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Philae has landed

The European Space Agency’s (ESA) Rosetta mission has soft-landed its Philae probe on a comet, the first time in history that such an extraordinary feat has been achieved.

After a tense wait during the seven-hour descent to the surface of Comet 67P/Churyumov-Gerasimenko, the signal confirming the successful touchdown arrived on Earth at 16:03 GMT on November 12.

The confirmation was relayed via the Rosetta orbiter to Earth and picked up simultaneously by ESA’s ground station in Malargüe, Argentina and NASA’s station in Madrid, Spain. The signal was immediately confirmed at ESA’s Space Operations Centre, ESOC, in Darmstadt, and DLR’s Lander Control Centre in Cologne, both in Germany.

The first data from the lander’s instruments were transmitted to the Philae Science, Operations and Navigation Centre at France’s CNES space agency in Toulouse.

“Our ambitious Rosetta mission has secured a place in the history books: not only is it the first to rendezvous with and orbit a comet, but it is now also the first to deliver a lander to a comet’s surface,” noted Jean-Jacques Dordain, ESA’s Director General.

“With Rosetta we are opening a door to the origin of planet Earth and fostering a better understanding of our future. ESA and its Rosetta mission partners have achieved something extraordinary today.”

Philae, as seen from the Rosetta parent craft, descending to the comet.

Philae, as seen from the Rosetta parent craft, descending to the comet.

A game-changer

“After more than 10 years travelling through space, we’re now making the best ever scientific analysis of one of the oldest remnants of our Solar System,” said Alvaro Giménez, ESA’s Director of Science and Robotic Exploration.

“Decades of preparation have paved the way for today’s success, ensuring that Rosetta continues to be a game-changer in cometary science and space exploration.”

“We are extremely relieved to be safely on the surface of the comet, especially given the extra challenges that we faced with the health of the lander,” said Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Centre.

“In the next hours we’ll learn exactly where and how we’ve landed, and we’ll start getting as much science as we can from the surface of this fascinating world.”

Rosetta was launched on 2 March 2004 and travelled 6.4 billion kilometres through the Solar System before arriving at the comet on 6 August 2014.

“Rosetta’s journey has been a continuous operational challenge, requiring an innovative approach, precision and long experience,” said Thomas Reiter, ESA Director of Human Spaceflight and Operations.

“This success is testimony to the outstanding teamwork and the unique know-how in operating spacecraft acquired at the European Space Agency over the decades.”

510 million kilometres from Earth

The landing site, named Agilkia and located on the head of the bizarre double-lobed object, was chosen just six weeks after arrival based on images and data collected at distances of 30–100 km from the comet.

Those first images soon revealed the comet as a world littered with boulders, towering cliffs and daunting precipices and pits, with jets of gas and dust streaming from the surface.

Following a period spent at 10 km to allow further close-up study of the chosen landing site, Rosetta moved onto a more distant trajectory to prepare for Philae’s deployment.

Philae's first view from the surface of Comet 67P/Churyumov-Gerasimenko. One of the lander’s three feet can be seen in the foreground. The image is a two-image mosaic.

Philae’s first view from the surface of Comet 67P/Churyumov-Gerasimenko. One of the lander’s three feet can be seen in the foreground. The image is a two-image mosaic.

Five critical go/no-go decisions were made last night and early this morning, confirming different stages of readiness ahead of separation, along with a final pre-separation manoeuvre by the orbiter.

Deployment was confirmed at 09:03 GMT (10:03 CET) at a distance of 22.5km from the centre of the comet. During the seven-hour descent, which was made without propulsion or guidance, Philae took images and recorded information about the comet’s environment.

“One of the greatest uncertainties associated with the delivery of the lander was the position of Rosetta at the time of deployment, which was influenced by the activity of the comet at that specific moment, and which in turn could also have affected the lander’s descent trajectory,” said Sylvain Lodiot, ESA Rosetta Spacecraft Operations Manager.

“Furthermore, we’re performing these operations in an environment that we’ve only just started learning about, 510 million kilometres from Earth.”

