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11.09.2014
ROSETTA AND PHILAE SNAP SELFIE AT COMET
Using the CIVA imaging system on board Rosetta’s lander Philae, the spacecraft have snapped a ‘selfie’ at comet 67P/Churyumov-Gerasimenko.
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Rosetta mission selfie at comet 67P/C-G, taken on 7 September. Credit: ESA/Rosetta/Philae/CIVA
CIVA, the Comet Infrared and Visible Analyser, is one of ten instruments onboard Philae. The CIVA-P part of the instrument comprises seven micro-cameras that will take a 360 degree panoramic image of the landing site at visible wavelengths, once Philae is safely on the surface of 67P/C-G, including a section in stereo. CIVA-M is a visible/infrared microscope imager/spectrometer that will the study the composition, texture, and albedo of surface samples.
The latest selfie was taken during Sunday night from a distance of about 50 km from the comet, with one of CIVA-P’s cameras capturing the side of the Rosetta spacecraft and one of its 14 metre-long solar arrays, with 67P/C-G in the background.
Two images with different exposure times were combined to bring out the faint details in this very high contrast situation.
The image was taken as part of the preparations being made for Philae, as the lander team gear up for the first ever attempt to land on a comet. It was presented at the EPSC conference this week, during a presentation highlighting the status of the lander. Next week, on 15 September, the primary landing site for Philae will be announced.
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A PRELIMINARY MAP OF ROSETTA’S COMET
Scientists working on images of comet 67P/Churyumov-Gerasimenko have divided the comet’s surface into a number of different regions based on their morphology, revealing a unique, multifaceted world.
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Several morphologically different regions are indicated in this preliminary map, which is oriented with the comet’s ‘body’ in the foreground and the ‘head’ in the background.
Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
The map and new high-resolution images from the OSIRIS instrument were presented during the Rosetta special session at EPSC today.
With various areas dominated by cliffs, depressions, craters, boulders or even parallel grooves, 67P/C-G displays a multitude of different terrains. Some areas even appear to have been shaped by the comet’s activity.
This preliminary analysis provides the basis for a detailed scientific description of the comet’s surface, but a substantial amount of work involving more detailed OSIRIS images and data from other Rosetta instruments lies ahead to determine what each region represents in terms of their composition and evolution. One recent image from the OSIRIS narrow-angle camera is also shown here.
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Jagged cliffs and prominent boulders are visible in this image taken by OSIRIS on 5 September 2014 from a distance of 62 kilometres from comet 67P/Churyumov-Gerasimenko. The left part of the image shows a side view of the comet’s 'body', while the right is the back of its 'head'. One pixel corresponds to 1.1 metres.
Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
As both 67P/C-G and Rosetta travel closer to the Sun over the next months, the OSIRIS team will monitor the surface looking for changes. While the scientists do not expect the borderlines of the comet’s regions to vary dramatically during this one passage around the Sun, more subtle transformations of the surface may nevertheless help to explain how cometary activity created such a breath-taking world.
Next weekend, on 13 and 14 September 2014, the maps will play a key role as Rosetta’s Lander Team and the Rosetta orbiter scientists gather at CNES, Toulouse to determine a primary and backup landing site from the earlier pre-selection of five candidates.
Quelle: ESA
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Update: 20.45 MESZ
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COMETWATCH – 10 SEPTEMBER
Four-image NAVCAM mosaic comprising images taken on 10 September from a distance of 27.8 km from comet 67P/Churyumov-Gerasimenko (reminder: the distance is given to the centre of the comet). The image scale is approximately 2.5 metres per pixel.
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We know that many of you like exploring these images, and one feature you may quickly notice is the rather bright object seen near the centre of the slope in the upper right. We too were curious and looked at an image taken earlier and it was not visible (the shadow beneath it is coincidence; this is also seen in images without the object). Therefore it is most likely either an image artefact or a transient object in the foreground.
Indeed, if you adjust the contrast of the image you will see that there is a lot of ‘noise’ in the background. Some of this is simply detector noise and cosmic rays, but there seem to be a few bright objects that may be dust/ice particles between Rosetta and the comet.
In previous NAVCAM and OSIRIS images, we’ve already seen jets of gas laced with dust streaming away from the comet, and the instruments COSIMA and GIADA have started detecting dust, so it would be no surprise if these objects were also found to originate from the comet. In any case, it is a phenomenon that will clearly be studied in great detail at 67P/C-G over the coming weeks and months.
