Dramatic Outburst at Rosetta’s Comet Just Days Before Perihelion

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.

A short-lived outburst from Comet 67P/Churyumov–Gerasimenko was captured by Rosetta’s OSIRIS narrow-angle camera on 29 July 2015. The image at left was taken at 13:06 GMT and does not show any visible signs of the jet. It is very strong in the middle image captured at 13:24 GMT. Residual traces of activity are only very faintly visible in the final image taken at 13:42 GMT. The images were taken from a distance of 186 km from the centre of the comet.
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.

Comet 67P/Churyumov-Gerasimenko photographed from about 125 miles away on June 5 looks simply magnificent. Only two months from perihelion, the comet shows plenty of jets. One wonders what the chances are of one erupting underneath Philae and sending it back into orbit again. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
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 29 July 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
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.

This photo of 67P/C-G's nucleus shows the context for the outburst. Copyright: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
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.

 

The graph shows the relative abundances of various gases after the outburst, compared with the measurements two days earlier. Copyright: ESA/Rosetta/ROSINA/UBern/ BIRA/LATMOS/LMM/IRAP/MPS/SwRI/TUB/UMich
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.

Sources: 1, 2

Rosetta’s Comet Sparkles with Ice, Blows Dust From Sinkholes

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 Comet 67P/Churyumov-Gerasimenko in OSIRIS narrow-angle camera images acquired in September 2014. The insets point to the broad regions in which they were discovered (not to specific locations). In total, 120 bright regions, including clusters of bright features, isolated features and individual boulders, were identified in images acquired during September 2014 when the spacecraft was between 20-50 km from the comet center. The false colour images are red-green-blue composites assembled from monochrome images taken at different times and have been stretched and slightly saturated to emphasis the contrasts of colour such 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
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 seen on Comet 67P/Churyumov-Gerasimenko during September 2014. The two left hand images are subsets of OSIRIS narrow-angle camera images acquired on 5 September; the right hand images were acquired on 16 September. During this time the spacecraft was about 30-40 km from the comet center. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
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, its ice-covered surface making it one of the brightest objects in the Solar System, and Earth. At bottom are the Moon and Comet 67P. Credit: ESA
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
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
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 active regions in Seth as seen with Rosetta’s OSIRIS narrow-angle camera on 20 September 2014 from a distance of about 26 km from the surface. The image scale is about 45 cm/pixel. The Seth_01 pit is seen close to centre and measures approximately 220 m across and 185 m deep. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
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 Comet 67P/Churyumov¬Gerasimenko can be seen in the lower right portion of this OSIRIS wide-angle camera image. The contrast of the image has been deliberately 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 20 October 2014 from a distance of 7 km from the surface of the comet. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
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 on Comet 67P/Churyumov–Gerasimenko 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 particularly steep-sided, whereas pits without any observed activity are shallower and seem to be filled with dust. Middle-aged pits tend to exhibit boulders on their floors from mass-wasting of the sides. The image was taken with the OSIRIS narrow-angle camera from a distance of 28 km from the comet surface. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
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 explaining how Comet 67P/Churyumov–Gerasimenko’s pits may form through sinkhole collapse. The graphic shows a 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 (3, red arrow). Newly exposed material in the pit walls sublimates, accounting for the observed activity (3, blue arrows).
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!

Sources: 1, 2

Philae Wakes Up, Makes Contact!

Fantastic news! Philae’s alive and kicking. The lander “spoke” with its team on ground via Rosetta for 85 seconds — its first contact since going into hibernation in November.

Signals were received at ESA’s European Space Operations Center in Darmstadt at 4:28 p.m. EDT yesterday June 13. The lander sent more than 300 data packets reporting on its condition as well as information about the comet. 

“Philae is doing very well. It has an operating temperature of -35ºC (-31°F) and has 24 watts available,” said DLR Philae Project Manager Dr. Stephan Ulamec. “The lander is ready for operations.”

Philae spent two hours drifting above Comet 67P/C-G after its harpoons failed to anchor it to the surface. Credit: ESA
Philae spent two hours drifting above Comet 67P/C-G after its harpoons failed to anchor it to the surface. Credit: ESA

If coming out of hibernation isn’t surprising enough, it appears Philae has been awake for a while because it included historical data along with its current status in those packets. There are still more than 8000 data packets in Philae’s mass memory which will give the mission scientists information on what happened to the lander in the past few days on Comet 67P/C-G.

