ESA Rosetta - Lutetia's Lineaments: Dark side of asteroid hosts hidden crater

ESA's Rosetta spacecraft data. Tracing Lutetia’s grooves.

Credit: ESA /Rosetta /MPS for OSIRIS Team MPS /UPD /LAM /IAA /SSO /INTA /UPM /DASP /IDA

Grooves found on Lutetia, an asteroid encountered by ESA's Rosetta spacecraft, point to the existence of a large impact crater on the unseen side of the rocky world.

ESA's Rosetta spacecraft flew past Lutetia at a distance of 3168 km in July 2010, en route to its 2014 rendezvous with its target comet.

The spacecraft took images of the 100 km-wide asteroid for about two hours during the flyby, revealing numerous impact craters and hundreds of grooves all over the surface.

Impact craters are commonly seen on all Solar System worlds with solid surfaces, recording an intense history of collisions between bodies. However, grooves are much less prevalent.

To date, they have been discovered by visiting spacecraft only on the Martian moon Phobos and the asteroids Eros and Vesta.

The way in which grooves are formed on these bodies is still widely debated, but it likely involves impacts.

Shock waves from the impact travel through the interior of a small, porous body and fracture the surface to form the grooves.

"For Lutetia, by assuming that the grooves were formed in concentric patterns around their source impact crater, we identified 200 such features falling into distinct 'families', correlated with three different impact craters," describes Sebastien Besse, a research fellow at ESA's Technical Centre, ESTEC, in the Netherlands, and lead author of the paper published in Planetary and Space Science this month.

One of the groove systems on Lutetia is associated with the Massilia crater and another with the North Pole Crater Cluster, which comprises a number of superimposed craters. Both are on the asteroid's northern hemisphere.

This anaglyph 3D image of Lutetia can be viewed using stereoscopic glasses with red–green or red–blue filters. 

The two images making up this image were taken several minutes before Rosetta’s closest approach to the asteroid on 10 July 2010. 

The left-eye view was captured at 15:41:39 GMT from a distance of 4274 km from Lutetia’s surface and the right-eye view at 15:41:03 GMT from 4038 km (closest approach was at 15:45 GMT). 

Credit: ESA/H. Sierks (MPS, Göttingen, Germany)

But another group of grooves points to a crater not seen during Rosetta's brief flyby, in the asteroid's southern hemisphere.

Its implied presence has earned it the nickname 'Suspicio'. The grooves related to Suspicio cover a large area on the asteroid, suggesting it may span several tens of kilometres .

By comparison, Massilia, the largest known crater on Lutetia, is about 55 km wide, and the largest of the polar cluster is about 34 km across.

"These three major impacts seriously deformed Lutetia's surface," adds Sebastien.

Looking face on at the North Pole Crater Cluster (purple outline) on asteroid Lutetia, with Massilia crater to the lower left (red outline). 

Marked on the image are the concentric grooves or ‘lineaments’ associated with the large craters. 

The lineaments coloured blue infer the presence of a large crater, nicknamed Suspicio, on the unseen portion of Lutetia. 

Yellow denotes lineaments not associated with any of the craters discussed in this study. 

Credit: ESA /Rosetta /MPS for OSIRIS Team MPS /UPD /LAM /IAA /SSO /INTA /UPM /DASP /IDA

"As with grooves seen on other asteroids that may also be associated with impact events, this study provides new insights into the catastrophic history of these small bodies."

By observing how subsequent small craters lie over the grooves on Lutetia, the scientists determined the relative ages of the three larger cratering events.

Massilia is thought be the oldest of the three craters and the polar cluster the youngest, with Suspicio between.

The authors also looked at other, independent measurements of Lutetia, including ground-based observations with the Infrared Telescope Facility and space-based observations with ESA's Herschel and NASA's Spitzer.

The infra-red location of Suspicio crater on the unseen southern hemisphere of asteroid Lutetia (marked in blue). 

The hidden crater could be up to 45 km in diameter, the blue outlines correspond to diameter estimates of 15, 30 and 45 km, respectively. 

The crater is inferred based on the numerous grooves or ‘lineaments’ seen concentric to the crater in the northern hemisphere of the asteroid. 

There are no image data available for this side of the asteroid, as can be inferred from the blank shape model. 

Credit: ESA /Rosetta /MPS for OSIRIS Team MPS /UPD /LAM /IAA /SSO /INTA /UPM /DASP /IDA

The Infrared Telescope Facility suggested different compositions between the northern and southern hemisphere of the asteroid.

