Category: Comets

Hubble view of a jet on Comet Tempel 1. Image credit: Hubble. Click to enlarge.
In a dress rehearsal for the rendezvous between NASA’s Deep Impact spacecraft and comet 9P/Tempel 1, the Hubble Space Telescope captured dramatic images of a new jet of dust streaming from the icy comet.

The images are a reminder that Tempel 1’s icy nucleus, roughly half the size of Manhattan, is dynamic and volatile. Astronomers hope the eruption of dust seen in these observations is a preview of the fireworks that may come July 4, when a probe from the Deep Impact spacecraft will slam into the comet, possibly blasting off material and giving rise to a similar dust plume.

These observations demonstrate that Hubble’s sharp “eye” can see exquisite details of the comet’s temperamental activities. The Earth-orbiting observatory was 75 million miles away from the comet when these images were taken by the Advanced Camera for Surveys’ High Resolution Camera. The telescope’s views complement close-up images being taken by cameras aboard Deep Impact, which is speeding toward the comet.

The two images, taken seven hours apart on June 14, show Tempel 1 and its new jet. The image at left, taken at 2:17 a.m. (EDT), is a view of the comet before the outburst. The bright dot is light reflecting from the comet’s nucleus, which appears star-like in these images because it is too small even for Hubble to resolve. The nucleus, a potato-shaped object, is 8.7 miles (14 kilometers) wide and 2.5 miles (4 kilometers) long. Hubble’s viewing the nucleus is as difficult as someone trying to spot a potato in Salt Lake City from New York City.

The photo at right, snapped at 9:15 a.m. (EDT), reveals the jet [the bright fan-shaped area]. The jet extends about 1,400 miles (2,200 kilometers), which is roughly half the distance across the U.S. It is pointing in the direction of the Sun. Comets frequently show outbursts in activity, but astronomers still don’t know exactly why they occur. Tempel 1 has been moving closer to the Sun, and perhaps the increasing heat opened up a crack in the comet’s dark, crusty surface. Dust and gas trapped beneath the surface could then spew out of the crack, forming a jet. Or, perhaps a portion of the crust itself was lifted off the nucleus by the pressure of heated gases beneath the surface. This porous crust might then crumble into small dust particles shortly after leaving the nucleus, producing a fan-shaped coma on the sunward side. Whatever the cause, the new feature may not last for long.

Astronomers hope that the July 4 collision will unleash more primordial material trapped inside the comet, which formed billions of years ago. Comets are thought to be “dirty snowballs,” porous agglomerates of ice and rock that dwell in the frigid outer boundaries of our solar system. Periodically, they make their journey into the inner solar system as they loop around the Sun.

The contrast in these images has been enhanced to highlight the brightness of the new jet.

Original Source: Hubble News Release

Deep Impact’s first view of Comet Temple 1 from a distance of 64 million kilometers (39.7 million miles). Image credit: NASA/JPL. Click to enlarge.
Sixty-nine days before it gets up-close-and-personal with a comet, NASA’s Deep Impact spacecraft successfully photographed its quarry, comet Tempel 1, from a distance of 64 million kilometers (39.7 million miles).

The image, the first of many comet portraits it will take over the next 10 weeks, will aid Deep Impact’s navigators, engineers and scientists as they plot their final trajectory toward an Independence Day encounter. “It is great to get a first glimpse at the comet from our spacecraft,” said Deep Impact Principal Investigator Dr. Michael A’Hearn of the University of Maryland, College Park, Md. “With daily observations beginning in May, Tempel 1 will become noticeably more impressive as we continue to close the gap between spacecraft and comet. What is now little more than a few pixels across will evolve by July 4 into the best, most detailed images of a comet ever taken.”

The ball of dirty ice and rock was detected on April 25 by Deep Impact’s medium resolution instrument on the very first attempt. While making the detection, the spacecraft’s camera saw stars as dim as 11th visual magnitude, more than 100 times dimmer than a human can see on a clear night.