Another nice observation you might like to make while playing around with the contrast settings is that faint details can be brought out in the ‘neck’ region of 67P/C-G, which on first look is seemingly obscured by shadows. It appears as though the neck is being illuminated by the reflection of sunlight off the main body of the comet below.
Quelle: ESA
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Update: 12.09.2014
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ROSINA TASTES THE COMET’S GASES
Rosetta’s ROSINA instrument, the Rosetta Orbiter Sensor for Ion and Neutral Analysis, has detected its first cometary volatile molecules. The results were presented at the European Planetary Science Congress, EPSC, held in Portugal this week.
The detections were made early August when Rosetta was within 200 km of comet 67P/Churyumov-Gerasimenko, and over 500 million kilometres from the Sun – the first time that a comet’s coma has been analysed in situ this far from the Sun.
Since then, ROSINA has been almost continuously measuring the density and the composition of the comet’s coma. It has already acquired more than 40,000 high- and low-resolution spectra with its two mass spectrometers
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ROSINA's reflectron time of flight mass spectrometer (RTOF).
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Overall, the density of the coma is relatively low at this early stage, far from the Sun, but should increase as activity picks up, as the comet moves closer to the Sun over the next year. The density is seen to vary during the comet ‘day’, as it rotates over a 12.4 hour period.
As expected, the main species in the comet’s coma are found to be water, carbon monoxide, and carbon dioxide, which are being released from below the surface layer of the nucleus, which VIRTIS has shown to be dark, porous, and probably dry.
However, ROSINA has made the surprising observation that the ratio between these species varies quite significantly, depending on where in the coma Rosetta is. Sometimes carbon monoxide is almost as abundant as water; sometimes it’s only around 10%. In addition, ROSINA has not only detected these main species already, but many of the expected minor ones, such as ammonia, methane, and methanol.
As Rosetta gets closer to the comet and as comet activity increases, it will soon be possible to measure the ratio of hydrogen to deuterium – an isotope of hydrogen with an added neutron – in the cometary water. This ratio is constant in Earth’s ocean water and thus can be used as a way of tracing the still unknown origin of that water: for example, was it incorporated into the Earth at the time of formation, or was it delivered from space at some later date?
In particular, 67P/C-G is a Kuiper belt comet, and the hydrogen to deuterium ratio measured for its water will help constrain how much of Earth’s water could have come from a population of impacting Kuiper belt comets, soon after the birth of the Solar System.
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Rosina's double focusing mass spectrometer (DFMS).
Credit: ESA/Rosetta/ROSINA/UBern/ BIRA/LATMOS/LMM/IRAP/MPS/SwRI/TUB/UMich
Quelle: ESA
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GIADA TRACKS THE DUST
Following the trail of a minuscule dust particle through the depths of space may seem far-fetched, but that is effectively what the GIADA team have been doing recently, as they described at the European Planetary Science Congress this week.
During the Rosetta special session at EPSC, the GIADA team reported the detection of 27 dust grains associated with Comet 67P/Churyumov-Gerasimenko during the month of August.
Four of the grains were detected as Rosetta was approaching the comet, nine during the first series of pyramid trajectories at a distance of about 90 km from the comet surface, and the other fourteen along the second series of pyramid trajectories at 60 km distance.
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Positions along the Rosetta flight path of 27 dust grains (red dots) detected by GIADA in August 2014. Five grains (yellow dots) were detected by both the Grain Detection System and the Impact Sensor.
Image credit: ESA/Rosetta/GIADA/Univ Parthenope NA/INAF-OAC/IAA/INAF-IAPS
Of the 27 grains, five were seen by the Grain Detection System, which detects the grains and measures some of their optical properties, and also by the Impact Sensor, which measures their momentum.
Thus for this handful of grains, the team were able to measure their masses and velocities. Such measurements are particularly important, as they will allow the scientists to trace the paths of grains back to the comet and to even identify which regions on the comet they may have been ejected from. For these first five grains, that analysis is on-going.
The figure above shows the positions along the Rosetta flight path of 27 dust grains (red dots) detected by GIADA in August 2014. Five grains (yellow dots) were detected by both the Grain Detection System and the Impact Sensor. Some of the data points overlap or are hidden behind the yellow symbols.
Quelle: ESA
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Update: 14.09.2014
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SCIENCE WITH THE LANDER – WHAT TO EXPECT WHEN PHILAE MEETS 67P
When Rosetta’s Philae lander touches down on comet 67P/Churyumov-Gerasimenko in two months time, a new chapter will begin for the mission. At the European Planetary Science Congress this week, participants heard from the lander team about the science plans.