Not all went according to plan

Touchdown was planned to take place at a speed of around 1 m/s, with the three-legged landing gear absorbing the impact to prevent rebound, and an ice screw in each foot driving into the surface.

But during the final health checks of the lander before separation, a problem was detected with the small thruster on top that was designed to counteract the recoil of the harpoons to push the lander down onto the surface.

The conditions of landing – including whether or not the thruster performed – along with the exact location of Philae on the comet are being analysed.

An extended science phase using the rechargeable secondary battery may be possible, assuming Sun illumination conditions allow and dust settling on the solar panels does not prevent it.

This extended phase could last until March 2015, after which conditions inside the lander are expected to be too hot for it to continue operating.

Philae's first multi-image panorama from the surface of the comet.

Philae’s first multi-image panorama from the surface of the comet.

Answering the big questions

Science highlights from the primary phase will include a full panoramic view of the landing site, including a section in 3D, high-resolution images of the surface immediately underneath the lander, on-the-spot analysis of the composition of the comet’s surface materials, and a drill that will take samples from a depth of 23 cm and feed them to an onboard laboratory for analysis.

The lander will also measure the electrical and mechanical characteristics of the surface. In addition, low-frequency radio signals will be beamed between Philae and the orbiter through the nucleus to probe the internal structure.

The detailed surface measurements that Philae makes at its landing site will complement and calibrate the extensive remote observations made by the orbiter covering the whole comet.

“Rosetta is trying to answer the very big questions about the history of our Solar System. What were the conditions like at its infancy and how did it evolve? What role did comets play in this evolution? How do comets work?” said Matt Taylor, ESA Rosetta project scientist.

“Today’s successful landing is undoubtedly the cherry on the icing of a 4 km-wide cake, but we’re also looking further ahead and onto the next stage of this ground-breaking mission, as we continue to follow the comet around the Sun for 13 months, watching as its activity changes and its surface evolves.”

A long and hard journey

While Philae begins its close-up study of the comet, Rosetta must manoeuvre from its post-separation path back into an orbit around the comet, eventually returning to a 20 km orbit on 6 December.

Next year, as the comet grows more active, Rosetta will need to step further back and fly unbound ‘orbits’, but dipping in briefly with daring flybys, some of which will bring it within just 8 km of the comet centre.

The comet will reach its closest distance to the Sun on 13 August 2015 at about 185 million km, roughly between the orbits of Earth and Mars. Rosetta will follow it throughout the remainder of 2015, as they head away from the Sun and activity begins to subside.

“It’s been an extremely long and hard journey to reach today’s once-in-a-lifetime event, but it was absolutely worthwhile. We look forward to the continued success of the great scientific endeavour that is the Rosetta mission as it promises to revolutionise our understanding of comets,” said Fred Jansen, ESA Rosetta mission manager.

You can keep up to date with the latest Rosetta news at ESA’s Rosetta blog.

Adapted from information issued by ESA. Images courtesy ESA / Rosetta / Philae / CIVA.

The day we met Halley

HISTORY WAS MADE 25 years ago when a small spacecraft swept to within 600 km of Halley’s comet. The European Space Agency’s (ESA) Giotto probe was nearly destroyed by the encounter, but what it saw changed our picture of comets forever.

As debuts go, it doesn’t get any better than Giotto. The spacecraft was ESA’s first deep-space mission. Built to a design that drew on the Geos Earth-orbiting research satellites, it was fitted with shielding to protect it from the ‘sand-blasting’ it was going to receive as it sped through the comet’s tail.

It was originally conceived as a joint mission with NASA, the Tempel-2 Rendezvous-Halley Intercept mission. When the USA pulled out after budget cuts, ESA took the bold decision to forge on, finding Japan and Russia willing to contribute their own missions. Together, they sent a flotilla, with the Russian missions serving as pathfinders to guide Giotto to its dangerous encounter.

Comet Halley's nucleus

Giotto's encounter with Comet Halley provided the first ever opportunity to take images of a comet nucleus, which turned out to be blacker than coal.

