Philae has been found! Credit: Main image and lander inset: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; context: ESA/Rosetta/ NavCam.
The search is over, and looking at these images, no wonder it was so hard to find the little Philae lander!
The high-resolution camera on board the Rosetta spacecraft has finally spotted Philae “wedged into a dark crack on Comet 67P/Churyumov-Gerasimenko,” the ESA team said. They also said that now, seeing the lander’s orientation, it’s clear why establishing communications was so difficult following its landing on November 12, 2014.
Close-up of the Philae lander. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Rosetta, orbiting the comet and getting ready for its own demise/touchdown on 67P, focused its OSIRIS narrow-angle camera towards a few candidate sites on September 2, 2016 as the orbiter came just 2.7 km of the comet’s surface. Clearly visible in the zoomed in versions are the main body of the lander, along with two of its three legs.
“With only a month left of the Rosetta mission, we are so happy to have finally imaged Philae, and to see it in such amazing detail,” says Cecilia Tubiana of the OSIRIS camera team, the first person to see the images when they were downlinked from Rosetta on September 4.
Tubiana told Universe Today via email that Philae wasn’t too hard to find in the images. “Philae was in hiding in shadow, and as soon as we stretched the brightness to ‘see’ into the shadow, Philae was there!”
She added that nothing else about Philae’s condition has been revealed from the images so far.
The Philae lander was last seen after it first touched down at a region called Agilkia on the odd-shaped, two-lobed comet 67P. During its dramatic touchdown, the lander flew, landed, bounced and then repeated that process for more than two hours across the surface, with three or maybe four touchdowns. The harpoons that were to anchor Philae to the surface failed to fire, and scientists estimated the lander may have bounced as high as 3.2 kilometers (2 miles) before becoming wedged in the shadows of a cliff on the comet. After three days, Philae’s primary battery ran out of power and the lander went into hibernation, only to wake up again and communicate briefly with Rosetta in June and July 2015 as the comet came closer to the Sun and more power was available.
Philae’s final location had been plotted but until yesterday, never actually seen by Rosetta’s cameras. Radio ranging data was used to narrow down the search to an area spanning a few tens of meters, and a number of potential candidate objects were identified in relatively low-resolution images taken from larger distances.
Philae close-up, labelled. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.
Compare some of the features of the cliff in the image above to this image taken by Philae of its surroundings:
The Philae lander captured a picture of a nearby cliff, nicknamed “Perihelion Cliff”, on the nucleus of Comet 67P/Churyumov-Gerasimenko. Credit: ESA/Rosetta/Philae/CIVA.
“After months of work, with the focus and the evidence pointing more and more to this lander candidate, I’m very excited and thrilled that we finally have this all-important picture of Philae sitting in Abydos,” said ESA’s Laurence O’Rourke, who has been coordinating the search efforts over the last months at ESA, with the OSIRIS and SONC/CNES teams.
At 2.7 km, the resolution of the OSIRIS narrow-angle camera is about 5 cm/pixel, which is sufficient to reveal features of Philae’s 1 m-sized body and its legs.
“This wonderful news means that we now have the missing ‘ground-truth’ information needed to put Philae’s three days of science into proper context, now that we know where that ground actually is!” says Matt Taylor, ESA’s Rosetta project scientist.
An OSIRIS narrow-angle camera image taken on 2 September 2016 from a distance of 2.7 km in which Philae was definitively identified. The image has been processed to adjust the dynamic range in order to see Philae while maintaining the details of the comet’s surface. Philae is located at the far right of the image, just above center. The image scale is about 5 cm/pixel. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.
The discovery comes less than a month before Rosetta descends to the comet’s surface. On September 30, the orbiter will be sent on a final one-way mission to investigate the comet from close up, including the open pits in a region called Ma’at, where it is hoped that critical observations will help to reveal secrets of the body’s interior structure.
“Now that the lander search is finished we feel ready for Rosetta’s landing, and look forward to capturing even closer images of Rosetta’s touchdown site,” adds Holger Sierks, principal investigator of the OSIRIS camera.
The Rosetta team said they would be providing more details about the search as well as more images in the near future.
Rosetta’s scientific camera OSIRIS show the sudden onset of a well-defined jet-like feature emerging from the side of the comet’s neck, in the Anuket region. Image Credit: ESA/Rosetta/OSIRIS
A comet on a comet? That’s what it looks like, but you’re witnessing the most dramatic outburst ever recorded at 67P/Churyumov-Gerasimenko by the Rosetta spacecraft. The brilliant plume of gas and dust erupted on July 29 just two weeks before perihelion.
In a remarkable display of how quickly conditions on a comet can change, the outburst lasted only about 18 minutes, but its effects reverberated for days.
In this sequence of images, the one at left was taken at 8:06 a.m. CDT and doesn’t show any visible signs of the jet. 18 minutes later at 8:24, it’s very bright and distinct (middle image) with only residual traces of activity remaining in the final photo made at 8:42. The photos were taken from a distance of 116 miles (186 km) from the center of the comet. Copyright: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
In a sequence of images taken by Rosetta’s scientific camera OSIRIS, the brilliant, well-defined jet erupts from the side of the comet’s neck in the Anuket region. It was first seen in a photo taken at 8:24 a.m. CDT, but not in one taken 18 minutes earlier, and had faded significantly in an image captured 18 minutes later. The camera team estimates the material in the jet was traveling at a minimum of 22 mph (10 meters/sec), but possibly much faster.
