Rosetta Archives

June 13, 2015December 23, 2015 by Bob King

Have We Found Rosetta’s Lost Philae Lander?

Left image from Rosetta’s OSIRIS narrow-angle camera shows the Philae lander on November 12, 2014 after it left the spacecraft for the comet's nucleus. Right: Close-up of a promising candidate for the lander photographed on December 12. Copyright: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

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.

June 8, 2015December 23, 2015 by Jason Major

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

OSIRIS image of 67P/C-G from April 25, 2015

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

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

June 4, 2015December 23, 2015 by Ken Kremer

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

This single frame Rosetta navigation camera image was taken from a distance of 77.8 km from the centre of Comet 67P/Churyumov-Gerasimenko on 22 March 2015. The image has a resolution of 6.6 m/pixel and measures 6 x 6 km. The image is cropped and processed to bring out the details of the comet’s activity. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

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

“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.

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

May 22, 2015December 23, 2015 by Jason Major

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

A shadowed cliff on comet 67P/C-G imaged by Rosetta in Oct. 2014 (Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0)

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)

March 10, 2015December 23, 2015 by Nancy Atkinson

First Attempt to Contact Hibernating Philae Lander Will Be March 12

Artist rendition of the Philae lander on Comet 67P/Churyumov-Gerasimenko. Credit: DLR.

Where is the Philae lander and will it wake up again? Those are the questions the team at the DLR Lander Control Center will be trying to answer starting this week. Thursday, March 12 provides the first possibility to receive a signal from Rosetta’s lander, sitting somewhere on Comet 67P/Churyumov-Gerasimenko.

“It could be that the lander has already woken up from its winter sleep 500 million kilometers away, but does not yet have sufficient power to inform the team on Earth,” said Koen Geurts from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt) in a blog post today.

The animated image below provides strong evidence that Philae touched down for the first time almost precisely where intended. The animation comprises images recorded by Rosetta's navigation camera as the orbiter flew over the (intended) Philae landing site on November 12th. The dark area is probably dust raised by the craft on touchdown. The boulder to the right of the circle is seen in detail in the photo below. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0 — The animated image below provides strong evidence that Philae touched down for the first time almost precisely where intended. The animation comprises images recorded by Rosetta’s navigation camera as the orbiter flew over the (intended) Philae landing site on November 12th. The dark area is probably dust raised by the craft on touchdown. The boulder to the right of the circle is seen in detail in the photo below. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

The lander has been sleeping in a shaded spot on the comet’s surface after its dramatic touchdown (actually, three touchdowns) four months ago on Nov. 12, 2014 when it flew, landed, bounced and then repeated that process for more than two hours across the surface. Scientists estimated it could have bounced as high as 3.2 kilometers (2 miles) before becoming wedged in a spot that –- at that time — didn’t get much sunlight. The solar-powered lander quickly ran out of power, just hours after landing.

The team admits they would be very lucky if a signal were to be received from Philae at the first opportunity, which is 05:00 CET on March 12, 2015 (midnight on March 11 EDT) when the communication unit on the Rosetta orbiter will be switched on to call the lander.

While the comet is coming ever-closer to the Sun, Philae needs to receive enough solar energy to activate a few systems before it can wake up and begin communicating.

“Philae currently receives about twice as much solar energy as it did in November last year,” said Lander Project Manager Stephan Ulamec from DLR. “Comet 67P/Churyumov-Gerasimenko and its companion, Philae, are now only 300 million kilometers from the Sun. It will probably still be too cold for the lander to wake up, but it is worth trying. The prospects will improve with each passing day.”

The team did give a caveat that several conditions must be met for Philae to wake up and start operating again. By no means is it a given that Philae will awake.

First, the interior of the lander must be at least at minus 45 degrees Celsius before Philae can wake up from its winter sleep. In addition, the lander must be able to generate at least 5.5 watts using its solar panels to wake up. The temperatures are significantly lower in the shadowed region where it sits (named Abydos, even though the exact location has not been identified) than at the originally planned landing location.

While hibernating, the lander has been gathering and storing as much power as possible to heat up and Geurts said that as soon as Philae ‘realizes’ that it is receiving more than 5.5 watts of power and its internal temperature is above minus 45 degrees Celsius, it will turn on, heat up further and attempt to charge its battery.

Then, once awakened, Philae will switch on its receiver every 30 minutes and listens for a signal from the Rosetta orbiter. This, too, can be performed in a very low power state, but Philae needs a total of 19 watts to begin operating and allow two-way communication.

