A detailed update on the efforts to contact Philae

Link here.

The story is fascinating because the lander’s behavior and response to commands has been quite puzzling. They have had about a half dozen short contacts of varying length, all interspersed with a lot of intermittencies. At the moment they have not entirely given up on Philae, since based on what they know of its location and condition it could remain functional through the end of this year. They also recognize that re-establishing contact is becoming increasingly unlikely. The big hope is that once the comet moves farther away from the sun and becomes less active, they will be able to move Rosetta in closer, when the chances of contact will improve.

Comet 67P/C-G goes boom!

Outburst on Comet 67P/C-G

Cool image time! On August 22, just days after its closest approach to the sun, Rosetta caught the outburst, image above, from the larger lobe on Comet 67P/C-G.

The image scale is 28.6 m/pixel and the image measures 29.3 km across. Although the activity is extraordinarily bright even in the original (below), the image above has been lightly enhanced to give a better view of the outline of the nucleus in the lower part of the image, as well as to show the full extent of the activity.

The most interesting images, I think, will actually come later, when the activity dies down and they can bring Rosetta in closer again. We will then be able to compare the nucleus both before and after this outburst, getting a sense of how the comet changes with each close pass to the sun.

Comet 67P/C-G’s fractured surface

Rosetta scientists today published a paper describing the many different types of fractures they have identified on the surface of Comet 67P/C-G.

Ramy’s team identified three distinct settings in which the fractures occur: networks of long narrow fractures, fractures on cliffs and fractured boulders. In addition, several unique features were identified: the parallel fractures running across Hathor’s 900 m-high cliffs, an isolated 500 metre-long crevice in the Anuket region of the comet’s neck, and a 200 m-long complex crack system in Aker on the large lobe. “The fractures show a variety of morphologies and occur all over the surface and at all scales: they are found in the towering 900 m-high cliffs of Hathor right down to the surfaces of boulders a few metres across,” describes lead author M. Ramy El-Maarry from the University of Bern.

The most prevalent setting appears to be networks of narrow fractures that extend for a few metres to 250 m in length, typically on relatively flat surfaces. Interestingly, in some locations, the fractures appear to cross cut each other in polygonal patterns at angles of 90º – on Earth and Mars this is often an indicator of ice that has contracted below the surface.

While their focus is on the geology of the comet and its development as indicated by the fractures, what I see is the root cause of the comet’s eventual destruction. Its two-lobed shape is inherently unstable, and these fractures illustrate this. At some point, the comet will break apart. The fractures indicate where the first breaks might occur.

Sudden outburst activity on Comet 67P/C-G

jet on Comet 67P/C-G

Cool image time! As Comet 67P/C-G approaches perihelion, Rosetta is detecting and imaging more and more activity coming from the nucleus, including a power outburst lasting less than a half hour.

In the approach to perihelion over the past few weeks, Rosetta has been witnessing growing activity from Comet 67P/Churyumov–Gerasimenko, with one dramatic outburst event proving so powerful that it even pushed away the incoming solar wind.

The comet reaches perihelion on Thursday, the moment in its 6.5-year orbit when it is closest to the Sun. In recent months, the increasing solar energy has been warming the comet’s frozen ices, turning them to gas, which pours out into space, dragging dust along with it.

The three pictures above were taken 18 minutes apart. The first shows nothing, and in the last the jet has almost completed dissipated. In the middle image, however, the jet is well defined, and data from the spacecraft indicated that it was so strong that it “had pushed away the solar wind magnetic field from around the nucleus.”

Philae results published

Cool image time! The Philae science team yesterday published in Science a set of papers describing their results from the lander’s approach and bouncing landing on Comet 67P/C-G.

Data were obtained during the lander’s seven-hour descent to its first touchdown at the Agilkia landing site, which then triggered the start of a sequence of predefined experiments. But shortly after touchdown, it became apparent that Philae had rebounded and so a number of measurements were carried out as the lander took flight for an additional two hours some 100 m above the comet, before finally landing at Abydos.

Some 80% of the first science sequence was completed in the 64 hours following separation before Philae fell into hibernation, with the unexpected bonus that data were ultimately collected at more than one location, allowing comparisons between the touchdown sites.

The images from lander so far released show the approach to the first site, with one boulder getting larger and larger as it descends, followed by images at the final landing site, showing a fractured, uneven, and very rough surface with the lander apparently sitting sideways with one foot off the ground.

An animation of the first touchdown, created by these images, can be viewed here.

Update: A good summary of the results can be read here.

How Comet 67P/C-G interacts with the solar wind

Accumulating data from Rosetta is now giving scientists an excellent picture of how this comet interacts with the solar wind as it moves in towards its closest approach to the Sun.