It’s the brightest jet ever seen by Rosetta. Normally, the camera has to be set to overexpose 67P/C-G’s nucleus to reveal the typically faint, wispy jets. Not this one. You can truly appreciate its brilliance because a single exposure captures both nucleus and plume with equal detail.
Jets are normally faint and require special processing or longer exposures to bring out in photos., overexposing the nucleus in the process. Comet 67P/Churyumov-Gerasimenko photographed from about 125 miles away on June 5 Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
We all expected fireworks as the comet approached perihelion in its 6.5 year orbit around the Sun. Comets are brightest at and shortly after perihelion, when they literally “feel the heat”. Solar radiation vaporizes both exposed surface ices and ice locked beneath the comet’s coal-black crust. Vaporizing subsurface ice can created pressurized pockets of gas that seek a way out either through an existing vent or hole or by breaking through the porous crust and erupting geyser-like into space.
Jets carry along dust that helps create a comet’s fuzzy coma or temporary atmosphere, which are further modified into tails by the solar wind and the pressure of sunlight. When conditions and circumstances are right, these physical processes can build comets, the sight of which can fill the human heart with both terror and wonder.
The decrease in magnetic field strength measured by Rosetta’s RPC-MAG instrument during the outburst event on July 29, 2015. This is the first time a ‘diamagnetic cavity’ has been detected at Comet 67P/Churyumov–Gerasimenko and is thought to be caused by an outburst of gas temporarily increasing the gas flux in the comet’s coma, and pushing the pressure-balance boundary between it and incoming solar wind farther from the nucleus than expected under ‘normal’ levels of activity. Credit: ESA/Rosetta/RPC/IGEP/IC
This recent show of activity may be just the start of a round of outbursts at 67P/C-G. While perihelion occurs on this Thursday, a boost in a comet’s activity and brightness often occurs shortly after, similar to the way the hottest part of summer lags behind the date of summer solstice.
Rosetta found that the brief and powerful jet did more than make a spectacle — it also pushed away the solar wind’s magnetic field from around the nucleus as observed by the ship’s magnetometer. Normally, the Sun’s wind is slowed to a standstill when it encounters the gas cloud surrounding the nucleus.
“The solar wind magnetic field starts to pile up, like a traffic jam, and eventually stops moving towards the comet nucleus, creating a magnetic field-free region on the Sun-facing side of the comet called a ‘diamagnetic cavity’,” explained Charlotte Götz, magnetometer team member, on the ESA Rosetta website.
The red circle shows the location of the July 29, 2015 outburst on 67P/C-G. Copyright: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Only once before at Halley’s Comet has a magnetically “empty” region like this been observed. But that comet was so much more active than 67P/C-G and up until July 29, Halley’s remained the sole example. But following the outburst on that day, the magnetometer detected a diamagnetic cavity extending out at least 116 miles (186 km) from the nucleus. This was likely created by the outburst of gas, forcing the solar wind to ‘stop’ further away from the comet and thus pushing the cavity boundary outwards beyond where Rosetta was flying at the time.
Pew! The graph shows the relative abundances of various gases after the outburst, compared with the measurements two days earlier. Water remained the same, but CO2 and especially increased dramatically. Copyright: ESA/Rosetta/ROSINA/UBern/ BIRA/LATMOS/LMM/IRAP/MPS/SwRI/TUB/UMich
Soon afterward the outburst, the comet pressure sensor of ROSINA detected changes in the structure of the coma, while its mass spectrometer recorded changes in the composition of outpouring gases. Compared to measurements made two days earlier, carbon dioxide increased by a factor of two, methane by four, and hydrogen sulphide by seven, while the amount of water stayed almost constant. No question about it – with all that hydrogen sulfide (rotten egg smell), the comet stunk! Briefly anyway.
It was also more hazardous. In early July, Rosetta recorded and average of 1-3 dust hits a day, but 14 hours after the event, the number leapt to 30 with a peak of 70 hits in one 4-hour period on August 1. Average speeds picked up, too, increasing from 18 mph (8 m/s) to about 45 mph (20 m/s), with peaks at 67 mph (30 m/s). Ouch!
“It was quite a dust party!” said Alessandra Rotundi, principal investigator of GIADA (Grain Impact Analyzer and Dust Accumulator).
67P/C-G’s little party apparently wasn’t enough to jack up its brightness significantly as seen from Earth, but that doesn’t mean future outbursts won’t. We’ll be keeping an eye on any suspicious activity through perihelion and beyond and report back here.
We've never seen a comet as close as this. Taken shortly before touchdown by the Philae lander on November 12, 2014, you're looking across a scene just 32 feet from side to side (9.7-meters) or about the size of a living room. Part of the lander is visible at upper right. Credit: ESA/Rosetta/Philae/ROLIS/DLR
With just 12 days before Comet 67P/Churyumov-Gerasimenko reaches perihelion, we get a look at recent images and results released by the European Space Agency from the Philae lander along with spectacular 3D photos from Rosetta’s high resolution camera.