My #lifeonacomet has just begun @ESA_Rosetta. I'll tell you more about my new home, comet #67P soon… zzzzz #CometLanding

— Philae Lander (@Philae2014) November 15, 2014

Until March 20, Rosetta will be transmitting to the lander and listening for a response. The team said the most likely time for contact is during the 11 flybys where the orbiter’s path puts it in a particularly favorable position with respect to the lander during comet ‘daytime’ – that is, when Philae is in sunlight and being supplied with power by its solar panels. Communication will be attempted continuously because Philae’s environment could have changed since the landing.

“If we cannot establish contact with Philae before 20 March, we will make another attempt at the next opportunity,” said Ulamec. “Once we can communicate with Philae again, the scientific work can begin.”

Once Philae wakes up and can transmit, it will first send data about the health of its systems.

“We will then evaluate the data. What is the state of the rechargeable battery? Is everything on the lander still functioning? What is the temperature? How much energy is it receiving?” said Geurts.

Then the team will determine if all 10 instruments will be able to function with the available power. If sufficient energy cannot be stored in the battery, the solar energy available during the comet daytime will determine whether a reduced version of the science operations can be performed.

Currently, scientists believe that Philae is in sunlight for 1.3 hours. A day on 67P/Churyumov-Gerasimenko lasts 12.4 hours. If the battery can be charged as planned, then science operations could be done even at night. But in the event that the rechargeable battery on board Philae did not survive the intense cold of its hibernation, the engineers are prepared. “We are working to ensure that we can operate the lander and its instruments at least during the comet’s daytime, when it is in direct sunlight.”

Also, new commands have been sent to Philae to optimize the heating and provide energy savings to improve its chances of communication with Earth. Even if Philae does not have enough energy yet to answer, it could receive and execute these commands. This is referred to as ‘blind commanding’ by the engineers, because the lander is initially very unlikely give them feedback.

Philae’s exact location is still being determined by looking at images acquired by the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) on board the Rosetta orbiter.

Read more about Philae at the DLR website.

March 9, 2015December 23, 2015 by Bob King

Dust Whirls, Swirls and Twirls at Rosetta’s Comet

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. Credits: — 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: — 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 Hathor region in the neck between the two lobes. Credit: — 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 3.0

A separate image taken on Feb. 28. According to ESA, 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: — Look 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.

February 16, 2015December 23, 2015 by Jason Major

The First Images Are In from Rosetta’s Valentine’s Day Comet Flyby

The surface of 67P/C-G imaged by Rosetta on Feb. 14, 2015 from about 8.9 km (ESA/Rosetta/NavCam – CC BY-SA IGO 3.0)

On Saturday, Feb. 14, the Rosetta spacecraft swooped low over the surface of comet 67P/C-G in the first dedicated close pass of its mission, coming within a scant 6 km (3.7 miles) at 12:41 UTC. The image above is a mosaic of four individual NavCam images acquired just shortly afterwards, when Rosetta was about 8.9 km from the comet.

The 45m "Cheops" boulder on comet 67P/C-G (ESA/Rosetta/Navcam) — The 45m “Cheops” boulder on comet 67P/C-G (ESA/Rosetta/Navcam)

The view above looks across much of the Imhotep region along the flat bottom of comet 67P’s larger lobe. (See a map of 67P’s named regions here.) At the top is the flat “plain” where the Cheops boulder cluster can be seen – the largest of which is 45 meters (148 feet) across.

The zero phase angle of sunlight during the pass made for fairly even illumination across the comet’s surface.

The image scale on the full mosaic is 0.76 m/pixel and the entire view encompasses a 1.35 × 1.37 km-wide area.

Other NavCam images acquired before and after the pass have been assembled into mosaics – check those out below:

Four-image mosaic made from NavCam images acquired on Feb. 14, 2015 at a distance of 35 km. Credits: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0.

Four-image mosaic made from NavCam images acquired on Feb. 14, 2015 at a distance of 12.6 km. Credits: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0.

Four-image mosaic made from NavCam images acquired on Feb. 14, 2015 at 19:42 UTC at a distance of 31.6 km. Credits: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0.

In addition to NavCam images of 67P, Rosetta also acquired high-resolution OSIRIS images of the comet and gathered scientific data about its coma environment during the flyby. These data will be downlinked and processed over the next week or so.

Flybys will be regular parts of Rosetta’s operations over the course of 2015, but due to the comet’s increasing activity none will bring the spacecraft as close as this particular pass.

Rosetta is now moving out to a distance of about 250 km (155 miles) from 67P. Watch a video below of how the Feb. 14 flyby was planned and executed:

Source: ESA’s Rosetta blog

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(Also, on Feb. 9, Rosetta captured a full-frame NavCam image of 67P from 105 km. I’ve edited that image for additional contrast and added a blue tint. Enjoy!)