Rosetta’s orbiter instruments are producing their first preliminary scientific results and many of these were presented at the European Planetary Science Congress (EPSC) that took place this week in Lisbon, Portugal. While scientists are eagerly examining the data and making the first steps towards characterising comet 67P/C-G, there is also something else on their mind: the selection of the primary landing site and the prospect of the science that can be done when Philae is safely settled on the comet.
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The approximate locations of the five candidate landing sites are marked on these OSIRIS narrow-angle camera images taken on 16 August from a distance of about 100 km. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
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During the Rosetta Special Session at EPSC, the lander science team explained the landing site selection process that began almost as soon as Rosetta arrived at the comet in August, and that will conclude in mid-October with the formal Go for landing from ESA. They emphasised the important role played by the orbiter instruments, in particular ALICE, MIRO, OSIRIS, ROSINA and VIRTIS, in identifying suitable candidate landing sites. Philae will get a chance to repay the compliment when on the comet surface, by providing ground-truth measurements for the orbiter instruments.
This weekend, the primary landing site will be selected from the shortlist of five candidates. The team explained that the landing will be a passive one, meaning that the exact location of landing will be determined by the relative position of Rosetta and the comet at the time of Philae’s deployment, and the speed and direction of the deployment: there is no active steering down onto the surface.
As all of these parameters have uncertainties associated with them, the Rosetta and Philae operations teams can only predict the landing point in advance to within an ellipse typically 1 kilometre long on the surface of 67P/C-G. This is larger than any of the apparently smooth terrains on the reachable parts of the surface of the nucleus, adding to the challenge of selecting the best possible site.
As soon as Philae is released from the orbiter, the lander’s first science will begin. This is called the separation, descent, and landing (SDL) phase and it will last about 5 to 10 hours – the duration will depend on which landing site is selected and what trajectory needs to be flown to deliver the lander.
During the SDL phase, many of the lander instruments will be active. During the separation and descent of Philae:
CIVA will make a ‘Farewell’ image of the orbiter;
ROLIS will take images during the descent;
COSAC and PTOLEMY will sample the ‘atmosphere’ of the comet as the lander approaches the surface;
ROMAP will measure the interaction between the solar wind and the cometary plasma;
SESAME/DIM and SESAME/PP will measure the dust and the plasma environment, respectively;
CONSERT, along with other experiments on the orbiter and the lander, will measure the rate of descent and, at the same time, will sense the uppermost surface layers of the comet nucleus.
Immediately upon landing:
CIVA will make a panoramic image of the landing site; this will be used together with other information from the lander to determine where and how Philae has landed.
MUPUS will measure the deceleration of the harpoons as they are fired to anchor Philae to the surface;
SESAME/CASSE will measure the elastic properties of the surface.
With Philae safely on the surface, another series of measurements will begin, marking the start of the so-called first science sequence (FSS). This phase will last for a maximum of 54 hours, and the main goal of this phase is to secure a set of the most important scientific measurements at the surface of the comet. The FSS is split into several blocks with distinct science goals.
For the first several hours, a pre-programmed automated sequence of measurements is made. At this stage:
ROLIS will take images of the surface with micrometre resolution;
ROMAP will measure the magnetic and plasma properties of the surface environment;
MUPUS will measure the surface and subsurface temperature at the landing site;
CONSERT will begin operations to probe the comet interior through one complete revolution of the nucleus.
While this automated sequence is running, the lander operators will determine how Philae is oriented by examining the telemetry data for the solar panels - the power distribution of the panels will let them work out the position of the Sun with respect to Philae and thus Philae’s orientation. They can also compare the panoramic image of the horizon taken by CIVA-P with images of the surface mapped onto digital terrain models. By the time the automated sequence is completed, the lander operators will know how Philae is oriented and can command the lander to rotate to put it in the best position to illuminate the solar panels – this is crucial to ensure that the batteries can be charged as efficiently as possible.
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Philae's instruments. Credit: ESA/ATG medialab
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The next sequence of measurements during the FSS is mainly dedicated to investigating the composition of the subsurface, thus the most pristine constituents. During this period, SD2 will drill into the comet surface to take a sample of a few cubic millimetres of material from beneath the surface. While SD2 drills, COSAC and PTOLEMY will sense the release of gases in the surroundings. SD2 will drill twice during this block, with each sample being further heated in an oven to release chemical species that do not otherwise sublimate from solid state. The first sample goes to PTOLEMY to measure how much carbon, hydrogen, oxygen and nitrogen there is, and to identify their isotopic composition, while the second sample goes to COSAC to identify and characterise the heavier molecular compounds. Measurements of the dust in the environment will be made with SESAME.