They have seen that the number of water ions – molecules of water that have been stripped of one electron – accelerated away from the comet increased hugely as 67P/C-G moved between 3.6AU (about 538 million km) and 2.0AU (about 300 million km) from the Sun. Although the day-to-day acceleration is highly variable, the average 24-hour rate has increased by a factor of 10,000 during the study, which covered the period August 2014 to March 2015.

The water ions themselves originate in the coma, the atmosphere of the comet. They are placed there originally by heat from the Sun liberating the molecules from the surface ice. Once in gaseous form, the collision of extreme ultraviolet light displaces electrons from the molecules, turning them into ions. Colliding particles from the solar wind can do this as well. Once stripped of some of their electrons, the water ions can then be accelerated by the electrical properties of the solar wind.

Not all of the ions are accelerated outwards, some will happen to strike the comet’s surface. Solar wind particles will also find their way through the coma to hit home. When this happens, they cause a process called sputtering, in which they displace atoms from material on the surface – these are then ‘liberated’ into space.

There’s more at the link, including animations and simulations.

Philae status update

Engineers on the Rosetta team are struggling to figure out why they cannot get a solid communications lock with their Philae lander, and have come up with several explanations.

One possible explanation being discussed at DLR’s Lander Control Center is that the position of Philae may have shifted slightly, perhaps by changing its orientation with respect to the surface in its current location. The lander is likely situated on uneven terrain, and even a slight change in its position – perhaps triggered by gas emission from the comet – could mean that its antenna position has also now changed with respect to its surroundings. This could have a knock-on effect as to the best position Rosetta needs to be in to establish a connection with the lander.

Another separate issue under analysis is that one of the two transmission units of the lander appears not to be working properly, in addition to the fact that one of the two receiving units is damaged. Philae is programmed to switch periodically back and forth between these two transmission units, and after tests on the ground reference model, the team has sent a command to the lander to make it work with just one transmitter. As Philae is able to receive and accept commands of this kind in the “blind”, it should execute it as soon as it is supplied with solar energy during the comet’s day.

They have heard from Philae since July 9. Because of comet activity they have had to pull Rosetta back away from the nucleus to protect it, and are now focusing its primary activity on observations, not communications with Philae. They will continue to try to bring Philae back to full functioning life, but the priority is now the comet.

The approaching perihelion of Comet 67P/C-G

The Rosetta science team has prepared a FAQ outlining what we should expect next month as Comet 67P/C-G reaches and passes its closest point to the Sun, with Rosetta (and hopefully Philae) there to watch.

The most interesting detail they note is this:

Will the comet break apart during perihelion?

The comet has not broken apart during its many previous orbits, so it is not expected to do so this time, but it cannot be ruled out. Scientists are keen to watch the possible evolution of a 500 m-long fracture that runs along the surface of the neck on the comet during the peak activity.

You can see an image from Rosetta that shows this fracture here. As I wrote then,

The biggest fracture line appears to be a meandering line that is traveling from the image’s top center to its mid-right. There also appear to be parallel lines below it. As we are looking at the nucleus’s neck, these lines suggest that the connection between the two large lobes is somewhat strained, and that it is not unlikely that these two sections will break apart at some time in the future. Though there is no way to predict at this time when that will happen, it will be truly exciting if it happens when Rosetta is in the neighborhood.

New radio communications from Philae

On July 9 Philae successfully transmitted data to Rosetta for the first time in more than two weeks.

Although the connection failed repeatedly after that, it remained completely stable for those 12 minutes. “This sign of life from Philae proves to us that at least one of the lander’s communication units remains operational and receives our commands,” said Koen Geurts, a member of the lander control team at DLR Cologne.

The mood had been mixed over the last few days; Philae had not communicated with the team in the DLR Lander Control Center (LCC) since 24 June 2015. After an initial test command to turn on the power to CONSERT on 5 July 2015, the lander did not respond. Philae’s team began to wonder if the lander had survived on Comet 67P/Churyumov-Gerasimenko.

The intermittent nature of Philae’s attempts at communication are puzzling. Normally, they either would have communications or they would not. For good communications to break off like this repeatedly is puzzling. It is almost as if there is a loose wire causing communications to go on and off, which seems an unlikely explanation for this problem.

The jets on Comet 67P/C-G come from its sinkholes

More on the comet sinkholes! New data from Rosetta has now confirmed that some of the plumes or jets that the spacecraft has seen emanating from Comet 67P/C-G come directly from the sinkholes that they have discovered on the nucleus.

In a study reported today in the science journal Nature, 18 quasi-circular pits have been identified in the northern hemisphere of the comet, some of which are the source of continuing activity. The pits are a few tens to a few hundreds of metres in diameter and extend up to 210 m below the surface to a smooth dust-covered floor. Material is seen to be streaming from the most active pits. “We see jets arising from the fractured areas of the walls inside the pits. These fractures mean that volatiles trapped under the surface can be warmed more easily and subsequently escape into space,” says Jean-Baptiste Vincent from the Max Planck Institute for Solar System Research, lead author of the study.