Scientists, controllers and engineers gathered at ESA’s control centre in Darmstadt, Germany, on the night of 13-14 March 1986 to witness the flyby.

“It was a once-in-a-lifetime event and it had a big impact on the general public,” says Giotto’s former Deputy Project Scientist, Gerhard Schwehm.

Heart of the comet

The scientific harvest from Giotto changed people’s perception of comets. By measuring its composition, Giotto confirmed Halley as a primitive remnant of the Solar System, billions of years old. It detected complex molecules locked in Halley’s ices that could have provided the chemical building blocks of life on Earth.

Yet the biggest triumph was the image of Halley itself. “It may sound simple to say that but the picture was the best thing, the moment you saw it…it was tremendous,” remembers Gerhard.

Countless people have seen the ghostly shimmer of Halley’s comet from Earth. Records of it stretch back to China in 240 BCE. It famously appears on the Bayeux Tapestry, and the Italian artist Giotto di Bondone used it to symbolize the star of Bethlehem in his masterpiece, The Adoration of the Magi.

Part of the Bayeux Tapestry

Comet Halley, in its 1066 appearance, is shown in the Bayeux Tapestry.

But none saw what his spacecraft namesake saw: the very heart of the comet, the nucleus.

Just 10 x 15 km, it surprised everyone by being darker than coal, reflecting just 4% of the light falling on its surface.

Instead of the whole surface boiling away, ‘jets’ were localized in specific areas.

Life after Halley

Giotto nearly did not survive. As expected, the probe was pummelled. Dust from the comet ripped into it at speeds of 68 km/s, eroding away the shielding and the sensors, destroying the camera.

But Giotto itself lived on and was sent to meet a second comet, Grigg-Skjellerup, in 1992.

Since Giotto’s encounter, Halley has continued its journey, covering about a third of its 76-year orbit. Although it will not return until 2061, there are other cometary targets.

“Giotto ignited the planetary science community in Europe—we had demonstrated that we could successfully lead demanding missions—and people started thinking about what else we could do,” says Gerhard.

Artist's impression of the Rosetta spacecraft

ESA's Rosetta spacecraft is on its way to a rendezvous with Comet 67P/Churyumov-Gerasimenko in 2014.

ESA’s Rosetta mission is next. The spacecraft is en route to comet Churyumov-Gerasimenko, for arrival in 2014. It will study the comet and release a lander to analyse the surface material.

Recently, Rosetta flew by asteroid Lutetia and is now preparing to hibernate for the rest of its cruise. Once at Churyumov-Gerasimenko, Rosetta will follow the comet for months.

Where Giotto gave us the night of the comet, Rosetta promises the year of the comet.

Adapted from information issued by ESA. Image credits: Halley Multicolour Camera Team / Giotto Project / ESA / AOES Medialab.

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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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Zooming in on an asteroid

Approaching asteroid Lutetia

A sequence of images taken by the Rosetta spacecraft as it closed in on the asteroid Lutetia on July 10, 2010.

Europe’s comet-bound spacecraft Rosetta flew past the asteroid Lutetia on July 10, 2010, sending back tremendous images of the 130km-long rocky world.

The European Space Agency has put together this sequence of images (above) to show us what the view was like as Rosetta approached Lutetia. The rotation of the asteroid can be discerned, as can the craters pock-marking its surface.

Rosetta’s closest approach came at a distance of 3,162 kilometres.

Rosetta is on course for a rendezvous with its ultimate target, the comet Churyumov-Gerasimenko, which it will reach in 2014.

For more Rosetta images of Lutetia, see our earlier story, Asteroid fly-by success!

Adapted from information issued by OSIRIS Team MPS / UPD / LAM / IAA / RSSD / INTA / UPM / DASP / IDA.

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Asteroid fly-by success!

Asteroid Lutetia

An amazing image of asteroid Lutetia taken at the moment of closest approach during the fly-by successfully accomplished by the Rosetta spacecraft.

  • Fly-by of asteroid of Lutetia accomplished
  • Rosetta spacecraft worked flawlessly
  • Now on target for Comet Churyumov-Gerasimenko

Asteroid Lutetia has been revealed as a battered world of many craters.