Philae went into hibernation on November 15, 2014 after running out of battery power. Credit: ESA
Philae went into hibernation on November 15, 2014 after running out of battery power. Credit: ESA

Philae shut down on November 15 after about 60 hours of operation on the comet after landing at the base of a steep cliff in a shaded area that prevented the solar panels from charging its batteries. Since March 12, the Rosetta lander has been “listening” for a signal from the lost lander.

First image taken by Philae after landing on the comet on November 12, 2015. It shows a steep cliff and one of the  lander's legs. Credit: ESA/ROSETTA/PHILAE/CIVA
First image taken by Philae after landing on Comet 67P/Churyumov-Gerasimenko on November 12, 2014 showing a steep cliff and one of the lander’s legs. Credit: ESA/ROSETTA/PHILAE/CIVA

Throughout, mission scientists remained hopeful that the comet’s changing orientation and increase in the intensity of sunlight as it approached perihelion would eventually power up the little lander. Incredible that it really happened.

Yesterday, we looked at the many attempts to find Philae. A day later it’s found us!

Both amateurs and professional astronomers across the world are in constant contact sharing observations of Comet 67P/C-G and news from the Rosetta mission. Klim Churyumov, co-discoverer of the comet, had this to say upon hearing the news of Philae’s awakening:

“Hurrah! Hurrah! Hurrah! Landing probe Philae awake! Everybody, please accept my sincere congratulations! It happened on 13 June 2015 in the day of birthday of my mother – Antonina Mikhailovna (108 years have passed since the day of her birth). And I’m starting from 13 November 2014 to this day, every morning pronounced a short prayer: “Lord, please wake Philae and support Rosetta”. God and the Professional Navigators woke Philae! It is fantastic! All the best! – Klim Churyumov.

How poignant Philae awoke on Klim’s mother’s birthday!

Padma A. Yanamandra-Fisher, Rosetta Coordinator of Amateur Observations for 67P/C-G (and Senior Research Scientist at the Space Science InstituteKlim Churyumov, at the ACM meeting in Helsinki
Padma Yanamandra-Fisher (left), Senior Research Scientist at the Space Science Institute, who runs the PACA site, and comet co-discoverer Klim Churyumov. Courtesy Padma Yanamandra-Fisher

Churyumov made his statement on the Pro-Am Collaborative Astronomy (PACA) site devoted to pro-amateur collaboration during comet observing campaigns. I encourage you to check out the group and participate by submitting your own observations of Comet 67P as it brightens this summer and early fall.

* UPDATE: In the coming days, the mission teams will reestablish contact with Philae and increase the amount of time it can “talk” with the lander. Once regular contact is established, science observations can begin again. Slowly. One instrument at a time.

The first instruments activated, those measuring temperature, magnetic fields and electrical conductivity on the comet, make small demands on Philae’s power. Slightly more power-hungry operations like picture taking and radio ranging will follow. Using the images and new data, scientists should be able to pinpoint the lander’s location.

After these steps, mission engineers will attempt to recharge the probe’s drained batteries to fire up its ovens (used to heat samples to determine their composition) and run the drill to collect fresh material.

Here’s a cool link to see LIVE telemetry from Philae.

Have We Found Rosetta’s Lost Philae Lander?

It’s only a bright dot in a landscape of crenulated rocks, but the Rosetta team thinks it might be Philae, the little comet lander lost since November. 

The Rosetta and Philae teams have worked tirelessly to search for the lander, piecing together clues of its location after a series of unfortunate events during its planned landing on the surface of Comet 67P/Churyumov-Gerasimenko last November 12.

The journey of Rosetta’s Philae lander as it approached and then rebounded from its first touchdown on Comet 67P/Churyumov–Gerasimenko on November 12, 2014. The mosaic comprises a series of images captured by Rosetta’s OSIRIS camera over a 30 minute period spanning the first touchdown. The time of each of image is marked on the corresponding insets and is in Greenwich Mean Time. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Mosaic photo capturing Philae’s flight above the comet’s nucleus and one of its three touchdowns on November 12, 2014. The images cover a 30 minute period spanning the first touchdown. The Greenwich Mean Time time of each of image is marked on the corresponding insets. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Philae first touched down at the Agilkia landing site that day, but the harpoons that were intended to anchor it to the surface failed to work, and the ice screws alone weren’t enough to do the job. The lander bounced after touchdown and sailed above the comet’s nucleus for two hours before finally settling down at a site called Abydos a kilometer from its intended landing site.