Comet 67P on Feb. 9, 2015 from 105 km (65 miles)

February 9, 2015December 23, 2015 by Jason Major

Rosetta’s Comet Really “Blows Up” in Latest Images

Jet activity on Comet 67P/C-G imaged on Jan. 31 and Feb. 3, 2015. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0. Edit by Jason Major.

First off: no, comet 67P/Churyumov-Gerasimenko is not about to explode or disintegrate. But as it steadily gets nearer to the Sun the comet’s jets are getting more and more active and they’re putting on quite a show for the orbiting Rosetta spacecraft! Click the image for a jeterrific hi-res version.

The images above were captured by Rosetta’s NavCam on Jan. 31 and Feb. 3 from a distance of about 28 km (17 miles). Each is a mosaic of four separate NavCam acquisitions and they have been adjusted and tinted in Photoshop by yours truly to further enhance the jets’ visibility. (You can view the original image mosaics and source frames here and here.)

These dramatic views are just a hint at what’s in store; 67P’s activity will only be increasing in the coming weeks and months and, this weekend, Rosetta will be swooping down for an extreme close pass over its surface!

Detail of 67P from the Feb. 3 NavCam image

This Saturday, Feb. 14, Rosetta will be performing a very close pass of the comet’s nucleus, soaring over the Imhotep region at an altitude of only 6 km (3.7 miles) at 12:41 UTC. This will allow the spacecraft to closely image the comet’s surface, as well as investigate the behavior of its jets and how they interact with its developing coma.

“The upcoming close flyby will allow unique scientific observations, providing us with high-resolution measurements of the surface over a range of wavelengths and giving us the opportunity to sample – taste or sniff – the very innermost parts of the comet’s atmosphere,” said Rosetta project scientist Matt Taylor.

Read more about Rosetta’s Valentine’s Day close pass here and watch an animation of how it will be executed below.

Source: ESA

UPDATE: Here’s an image of 67P captured by Rosetta on Feb. 6 from a distance of 124 km (77 miles) as it moved into a higher orbit in preparation of its upcoming close pass. It’s the first single-frame image of the comet since leaving bound orbits.

The image has been processed to add a contrasting tint and enhance jet activity. See the original image here.

Single-frame NavCam image of comet 67P/C-G imaged on Feb. 6, 2015. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0. Edited by Jason Major.

February 5, 2015December 23, 2015 by Bob King

Rosetta to Snuggle Up to Comet 67P for Closest Encounter Yet

Rosetta will dance close to 67P on Valentine's Day coming to within 3.7 miles of the comet. Credit: Bob King

Who doesn’t like to snuggle up with their Valentine on Valentine’s Day? Rosetta will practically whisper sweet nothings into 67P’s ear on February 14 when it swings just 3.7 miles (6 km) above its surface, its closest encounter yet.

Rosetta had been orbiting the comet at a distance of some 16 miles (26 km) but beginning yesterday, mission controllers used the spacecraft’s thrusters to change its orbit in preparation for the close flyby. First, Rosetta will move out to a distance of roughly 87 miles (140 km) from the comet this Saturday before swooping in for the close encounter at 6:41 a.m. CST on Feb. 14. Closest approach happens over the comet’s larger lobe, above the Imhotep region.

The relative position of Rosetta with Comet 67P/Churyumov–Gerasimenko at the moment of closest approach this Valentine's Day when the spacecraft will pass just 3.7 miles (6 km) above the comet’s large lobe. Credit: ESA/C.Carreau — The relative position of Rosetta with Comet 67P/Churyumov–Gerasimenko at the moment of closest approach this Valentine’s Day when the spacecraft will pass just 3.7 miles (6 km) above the comet’s large lobe. Credit: ESA/C.Carreau with additions by the author

The close encounter will provide opportunities for Rosetta’s science instruments to photograph 67P’s surface at high resolution across a range of wavelengths as well as get a close sniff of what’s inside its innermost coma or developing atmosphere. Scientists will also be looking closely at the outflowing gas and dust to see how it evolves during transport from the comet’s interior to the coma and tail.

As Rosetta swoops by its view of the comet will continuously change. Instruments will collect data on how 67P’s dust grains reflect light across a variety of orbital perspectives – from shadowless lighting with the Sun at the orbiter’s back to slanted lighting angles – to learn more about its properties.