Slow animation of images taken by Philae’s Rosetta Lander Imaging System, ROLIS, trace the lander’s descent to the first landing site, Agilkia, on Comet 67P/Churyumov–Gerasimenko on November 12, 2014. Credits: ESA/Rosetta/Philae/ROLIS/DLR
Remarkably, some 80% of the first science sequence was completed in the 64 hours before Philae fell into hibernation. Although unintentional, the failed landing attempt led to the unexpected bonus of getting data from two collection sites — the planned touchdown at Agilkia and its current precarious location at Abydos.
After first touching down, Philae was able to use its gas-sniffing Ptolemy and COSAC instruments to determine the makeup of the comet’s atmosphere and surface materials. COSAC analyzed samples that entered tubes at the bottom of the lander and found ice-poor dust grains that were rich in organic compounds containing carbon and nitrogen. It found 16 in all including methyl isocyanate, acetone, propionaldehyde and acetamide that had never been seen in comets before.
While you and I may not be familiar with some of these organics, their complexity hints that even in the deep cold and radiation-saturated no man’s land of outer space, a rich assortment of organic materials can evolve. Colliding with Earth during its early history, comets may have delivered chemicals essential for the evolution of life.
This 3D image focuses on the largest boulder seen in the image captured 221 feet (67.4 m) above Comet 67P/Churyumov–Gerasimenko looks best in a pair of red-blue 3D glasses. Many fractures, along with a tapered ‘tail’ of debris and excavated ‘moat’ around the 5 m-high boulder, are plain to see. Credit: ESA/Rosetta/Philae/ROLIS/DLR
Ptolemy sampled the atmosphere entering tubes at the top of the lander and identified water vapor, carbon monoxide and carbon dioxide, along with smaller amounts of carbon-bearing organic compounds, including formaldehyde. Some of these juicy organic delights have long been thought to have played a role in life’s origins. Formaldehyde reacts with other commonly available materials to form complex sugars like ribose which forms the backbone of RNA and is related to the sugar deoxyribose, the “D” in DNA.
ROLIS (Rosetta Lander Imaging System) images taken shortly before the first touchdown revealed a surface of 3-foot-wide (meter-size) irregular-shaped blocks and coarse “soil” or regolith covered in “pebbles” 4-20 inches (10–50 cm) across as well as a mix of smaller debris.
Philae used its thermal sensor to measure daily highs and lows on the comet (top graph). The bottom graph shows time vs. depth when Philae used its penetrator to hammer into the soil. Credit: Spacecraft graphic: ESA/ATG medialab; data from Spohn et al (2015)
Agilkia’s regolith, the name given to the rocky soil of other planets, moons, comets and asteroids, is thought to extend to a depth of about 6 feet (2 meters) in places, but seems to be free from fine-grained dust deposits at the resolution of the images. The 16-foot-high boulder in the photo above has been heavily fractured by some type of erosional process, possibly a heating and cooling cycle that vaporized a portion of its ice. Dust from elsewhere on the comet has been transported to the boulder’s base. This appears to happen over much of 67P/C-G as jets shoot gas and dust into the coma, some of which then settles out across the comet’s surface.
Another suite of instruments called MUPUS used a penetrating “hammer” to reveal a thin layer of dust about an inch thick (~ 3 cm) overlying a much harder, compacted mixture of dust and ice at Abydos. The thermal sensor took the comet’s daily temperature which varies from a high around –229° F (–145ºC) to a nighttime low of about –292° F (–180ºC), in sync with the comet’s 12.4 hour day. The rate at which the temperature rises and falls also indicates a thin layer of dust rests atop a compacted dust-ice crust.
Based on the most recent calculations using CONSERT data and detailed comet shape models, Philae’s location has been revised to an area covering 69 x 112 feet (21 x 34 m). The best fit area is marked in red, a good fit is marked in yellow, with areas on the white strip corresponding to previous estimates now discounted. Credit: ESA/Rosetta/Philae/CONSERT
CONSERT, which passed radio waves through the nucleus between the lander and the orbiter, showed that the small lobe of the comet is a very loosely compacted mixture of dust and ice with a porosity of 75-85%, about that of lightly compacted snow. CONSERT was also used to help triangulate Philae’s location on the surface, nailing it down to an area just 69 x 112 feet ( 21 x 34 m) wide.
The orbit of Comet 67P/Churyumov–Gerasimenko and its approximate location around perihelion, the closest the comet gets to the Sun. The positions of the planets are correct for August 13, 2015. The comet will pass closest to Earth in February 2016 at 135.6 million miles but will be brightest this month right around perihelion. Copyright: ESA
In fewer than two weeks, the comet will reach perihelion, its closest approach to the Sun at 116 million miles (186 million km), and the time when it will be most active. Rosetta will continue to monitor 67P C-G from a safe distance to lessen the chance an errant chunk of comet ice or dust might damage its instruments. Otherwise it’s business as usual. Activity will gradually decline after perihelion with Rosetta providing a ringside seat throughout. The best time for viewing the comet from Earth will be mid-month when the Moon is out of the morning sky. Watch for an article with maps and directions soon.