Sebastien and his colleagues propose that a large impact, presumably the one forming Suspicio, excavated enough material of a different composition to account for the observed differences.

"Our study ties together several independent analyses of Lutetia into one coherent story that is consistent with the presence of a large impact crater on the far side of the asteroid," says co-author Michael Küppers, from ESA's Space Astronomy Centre in Spain.

"Four years on and we are delighted still to be learning from just two hours' worth of data collected during the Lutetia flyby," says Matt Taylor, ESA's Rosetta project scientist.

"Rosetta is now in its main mission phase at its comet, where we are on the cusp of fantastic results. Rosetta is a true small bodies mission, two asteroids and one comet in single trip."

More information: S. Besse, M. Küppers, O.S. Barnouin, N. Thomas, J. Benkhoff, "Lutetia׳s lineaments," Planetary and Space Science, Volume 101, 15 October 2014, Pages 186-195, ISSN 0032-0633, dx.doi.org/10.1016/j.pss.2014.07.007

ESA's Rosetta flyby of asteroid Lutetia. - YouTube

A long-awaited data set is finally public (well, long-awaited by me, at least). The Rosetta team has now published their data from the July 10, 2010, flyby of asteroid (21) Lutetia.

At the time, it was the largest asteroid yet visited by a spacecraft, so it dominated the asteroids and comets montage poster I put together.

This data set is absolutely stunning, and my friends in the amateur image processing community wasted no time in creating art out of it. First, I give you a movie of Rosetta's flyby, processed by Ian Regan.

The flickering occurs because Rosetta was cycling through different-color filters as it flew past. I had to play this one a few times. Wow.

ESA Rosetta flyby: The complex history of asteroid Lutetia

The long and tumultuous history of asteroid (21) Lutetia is revealed by a comprehensive analysis of the data gathered by ESA's Rosetta spacecraft when it flew past this large main-belt asteroid on 10 July 2010.

New studies have revealed the asteroid's surface morphology, composition and other properties in unprecedented detail.

In particular, extensive studies of Lutetia's geological features have opened a unique window into the complex history of this peculiar object.

On its way to rendezvous with comet 67P/Churyumov-Gerasimenko, ESA's Rosetta spacecraft flew by the main-belt asteroid (21) Lutetia, reaching the closest approach, at a distance of about 3170 km, on 10 July 2010. From this unique vantage point, Rosetta gathered high-resolution images, spectra, and other data, providing scientists with a valuable dataset with which to probe this peculiar asteroid in great detail.

The first results from the flyby, published in late 2011, revealed the mass and volume of Lutetia, leading to an estimate of the asteroid's density, which turned out to be surprisingly high.

Data from the flyby also suggested that Lutetia is a primordial planetesimal formed during the very early phases of the Solar System. These and other findings called for further investigations about the nature and history of Lutetia.

"The images collected by Rosetta during the flyby have uncovered, for the first time, the wide variety of craters and other geological features that scar the surface of Lutetia," notes Rita Schulz, Rosetta Project Scientist at ESA.

"Scientists have explored this rich pool of data thoroughly in order to characterise many of Lutetia's properties, from its surface morphology and composition to its shape and internal structure, revealing its underlying geological history," she adds. The results of these studies are reported in a series of 21 papers published in a special issue of the journal Planetary and Space Science.

The OSIRIS camera on Rosetta has surveyed the part of Lutetia that was visible during the flyby - about half of its entire surface, mostly coinciding with the asteroid's northern hemisphere.

These unique, close-up images have allowed scientists to identify regions characterised by very distinct geological properties with an accuracy of a few hundred metres.

Counting craters is a powerful tool that is used to compare the regions and to uncover their past history. By recording the number, spatial distribution, shapes and sizes of the hundreds of craters that mark the surface of each region, it is possible to date the epoch when these craters were produced by collisions with smaller bodies. In the case of the largest craters, it is even possible to reconstruct the details of the impact that created them.

By tracing craters and other features on Lutetia's surface, scientists have put together a geological map for the asteroid. Their studies have shown that Lutetia's surface comprises regions spanning a wide range of ages: each of them reveals a chapter in the long and tumultuous history of this asteroid.

At one end of this age spectrum, the two heavily cratered Achaia and Noricum regions represent the most ancient portions on the surface of Lutetia: with ages between 3.4 and 3.7 billion years or more, they are almost as old as the asteroid itself.

Some of the craters that densely populate these two regions date back to an early epoch in the Solar System's history, right after the so-called Late Heavy Bombardment, when the flux of bodies impacting asteroids, planets and their satellites was significantly larger than it is at present.