No one yet knows exactly where Philae is, but an all-out search has finally turned up a possible candidate.

Approximate locations of five lander candidates initially identified in high-resolution photos taken in December 2014, from a distance of about 12.4 miles (20 km) from the comet's center. The candidates identify Philae-sized features about 3-6 feet (1-2 meters) across. The contrast has been stretched in some of the images to better reveal the candidates. All but one of these candidates (top left) have subsequently been ruled out. The candidate at top left lies near to the current CONSERT ellipse (see below). Credit: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0; insets: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Approximate locations of five lander candidates initially identified in high-resolution photos taken in December 2014, from a distance of about 12.4 miles (20 km) from the comet’s center. The candidates identify Philae-sized features about 3-6 feet (1-2 meters) across. The contrast has been stretched in some of the images to better reveal the candidates. All but one of them (top left) have subsequently been ruled out. The candidate at top left lies near to the current CONSERT ellipse (see below). Credit: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0; insets: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Rosetta’s navigation and high-resolution cameras identified the first landing site and also took several pictures of Philae as it traveled above the comet before coming down for a final landing. Magnetic field measurements taken by an instrument on the lander itself also helped establish its location and orientation during flight and touchdown. The lander is thought to be in rough terrain perched up against a cliff and mostly in shadow.

High resolution images of the possible landing zone were taken by Rosetta back in December when it was about 11 miles (18 km) from the comet’s surface. At this distance, the OSIRIS narrow-angle camera has a resolution of 13.4 inches (34 cm) per pixel. The body of Philae is just 39 inches (1-meter) across, while its three thin legs extend out by up to 4.6 feet (1.4-meters) from its center. In other words, Philae’s just a few pixels across — a tiny target but within reach of the camera’s eye.

The current 50 x 525 feet (16 x 160 m) CONSERT ellipse overlaid on an OSIRIS narrow-angle camera image of the same region. It's believed Philae is located within or near this ellipse. Copyright Ellipse: ESA/Rosetta/Philae/CONSERT; Image: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
The current 50 x 525 feet (16 x 160 m) CONSERT ellipse overlaid on an OSIRIS narrow-angle camera image of the same region. It’s believed Philae is located within or near this ellipse. Copyright Ellipse: ESA/Rosetta/Philae/CONSERT; Image: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

The candidates in the photo above are “all over the place.” To narrow down the location, the Rosetta team used radio signals sent between Philae and Rosetta as part of the COmet Nucleus Sounding Experiment or CONSERT after the final touchdown. According to Emily Baldwin’s recent posting on the Rosetta site:

“Combining data on the signal travel time between the two spacecraft with the known trajectory of Rosetta and the current best shape model for the comet, the CONSERT team have been able to establish the location of Philae to within an ellipse roughly 50 x 525 feet (16 x 160 meters) in size, just outside the rim of the Hatmehit depression.”

Zooming in towards the current CONSERT ellipse, a number of bright dots are seen in the region. As only one (at most) of these could be the lander, the majority must be associated with surface features on the comet nucleus. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Zooming in to the CONSERT ellipse, a number of bright dots are seen in the region. Since only one could be the lander, the majority must be associated with surface features on the comet nucleus.
Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

So what can we see there? Zooming in closer, a number of glints or bright spots appear, and they change depending on the viewing angle. But among those glints, one might be Philae. What mission scientists examined images of the area under the same lighting conditions before Philae landed and then put them side by side with those taken after November 12. That way any transient glints could be eliminated, leaving what’s left as a potential candidate.