This is followed by some experiments to study the surface properties. The MUPUS hammer is released and embeds itself into the ground so that it can measure the temperature at various depths in the subsurface. The acoustic signals of the vibrations of the hammer action will be detected by acoustic sensors in the feet of SESAME/CASSE and will be used to measure the mechanical properties of the nucleus. APXS will be deployed to measure the elemental composition of the surface material. SESAME/DIM will investigate dust impacts further, and the dielectric properties of the ground will be measured by SESAME/PP, which can provide some indications about the presence of water ice beneath the surface.
In the next block of measurements, another drill sample will be taken by SD2 and delivered to an oven in which CIVA-M will acquire microscopic images of the samples, both in the visible and in the infrared, to infer its composition. The sample will then be analysed with COSAC at lower oven temperatures than before.
Power and battery recharging permitting, there is the prospect of continuing science operations on the comet surface for the long-term science (LTS) phase, which could run from November until March 2015. The emphasis during this period will be on studying how the conditions and environment at the landing site change as the comet gets closer to the Sun, and to make some additional studies that are among the more challenging of Philae’s science goals. These include searching for comet quakes with SESAME, using COSAC to look for evidence of amino acids in a drilled sample, and making tomographic measurements with CONSERT, by transmitting radio signals between Philae and Rosetta through different parts of the interior of the comet to look for heterogeneity on smaller scales.
However, it is expected that by March 2015, the temperatures of the compartments on the lander will have reached levels that are too high for Philae to continue operating, and the lander’s science mission will come to an end.
Quelle: ESA
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Update: 15.09.2014
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Landestelle für Kometen-Mission Rosetta Lander gewählt!
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Site J, denoted by the plus sign, marks the spot on comet 67P/Churyumov–Gerasimenko where Rosetta's lander Philae will attempt to touch down in November 2014.
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Philae, the Rosetta mission lander, will attempt to touch down on a spot called site J on comet 67P/Churyumov–Gerasimenko. The site selection was announced September 15 during a press briefing in Paris. Site J is on the smaller lobe of the comet, which is shaped like a rubber duck. Philae is slated to land on comet 67P/Churyumov–Gerasimenko on November 11.
Quelle: ScienceNews
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Rosetta’s lander Philae will target Site J, an intriguing region on Comet 67P/Churyumov–Gerasimenko that offers unique scientific potential, with hints of activity nearby, and minimum risk to the lander compared to the other candidate sites.
Site J is on the ‘head’ of the comet, an irregular shaped world that is just over 4 km across at its widest point. The decision to select Site J as the primary site was unanimous. The backup, Site C, is located on the ‘body’ of the comet.
The 100 kg lander is planned to reach the surface on 11 November, where it will perform indepth measurements to characterise the nucleus in situ, in a totally unprecedented way.
But choosing a suitable landing site has not been an easy task.
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Context image showing the location of the primary landing site for Rosetta’s lander Philae.
Site J is located on the head of Comet 67P/Churyumov–Gerasimenko. An inset showing a close up of the landing site is also shown. The inset image was taken by Rosetta’s OSIRIS narrow-angle camera on 20 August 2014 from a distance of about 67 km. The image scale is 1.2 metres/pixel. The background image was taken on 16 August from a distance of about 100 km. The comet nucleus is about 4 km across.
The primary landing site was chosen from five candidates during the Landing Site Selection Group meeting held on 13–14 September 2014.
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“As we have seen from recent close-up images, the comet is a beautiful but dramatic world – it is scientifically exciting, but its shape makes it operationally challenging,” says Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center.
“None of the candidate landing sites met all of the operational criteria at the 100% level, but Site J is clearly the best solution.”
“We will make the first ever in situ analysis of a comet at this site, giving us an unparalleled insight into the composition, structure and evolution of a comet,” says Jean-Pierre Bibring, a lead lander scientist and principal investigator of the CIVA instrument at the IAS in Orsay, France.
“Site J in particular offers us the chance to analyse pristine material, characterise the properties of the nucleus, and study the processes that drive its activity.”
