets and was one of three spacecraft that for the first time found clear evidence of water on Moon. It has also provided data for a publication due to be published in the Astrophysical Journal, about identifying planetary bodies by their colors, which could help us to identify planets similar to Earth.