‘Before’ and ‘after’ comparison images of a promising candidate located near the CONSERT ellipse as seen in images from Rosetta. Each box covers roughly 65x65 feet (20 x 20 m) on the comet. The left-hand image shows the region as seen on 22 October (before the landing of Philae) from a distance of about 6 miles from the center of the comet, while the center and right-hand images show the same region on December 12 and 13 from 12 miles (20 km) after landing. The candidate is only seen in the two later pictures. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
‘Before’ and ‘after’ comparison images of a promising candidate located near the CONSERT ellipse as seen in images from Rosetta. Each box covers roughly 65×65 feet (20 x 20 m) on the comet. The left-hand image shows the region as seen on 22 October (before the landing of Philae) from a distance of about 6 miles from the center of the comet, while the center and right-hand images show the same region on December 12 and 13 from 12 miles (20 km) after landing. The candidate is only seen in the two later pictures.
Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

In photos taken on December 12 and 13, a bright spot is seen that didn’t appear in the earlier photos. Might this be Philae? It’s possible and the best candidate yet. But it may also be a new physical feature that developed between November and December. Comet surfaces are forever changing as sunlight sublimates ice both on and beneath the surface

For now, we still can’t be sure if we’ve found Philae. Higher resolution pictures will be required as will patience. The comet’s too close to the Sun right now and too active. Rubble flying off the nucleus could damage Rosetta’s instruments. Mission scientists will have to wait until well after the comet’s August perihelion (closest approach to the Sun) for a closer look.

Comet 67P/Churyumov-Gerasimenko photographed from about 125 miles away on June 5 looks simply magnificent. Only two months from perihelion, the comet shows plenty of jets. One wonders what the chances are of one erupting underneath Philae and sending it back into orbit again. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
Magnificent! Comet 67P/Churyumov-Gerasimenko photographed by Rosetta from about 125 miles away on June 5, 2015. Now only two months from perihelion, the comet’s crazy with jets of dust and gas. One wonders what the chances are of a gassy geyser erupting beneath or near Philae and sending it back into orbit again. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Meanwhile, mission teams remain hopeful that with increasing sunlight at the comet this summer, Philae’s solar panels will recharge its batteries and the three-legged lander will wake up and resume science studies. Three attempts have been made to contact Philae this spring and more will be made but so far, we’ve not heard a peep.

For the time being, Philae’s like that lost child in a shopping mall. The search party’s been dispatched, clues have been found and it’s only a matter of time before we see her smiling face again.

Rosetta’s Comet Keeps On Jetting Even After the Sun Goes Down

67P/Churyumov-Gerasimenko certainly isn’t a comet that dreads sundown. Images acquired by the OSIRIS instrument aboard ESA’s Rosetta spacecraft in April 2015 reveal that some of the comet’s dust jets keep on firing even after the Sun has “set” across those regions. This shows that, as the comet continues to approach its August perihelion date, it’s now receiving enough solar radiation to warm deeper subsurface materials.

“Only recently have we begun to observe dust jets persisting even after sunset,” said OSIRIS Principal Investigator Holger Sierks from the Max Planck Institute for Solar System Research.

The image above was captured by OSIRIS on April 25 and shows active jets near the center, originating from shadowed areas on the comet’s smaller “head” lobe. The region is called Ma’at – see maps of 67P’s regions here and here.

(Also it looks kind of like an overexposed image of a giant angry lemming. But that’s pareidolia for you.)

Detail of the active jets. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Detail of the active jets. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

It’s thought that the comet has now come close enough to the Sun – 220.8 million kilometers, at the time of this writing – that it can store heat below its surface… enough to keep the sublimation process going within buried volatiles well after it rotates out of direct solar illumination.

Read more: What Are Comets Made Of?

Comet 67P and Rosetta (and Philae too!) will come within 185.9 million km of the Sun during perihelion on Aug. 13, 2015 before heading back out into the Solar System. Find out where they are now.

Source: ESA’s Rosetta blog

Weekly Space Hangout – June 5, 2015: Stephen Fowler, Creative Director at InfoAge

Host: Fraser Cain (@fcain)
Special Guest: This week we welcome Stephen Fowler, who is the Creative Director at InfoAge, the organization behind refurbishing the TIROS 1 dish and the Science History Learning Center and Museum at Camp Evans, Wall, NJ.

Guests:
Jolene Creighton (@jolene723 / fromquarkstoquasars.com)
Morgan Rehnberg (cosmicchatter.org / @MorganRehnberg )

Continue reading “Weekly Space Hangout – June 5, 2015: Stephen Fowler, Creative Director at InfoAge”

Rosetta Discovery of Surprise Molecular Breakup Mechanism in Comet Coma Alters Perceptions

A NASA science instrument flying aboard the European Space Agency’s (ESA) Rosetta spacecraft has made a very surprising discovery – namely that the molecular breakup mechanism of “water and carbon dioxide molecules spewing from the comet’s surface” into the atmosphere of comet 67P/Churyumov-Gerasimenko is caused by “electrons close to the surface.”