“This is the first of literally thousands of images we will take of Tempel 1 for both science and navigational purposes,” said Deputy Program Manager Keyur Patel at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Our goal is to impact a one-meter long (39-inch) spacecraft into about a 6.5-kilometer wide (4-mile) comet that is bearing down on it at 10.2 kilometers per second (6.3 miles per second), while both are 133.6 million kilometers (83 million miles) away from Earth. By finding the comet as early and as far away as we did is a definite aid to our navigation.”

To view the comet image on the Internet, visit http://www.nasa.gov/deepimpact or http://deepimpact.jpl.nasa.gov/.

Deep Impact is comprised of two parts, a “flyby” spacecraft and a smaller “impactor.” The impactor will be released into the comet’s path for a planned high-speed collision on July 4. The crater produced by the impact could range in size from the width of a large house up to the size of a football stadium and from 2 to 14 stories deep. Ice and dust debris will be ejected from the crater, revealing the material beneath.

The Deep Impact spacecraft has four data collectors to observe the effects of the collision – a camera and infrared spectrometer comprise the high resolution instrument, a medium resolution instrument, and a duplicate of that camera on the impactor (called the impactor targeting sensor) that will record the vehicle’s final moments before it is run over by comet Tempel 1 at a speed of about 37,000 kilometers per hour (23,000 miles per hour).

The overall Deep Impact mission management for this Discovery class program is conducted by the University of Maryland. Deep Impact project management is handled by the Jet Propulsion Laboratory. The spacecraft was built for NASA by Ball Aerospace & Technologies Corporation, Boulder, Colo.

For more information about Deep Impact on the Internet, visit NASA Deep Impact.

Original Source: NASA/JPL News Release

Image credit: ESA
One of the ingenious instruments on board Rosetta is designed to ?smell? the comet for different substances, analysing samples that have been ?cooked? in a set of miniature ovens.

ESA?s Rosetta will be the first space mission ever to land on a comet. After its lander reaches Comet 67P/Churyumov-Gerasimenko, the main spacecraft will follow the comet for many months as it heads towards the Sun.

Rosetta’s task is to study comets, which are considered the primitive building blocks of the Solar System. This will help us to understand if life on Earth began with the help of ‘comet seeding’.

The Ptolemy instrument is an ?Evolved Gas Analyser?, the first example of a new concept in space instruments, devised to tackle the challenge of analysing substances ?on location? on bodies in our Solar System.

Weighing just 4.5 kilograms and about the size of a shoe box, it was produced by a collaboration of the UK?s Rutherford Appleton Laboratory and Open University.

The analysis of these samples from the surface of the comet will establish what the cometary nucleus is made from, providing valuable information about these most primitive objects.

After the lander touches down on the comet, the Ptolemy instrument will collect comet nucleus material, believed to be a frozen mixture of ices, dust and tar, using the Sampling, Drilling and Distribution system (SD2) supplied by Tecnospazio Milano of Italy. SD2 will drill for small cores of ice and dust from depths of down to 250 millimetres.

Samples collected in this way will be delivered to one of four tiny ?ovens? dedicated to Ptolemy, which are mounted on a circular, rotatable carousel. The German-supplied carousel has 32 of these ovens, with the remainder being used by other Rosetta instruments.

Of the four Ptolemy ovens, three are for solid samples collected and delivered by SD2 while the fourth will be used to collect volatile materials from the near-surface cometary atmosphere.

By heating the solid samples to 800 ?C, the oven converts them into gases which then pass along a pipe into Ptolemy. The gas will then be separated into its constituent chemical species using a gas chromatograph.

Ptolemy can then determine which chemicals are present in the comet sample, and hence help to build up a detailed picture of what the comet is made from.

It does this using the world?s smallest ?ion-trap mass spectrometer?, a small, low-power device built with the latest miniature technology. This device will find out what gases are present in any particular sample and measure stable isotope ratios.

Original Source: ESA News Release

Image credit: ESA
ESA’s comet-chaser Rosetta, whose 10-year journey to its final target Comet 67P/Churyumov-Gerasimenko started on 2 March, is well on its way. The first phase of commissioning is close to completion and Rosetta has successfully performed its first scientific activity – observation of Comet Linear.