The European Space Agency’s (ESA) Rosetta mission has returned the first close-up images of the asteroid, showing that it is most probably a primitive survivor from the violent birth of the Solar System.

Asteroid Lutetia

At a distance of 36,000km, the OSIRIS Narrow Angle Camera (NAC) took this image of Lutetia, catching the planet Saturn in the background.

The fly-by has been a spectacular success with Rosetta performing faultlessly. Closest approach took place at 2:10am Sunday, Sydney time, (16:10 UTC Saturday), at a distance of 3,162 km.

The images show that Lutetia is heavily cratered, having suffered many impacts during its 4.5 billion years of existence. As Rosetta drew close, a giant bowl-shaped depression stretching across much of the asteroid rotated into view.

The images confirm that Lutetia is an elongated body, with its longest side around 130km.

The images come from the OSIRIS instrument, which combines a wide angle and a narrow angle camera. At closest approach, details down to a scale of 60 metres can be seen over the entire surface of Lutetia.

“I think this is a very old object. Tonight we have seen a remnant of the Solar System’s creation,” says Holger Sierks, OSIRIS principal investigator, Max Planck Institute for Solar System Research, Lindau.

Rosetta raced past the asteroid at 15 km/s, completing the fly-by in just one minute. But the cameras and other instruments had been working for hours and in some cases days beforehand, and will continue afterwards. Shortly after closest approach, Rosetta began transmitting data to Earth for processing.

Asteroid Lutetia

A sequence of images taken as Rosetta approached Lutetia. The first image was taken about 9.5 hours before closest approach, 510000 km from the asteroid; the last one about 1.5 hours before closest approach, 8,100 km from the asteroid. The resolution changes from 9.6 km/pixel to 1.5 km/pixel.

Asteroid Lutetia

The final sequence of images of Lutetia before Rosetta's closest approach.

Ready for its next target

Lutetia has been a mystery for many years. Ground-based telescopes have shown that the asteroid presents confusing characteristics.

In some respects it resembles a C-type asteroid, a primitive body left over from the formation of the Solar System. In others, it looks like an M-type asteroid. These have been associated with iron meteorites, are usually reddish in colour and thought to be fragments of the cores of much larger objects.

Rosetta operated a full suite of instruments at the encounter, looking for evidence of a thin atmosphere, magnetic effects, and surface chemical composition as well as the asteroid’s density.

Asteroid Lutetia

Farewell Lutetia — Rosetta looked back for a final glimpse as it zoomed past.

They also attempted to catch any dust grains that may have been floating in space near the asteroid for on-board analysis. The results from these instruments will come in time.

The fly-by marks the attainment of one of Rosetta’s main objectives. The spacecraft will now continue to its primary target, 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 nucleus.

Adapted from information issued by ESA 2010 MPS for OSIRIS Team  / MPS / UPD / LAM / IAA / RSSD / INTA / UPM / DASP / IDA.

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Rosetta’s blind date with Lutetia

Artist’s impression of Rosetta about to rendezvous with Comet 67P/Churyumov-Gerasimenko in 2014.

Artist’s impression of Rosetta's rendezvous with Comet 67P/Churyumov-Gerasimenko in 2014.

  • Rosetta probe on its way to a comet
  • Will fly past an asteroid on July 10
  • Comet rendezvous due in 2014

ESA’s comet-chaser spacecraft Rosetta is heading for a blind date with asteroid Lutetia. Rosetta does not yet know what Lutetia looks like up-close, but beautiful or otherwise, the two will meet on July10.

Like many first dates, Rosetta will meet Lutetia on a Saturday night, flying to within 3,200 km of the space rock. Rosetta started taking navigational sightings of Lutetia at the end of May so that ground controllers can determine any course corrections required to achieve their intended flyby distance.

The close pass will enable around two hours of good imaging. The spacecraft will instantly begin beaming the data back to Earth and the first pictures will be released later that evening.

Rosetta flew by asteroid Steins in 2008, and other space missions have encountered a handful of asteroids. Each asteroid has proven to be an individual and Lutetia is expected to continue the trend.