The surprising results relating to the emission of the comet coma came from measurements gathered by the probes NASA funded Alice instrument and is causing scientists to completely rethink what we know about the wandering bodies, according to the instruments science team.

“The discovery we’re reporting is quite unexpected,” said Alan Stern, principal investigator for the Alice instrument at the Southwest Research Institute (SwRI) in Boulder, Colorado, in a statement.

“It shows us the value of going to comets to observe them up close, since this discovery simply could not have been made from Earth or Earth orbit with any existing or planned observatory. And, it is fundamentally transforming our knowledge of comets.”

A paper reporting the Alice findings has been accepted for publication by the journal Astronomy and Astrophysics, according to statements from NASA and ESA.

Alice is a spectrograph that focuses on sensing the far-ultraviolet wavelength band and is the first instrument of its kind to operate at a comet.

Until now it had been thought that photons from the sun were responsible for causing the molecular breakup, said the team.

The carbon dioxide and water are being released from the nucleus and the excitation breakup occurs barely half a mile above the comet’s nucleus.

“Analysis of the relative intensities of observed atomic emissions allowed the Alice science team to determine the instrument was directly observing the “parent” molecules of water and carbon dioxide that were being broken up by electrons in the immediate vicinity, about six-tenths of a mile (one kilometer) from the comet’s nucleus.”

The excitation mechanism is detailed in the graphic below.

Rosetta’s continued close study of Comet 67P/Churyumov-Gerasimenko has revealed an unexpected process at work close to the comet nucleus that causes the rapid breakup of water and carbon dioxide molecules.   Credits: ESA/ATG medialab; ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; ESA/Rosetta/NavCam – CC BY-SA IGO 3.0
Rosetta’s continued close study of Comet 67P/Churyumov-Gerasimenko has revealed an unexpected process at work close to the comet nucleus that causes the rapid breakup of water and carbon dioxide molecules. Credits: ESA/ATG medialab; ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; ESA/Rosetta/NavCam – CC BY-SA IGO 3.0

“The spatial variation of the emissions along the slit indicates that the excitation occurs within a few hundred meters of the surface and the gas and dust production are correlated,” according to the Astronomy and Astrophysics journal paper.

The data shows that the water and CO2 molecules break up via a two-step process.

“First, an ultraviolet photon from the Sun hits a water molecule in the comet’s coma and ionises it, knocking out an energetic electron. This electron then hits another water molecule in the coma, breaking it apart into two hydrogen atoms and one oxygen, and energising them in the process. These atoms then emit ultraviolet light that is detected at characteristic wavelengths by Alice.”

“Similarly, it is the impact of an electron with a carbon dioxide molecule that results in its break-up into atoms and the observed carbon emissions.”

After a decade long chase of over 6.4 billion kilometers (4 Billion miles), ESA’s Rosetta spacecraft arrived at the pockmarked Comet 67P/Churyumov-Gerasimenko on Aug. 6, 2014 for history’s first ever attempt to orbit a comet for long term study.

Since then, Rosetta deployed the Philae landing craft to accomplish history’s first ever touchdown on a comets nucleus. It has also orbited the comet for over 10 months of up close observation, coming at times to as close as 8 kilometers. It is equipped with a suite 11 instruments to analyze every facet of the comet’s nature and environment.

Comet 67P is still becoming more and more active as it orbits closer and closer to the sun over the next two months. The pair reach perihelion on August 13, 2015 at a distance of 186 million km from the Sun, between the orbits of Earth and Mars.

Alice works by examining light emitted from the comet to understand the chemistry of the comet’s atmosphere, or coma and determine the chemical composition with the far-ultraviolet spectrograph.

According to the measurements from Alice, the water and carbon dioxide in the comet’s atmospheric coma originate from plumes erupting from its surface.

“It is similar to those that the Hubble Space Telescope discovered on Jupiter’s moon Europa, with the exception that the electrons at the comet are produced by solar radiation, while the electrons at Europa come from Jupiter’s magnetosphere,” said Paul Feldman, an Alice co-investigator from the Johns Hopkins University in Baltimore, Maryland, in a statement.

