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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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Comet mission on course

The European Space Agency’s (ESA) Rosetta spacecraft made a successful fly-by of asteroid Lutetia on July 10-11, but its real target is comet Churyumov-Gerasimenko. It will rendezvous with the comet in 2014, mapping it and studying it. It will then accompany the comet for months, from near the orbit of Jupiter down to its closest approach to the Sun.

In November 2014, Rosetta will deploy a mini-spacecraft called Philae to land on the comet’s nucleus.

This video was made just before Rosetta’s fly-by of Lutetia.

Adapted from information issued by Euronews / ESA.

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Remembering Halley

This week marks the 25th anniversary of the launch of Giotto, the European Space Agency’s mission to Comet Halley.

Giotto was one of a small number of spacecraft sent to the famous comet, flying close by its nucleus and sending back remarkable, first-ever close-up images of a comet.

This video was released in 2006 to commemorate the 20th anniversary of Giotto’s encounter with Halley, and details the many extraordinary things that were learned.

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Comet probe pays visit to Earth

Artist's impression of Deep Impact and comet Tempel 1

Artist's impression of the then Deep Impact spacecraft visiting Comet Tempel 1 in 2005. Now renamed EPOXI, the spacecraft will visit another comet in November 2010.

  • EPOXI mission bound for Comet Hartley 2
  • To make fly-by of Earth to pick up speed
  • Due to reach the comet in November 2010

On Sunday, NASA’s historic Deep Impact spacecraft will fly past Earth for the fifth and last time on its current University of Maryland-led EPOXI mission. At time of closest approach to Earth, the spacecraft will be about 30,400 kilometres (18,900 miles) above the South Atlantic.

Mission navigators have tailored this trajectory to change the shape of the spacecraft’s orbit and to boost it on its way to the mission’s ultimate fly-by, a close encounter with comet Hartley 2 in November.

Diagram showing EPOXI's orbit and fly-bys

EPOXI will make a fly-by of Earth on June 26, and reach Comet Hartley 2 in November 2010.

“The speed and orbital track of the spacecraft can be changed by changing aspects of its fly-by of Earth, such as how close it comes to the planet,” explained University of Maryland astronomer Michael A’Hearn, principal investigator for both the EPOXI mission and its predecessor mission, Deep Impact.

“There is always some gravity boost at a fly-by and in some cases, like this one, it is the main reason for a fly-by,” said A’Hearn.

“The last Earth fly-by was used primarily to change the tilt of the spacecraft’s orbit to match that of comet Hartley 2, and we are using Sunday’s fly-by to also change the shape of the orbit to get us to the comet.”

The Deep Impact mission made history and headlines worldwide when it smashed a probe into comet Tempel 1 on July 4, 2005.

“Earth is a great place to pick up orbital velocity,” said Tim Larson, the EPOXI project manager from NASA’s Jet Propulsion Laboratory. “This fly-by will give our spacecraft a 1.5-kilometer-per-second [3,470 mph] boost, setting us up to get up close and personal with comet Hartley 2.”

A recycled mission

EPOXI is an extended mission of the Deep Impact fly-by spacecraft. Its name is derived from this mission’s two tasked science investigations—the Deep Impact Extended Investigation (DIXI) and the Extrasolar Planet Observation and Characterization (EPOCh).

Impact on Comet Tempel 1

In 2005, an impactor was collided with Comet Tempel 1, resulting in this huge flash.

On November 4, 2010, the mission will conduct an extended encounter with Hartley 2, studying the comet using all three of the spacecraft’s instruments (two telescopes with digital colour cameras and an infrared spectrometer).

On its original mission, the Deep Impact fly-by spacecraft had a companion probe spacecraft that was smashed into comet Tempel 1 to reveal for the first time the inner material of a comet.

Although scientific objectives have never been a primary purpose of the Deep Impact/EPOXI spacecraft’s fly-bys of Earth, the mission team has used the spacecraft’s instruments to find clear evidence of water on the Moon and to study light reflected from Earth as a template that scientists eventually may be able be use to identify Earth-like planets around other stars.

