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Close-up look at a comet

Comet Hartley 2

First views of comet Hartley 2, courtesy NASA / JPL-Caltech / UMD.

NASA’s EPOXI mission spacecraft successfully flew past Comet Hartley 2 at 1:00am Sydney time Friday. Scientists say initial images from the flyby provide new information about the comet’s volume and material spewing from its surface.

“Early observations of the comet show that, for the first time, we may be able to connect activity to individual features on the nucleus,” said EPOXI principal investigator Michael A’Hearn of the University of Maryland, College Park. “We certainly have our hands full. The images are full of great cometary data, and that’s what we hoped for.”

EPOXI is an extended mission that uses the already in-flight Deep Impact spacecraft. Its encounter phase with Hartley 2 began on November 3, when the spacecraft began to point its two imagers at the comet’s nucleus. Imaging of the nucleus began one hour later.

“The spacecraft has provided the most extensive observations of a comet in history,” said Ed Weiler, associate administrator for NASA’s Science Mission Directorate at the agency’s Headquarters in Washington. “Scientists and engineers have successfully squeezed world-class science from a re-purposed spacecraft at a fraction of the cost to taxpayers of a new science project.”

Comet Hartley 2

A view of Hartley 2 as the EPOXI mission approached the comet, courtesy NASA / JPL-Caltech / UMD

Comet Hartley 2

Hartley 2 is an unusually active comet, emitting streams of gas and dust. Courtesy NASA / JPL-Caltech / UMD.

Images from the EPOXI mission reveal Comet Hartley 2 to have 100 times less volume than comet Tempel 1, the first target of Deep Impact. More revelations about Hartley 2 are expected as analysis continues.

Initial estimates indicate the spacecraft was about 700 kilometres from the comet at the closest-approach point. That’s almost the exact distance that was calculated by engineers in advance of the flyby.

“It is a testament to our team’s skill that we nailed the flyby distance to a comet that likes to move around the sky so much,” said Tim Larson, EPOXI project manager at NASA’s Jet Propulsion Laboratory. “While it’s great to see the images coming down, there is still work to be done. We have another three weeks of imaging during our outbound journey.”

The name EPOXI is a combination of the names for the two extended mission components: the Extrasolar Planet Observations and Characterisation (EPOCh), and the flyby of Comet Hartley 2, called the Deep Impact Extended Investigation (DIXI). The spacecraft has retained the name Deep Impact. In 2005, Deep Impact successfully released an impactor into the path of Comet Tempel 1.

Comet Hartley 2

Another view of comet Hartley 2, courtesy NASA / JPL-Caltech / UMD.

Comet Hartley 2

Like all comets, Hartley 2 is a mixture of various ices, dust and rocky rubble. Courtesy NASA / JPL-Caltech / UMD.

Adapted from information issued by NASA / JPL-Caltech / UMD.

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Encounter with a comet

Artist's concept of Deep Impact encounter

Artist's concept of the Deep Impact spacecraft's previous encounter, with Comet Tempel 1 (not to scale). Deep Impact, renamed the EPOXI mission, will encounter another comet, Hartley 2, on November 4.

  • EPOXI spacecraft to visit Comet Hartley 2
  • Close fly-by set for November 4
  • Only fifth mission to rendezvous with a comet

NASA’s Deep Impact/EPOXI spacecraft is hurtling toward Comet Hartley 2 for a breathtaking 700-kilometre flyby on November 4. Mission scientists say all systems are go for a close encounter with one of the smallest yet most active comets they’ve seen.

“There are billions of comets in the Solar System, but this will be only the fifth time a spacecraft has flown close enough to one to snap pictures of its nucleus,” says Lori Feaga of the EPOXI science team. “This one should put on quite a show!

Cometary orbits tend to be highly elongated; they travel far from the Sun and then swing much closer. At encounter time, Hartley 2 will be nearing the Sun and warming up after its cold, deep space sojourn. The ices in its nucleus will be vaporising furiously—spitting out dust and spouting gaseous geysers or jets.

“Hartley 2’s nucleus is small, less than a mile in diameter,” says Feaga. “But its surface offgasses at a higher rate than [cometary] nuclei we’ve seen before. We expect more jets and outbursts from this one.”

EPOXI will swoop down into the comet’s bright coma—the sparkling cloud of debris, illuminated by the Sun—shrouding the nucleus. The spacecraft’s cameras, taking high-resolution (7 metres per pixel at closest approach) pictures all the while, will reveal this new world in all its fizzy glory.

Comet Hartley 2

Comet Hartley 2, photographed on October 13 by Nick Howes using the 2-metre Faulkes North Telescope in Hawaii.

“We hope to see features of the comet’s scarred face: craters, fractures, vents,” says Sebastien Besse of the science team. “We may even be able to tell which features are spewing jets!”

The spacecraft’s instruments are already trained on their speeding target.