Jets of gas and dust are blasting from the active neck of comet 67P/Churyumov-Gerasimenko in this photo mosaic assembled from four images taken on 26 September 2014 by the European Space Agency’s Rosetta spacecraft at a distance of 26.3 kilometers (16 miles) from the center of the comet. Credit: ESA/Rosetta/NAVCAM/Marco Di Lorenzo/Ken Kremer/kenkremer.com
Rosetta discovered an unexpected process at comet nucleus that causes the rapid breakup of water and carbon dioxide molecules. Jets of gas and dust are blasting from the active neck of comet 67P/Churyumov-Gerasimenko in this photo mosaic assembled from four images taken on 26 September 2014 by the European Space Agency’s Rosetta spacecraft at a distance of 26.3 kilometers (16 miles) from the center of the comet. Credit: ESA/Rosetta/NAVCAM/Marco Di Lorenzo/Ken Kremer/kenkremer.com

Other instruments aboard Rosetta including MIRO, ROSINA and VIRTIS, which study relative abundances of coma constituents, corroborate the Alice findings.

“These early results from Alice demonstrate how important it is to study a comet at different wavelengths and with different techniques, in order to probe various aspects of the comet environment,” says ESA’s Rosetta project scientist Matt Taylor, in a statement.

“We’re actively watching how the comet evolves as it moves closer to the Sun along its orbit towards perihelion in August, seeing how the plumes become more active due to solar heating, and studying the effects of the comet’s interaction with the solar wind.”

Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.

Ken Kremer

How Long Will Our Spacecraft Survive?

There are many hazards out there, eager to disrupt and dismantle the mighty machines we send out into space. How long can they survive to perform their important missions?

Every few months, an eager new spacecraft arrives on the launch pad, ready for its date with destiny. If we don’t blow it all to bits with a launch vehicle failure, it’ll be gently placed into orbit with surgical precision. Then it’ll carry out a noble mission of exploring the Solar System, analyzing the Earth, or ensuring we have an infinite number of radio stations in our cars, allowing us to never be satisfied with any of them.

Space is hostile. Not just to fragile hu-mans, but also to our anthropomorphized Number Five is alive robotic spacecraft which we uncaringly send to do our bidding. There are many hazards out there, eager to disrupt and dismantle our stalwart electronic companions. Oblivion feeds voraciously on our ever trusting space scouts and their tiny delicate robotic hearts, so many well before their time.

How long have they got? How long will our spacecraft survive as we cast them on their suicide missions to “go look at stuff on behalf of the mighty human empire”? When spacecraft are hurled into the void, all mission planners know they’re living on borrowed time.

The intrepid Mars Exploration Rovers, Spirit and Opportunity, were only expected to operate for 3 months. NASA’s Spitzer Space Telescope carried a tank of expendable helium coolant to let it see the dimmest objects in the infrared spectrum.

Sometimes the spacecraft wear down for unexpected reasons, like electronic glitches, or parts wearing out. Hubble was equipped with rotating gyroscopes that eventually wore out over time, making it more difficult to steer at its targets, and only an intervention by rescue and repair allowed the mission to keep going.

In general, a spacecraft is expected to last a few months to a few years. Spirit and Opportunity only had a planned mission of 3 months. It took Spirit more than 6 dauntless years to finally succumb to the hostile Martian environment. Opportunity is still kicking more than a decade later, thanks to some very careful driving and gusts of Martian wind clearing off its solar panels which didn’t surprise anybody.

Artist impression of Rosetta and Asteroid 2867 Steins. Credit:  ESA
Artist impression of Rosetta and Asteroid 2867 Steins. Credit: ESA

ESA’s Rosetta spacecraft needed to survive for 10 years in a dormant state before its encounter with Comet 67/P. It’s expected to last until the end of 2015. Then its orbit will carry it too far from the Sun to operate its solar panels, then it’ll go to sleep one last time.

As a testament to luck and remarkable feats of engineering, some survive much longer than anyone ever expected. NASA’s Voyager Spacecraft, launched in 1977, are still going and communicating with Earth. It’s believed they’ll survive until 2025, when their radioisotope thermoelectric generators stop producing power.

At which point they’ll return to the Earth at the heart of a massive alien spacecraft and scare the bejeebus out of us.

… And I know what you’re thinking. Once our spacecraft stop functioning, they’ll still exist. Perhaps getting close enough to another source of solar energy to start transmitting again.