An animation of asteroid (2867) Steins

An animation of asteroid (2867) Steins, which was visited by Rosetta in September 2008.

The mystery of Lutetia

Although recent high-resolution ground-based images have given some idea of the overall shape of Lutetia, astronomers no idea what it looks like in detail. Rosetta will tell us that.

Orbiting in the main belt of asteroids between Mars and Jupiter, initially it was thought that Lutetia is around 95 km in diameter but only mildly off-circular. Recent estimates suggest 134 km, with a pronounced elongated shape. Rosetta will tell us for certain and will also investigate the composition of the asteroid, wherein lies another mystery.

By any measure, Lutetia is quite large. Planetary scientists believe that it is a primitive asteroid, left on the shelf for billions of years because no planet consumed it as the Solar System formed. Indeed, most measurements appear to back this picture, making the asteroid out to be a ‘C-type’, which contains primitive compounds of carbon.

However, some measurements suggest that Lutetia is an ‘M-type’, which could mean there are metals in its surface. “If Lutetia is a metallic asteroid then we have found a real winner,” says Rita Schulz, ESA Rosetta Project Scientist.

That’s because although metallic asteroids do exist, they are thought to be fragments of the metallic core of larger asteroids that have since been shattered into pieces. If Lutetia is made of metal or even contains large amounts of metal, Dr Schulz says that the traditional asteroid classification scheme will need rethinking. “C-class asteroids should not have metals on their surfaces,” she says.

A busy fly-by

Asteroid science stands to gain once this observational conundrum is resolved because Rosetta’s data will provide a valuable collection of ‘ground truths’ that can be used to resolve conflicting ground-based observations not just for Lutetia but for other asteroids as well.

For 36 hours around the moment of closest approach, Rosetta will be in almost continuous contact with the ground. The only breaks will come as Earth rotates and engineers have to switch from one tracking station to another.

Artist’s impression of Rosetta as it flies by asteroid Steins

Rosetta encountered asteroid Steins in 2008. Next stop is asteroid Lutetia on July 10, 2010.

Good contact is essential because the uncertainties in the asteroid’s position and shape may demand last minute fine-tuning to keep it centred in Rosetta’s instruments during the flyby. “The skeleton of the operation is in place, and we have the ability to update our plans at any time,” says Andrea Accomazzo, ESA Rosetta Spacecraft Operations Manager.

Stay in touch with the flyby as it happens by visiting the Rosetta blog.

Mission to a comet

Rosetta’s 11-year expedition began in March 2004, with an Ariane 5 launch from Kourou in French Guiana, and the spacecraft was then sent towards the outer Solar System. The long journey includes three gravity assists at Earth (2004, 2007, 2009), one at Mars (2007), and two asteroid encounters: (2867) Steins (2008) and (21) Lutetia (2010).

After the third Earth-gravity assist and a large deep-space manoeuvre, the spacecraft will go into hibernation (July 2011 – January 2014). During this period, Rosetta will record its maximum distances from the Sun (about 800 million kilometres) and Earth (about 1 thousand million kilometres).

The spacecraft will be reactivated prior to the comet-rendezvous manoeuvre, during which the thrusters will fire for several hours to slow the relative drift rate between the spacecraft and comet to about 25 m/s.

Built by EADS Astrium, the Rosetta probe consists of a 3,065-kg spacecraft (1,578-kg dry mass) designed to enter orbit around the comet’s nucleus in August 2014 after a series of gravity assist manoeuvres to gain enough orbital energy, with three swing-bys at Earth (March 2005, November 2007 and November 2009) and one at Mars (February 2007).

The spacecraft carries 11 science instruments to probe the comet’s nucleus and map its surface in fine detail. It will also land a package of instruments (the Philae Lander) to study some of the most primitive, unprocessed material in the Solar System.

The mission will provide clues to the physical and chemical processes at work during the formation of planets, beginning 4.6 billion years ago.

Adapted from information issued by ESA / C.Carreau / AOES Medialab / J. Huart.