The commissioning activities, which started a couple of days after launch, included the individual activation of all instruments on board the Rosetta orbiter and the Philae lander. This first check-out worked flawlessly and showed that the spacecraft and all instruments are functioning well and in excellent shape.

The commissioning tests also paved the way for Rosetta’s first scientific activity: observation of Comet C/2002 T7 (LINEAR), which is currently travelling for the first and only time through the inner Solar System and offered Rosetta an excellent opportunity to make its first scientific observation.

On 30 April, the OSIRIS camera system, which was scheduled for commissioning on that date, took images of this unique cometary visitor. Later that day, three more instruments on board Rosetta (ALICE, MIRO and VIRTIS) were activated in parallel to take measurements of the comet. Although the parallel activation of the instruments was not planned until later in the year, the Rosetta team felt confident that this could be done without any risk because of the satisfactory progress of the overall testing.

The first data from the remote-sensing observations confirm the excellent performance of the instruments. The four instruments took images and spectra of Comet C/2002 T7 (LINEAR) to study its coma and tail in different wavelengths, from ultraviolet to microwave. Rosetta successfully measured the presence of water molecules in the tenuous atmosphere around the comet. Detailed analysis of the data will require the complete calibration of the instruments, which will take place in the coming months. The OSIRIS camera produced high-resolution images of Comet C/2002 T7 (LINEAR) from a distance of about 95 million kilometres. The image (above) showing a pronounced nucleus and a section of the tenuous tail extending over about 2 million kilometres was obtained by OSIRIS in blue light.

The successful observation of Comet Linear was a first positive test for Rosetta’s ultimate goal, Comet 67P/Churyumov-Gerasimenko, which will be reached in 2014. Rosetta will be the first mission to undertake a long-term exploration of a comet at close quarters whilst accompanying it on its way towards the Sun.

The unprecedented in-depth study conducted by the Rosetta orbiter and its Philae lander will help scientists decipher the formation of our Solar System around 4600 million years ago and provide them with clues of how comets may have contributed to the beginning of life on Earth. In particular, the Philae lander, developed by a European consortium under the leadership of the German Aerospace Research Institute (DLR), will analyse the composition and structure of the comet’s surface.

After Rosetta’s first deep-space manoeuvres were carried out on 10 and 15 May with the highest accuracy, the first phase of commissioning is set to be completed in the first week of June. Rosetta will then go into a quiet ?cruise mode? until September, when the second phase of commissioning is scheduled to start. These activities, including the interference and pointing campaign, will last until December.

So the Rosetta spacecraft is well under way on its epic 10-year voyage, to do what has never before been attempted ? orbiting and landing on a comet.

Original Source: ESA News Release

Image credit: ESA
On 22 March 2004, the ESA/NASA SOHO solar observatory spacecraft discovered its 750th comet since its launch in December 1995.

SOHO comet 750 was discovered by the German amateur astronomer Sebastian H?nig, one of the most successful SOHO comet-hunters. It was a part of the Kreutz family of ‘sungrazing’ comets, which usually evaporate in the hot solar atmosphere.

The LASCO coronagraph on SOHO, designed for seeing outbursts from the Sun, uses a mask to block the bright rays from the visible surface. It monitors a large volume of surrounding space and, as a result, has become the most prolific ‘discoverer’ of comets in the history of astronomy. Its images are displayed on the internet.

More than 75% of the discoveries have come from amateur comet hunters around the world, watching these freely available SOHO images on the internet. So, anyone with internet access can take part in the hunt for new comets and be a ‘comet discoverer’! Click here for information about how to search for your own comet.

SOHO is a mission of international co-operation between ESA and NASA, launched in December 1995. Every day SOHO sends thrilling images from which research scientists learn about the Sun’s nature and behaviour. Experts around the world use SOHO images and data to help them predict ‘space weather’ events affecting our planet.

Original Source: ESA News Release

Image credit: ESA
Rosetta?s lander Philae will do something never before attempted: land on a comet. But how will it do this, when the kind of surface it will land on is unknown?