Active sinkholes found on Comet 67P/C-G

pits on Comet 67P/C-G

Cool image time! Using Rosetta’s high resolution camera scientists have located a number of active pits similar to sinkholes on Earth on Comet 67P/C-G.

Based on the Rosetta observations, the team has proposed a model for the formation of these sinkholes. A source of heat beneath the comet’s surface causes ices (primarily water, carbon monoxide and carbon dioxide) to sublimate. The voids created by the loss of these ice chunks eventually grow large enough that their ceilings collapse under their own weight, giving rise to the deep, steep-sided circular pits seen on the surface of comet 67P/Churyumov-Gerasimenko.

The collapse exposes comet ices to sunlight for the first time, which causes the ice chunks to begin sublimating immediately. These deeper pits are therefore thought to be relatively young. Their shallower counterparts, on the other hand, are most likely older sinkholes with more thoroughly eroded sidewalls and bottoms that have been filled in by dust and ice chunks.

Essentially, they have found that decay of the comet’s nucleus has been mostly gentle and steady, rather than explosive, punctuated with sudden abrupt events.

An update on Rosetta’s effort to re-establish contact with Philae

This update describes the status of the effort by the Rosetta science team to re-establish a stable communications channel with the Philae lander on the surface of Comet 67P/C-G.

Confirmed contacts between Rosetta and Philae have been made on 13, 14, 19, 20, 21, 23, and 24 June, but were intermittent during those contact periods. For example, the contact on 19 June was stable but split into two short periods of two minutes each. Conversely, the contact on 24 June started at 17:20 UT (on board Rosetta) and ran for 20 minutes, but the quality of the link was very patchy and only about 80 packets of telemetry were received. Prior to this, on Tuesday, 23 June, there was a 20-second contact, but no stable link was established and consequently no telemetry data were received.

There are many reasons why the contacts have been so intermittent, much of it related to Philae’s position on the surface. To improve things, they are carefully adjusting Rosetta’s position relative to the comet while avoiding placing the spacecraft in a position where the coma’s dust will cause problems.

The icy patches on Comet 67P/C-G

Data from Rosetta’s high resolution camera have identified more than a hundred small patches of ice on the surface of Comet 67P/C-G.

Some of these bright features are found in clusters, while others appear isolated, and when observed at high resolution, many of them appear to be boulders displaying bright patches on their surfaces.

The clusters of bright features, comprising a few tens of metre-sized boulders spread over several tens of metres, are typically found in debris fields at the base of cliffs. They are most likely the result of recent erosion or collapse of the cliff wall revealing fresher material from below the dust-covered surface.

By contrast, some of the isolated bright objects are found in regions without any apparent relation to the surrounding terrain. These are thought to be objects lifted up from elsewhere on the comet during a period of cometary activity, but with insufficient velocity to escape the gravitational pull of the comet completely.

Most of the images from Rosetta’s high resolution camera have been held back so that the project scientists could publish their papers from the data. This release is in conjunction with one of those papers [pdf].

Philae contacts Rosetta again

Philae today sent another 2 minutes worth of information to Rosetta.

The downlink was stable; the two contacts received by Rosetta lasted two minutes each. Both delivered numerous packets of lander housekeeping and status data, 185 in total, which are still being analysed at the time of this writing. No science data were anticipated or received.

Rosetta repositions to improve contact with Philae

Engineers have begun shifting Rosetta’s trajectory paralleling Comet 67P/C-G in order to maximize communications with the lander Philae.

Commands to adjust the trajectory were successfully uploaded Monday evening; further commands will be uplinked on Thursday evening. The spacecraft will perform two manoeuvres, one on Wednesday morning and the second on Saturday morning. The effect of the two ‘dog-leg’ burns will be to bring the orbiter to a distance of 180 km from the comet and to reproduce the orbiter-comet geometry of the first contact.

We should therefore not expect further news from Philae for the rest of this week.

Is this Philae?

Philae?

Cool image time! The Rosetta science team has spent much effort trying to locate Philae, which attempted to land on Comet 67P/C-G in November. The image on the right shows what they think is their best candidate, the bright feature in the center. It was not there prior to Philae’s landing attempt.

Because there are many uncertainties, however, this might not be Philae.

Ultimately, a definitive identification of this or any other candidate as being Philae will require higher-resolution imaging, in turn meaning closer flybys. This may not be possible in the near-term, as issues encountered in navigating close to the comet mean that the opportunity to make flybys at significantly less than 20 km from the surface may be on hold until later in the mission. But after the comet’s activity has subsided, Rosetta should be able to safely operate in close proximity to the comet nucleus again.