Massilia, the largest crater identified on the asteroid, is located in a younger region named Narbonensis. With a diameter of 57 km, this crater provides evidence of the most dramatic event in the history of Lutetia: numerical simulations suggest that the 'projectile' responsible for producing this very wide crater was quite large, with a diameter of about 7.5 km.

However, the probability of such a large body colliding with the asteroid is quite low, and so this must have occurred when Lutetia was relatively young.

The youngest patch on the surface of Lutetia is the Baetica region, located in the vicinity of the asteroid's North Pole. This region hosts a number of superimposed craters, named the North Polar Crater Cluster (NPCC), which include three large ones with sizes exceeding 10 km.

These craters represent the signature left by a series of subsequent impacts that took place quite recently on geological timescales - namely, in the last few hundred million years.

The smooth appearance of the craters in Baetica, which have not been dotted yet with many smaller craters, indicate that its surface is much younger than the heavily battered areas of Lutetia.

Furthermore, this region still bears signs of the events that created the NPCC, as indicated by the ejecta that were released during the impacts and then spread on the surrounding area, rather than leaving the asteroid's surface, as a result of its relatively strong gravitational pull. The presence of these 'fresh' deposits, which include many large boulders with sizes up to 300 metres, is another hint at this region's young age.

In addition to craters, other geological markers, such as lineaments and faults, represent an important window into the turbulent past of asteroids and other Solar System bodies.

The remarkable images collected by OSIRIS during the flyby have revealed an intricate network of linear features covering long distances across Lutetia's surface, up to 80 km in some cases.

ESA Rosetta: Asteroid Lutetia: postcard from the past

Landslides on Lutetia are thought to have been caused by the vibrations created by impacts elsewhere on the asteroid dislodging pulverised rocks.

Credits: ESA 2011 MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA

ESA's Rosetta spacecraft has revealed asteroid Lutetia to be a primitive body, left over as the planets were forming in our Solar System. Results from Rosetta's fleeting flyby also suggest that this mini-world tried to grow a metal heart.

Rosetta flew past Lutetia on 10 July 2010 at a speed of 54 000 km/hr and a closest distance of 3170 km.

At the time, the 130 km-long asteroid was the largest encountered by a spacecraft. Since then, scientists have been analysing the data taken during the brief encounter.

All previous flybys went past objects, which were fragments of once-larger bodies. However, during the encounter, scientists speculated that Lutetia might be an older, primitive 'mini-world'.

Several images have been combined into a map of the asteroid.

This image represents the total area viewed by the spacecraft during the flyby, which amounted to more than 50% of Lutetia’s surface.

Credits: ESA 2011 MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA

Now they are much more certain. Images from the OSIRIS camera reveal that parts of Lutetia's surface are around 3.6 billion years old. Other parts are young by astronomical standards, at 50–80 million years old.

Astronomers estimate the age of airless planets, moons, and asteroids by counting craters. Each bowl-shaped depression on the surface is made by an impact.

The older the surface, the more impacts it will have accumulated. Some parts of Lutetia are heavily cratered, implying that it is very old.

On the other hand, the youngest areas of Lutetia are landslides, probably triggered by the vibrations from particularly jarring nearby impacts.

Debris resulting from these many impacts now lies across the surface as a 1 km-thick layer of pulverised rock.

This map of Lutetia is centred on the north pole. 

The number of craters in the asteroid's various regions have been used to date the surface. 

Some parts of the surface are 3.6 billion years old, while others are just 50–80 million years old.

Credits: ESA 2011 MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA

There are also boulders strewn across the surface: some are 300–400 m across, or about half the size of Ayers Rock, in Australia. 

Some impacts must have been so large that they broke off whole chunks of Lutetia, gradually sculpting it into the battered wreck we see today. 

"We don't think Lutetia was born looking like this," says Holger Sierks, Max-Planck-Institut für Sonnensystemforschung, Lindau, Germany. "It was probably round when it formed."

Rosetta's VIRTIS spectrometer found that Lutetia's composition is remarkably uniform across all the observed regions.

"It is striking that an object of this size can bear scars of events so different in age across its surface while not showing any sign of surface compositional variation," says Fabrizio Capaccioni, INAF, Rome, Italy.

 

This is just the start of the mystery.

Read further 

Asteroid Lutetia Wrapped in Thick Dust Blanket

If astronauts ever visit the asteroid Lutetia, they may have to strap on snowshoes to avoid sinking into its nearly half-mile-thick layer of dust.