Comet 67P/C-G on July 20, 2015 taken from a distance of 106 miles (171 km) from the comet’s center. Rosetta has been keeping a safe distance recently as 67P/C-G approaches the August 13th perihelion. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
“With perihelion fast approaching, we are busy monitoring the comet’s activity from a safe distance and looking for any changes in the surface features, and we hope that Philae will be able to send us complementary reports from its location on the surface,” said Philae lander manager Stephan Ulamec.
OSIRIS narrow-angle camera image showing the smooth nature of the dust covering the Ash region and highlighting the contrast with the more brittle material exposed underneath in Seth. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
More about Philae’s findings can be found in the July 31 issue of Science. Before signing off, here are a few detailed, 3D images made with the high-resolution OSIRIS camera on Rosetta. Once you don a pair of red-blue glasses, click the photos for the high-res versions and get your mind blown.
Mosaic of two images showing an oblique view of the Atum region and its contact with Apis, the flat region in the foreground. This region is rough and pitted, with very few boulders. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDAImage highlighting an alcove structure at the Hathor-Anuket boundary on the comet’s small lobe. The layering seen in the alcove could be indicative of the internal structure of the comet. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDAImhotep region in 3D. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Example of a cluster of bright spots on Comet 67P/Churyumov-Gerasimenko found in the Khepry region. The bright patches are thought to be exposures of water-ice. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Comet 67P/C-G may be tiny at just 2.5 miles (4 km) across, but its diverse landscapes and the processes that shape them astound. To say nature packs a lot into small packages is an understatement.
In newly-released images taken by Rosetta’s high-resolution OSIRIS science camera, the comet almost seems alive. Sunlight glints off icy boulders and pancaking sinkholes blast geysers of dust into the surrounding coma.
Examples of six different bright patches identified on the surface of 67P/C-G in images taken last September when Rosetta was 20-50 km from the comet. The center panel points to the broad regions in which they were discovered (not specific locations). 120 bright regions, including clusters of bright features, isolated features and individual boulders, were seen. The false color images were taken at different times and have been stretched and slightly saturated to emphasis color contrasts so that dark terrains appear redder and bright regions appear significantly bluer compared with what the human eye would normally see. Credit: SA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
More than a hundred patches of water ice some 6 to 15 feet across (a few meters) dot the comet’s surface according to a new study just published in the journal Astronomy & Astrophysics. We’ve known from previous studies and measurements that comets are rich in ice. As they’re warmed by the Sun, ice vaporizes and carries away embedded dust particles that form the comet’s atmosphere or coma and give it a fuzzy appearance.
Examples of icy bright patches and clusters seen in September 2014. The two left hand images are crops of OSIRIS narrow-angle camera images acquired on September 5; the right hand images are from September 16. During this time the spacecraft was about 19-25 miles (30-40 km) from the comet center. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Not all that fine powder leaves the comet. Some settles back to the surface, covering the ice and blackening the nucleus. This explains why all the comets we’ve seen up close are blacker than coal despite being made of material that’s as bright as snow.
True brightness comparisons of four different Solar System bodies. At top are Saturn’s moon Enceladus and Earth. At bottom are the Moon and Comet 67P. Enceladus’ ice-covered surface makes it one of the brightest objects in the Solar System. In contrast, 67P is one of the darkest, its icy surface coated in dark mineral dust and organic compounds. Credit: ESA
Scientists have identified 120 regions on the surface of Comet 67P/Churyumov-Gerasimenko that are up to ten times brighter than the average surface brightness. Some are individual boulders, while others form clusters of bright specks. Seen in high resolution, many appear to be boulders with exposures of ice on their surfaces; the clusters are often found at the base of overhanging cliffs and likely got there when cliff walls collapsed, sending an avalanche of icy rocks downhill and exposing fresh ice not covered by dark dust.
An individual boulder about 12 feet across with bright patches on its surface in the Hatmehit region. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
More intriguing are the isolated boulders found here and there that appear to have no relation to the surrounding terrain. Scientists think they arrived George Jetson style when they were jetted from the comet’s surface by the explosive vaporization of ice only to later land in a new location. The comet’s exceedingly low gravity makes this possible. Let that image marinate in your mind for a moment.
All the ice-glinting boulders seen thus far were found in shadowed regions not exposed to sunlight, and no changes were observed in their appearance over a month’s worth of observations.
“Water ice is the most plausible explanation for the occurrence and properties of these features,” says Antoine Pommerol of the University of Bern and lead author of the study.
How do we know it’s water ice and not CO2 or some other form of ice? Easy. When the observations were made, water ice would have been vaporizing at the rate of 1 mm per hour of solar illumination. By contrast, carbon monoxide or carbon dioxide ice, which have much lower freezing points, would have rapidly sublimated in sunlight. Water ice vaporizes much more slowly in comparison.
Lab tests using ice mixed with different minerals under simulated sunlight revealed that it only took a few hours of sublimation to produce a dust layer only a few millimeters thick. But it was enough to conceal any sign of ice. They also found that small chunks of dust would sometimes break away to expose fresh ice beneath.
“A 1 mm thick layer of dark dust is sufficient to hide the layers below from optical instruments,” confirms Holger Sierks, OSIRIS principal investigator at the Max Planck Institute for Solar System Research.