The other possibility of further refining Philae’s location would come if the lander were to receive enough power to wake-up from its hibernation and resume its scientific study of 67P/C-G. Then, CONSERT could be used to perform additional ranging measurements and significantly reduce the uncertainties on the lander’s location. At the moment, Philae is still in hibernation, but the mission team remain hopeful that, as the comet moves closer to the Sun along its orbit, the lander will receive enough power in the coming weeks or months to wake up and transmit a signal to Rosetta.

Jets on Comet 67P/C-G now persist into the night

jets from Comet 67P/C-G

Cool image time! Rosetta’s high resolution camera is now finding that, due to increased activity as Comet 67P/C-G approaches the sun, jets of material now continue to evaporate off the surface even after sunset.

“Only recently have we begun to observe dust jets persisting even after sunset”, says OSIRIS Principal Investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Germany. In the past months, the comet’s activity originated from illuminated areas on the day side. As soon as the Sun set, these jets subsided and did not re-awake until after the next sunrise. (An exception poses an image from 12 March, 2015 showing the onset of a dust jet on the brink of dawn.)

According to OSIRIS scientists, the jets now occurring even after sunset are another sign of the comet’s increasing activity. “Currently, 67P is rapidly approaching perihelion in mid-August”, says Sierks. At the time the image was taken, comet and Sun were only 270 million kilometers apart. “The solar irradiation is getting more and more intense, the illuminated surface warmer and warmer”, Sierks adds.

Because the jets are now remaining active into the night, it is allowing us to see more precisely their points of origin on the surface, which can then be studied more closely in daylight. Previously it was difficult in daylight to pinpoint the exact spot where the jets began.

Rosetta team proposes landing on comet to finish mission

Rather than simply turn off the spacecraft when its funding runs out at the end of 2015, Rosetta’s science team have proposed that the mission get a nine month extension, during which they will slowly spiral into the comet and gently land.

Their proposal is similar to what American scientists did with their NEAR spacecraft, which hadn’t been designed to land on an asteroid but was successfully eased onto the surface of Eros, where it operated for a very short time.

Another major image release from Rosetta

Time for many cool images! The Rosetta science team has just released to the public another batch of images from its navigational camera.

The 1776 images cover the period between 23 September and 21 November 2014, corresponding to Rosetta’s close study of the comet down to distances of just 10 km from the comet centre – 8 km from the surface – and the images taken during and immediately following the landing of Philae on the comet.

You can browse through them at your leisure, making your own discoveries if you have a sharp eye and know something about planetary geology.

Balanced rock on Comet 67P/C-G

balanced rock on Comet 67P/C-G

Cool image time! Rosetta’s high resolution camera has discovered a group of balancing rocks on the surface of Comet 67P/C-G.

The image on the right, cropped and brightened by me, shows the most dramatic of these rocks. The scientists are as yet uncertain on how these rocks got to where they are.

“How this apparent balancing rock on Comet 67P/C-G was formed is not clear at this point,” says OSIRIS Principal Investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Germany. One possibility is that transport processes related to cometary activity played a role, causing such boulders to move from their original site and reach a new location.

It is also possible that the rocks were sitting on a base of ice that simply evaporated away over time.

Rosetta team releases almost 1300 images of Comet 67P/C-G

The science team for Rosetta’s navigation camera have released to the public 1297 images taken of Comet 67P/C-G as the spacecraft began its approach on August 1, 2014 through September 23, 2014.

The release also included a video assembled from these images, showing the comet nucleus as Rosetta approached from August 1 to August 22. I have embedded that video below. As you watch, you will think, “How does this thing stay together?” Though the video shows the nucleus’ rotation at a highly accelerated rate, which exaggerates the stresses on the object, the question is a good one, and in fact, is actually predicting the future. Eventually, this nucleus will break up.

Rosetta records the appearance of a new jet on Comet 67P/C-G

jet appears on comet

Cool image time! Images taken two minutes apart by Rosetta have captured the emergence of a new jet on Comet 67P/C-G.

The two images released today show the remarkable onset of such a jet for the first time. They were taken on 12 March from a distance of 75 kilometres. In the first image, obtained at 07:13 CET, several rays of dust jets frame the upper, illuminated side of the comet. The dark underside shows no such features. Two minutes later, the picture has changed: a spectacular new jet has emerged on the dark side, hurtling dust into space and displaying a clearly discernable fine structure.

This was the first jet observed in a shadowed area, and the scientists think this jet might have started because it was just before dawn there.

Rosetta team adopts new approach strategy

Because of the problems Rosetta experienced during its last close fly-by of Comet 67P/C-G the engineering team has worked out a new approach strategy for future observations.

Essentially, they are postponing any close fly-bys for the near future. Instead, they will observe from farther away, while reassessing the situation and planing for later opportunities.

Meanwhile, on April 12 the next opportunity to listen for Philae begins.

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