Adapted from information issued by the University of Maryland / NASA / JPL-Caltech / UMD / Pat Rawlings.

Famous comets are foreigners

Comet Halley

Comet Halley, and other famous comets, could have been "stolen" from other stars systems.

  • Comets formed within a cluster of stars
  • Sun captured comets when the stars dispersed
  • 90% could be from beyond the Solar System

Many of our Solar System’s most well known comets—including Halley, Hale-Bopp and, most recently, McNaught—could have been stolen from other stars, according to a new idea by an international team of astronomers.

The team used computer simulations to show that the Sun may have captured small icy bodies from its sibling stars when it was still young.

While the Sun currently has no companion stars, it is believed to have formed in a star cluster containing hundreds of closely packed stars that were embedded in a dense nebula of gas.

During this time, each star formed a large number of small icy bodies (comets) in a cloud from which its planets also formed.

Most of these comets were slung out of these young systems by the gravity of the newly forming planets, becoming tiny, free-floating ice balls in deep space.

The Sun’s star cluster eventually scattered, the individual stars going their own ways. The new computer models show that the Sun gravitationally captured a large cloud of comets as the cluster dispersed.

“When it was young, the Sun shared a lot of ‘spit’ with its siblings, and we can see that stuff today,” says lead author Dr Hal Levison of the Southwest Research Institute.

An artist's impression of the Oort cloud

An artist's impression of the Oort cloud, a swarm of comets that surrounds the Solar System.

90% of comets are foreigners

The scientists say this leads to the exciting possibility that the Sun’s current comet cloud contains a potpourri that includes material from a large number of the Sun’s infant stellar siblings.

Evidence for the scenario comes from the roughly spherical cloud of comets, known as the Oort cloud, that surrounds the Sun, extending halfway to the nearest star.

It has been commonly assumed this cloud formed from the flattened gas and dust cloud that surrounded the young Sun. However, because detailed models show that comets that formed as part the Solar System would have produced a thinner cloud than that known today, an extra source of comets is required.

Dr Levison says that “we can conclude that more than 90 percent of the observed Oort cloud comets” came from beyond the Solar System.

“The formation of the Oort cloud has been a mystery for over 60 years and our work likely solves this long-standing problem,” says Dr Ramon Brasser of the Observatoire de la Côte d’Azur, France.

Adapted from information issued by Southwest Research Institute / NASA.

Comet crash caused climate change?

Artist's impression of an asteroid or comet striking the Earth.

Artist's impression of a comet striking the Earth.

Earth was struck by thousands of cometary fragments over the course of an hour 13,000 years ago, leading to a dramatic cooling of the planet, according to astronomer Professor Bill Napier of the Cardiff University Astrobiology Centre.

The cooling, by as much as 8 degrees C, interrupted the warming which was occurring at the end of the last ice age and caused glaciers to readvance.

Evidence has been found that this catastrophic change was associated with some extraordinary extraterrestrial event.

The change is marked by the occurrence of a “black mat” layer a few centimetres thick found in rock layers at many sites throughout the United States containing high levels of soot indicative of continental-scale wildfires.

There are also microscopic hexagonal diamonds (nano-diamonds), which are produced by high-pressure shock events and are found only in meteorites or impact craters.

These findings led to the suggestion that the catastrophic changes of that time were caused by the impact of an asteroid or comet 4 km across on the Laurentide ice sheet, which at that time covered what would become Canada and the northern part of the United States.

The cooling lasted over a thousand years, and its onset coincides with the rapid extinction of 35 genera of North American mammals, as well as the disruption of the Palaeoindian culture.

The chief objection to the idea is that the odds against the Earth being struck by an asteroid this large only 13,000 years ago are a thousand to one against. And the heat generated by the rising fireball would have been limited by the curvature of the horizon and could not explain the continent-wide occurrence of wildfires.

Multiple comet crashes the cause?