Comet 67P/C-G on June 21, 2015. The nucleus is a mixture of frozen ices and dust. As the comet approaches the Sun, sunlight warms its surface, causing the ices to boil away. This gas streams away carrying along large amounts of dust, and together they build up the coma. Copyright: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0
It appears then that Comet 67P’s surface is mostly covered in dark dust with small exposures of fresh ice resulting from changes in the landscape like crumbling cliffs and boulder-tossing from jet activity. As the comet approaches perihelion, some of that ice will become exposed to sunlight while new patches may appear. You, me and the Rosetta team can’t wait to see the changes.
High-resolution view of an active pit photographed last September from a distance of about 16 miles (26 km) from the comet’s surface in the Seth region. The image scale is about 45 cm a pixel. The Seth_01 pit measures approximately 720 feet (220 m) across and 605 feet (85 m) deep. Note the smooth deposits of dust around the pit. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Ever wonder how a comet gets its jets? In another new study appearing in the science journal Nature, a team of researchers report that 18 active pits or sinkholes have been identified in the comet’s northern hemisphere. These roughly circular holes appear to be the source of the elegant jets like those seen in the photo above. The pits range in size from around 100 to 1,000 feet (30-100 meters) across with depths up to 690 feet (210 meters). For the first time ever, individual jets can be traced back to specific pits.
In specially processed photos, material can be seen streaming from inside pit walls like snow blasting from a snowmaking machine. Incredible!
Active pits detected in the Seth region of the comet. The contrast of the image has been stretched to reveal the details of the fine-structured jets against the shadow of the pit, which are interpreted as dusty streams rising from the fractured wall of the pit. The image was acquired on October 20, 2014 from a distance of 4.3 miles (7 km) from the surface of the comet. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
“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,” said Jean-Baptiste Vincent from the Max Planck Institute for Solar System Research, lead author of the study.
Similar to the way sinkholes form on Earth, scientists believe pits form when the ceiling of a subsurface cavity becomes too thin to support its own weight. With nothing below to hold it place, it collapses, exposing fresh ice below which quickly vaporizes. Exiting the hole, it forms a collimated jet of dust and gas.
Pits Ma’at 1, 2 and 3 show differences in appearance that may reflect their history of activity. While pits 1 and 2 are active, no activity has been observed from pit 3. The young, active pits are very steep-sided; pits without any observed activity are shallower and seem to be filled with dust. Middle-aged pits tend to have boulders on their floors from mass-wasting of the sides. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
The paper’s authors suggest three ways for pits to form:
* The comet may contain voids that have been there since its formation. Collapse could be triggered by either vaporizing ice or seismic shaking when boulders ejected elsewhere on the comet land back on the surface.
* Direct sublimation of pockets of volatile (more easily vaporized) ices like carbon dioxide and carbon monoxide below the surface as sunlight warms the dark surface dust, transferring heat below.
* Energy liberated by water ice changing its physical state from amorphous to its normal crystalline form and stimulating the sublimation of the surrounding more volatile carbon dioxide and carbon monoxide ices.
Graphic showing how pits may form through sinkhole collapse in the comet’s dusty surface layer covering a mixture of dust and ices. 1. Heat causes subsurface ices to sublimate (blue arrows), forming a cavity. 2.When the ceiling becomes too weak to support its own weight, it collapses, creating a deep, circular pit (orange arrow). Newly exposed material in the pit walls sublimates (blue arrows). Credit: ESA/Rosetta/J-B Vincent et al (2015)
The researchers think they can use the appearance of the sinkholes to age-date different parts of the comet’s surface — the more pits there are in a region, the younger and less processed the surface there is. They point to 67P/C-G’s southern hemisphere which receives more energy from the Sun than the north and at least for now, shows no pit structures.
The most active pits have steep sides, while the least show softened contours and are filled with dust. It’s even possible that a partial collapse might be the cause of the occasional outbursts when a comet suddenly brightens and enlarges as seen from Earth. Rosetta observed just such an outburst this past April. And these holes can really kick out the dust! It’s estimated a typical full pit collapse releases a billion kilograms of material.
With Rosetta in great health and perihelion yet to come, great things lie ahead. Maybe we’ll witness a new sinkhole collapse, an icy avalanche or even levitating boulders!
Montage of four single-frame images of Comet 67P/C-G taken by Rosetta’s Navigation Camera (NAVCAM) at the end of February 2015. The images were taken on 25 February (top left), 26 February (top right) and on two occasions on 27 February (bottom left and right). Exposure times are 2 seconds each and the images have been processed to bring out the details of the comet's many jets. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
Tell me this montage shouldn’t be hanging in the Lourve Museum. Every time I think I’ve seen the “best image” of Rosetta’s comet, another one takes its place. Or in this case four! When you and I look at a comet in our telescopes or binoculars, we’re seeing mostly the coma, the bright, fluffy head of the comet composed of dust and gas ejected by the tiny, completely invisible, icy nucleus.
As we examine this beautiful set of photos, we’re privileged to see the individual fountains of gas and dust that leave the comet to create the coma. Much of the outgassing comes from the narrow neck region between the two lobes.