“We’re still pretty far out, so we don’t yet see a nucleus,” explains Besse. “But our daily observations with the spectrometer and cameras are already helping us identify the species and amounts of gases in the coma and learn how they evolve over time as we approach.”

Solar System leftovers

The aim of the mission is to gather details about what the nucleus is made of and compare it to other comets. Because comets spend much of their time far from the sun, the cold preserves their composition—and that composition tells a great story.

“Comets are left-overs from the ‘construction’ of our Solar System,” explains Besse. “When the planets formed out of the ‘stuff’ in the solar nebula spinning around the sun, comets weren’t drawn in.”

Researchers study these pristine specimens of the primal solar system to learn something about how it formed, and how it birthed a life-bearing planet like Earth.

EPOXI mission logo

The EPOXI mission logo.

“These flybys help us figure out what happened 4.5 billion years ago,” says Feaga. “So far we’ve only seen four nuclei. We need to study more comets to learn how they differ and how they are the same. This visit will help, especially since Hartley 2 is in many ways unlike the others we’ve seen.”

EPOXI will provide not only a birds-eye view of a new world but also the best extended view of a comet in history.

“This spacecraft is built for close encounters. Its instruments and our planned observations are optimised for this kind of mission. When, as Deep Impact, it flew by Tempel 1, it turned its instruments away from the nucleus to protect them from debris blasted up by the impactor. This time we won’t turn away.”

The EPOXI team will be waiting at NASA’s Jet Propulsion Laboratory.

“We’ll start diving into the data as soon as we receive it,” says Feaga. “We’ll work round the clock, on our toes the whole time, waiting for the next thing to come down.”

Sounds like it could be intense.

“It’s already intense,” says Besse. “We’re getting more and more data, but at encounter we’ll be flooded!”

And that will be only the beginning.

Adapted from information issued by Dauna Coulter / Dr Tony Phillips / Science@NASA / Pat Rawlings / JPL / UMD.

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Second life: comet mission continues

Comet Hartley 2 seen by the EPOXI mission

The first view of Comet Hartley 2 (fuzz ball in the centre of the image) taken by the EPOXI mission, which is using NASA's Deep Impact spacecraft to study the comet in great detail. The rendezvous date will be November 4, 2010.

On Sunday, September 5, NASA’s Deep Impact spacecraft beamed down the first of more than 64,000 images it’s expected to take of Comet Hartley 2. The spacecraft, now on an extended mission known as EPOXI, has an appointment with the comet on November 4, 2010.

Deep Impact made headlines around the world in July 2005 when it conducted a fly-by of Comet Tempel 1 and fired a projectile into it. The projectile caused a huge explosion on impact and gouged out a huge chunk of the Temple 1’s surface and sub-surface ice, enabling Deep Impact’s instruments to give us our first view of the ice that lives below the surface of a comet.

Impact on comet Tempel 1

Flash back to 2005, when Deep Impact fired a projectile into Comet Tempel 1, causing a huge explosion that gave scientists their first look at the interior of a comet.

It was realised soon after that the Deep Impact spacecraft was still in good shape, and could be retargeted to take an up close look at a second comet, Hartley 2.

There won’t be any fireworks this time, though, as Deep Impact’s only projectile was destroyed in its deliberate 2005 collision with comet Tempel 1.

Instead, it will use all three of its instruments (two telescopes with digital colour cameras and an infrared spectrometer) to scrutinise Hartley 2 for more than two months.

The spacecraft is stilled called Deep Impact, but the mission has been renamed EPOXI…a combination of the names for the two new mission aims: the extrasolar planet observations, called Extrasolar Planet Observations and Characterisation (EPOCh), and the flyby of comet Hartley 2, called the Deep Impact Extended Investigation (DIXI).

Longest up-close views of a comet

“Like any tourist who can’t wait to get to a destination, we have already begun taking pictures of our comet…Hartley 2,” said Tim Larson, the project manager for EPOXI from NASA’s Jet Propulsion Laboratory.

“We have to wait for November 4 to get the close-up pictures of the cometary nucleus, but these approach images should keep the science team busy for quite some time as well.”

Deep Impact spacecraft

Artist's impression of the Deep Impact spacecraft.

The imaging campaign, along with data from all the instruments aboard Deep Impact, will afford the mission’s science team the best, extended view of a comet in history during Hartley 2’s pass through the inner Solar System.

With the exception of one, six-day break to calibrate instruments and perform a trajectory correction manoeuvre, the spacecraft will continuously monitor Hartley 2’s gas and dust output for the next 79 days.

This first image of comet Hartley 2 taken by Deep Impact was obtained by the spacecraft’s Medium Resolution Imager on September 5 when the spacecraft was 60 million kilometres (37.2 million miles) from the comet.

EPOXI is an extended mission that utilises the already “in flight” Deep Impact spacecraft to explore distinct targets of opportunity.

Adapted from information issued by NASA / JPL / University of Maryland.

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