Professor Napier has now come up with an model that accounts for the major features of the catastrophe without involving such an improbable event. According to his concept, the Earth ran into a dense trail of material from a large disintegrating comet.

Fragments of comet 73/P Schwassman-Wachmann 3

Comets sometimes break into many pieces, such as 73/P Schwassman-Wachmann 3, seen in this Hubble Space Telescope image from 2005.

He points out that there is compelling evidence that such a comet entered the inner planetary system between 20,000 and 30,000 years ago and has been fragmenting ever since, giving rise to a number of closely related meteor streams and asteroids known as the Taurid Complex.

In the course of the giant comet’s disintegration, the environment of the interplanetary system would have been hazardous and the Earth would probably have run through at least one dense swarm of cometary material.

The new model indicates that such an encounter would last for about an hour during which thousands of impacts would take place over continental areas, each releasing the energy of a megaton-class nuclear bomb, generating the extensive wildfires which took place at that time. The nano-diamonds at the extinction boundary would then be explained as having come in with the comet swarm.

One recent meteorite is known which may have come from this giant comet progenitor—the Tagish Lake meteorite, which fell over Yukon Territory in January 2000. It has the highest abundance of nano-diamonds of any meteorite so far analysed.

Professor Napier sums up his model: “A large comet has been disintegrating in the near-Earth environment for the past 20,000 to 30,000 years, and running into thousands of fragments from this comet is a much more likely event than a single large collision. It gives a convincing match to the major geophysical features at this boundary.”

Adapted from information issued by the RAS. Image credits: NASA / ESA / H. Weaver (JHU/APL) / M. Mutchler / Z. Levay (STScI) / G. Rhemann and M. Jager.

Colossal comet surprises scientists

Comet McNaught seen over the Pacific Ocean in 2007.

Comet McNaught seen over the Pacific Ocean in 2007.

Ulysses spacecraft data has been used to measure the region of solar wind disturbed by a comet. The comet, C/2006 P1 McNaught, is now known to hold the record for the largest effect on its surrounding space.

Comets have three parts: the core, or nucleus, made of ice and rock; the coma or head, which is a vast cloud of gas and dust surrounding the nucleus; and the tail, which is often split in two (one part composed of gas, the other of dust).

Scientists usually measure a comet by the size of its nucleus or the length of its tail(s).

But now, a group led by Dr Geraint Jones of University College London’s (UCL) Mullard Space Science Laboratory, has used data from the Ulysses spacecraft to measure the region of space disturbed by Comet McNaught’s presence.

Artist's impression of the Ulysses spacecraft flying through the tail of a comet.

Artist's impression of the Ulysses spacecraft flying through the tail of a comet.

Magnetic field measurements show evidence of a shockwave surrounding the comet, formed when ionised gas emitted from the nucleus joined the fast-flowing particles of the solar wind, causing the wind to slow down abruptly.

In early 2007, Comet McNaught became the brightest comet visible from Earth in 40 years.

Serendipitously, Ulysses made an unexpected crossing of Comet McNaught’s tail during this time, one of three unplanned encounters with comet tails during the spacecraft’s 19-year mission. (The other encounters included Comet Hyakutake in 1996, the current record-holder for the comet with the longest measured tail.)

Ulysses crossed McNaught’s gas tail at a distance downstream of the comet’s nucleus more than 1.5 times the distance between the Earth and the Sun. This is far beyond the spectacular tail of dust particles that was visible from Earth in 2007.

Ulysses took an incredible 18 days to travel through the solar wind affected by Comet McNaught, compared to just 2.5 days for Comet Hyakutake.

“This shows that the comet was not only spectacular from the ground; it was a truly immense obstacle to the solar wind,” says Dr Jones.

A comparison with crossing times for other comet encounters demonstrates the huge scale of Comet McNaught. The Giotto spacecraft’s encounter with Comet Grigg-Skjellerup in 1992 took less than an hour, while the famous Comet Halley took only a few hours.

Adapted from information issued by the RAS. Image credits: Sebastian Deiries, ESO / NASA / ESA.