With the surface composition and condition largely a mystery, engineers found themselves with an extraordinary challenge; they had to design something that would land equally well on either solid ice or powder snow, or any state in between.

In the tiny gravitational field of a comet, landing on hard icy surface might cause Philae to bounce off again. Alternatively, hitting a soft snowy one could result in it sinking. To cope with either possibility, Philae will touch as softly as possible. In fact, engineers have likened it more to docking in space.

Landing on a comet is nothing like landing on a large planet, you do not have to fight against the pull of the planet?s gravity, and there is no atmosphere.

The final touching velocity will be about one metre per second. That is near a walking pace. However, as anyone who has walked into a wall by mistake will tell you, it is still fast enough to do some damage. So, two other strategies have been implemented.

Firstly, to guard against bouncing off, Philae will fire harpoons upon contact to secure itself to the comet.

Secondly, to prevent Philae from disappearing into a snowy surface, the landing gear is equipped with large pads to spread its weight across a broad area ? which is how snowshoes work on Earth, allowing us to walk on powdery falls of snow.

When necessity forced Rosetta?s target comet to be changed in Spring 2003 from Comet Wirtanen to Comet 67P/Churyumov-Gerasimenko, the landing team re-analysed Philae?s ability to cope. Because Comet Churyumov-Gerasimenko is larger than Wirtanen, three times the radius, it will have a larger gravitational field with which to pull down Philae.

In testing it was discovered that the landing gear is capable of withstanding a landing of 1.5 metres per second ? this was better than originally assumed.

In addition, Rosetta will gently push out the lander from a low altitude, to lessen its fall. In the re-analysis, one small worry was that Philae might just topple, if it landed on a slope at high speed. So the lander team developed a special device called a ?tilt limiter?, and attached it to the lander before lift-off, to prevent this happening.

In fact, the unknown nature of the landing environment only serves to highlight why the Rosetta mission is vital in the first place. Astronomers and planetary scientists need to learn more about these dirty snowballs that orbit the Sun.

Original Source: ESA News Release

Image credit: NASA/JPL
On 2 January 2004, NASA’s Stardust spacecraft successfully survived flying through the coma (dust and gas cloud) surrounding comet 81P/Wild 2, captured thousands of fresh cometary dust particles released from the surface just hours before, and is now on its way home for Earth return set for January 2006.

During the flyby, the highest resolution images ever taken of a comet’s nucleus were obtained and have been the subject of intense study since the flyby. A short exposure image showing tremendous surface detail was overlain on a long exposure image taken just 10 seconds later showing jets.

“This spectacular composite image shows a surface feature unlike any other planetary surface see to date in our solar system”, says Prof Donald Brownlee, the Stardust Principal Investigator from the University of Washington. “Other than our sun, this is currently the most active planetary surface in our solar system, jetting dust and gas streams into space and leaving a trail millions of kilometers long.”

“The overall shape of the nucleus resembles a thick hamburger patty with a few bites taken out”, says Thomas Duxbury, the Stardust Project Manager from JPL. “The surface has significant relief on top of this overall shape that reflects billions of years of resurfacing from crater impacts and out gassing”.

One mystery from the close-views of Wild-2 was its pockmarks. “I looked at the images in stereo view,” said Brownlee. “One large depression has a bottom that is flat, with very steep walls [400-500 meters deep]. While any scientific evidence is only two days old,” most impact craters are expected to be bowl-shaped with much shallower aspect ratios (0.1-0.2), meaning they are five times wider than they are deep. Some of these depressions are not round, but scalloped and much deeper (aspect ratio, 0.4).

“I am from Washington state”, said Brownlee, “and when the comet is viewed in stereo pairs like that, it reminds me of Grand Cooley, with its steep cliffs and run-out areas at the bottom. Like flood areas from the Columbia River, if you were standing at the bottom of one of these comet depressions. But the floor of these comet depressions are incredibly complicated, like balls of clay have been mashed together and then etched.”