This photo taken on Feb. 27 shows the comet with peacock-like display of dusty jets. Below center is a streak that may be a dust particle that traveled during the exposure. Other small white spots are also likely dust or bits of comet that have broken off. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
All were taken between February 25-27 at distances around 50-62 miles (80 to 100 km) from the center of Comet 67P/Churyumov-Gerasimenko. Looking more closely, the comet nucleus appears to be “glowing” with a thin layer of dust and gas suspended above the surface. In the lower left Feb. 27 image, a prominent streak is visible. While this might be a cosmic ray zap, its texture hints that it could also be a dust particle captured during the time exposure. Because it moved a significant distance across the frame, the possible comet chunk may be relatively close to the spacecraft. Just a hunch.
Another close-up individual image from Rosetta’s NAVCAM. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
While most of Rosetta’s NAVCAM images are taken for navigation purposes, these images were obtained to provide context in support of observations performed at the same time with the Alice ultraviolet (UV) imaging spectrograph on Rosetta. Observing in ultraviolet light, Alice determines the composition of material in coma, the nucleus and where they interface. Alice will also monitor the production rates of familiar molecules like H2O, CO (carbon monoxide) and CO2 as they leave the nucleus and enter 67P’s coma and tail.
Alice makes its observations in UV light through a long, narrow slit seen here superimposed on a graphic of comet 67P/ C-G. Credit: ESA/NASA
From data collected so far, the Alice team has discovered that the comet is unusually dark in the ultraviolet, and that its surface shows no large water-ice patches. Water however has been detected as vapor leaving the comet as it’s warmed by the Sun. The amount varies as the nucleus rotates, but the last published measurements put the average loss rate at 1 liter (34 ounces) per second with a maximum of 5 liters per second. Vapors from sublimating carbon monoxide and carbon dioxide ice have also been detected. Sometimes one or another will dominate over water, but overall, water remains the key volatile material outgassed in the greatest quantity.
Particularly striking and collimated jets emerge from the comet’s shadowed Hathor region between the two lobes. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0Look at those spirals! In this separate image, taken Feb. 28, ESA suggests the curved shape of the outflowing material likely results from a combination of several factors, including the rotation of the comet, differential flows of near-surface gas, and gravitational effects arising due to the uneven shape of the comet. The viewing perspective of the image might also distort the true shape of the outflowing material. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
That and dust. In fact, 67P is giving off about twice as much dust as gas. We see the comet’s dual emissions by reflected sunlight, but because there’s so much less material in the jets than what makes up the nucleus, they’re fainter and require longer exposures and special processing to bring out without seriously overexposing the comet’s core.
67P’s coma will only grow thicker and more intense as it approaches perihelion on August 13.
Close-up of comet 67P showing the larger of the two lobes (boulder Cheops labelled), jets of dust and likely individual dust particles scattered around the comet. Credit: ESA/Rosetta/NAVCAM
Anyone who’s ever read a Charlie Brown comic strip knows “Pig-Pen”, the lovable boy who walks around in a constant cloud of his own dirt and dust. Every time he sighs, dust rises in a little cloud around him. Why bother to bathe? There’s dignity in debris, which “Pig-Pen refers to as the “dust of countless ages”. Comets shuffle around the Sun surrounded by a similar cloud of grime that’s as old as the Solar System itself.
Dust and gases released by the comet reflect so little light compared to the nucleus they require special processing to see clearly. In this photo, many of the small, irregular specks may be cometary dust grains captured in the 4.3 second exposure. Credit: ESA/Rosetta/NAVCAM
You’ve probably noticed little flecks and streaks in photos returned by the Rosetta spacecraft in the blackness of space surrounding comet 67P/Churyumov-Gerasimenko. After a recent year-end break, the Rosetta team has returned with new updates on the comet including a series of four images recently released as a mosaic. The pictures were processed to highlight surface features; the space around the nucleus is black in comparison. But if we take a closer look at what first appears void, we soon discover it’s not empty at all.
In photos taken January 3rd, the writer of ESA’s Rosetta blog notes that “some of the streaks and specks seen around the nucleus will likely be dust grains ejected from the comet, captured in the 4.3 second exposure time.”
At right is a streak that could either be a larger, fast-moving dust particle that trailed during the exposure or perhaps a cosmic ray hit. Credit: ESA/Rosetta/NAVCAM
Using an image-editing tool like Photoshop, we can hold back the glare of the nucleus and “open up” the shadows around the comet. Jets of dust released by vaporizing ice are the most obvious features to emerge. The soft, low-contrast plumes plow into the vacuum around the nucleus wrapping it in a silky cocoon of gas and dust – a tenuous atmosphere that reflects sunlight far more weakly than the comet itself.
The mosaic image of the comet taken on January 3rd and processed, like most of ESA’s comet images, to highlight surface features. Credit: ESA/Rosetta/NAVCAM
While staring at dust spots may not produce the same magical feelings as watching a sunrise, it’s fascinating nonetheless to contemplate what we’re seeing. If you’ve been struck by the beauty of a comet’s meteor-like head trailing a wispy tail, you’re looking at what countless individual grains of dust can do when sculpted by the master hand of the Sun. Perusing images of 67P, we see the process in its infancy as individual grains and small clots are released into space to be fashioned into something grander.