So, how long will our spacecraft hold together in something roughly robot-probe shaped? Any spacecraft orbiting a planet or Moon won’t last long geologically before they’re given a rocky kiss of death with help from a big group hug from gravity.

This might take a decade, a hundred years or a million. Eventually, that spacecraft is racing towards a well distributed grave on its new home.

Solar Dynamics Observatory. Credit: NASA
Solar Dynamics Observatory. Credit: NASA

A spacecraft that’s orbiting the Sun should last much longer. However, a gravitational threesome with a planet or large asteroid could drag it into a solar death spiral or hurl it into a planet. There are asteroids whipping around from the formation of the Solar System, and they haven’t crashed into anything… yet.

A lucky spacecraft might last hundreds of millions, or even billions of years. Our little robot friends that leave the gravitational pull of the Solar System have a chance of making it for the long haul.

Once they’re out in interstellar space, there will be very few micrometeorites to punch little holes in them. Unless they happen to run into another star – and that’s very unlikely – they’ll travel through space until they’re worn away over billions of years, and who knows what that means for future alien archaeology students. The golden records on the Voyager spacecraft were designed to still be playable for a billion years in space.

Artist's concept of NASA's Voyager spacecraft. Image credit: NASA/JPL-Caltech
Artist’s concept of NASA’s Voyager spacecraft. Image credit: NASA/JPL-Caltech

It’s tough to keep a spacecraft operating in space. It’s a really hostile place, ready to fry their little silicon brains, scuttle them with a micrometeorite, or just erode them away over an incomprehensible length of time.

Are horrible space agency fiends tossing our trusting big eyed robot pals to their doom on one-way missions into the abyss? Don’t worry viewers, I have it on good authority this is what the robots want.

Beloved astronaut Chris Hadfield said if Voyager had stayed at home where it’s safe, it would’ve been sad forever, because it never would have discovered things. I think he’s right, Voyager is as happy as it could be exploring the parts of our Universe the rest of us aren’t able to go and see for ourselves.

What’s your favorite spacecraft survivor story? Tell us in the comments below.

Rosetta’s View of a Comet’s “Great Divide”

The latest image to be revealed of comet 67P/Churyumov-Gerasimenko comes from October 27, 2014, before the Philae lander even departed for its surface. Above we get a view of a dramatically-shadowed cliff separating two regions on 67P, the high, smooth plateaus of Babi and the boulder-strewn, slumped valley of Aten. Both are located on the larger lobe of the comet, while parts of the Ma’at region on the smaller “head” lobe can be seen in the distance at upper left. (You can see a regional map of comet 67P here.)

The image scale is about 75 cm (2.4 feet) per pixel and the entire image spans 770 meters across – about half a mile. Based on that, the cliff is easily over 190 meters (630 feet) high!

Here's a diagram of the image above in context with the entire comet. (ESA)
Here’s a diagram of the image above in context with the entire comet. (ESA)

It’s thought that the morphological differences in the Babi and Aten regions – in both texture and altitude – are the result of a massive loss of material from Aten at some point in the comet’s history. According to the entry on the Rosetta blog, the entire volume of the Aten “scoop” is equivalent to about 50 Great Pyramids of Giza… a fitting analogy considering the choice to name features on 67P with an ancient Egyptian theme.

See Comet 67P’s Enormous “Cheops” Boulder

The image above is one of a slew of NavCam images that will be released at the end of the month on ESA’s Archive Browser, captured by Rosetta after establishing orbit around 67P.

Source: ESA’s Rosetta blog

NavCam image of 67P/C-G acquired on May 12, 2015. The elongated depression at the center of the illuminated region is Aten. ( ESA/Rosetta/NavCam – CC BY-SA IGO 3.0)
NavCam image of 67P/C-G acquired on May 12, 2015. The elongated depression at the center of the illuminated region is Aten. ( ESA/Rosetta/NavCam – CC BY-SA IGO 3.0)

Weekly Space Hangout – April 26, 2015: Special Cosmoquest Hangoutathon Edition

Host: Fraser Cain (@fcain)

Guests:
Morgan Rehnberg (cosmicchatter.org / @MorganRehnberg )
Nicole Gugliucci (cosmoquest.org / @noisyastronomer)
Nancy Atkinson (UniverseToday.com / @Nancy_A)

Continue reading “Weekly Space Hangout – April 26, 2015: Special Cosmoquest Hangoutathon Edition”