“The mission scientists with Deep Space I,” which flew by comet Borrelly, found surprising “mesas”, said Brownlee. “They speculated that these walls can sometimes face sunwards, and volatiles like ice and methane may evaporate or etch that surface. But on Wild-2, we see pits, not mesas. The two comets are quite different. We may have [with Wild-2] a young comet that evolves towards Borrelly, or vice versa.”

Three large comet jets registered on one of Stardust’s instruments, its dust counter. Three distinct peaks appeared with thousands of particle strikes each. Slightly less than an ounce of comet dust, or about a thimbleful, were collected over the spacecraft’s 12 minute pass through these large jets. “The secret of our mission is that we sample only the volatile material, that which is evaporating into space,” said Brownlee. “That’s the way we avoid any contaminants that might have left those impact-like marks on the comet’s surface. So it was better in this case to fly-through the lighter dust stream, than to land on this comet. We’d have to drive around a bit to find just the comet stuff.” In just such a science-fiction scenario of landing on a comet, the European mission, called Rosetta, will launch next month and travel to comet Churyumov-Gerasimenko in November 2014.

Preliminary scientific results obtained from the Wild 2 encounter are being presented at the Lunar and Planetary Science Conference in Houston, Texas by the Stardust science team. Stardust will bring samples of comet dust back to Earth in January 2006 to help answer fundamental questions about the origins of the solar system.

Original Source: NASA Astrobiology Magazine

Image credit: ESA
With just 21 days to the launch of the European Space Agency’s Rosetta comet mission, the spacecraft’s lander has been named “Philae”. Rosetta embarks on a 10-year journey to Comet 67P/Churyumov-Gerasimenko from Kourou, French Guiana, on 26 February.

Philae is the island in the river Nile on which an obelisk was found that had a bilingual inscription including the names of Cleopatra and Ptolemy in Egyptian hieroglyphs. This provided the French historian Jean-Fran?ois Champollion with the final clues that enabled him to decipher the hieroglyphs of the Rosetta Stone and unlock the secrets of the civilisation of ancient Egypt.

Just as the Philae Obelisk and the Rosetta Stone provided the keys to an ancient civilisation, the Philae lander and the Rosetta orbiter aim to unlock the mysteries of the oldest building blocks of our Solar System – comets.

Germany, France, Italy and Hungary are the main contributors to the lander, working together with Austria, Finland, Ireland and the UK. The main contributors held national competitions to select the most appropriate name. Philae was proposed by 15-year-old Serena Olga Vismara from Arluno near Milan, Italy. Her hobbies are reading and surfing the internet, where she got the idea of naming the lander Philae. Her prize will be a visit to Kourou to attend the Rosetta launch.

Study of Comet Churyumov-Gerasimenko will allow scientists to look back 4600 million years to an epoch when no planets existed and only a vast swarm of asteroids and comets surrounded the Sun. On arrival at the comet in 2014, Philae will be commanded to self-eject from the orbiter and unfold its three legs, ready for a gentle touchdown. Immediately after touchdown, a harpoon will be fired to anchor Philae to the ground and prevent it escaping from the comet’s extremely weak gravity. The legs can rotate, lift or tilt to return Philae to an upright position.

Philae will determine the physical properties of the comet’s surface and subsurface and their chemical, mineralogical and isotopic composition. This will complement the orbiter’s studies of the overall characterisation of the comet’s dynamic properties and surface morphology. Philae may provide the final clues enabling the Rosetta mission to unlock the secrets of how life began on Earth.

?Whilst Rosetta?s lander now has a name of its own, it is still only a part of the overall Rosetta mission. Let us look forward to seeing the Philae lander, Osiris, Midas and all the other instruments on board Rosetta start off on their great journey this month,? said Professor David Southwood, ESA Director of Science.

Original Source: ESA News Release

Image credit: ESA
The countdown to Rosetta?s rendezvous in space began on 1 March 1997. At the end of February 2004, seven years and not a few headaches later, the European Space Agency (ESA) probe will at last be setting off on its journey to meet 67P/Comet Churyumov-Gerasimenko.