Image of the first dust grain (center) captured by MIDAS. The bar at top left is 0.01 mm wide. Credit: Courtesy Mark Bentley
Rosetta’s Micro-Imaging Dust Analysis System or MIDAS measures the rate at which dust sweeps past the spacecraft and its size distribution. MIDAS catches dust grains by exposing a sticky target surface into space and waiting for a mote to drift by. It snatched its first one last November – a larger than expected mote measuring about 1/100 of a millimeter across with a complex shape and fluffy texture.
COSIMA’s first dust grains. Left: an image of the target plate (measuring 1 cm by 1 cm) on which the grains were collected; right: a section of the plate showing it on August 17th (top) when no dust grains were visible and 24 August 24th (bottom) when two large dust grains were detected. The plate is illuminated from the right by LEDs, and the length of the shadows is proportional to the height of the dust grains. Credit: ESA/Rosetta/MPS for COSIMA Team MPS/CSNSM/UNIBW/TUORLA/IWF/IAS/ESA/ BUW/MPE/LPC2E/LCM/FMI/UTU/LISA/UOFC/vH&S
Analysis of the composition of another dust grain named “Boris” made by the COSIMA instrument has identified sodium and magnesium. Magnesium is no surprise as 95% of known minerals observed in comets resemble olivine and pyroxenes, common in meteorites and in the upper mantle of the Earth. Sodium has also been seen before in comas and tails, and originates in dust grains, but its mineral source remains uncertain.
As we might study the makeup of the dust Pig-Pen leaves in his wake to identify traces of earthly dirt, micro-organisms, pollen, pollution, and even recent volcanic eruptions, so we examine each mote that sprays Rosetta’s way, looking for clues to the origin of the planets and Solar System.
The Cliffs of Churyumov-Gerasimenko: an enhanced and procosessed crop of an image from Rosetta's navcam. Credits: ESA/Rosetta/NAVCAM, processing by Stuart Atkinson.
Images from space don’t get more dramatic than this. Image processing wizard Stuart Atkinson zoomed in on one of the most intriguing views yet of Comet 67P/Churyumov-Gerasimenko, highlighting the contrasts of dark and light, smooth and rugged, soft contours and frighteningly vertical cliffs.
The orginal image, below, is a four-image mosaic made from images snapped by Rosetta’s navigation camera, taken from a distance of 20.1 km from the center of Comet 67P/Churyumov-Gerasimenko on 10 December. The image resolution is 1.71 m/pixel and the individual 1024 x 1024 frames measure 1.75 km across. The mosaic is slightly cropped and measures 2.9 x 2.6 km.
This four-image mosaic comprises images taken from a distance of 20.1 km from the center of Comet 67P/Churyumov-Gerasimenko on December 10, 2014. Credit: ESA/Rosetta/NAVCAM.
A 3-D image of Comet 67P/Churyumov–Gerasimenko taken from the Philae lander as it descended. The picture is a combination of two images from the Rosetta Lander Imaging System (ROLIS) taken about an hour before landing at 10:34 a.m. EST (3:34 p.m. UTC) on Nov. 12, 2014. Credit: ESA/Rosetta/Philae/ROLIS/DLR
The first soft comet landing Nov. 12 showed us how space missions can quickly drift to the unexpected. Philae’s harpoons to secure it failed to fire, and the spacecraft drifted for an incredible two hours across Comet 67P/Churyumov–Gerasimenko before coming to rest … somewhere. But where? And can the orbiting Rosetta spacecraft find it?
That’s been the obsession of the European Space Agency for the past couple of weeks. Controllers have pictures from Philae during its descent and brief science operations on the surface. They’ve managed to capture the little lander in incredible photographs from Rosetta. But the key to finding Philae will likely come from a different experiment altogether.
The experiment is called the Comet Nucleus Sounding Experiment by Radio wave Transmission (CONSERT) and is a piece of work between both lander and orbiter. Rosetta sent radio signals to Philae on the surface to get a better sense of what the insides of 67P are made of. But it turns out it can also be used to pinpoint the lander.
ESA recently released a landing zone of where, based on CONSERT data, it believes the lander came to rest. The next step will be to get the Rosetta spacecraft to examine the area in high-definition.
An estimation of Philae’s landing site on Comet 67P/Churyumov–Gerasimenko, based on data from the Comet Nucleus Sounding Experiment by Radio wave Transmission (CONSERT) experiment. Credit: ESA/Rosetta/Philae/CONSERT
“By making measurements of the distance between Rosetta and Philae during the periods of direct visibility between orbiter and lander, as well as measurements made through the core, the team have been able to narrow down the search to the strip presented in the image shown above,” ESA stated. “The determination of the landing zone is dependent on the underlying comet shape model used, which is why there are two candidate regions marked.”
Finding Philae is not only a goal to fulfill curiosity, but also to learn more about the comet itself. The team needs to know where the lander is sitting before they can fully analyze the CONSERT data, they said. So the search continues for the hibernating lander, which right now is in a shady spot and unable to transmit status updates since it can’t get enough sunlight to recharge. (This could change as 67P gets closer to the Sun, but nobody knows for sure.)