Dusty debris shrouds the huge asteroid to a depth of at least 2,000 feet (600 meters), scientists have calculated.

The dust probably resembles the regolith found on the moon, and it's a result of the intense cosmic pummeling Lutetia has endured from other space rocks since the birth of the solar system.

"It must have been produced by impacts," said Rita Schulz of the European Space Agency in a media briefing yesterday (Oct. 4) in Pasadena, Calif. The announcement came at a conference organized by the American Astronomical Society's Division of Planetary Sciences.

A visit to Lutetia

The new look at Lutetia, which is located in the asteroid belt between Mars and Jupiter, is the result of a close fly-by made by ESA's Rosetta spacecraft in July. Rosetta, whose chief task is chasing down and studying a comet, zoomed to within 1,900 miles (3,162 km) of Lutetia, making it the largest asteroid ever to be visited by a space probe.

Rosetta snapped some detailed photos and probed the space rock from afar with a suite of instruments. The data confirmed that Lutetia is an elongated body with its longest side spanning approximately 81 miles (130 km), ESA officials have said.

Nonetheless, it took some time for scientists to process and analyse much of Rosetta's data. Over the last few months, they scrutinized some of Lutetia's many craters, measuring how deep they are. Researchers then compared that information with predictions of how deep such craters are expected to be based on theoretical models.

The craters were much shallower than researchers had anticipated, Schulz said, because of the thick layer of dusty debris. Indeed, one of Rosetta's most dramatic photos shows a landslide of dust at the bottom of an enormous crater.

Based on Lutetia's size, Schulz said, the asteroid probably has a relatively high escape velocity — the speed needed to overcome the rock's gravitational pull. So about 90 percent of the debris ejected by Lutetia's many collisions with other cosmic bodies probably falls back onto the space rock's surface. Over the course of 4.6 billion years or so, this would add up to a pretty hefty dust coating.

Scientists think the regolith covering the moon was produced the same way.

ESA's Rosetta successfully flies by asteroid Lutetia

ESA European probe Rosetta successfully flies by asteroid Lutetia

The ESA European spacecraft Rosetta performed a fly-by of a massive asteroid Lutetia, on Saturday, the European Space Agency said, taking images that could one day help Earth defend itself from destruction.

Racing through the asteroid belt between Mars and Jupiter at 47,800 kph (29,925 mph), the billion-euro (1.25-billion-dollar) probe flew within 3,200 kms (2,000 miles) of the huge potato-shaped rock, Lutetia.

"The fly-by has been a spectacular success with Rosetta performing fautlessly," ESA said in a statement.

"Just 24 hours ago, Lutetia was a distant stranger. Now, thanks to Rosetta, it has becomme a close friend," the agency added.

Holger Sierks of Germany's Max Planck Institute, who is in charge of the spacecraft's Osiris (Optical, Spectroscopic and Infrared Remote Imaging System) camera said the more than 400 "phantastic images" showed many craters and details.

"Rosetta opened up a new world which will keep scientists busy for years," he added.

"We have completed the fly-by phase," Rosetta's director of operations Andrea Accomazzo said earlier on the ESA's website from the European Space Operations Centre in Darmstadt, Germany.

The aim of the fly-by of the asteroid, measuring 134 kms (83.75 miles) in diameter, is to measure Lutetia's mass and then calculate its density, knowledge which could one day be a lifesaver, according to ESA scientists.

If a rogue asteroid enters on a collision course with Earth, knowing its density will help the planet's defenders to determine whether they should try to deflect the rock or, instead, blow it up.

As Rosetta is around half a million kilometres from Earth, the probe's signal and images took 25 minutes to be received.

ESA's Rosetta: Date With Asteroid Lutetia

ESA's comet-chaser Rosetta is heading for a blind date with asteroid Lutetia. Rosetta does not yet know what Lutetia looks like but beautiful or otherwise the two will meet on 10 July.

Like many first dates, Rosetta will meet Lutetia on a Saturday night, flying to within 3200 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 allow around 2 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.

For a start, no one knows what it looks like. Orbiting in the main belt of asteroids between Mars and Jupiter, it appears as a single point of light to ground telescopes. The continuous variation in its brightness makes it clear that Lutetia is rotating and has an uneven surface. These observations allow astronomers to estimate its shape and size, but their determinations all differ.

Initially it was thought that Lutetia is around 95 km in diameter but only mildly elliptical. A more recent estimate suggests 134 km, with a pronounced elongation. 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 is 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.

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.

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.