The long-planned get-together will not however take place until the middle of 2014. A few months after arriving at the comet, Rosetta will release a small lander onto its surface. Then, for almost two years it will investigate Churyumov-Gerasimenko from close up.

Dr Gerhard Schwehm, lead scientist for the Rosetta project, explains that, ?With this mission we will be breaking new ground – this will be the first protracted cometary encounter.? The trip to the meeting place in space will certainly be a long one, located as it is some 4.5 astronomical units from the Sun, which translates into something like 675 million kilometres. Rosetta will be on the road for ten years, during which time it will clock up in excess of five billion kilometres.

Launch in February 2004
Rosetta will be waved off on 26 February when it lifts off from the space centre in Kourou, French Guiana, aboard an Ariane 5 launcher. Shortly after the spacecraft?s release, its solar panels will be deployed and turned towards the Sun to build up the necessary power reserves. Its various systems and experiments will be gradually brought into operation and tested. Just three months into the mission the first active phase will be over, followed by final testing of the experiments in October 2004. Rosetta will then spend the following years flying a lonely path to the comet, passing by the Earth, Mars, the Earth and the Earth again.

There is no alternative to this detour, for even Ariane 5, the most powerful launcher on the market today, lacks the power to hurl the probe on a direct route to the comet. To get the required momentum, it will rely on swing-by man?uvres, using the gravitation pull of Mars (in 2007) and the Earth (three times, in 2005, 2007 and 2008) to pick up speed.

Asteroids for company
A change is as good as a rest, and a meeting with at least one asteroid should help break the monotony for Rosetta. The spacecraft will come close to an asteroid at the end of 2008. Asteroids are, it will be remembered, rocky bodies, some as large as mountains, some even larger, that orbit the Sun in much the same way as planets.

?These ?brief encounters? are a scientific opportunity and also a chance to test Rosetta?s instrument payload,? says Gerhard Schwehm. But asteroid exploration also serves an entirely practical purpose: ?The more we find out about them, the better the prospect of being able one day to avert a possible collision.? Following a period of low-activity cruising, the probe?s course will be adjusted one last time in May 2011. From July 2011, a further two-and-a-half years’ radio silence will be observed, and Rosetta, left entirely to its own resources, will fly close to the Jupiter orbit.

Link-up in 2014
Finally, in January 2014, the probe will be reactivated and will, by October 2014, be only a few kilometres distant from Churyumov-Gerasimenko. This is where the dream of so many scientists becomes reality. Having deposited its precious lander cargo on the comet?s surface, Rosetta will continue to orbit Churyumov-Gerasimenko and together they will spend the next seventeen months flying towards the Sun.

Rosetta was built by an international consortium led by Astrium. The lander probe was developed in Cologne under the aegis of the DLR, Germany?s space agency, with contributions from ESA and research centres in Austria, Finland, France, Hungary, Ireland, Italy and Great Britain.

The comet explorer carries ten scientific instruments. Their job is to draw out the secrets of the comet?s chemical and physical composition and reveal its magnetic and electrical properties. Using a specially designed camera, the lander will take pictures in the macro and micro ranges and send all the data thus acquired back to Earth, via Rosetta.

?This will be our first ever chance to be there, at first hand, so to speak, as a comet comes to life,? Schwehm goes on to explain. When Churyumov-Gerasimenko gets to within about 500 million kilometres of the Sun, the frozen gases that envelop it will evaporate and a trail of dust will be blown back over hundreds of thousands of kilometres. When illuminated by the Sun, this characteristic comet tail then becomes visible from Earth. In the course of the mission, the processes at work within the cometary nucleus will be studied and measured more precisely than has ever before been possible, for earlier probes simply flew past their targets.

?As we will be accompanying Churyumov-Gerasimenko for two years, until the comet reaches its closest point to the Sun and travels away from it, we can at long last hope to acquire new knowledge about comets. We are confident we will come a step nearer to understanding the origins and formation of our solar system and the emergence of life on Earth.?

More information on the Rosetta launch can be found on: http://www.esa.int/rosetta

More on ESA Science Programme at: http://www.esa.int/science

Original Source: ESA News Release