“None of the candidate landing sites met all of the operational criteria at the 100% level, but Site J is clearly the best solution.”
“We will make the first ever in situ analysis of a comet at this site, giving us an unparalleled insight into the composition, structure and evolution of a comet,” says Jean-Pierre Bibring, a lead lander scientist and principal investigator of the CIVA instrument at the IAS in Orsay, France.
“Site J in particular offers us the chance to analyse pristine material, characterise the properties of the nucleus, and study the processes that drive its activity.”
The race to find the landing site could only begin once Rosetta arrived at the comet on 6 August, when the comet was seen close-up for the first time. By 24 August, using data collected when Rosetta was still about 100 km from the comet five candidate regions had been identified for further analysis.
Since then, the spacecraft has moved to within 30 km of the comet, affording more detailed scientific measurements of the candidate sites. In parallel, the operations and flight dynamics teams have been exploring options for delivering the lander to all five candidate landing sites.
Over the weekend, the Landing Site Selection Group of engineers and scientists from Philae’s Science, Operations and Navigation Centre at France’s CNES space agency, the Lander Control Centre at DLR, scientists representing the Philae Lander instruments and ESA’s Rosetta team met at CNES, Toulouse, France, to consider the available data and to choose the primary and backup sites.
Quelle: ESA
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Update: 17.09.2014
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PHILAE’S PRIMARY LANDING SITE IN 3D
This anaglyph image of Philae’s primary landing site on the ‘head’ of Comet 67P/Churyumov–Gerasimenko can be viewed using stereoscopic glasses with red–green/blue filters.
The two images used to make the anaglyph were taken on 26 August 2014 from a distance of 48 km with Rosetta’s OSIRIS narrow-angle camera. The image scale is 0.96 metres/pixel.
The primary landing location, Site J, was selected during the Landing Site Selection Group meeting held 13–14 September 2014.
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MIRO BATHES IN WATER VAPOUR
Rosetta’s MIRO instrument has detected an increase in the rate of water vapour coming from comet 67P/Churyumov-Gerasimenko over the past three months. This was reported by the MIRO team at the European Planetary Science Congress last week.
The Microwave Instrument for the Rosetta Orbiter (MIRO). The radio telescope has a diameter of 30 cm.
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MIRO first detected water vapour from the coma of comet 67P/C-G in June this year, when Rosetta was 350,000 km from the comet nucleus. At that distance, the nucleus was unresolved and the entire coma filled MIRO’s field of view. Now that Rosetta has rendezvoused with the comet, MIRO has begun observations to map the nucleus and coma in great detail.
During the Rosetta Special Session at the EPSC meeting, the MIRO team reported measurements made during the past three months that show that the amount of water vapour coming from the comet appears to vary as the nucleus rotates. They have measured a maximum rate of about 5 litres per second being lost by the comet, with an average rate of roughly 1 litre per second. This is markedly more than the comparatively modest rate of 300 millilitres per second measured in June.
Theoretical models predict that most of the water in the comet’s coma should exist over the sunlit side of the nucleus. Rosetta has mostly been flying over the sunlit side to date, and MIRO’s measurements are consistent with these predictions. But when Rosetta makes a flight over the night side of the comet later this month, MIRO will have the chance to directly measure the water production rate there.
In addition to water, the MIRO team have also detected ammonia and methanol, but somewhat to their surprise, they have yet to find evidence for carbon monoxide.
MIRO is also able to probe the temperature below the surface of the comet’s nucleus. At this stage, MIRO has measured subsurface temperatures between a maximum of 160 K and down to below 30 K. The coldest temperatures are associated with regions on the comet that are in darkness – the night side, areas on the sunlit side where shadows are produced by the local landscape, or in polar regions which have been in darkness for a few years.
The MIRO team estimates that they are probing a few centimetres beneath the surface or deeper. At a later stage, MIRO subsurface temperatures and VIRTIS surface temperatures will be combined to refine this estimate. With these measurements in hand, they will be able to calculate the temperature gradient in the nucleus, providing indications of the material that lies beneath the surface.
Quelle: ESA
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Update: 18.09.2014
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COMETWATCH
Four-image NAVCAM montage comprising images taken on 14 September from a distance of 30 km from comet 67P/Churyumov-Gerasimenko (reminder: the distance is given to the centre of the comet).
This is how the comet looked to Rosetta's navigation camera last Sunday, when experts from ESA, DLR, and CNES were gathered in Toulouse, France, to choose the primary and backup landing sites for Philae.