Rosetta, meanwhile, is in perfect health and continues to transmit incredible pictures of the comet, such as this one below released a couple of days ago. The montage you see includes the zone where Philae was supposed to have touched down, but it will take higher-resolution images from the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) to get a better look.
A montage of four images of Comet 67P/Churyumov–Gerasimenko taken by the Rosetta spacecraft on Nov. 20, 2014. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
As of November 2014, these are all of the planetary, lunar and small body surfaces where humanity has either lived, visited, or sent probes to. Composition by Mike Malaska, updated by Michiel Straathof. Image credits: Comet 67P/C-G [Rosetta/Philae]: ESA / Rosetta / Philae / CIVA / Michiel Straathof. Asteroid Itokawa [Hayabusa]: ISAS / JAXA / Gordan Ugarkovic. Moon [Apollo 17]: NASA. Venus [Venera 14]: IKI / Don Mitchell / Ted Stryk / Mike Malaska. Mars [Mars Exploration Rover Spirit]: NASA / JPL / Cornell / Mike Malaska. Titan [Cassini-Huygens]: ESA / NASA / JPL / University of Arizona. Earth: Mike Malaska
Correction, 11:33 a.m. EST: The University of Central Florida’s Phil Metzger points out that the image composition leaves out Eros, which NEAR Shoemaker landed on in 2001. This article has been corrected to reflect that and to clarify that the surfaces pictured were from “soft” landings.
And now there are eight. With Philae’s incredible landing on a comet earlier this week, humans have now done soft landings on eight solar system bodies. And that’s just in the first 57 years of space exploration. How far do you think we’ll reach in the next six decades? Let us know in the comments … if you dare.
More seriously, this amazing composition comes courtesy of two people who generously compiled images from the following missions: Rosetta/Philae (European Space Agency), Hayabusa (Japan Aerospace Exploration Agency), Apollo 17 (NASA), Venera 14 (Soviet Union), the Spirit rover (NASA) and Cassini-Huygens (NASA/ESA). Omitted is NEAR Shoemaker, which landed on Eros in 2001.
Before Philae touched down on Comet 67P/Churyumov–Gerasimenko Wednesday, the NASA Jet Propulsion Laboratory’s Mike Malaska created a cool infographic of nearly every place we’ve lived or visited before then. This week, Michiel Straathof updated the infographic to include 67P (and generously gave us permission to use it.)
And remember that these are just the SURFACES of solar system bodies that we have visited. If you include all of the places that we have flown by or taken pictures from of a distance in space, the count numbers in the dozens — especially when considering prolific imagers such as Voyager 1 and Voyager 2, which flew by multiple planets and moons.
To check out a small sampling of pictures, visit this NASA website that shows some of the best shots we’ve taken in space.
Magnetic field lines bound up in the sun’s wind pile up and drape around a comet’s nucleus to shape the blue ion tail. Notice the oppositely-directed fields on the comet’s backside. The top set points away from the comet; the bottom set toward. In strong wind gusts, the two can be squeezed together and reconnect, releasing energy that snaps off a comet’s tail. Credit: Tufts University
Tune in to the song of Comet Churyumov-Gerasimenko
Scientists can’t figure exactly why yet, but Comet 67P/Churyumov-Gerasimenko has been singing since at least August. Listen to the video – what do you think? I hear a patter that sounds like frogs, purring and ping-pong balls. The song is being sung at a frequency of 40-50 millihertz, much lower than the 20 hertz – 20 kilohertz range of human hearing. Rosetta’s magnetometer experiment first clearly picked up the sounds in August, when the spacecraft drew to within 62 miles (100 km) of the comet. To make them audible Rosetta scientists increased their pitch 10,000 times.
The sounds are thought to be oscillations in the magnetic field around the comet. They were picked up by the Rosetta Plasma Consortium, a suite of five instruments on the spacecraft devoted to observing interactions between the solar plasma and the comet’s tenuous coma as well as the physical properties of the nucleus. A far cry from the stuff you donate at the local plasma center, plasma in physics is an ionized gas. Ionized means the atoms in the gas have lost or gained an electron through heating or collisions to become positively or negatively charged ions. Common forms of plasma include the electric glow of neon signs, lightning and of course the Sun itself.
Having lost their neutrality, electric and magnetic fields can now affect the motion of particles in the plasma. Likewise, moving electrified particles affect the very magnetic field controlling them.
Scientists think that neutral gas particles from vaporizing ice shot into the coma become ionized under the action of ultraviolet light from the Sun. While the exact mechanism that creates the curious oscillations is still unknown, it might have something to do with the electrified atoms or ions interacting with the magnetic fields bundled with the Sun’s everyday outpouring of plasma called the solar wind. It’s long been known that a comet’s electrified or ionized gases present an obstacle to the solar wind, causing it to drape around the nucleus and shape the streamlined blue-tinted ion or gas tail.
“This is exciting because it is completely new to us. We did not expect this, and we are still working to understand the physics of what is happening,” said Karl-Heinz Glassmeier, head of Space Physics and Space Sensorics at the Technical University of Braunschweig, Germany.
While 67P C-G’s song probably won’t make the Top 40, we might listen to it just as we would any other piece of music to learn what message is being communicated.