The Imhotep region of comet 67P features a large, relatively smooth region. Rosetta will make high resolutions of Imhotep during its close flyby. Credit: ESA/Rosetta/Navcam — The Imhotep region of comet 67P features a large, relatively smooth region and a smattering of large boulders. Rosetta will make high resolutions of Imhotep during its close flyby. Credit: ESA/Rosetta/Navcam

“After this close flyby, a new phase will begin, when Rosetta will execute sets of flybys past the comet at a range of distances, between about 15 km (9 miles) and 100 km (62 miles),” said Sylvain Lodiot, ESA’s spacecraft operations manager.

During some of the close flybys, Rosetta trajectory will be almost in step with the comet’s rotation, allowing the instruments to monitor a single point on the surface in great detail as it passes by.

Helpful animation of how ESA mission controllers are changing Rosetta’s orbit to ready the probe for the Valentine’s Day flyby.

Perihelion, when the comet arcs closest to the Sun at a distance of 115.6 million miles (186 million km), occurs on August 13. Activity should be reaching its peak around that time. Beginning one month before, the Rosetta team will identify and closely examine one of the comet’s jets in wickedly rich detail.

“We hope to target one of these regions for a fly-through, to really get a taste of the outflow of the comet,” said Matt Taylor, ESA’s Rosetta project scientist.

Yum, yum. Can’t wait for that restaurant review!

February 2, 2015December 23, 2015 by Bob King

Rosetta Sees Fascinating Changes in Comet 67P

A new jet issues from a fissure in the rugged, dusty surface of Rosetta's comet. Credit: ESO/Rosetta/Navcam

It only makes sense. Sunlight heats a comet and causes ice to vaporize. This leads to changes in the appearance of surface features. For instance, the Sun’s heat can gnaw away at the ice on sunward-facing cliffs, hollowing them out and eventually causing them to collapse in icy rubble. Solar heating can also warm the ice that’s beneath the surface.

When it becomes a vapor, pressure can build up, cracking the ice above and releasing sprays of gas and dust as jets. New images compared to old suggest the comet’s surface is changing as it approaches the Sun.

Take a look at this photo taken on December 9 of a part of the neck of the comet called Hapi. I've labeled a boulder and three prominent cracks. Sunlight is coming from top and behind in this image. Compare to the photo below shot on Jan. 8. Credit: ESA/Rosetta/Navcam — Take a look at this photo taken on December 9 of a part of the neck of the comet called Hapi. I’ve labeled a boulder and three prominent cracks. Sunlight is coming from top and behind in this image. Compare to the photo below shot on Jan. 8. Credit: ESA/Rosetta/Navcam

Recent photos taken by the Rosetta spacecraft reveal possible changes on the surface of 67P/Churyumov-Gerasimenko that are fascinating to see and contemplate. In a recent entry of the Rosetta blog, the writer makes mention of horseshoe-shaped features in the smooth neck region of the comet called “Hapi”. An earlier image from Jan. 8 may show subtle changes in the region compared to a more recent image from Jan. 22. We’ll get to those in a minute, but there may be examples of more vivid changes.

Although the viewing angle and lighting geometry has changed some between this photo, taken Jan. 8, and the one above, it certainly appears that the three cracks have virtually disappeared in a month's time. The same boulder is flagged in both photos. Credit: ESA/Rosetta/Navcam — Although the viewing angle and lighting geometry has changed some between this photo, taken Jan. 8, and the one above, it certainly appears that the three cracks have virtually disappeared in a month’s time. The same boulder is flagged in both photos. Credit: ESA/Rosetta/Navcam

I did some digging around and found what appears to be variations in terrain between photos of the same Hapi region on Dec. 9 and Jan.8. Just as the other writer took care to mention, viewing angle and lighting are not identical in the images. That has to be taken into account when deciding whether a change in a feature is real or due to change in lighting or perspective.

Side by side comparison of the two image from Dec. 9, 2014 (left) and Jan. 8, 2015. Credit: ESA/Rosetta/Navcam

But take a look at those cracks in the December image that appear to be missing in January’s. The change, if real, is dramatic. If they did disappear, how? Are they buried in dust released by jets that later drifted back down to the surface?

Comparison of Jan. 22 and Jan. 9 photos of the "horseshoes" or depressions in 67P's Hapi region. Outside of differences in lighting, do you see any changes? Credit: ESA/Rosetta/Navcam — Comparison of Jan. 22 and Jan. 9 photos of the “horseshoes” or depressions in 67P’s Hapi region. Outside of differences in lighting, do you see any changes? Credit: ESA/Rosetta/Navcam

Now back to those horseshoe features. Again, the viewing angles are somewhat different, but I can’t see any notable changes in the scene. Perhaps you can. While comets are expected to change, it’s exciting when it seems to be happening right before your eyes.