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Four image montage of comet 67P/C-G, using images taken on 14 September. The four images are shown separated by black borders and there is some overlap between adjacent frames, so that some features appear in more than one image. Credits: ESA/Rosetta/NAVCAM
This is a mosaic obtained by combining the four frames, rotating by 180 degrees and cropping it. Site J, the primary landing site that was chosen for Philae, is visible towards the top-middle of the smaller head at the top of the rotated image, while the backup landing site, C, is on the lower-left side of the main body.
At this distance, the resolution of NAVCAM is roughly 2.5 metres per pixel. The phase angle in the image is 61.5 degrees.
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Four image mosaic of comet 67P/C-G, using images taken on 14 September (rotated by 180 degrees and cropped). Credit: ESA/Rosetta/NAVCAM
Quelle: ESA
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Update: 19.09.2014
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COMETWATCH – 19 SEPTEMBER
Four IMAGE NAVCAM montage comprising IMAGES taken in the early hours of this morning, 19 September, from a distance of 28.6 km from the centre of Comet 67P/Churyumov-Gerasimenko. For comparison, recall the OSIRIS image taken on 3 August from a distance of 285 km.
A mosaic, and the four individual frames are also PROVIDED below.
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Four image montage of comet 67P/C-G, using images taken on 19 September. The four images are shown separated by black borders and there is some overlap between adjacent frames, so that some features appear in more than one image. CREDITS: ESA/Rosetta/NAVCAM
This beautiful view shows off a wide range of the comet's features: from the jets emanating from the ‘neck’ region, to the steep cliffs towering over both smooth and grooved terrain, and to the hundreds of boulders scattered across the surface.
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Quelle: ESA
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Update: 25.09.2014
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ROSETTA’S NIGHT-TIME EXCURSION AND A ‘GO’ FOR 20 KM
For the last two weeks, Rosetta has been orbiting comet 67P/C-G at a distance of about 30 km on the “Global Mapping Phase” (GMP), and is now set to go even lower.
The aim of the GMP was to gather high-resolution science data to help characterise the potential landing sites for Philae, while also continuing to monitor how the spacecraft responds to the environment of an active comet, before getting closer still. See the table below for a recap of the manoeuvres conducted this month, starting with the transfer to the global mapping phase (TGM), and refer to the animation to help visualise these changes in trajectory.
Burn Date DV (m/s) Duration (min:sec)
TGM1 03/09 0.56 04:55
TGM2 07/09 0.45 04:18
GMP1 10/09 0.193 02:19
GMP slot 1 14/09 0.025 00:32
GMP2A 17/09 0.085 01:23
GMP2B 17/09 0.087 01:25
GMP slot 2 21/09 0.018 00:25
(DV = delta v; TGM = transfer to global mapping; GMP = global mapping phase; two more burns scheduled this month for 24/09 and 29/09)
In fact, as we discussed in an earlier blog post, rather than fly one complete orbit, the spacecraft conducted two seven-day-long half orbits at about 30 km, in different planes. That is, on 10 September, the spacecraft was at the terminator plane (the boundary between day and night, which is itself the 06:00/18:00 plane), and performed a thruster burn to insert onto the 30-km circular orbit. The orbital plane was then 60 degrees away from the Sun’s direction, such that the spacecraft orbited over areas of the comet in their ‘morning’ hours. Seven days later, when the spacecraft was again on the terminator plane, it conducted another thruster burn to change the orbital plane such that it had the same characteristics as the previous orbit – but instead was flying over ‘afternoon’ areas of the comet. Thus, from 18 September, the spacecraft was in a 28 km x 29 km orbit around the comet with an orbital period of 13 days 14 hours 59 minutes.
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Rosetta GMP orbits Credit: ESA
That brings us to today, when the spacecraft moves onto the night side of the comet to allow the instruments to look in more detail at the thermal characteristics of the comet. Note that by ‘night’ we are not actually referring to the spacecraft being in the dark, it remains illuminated by the Sun, but rather the ground track of the spacecraft’s instruments on the comet surface is on the night side. That is, the spacecraft flies along a 04:00 am arc, 30 degrees before the terminator plane.
Just before entering the ‘night’ arc, Rosetta will perform a very small manoeuvre to lower the orbit such that when it completes the arc, on 29 September, it will be at just 20 km from the comet. The command for this manoeuvre is already on board and executes today at 11:00 CEST (09:00 UTC) . At the same time Rosetta will begin the night excursion and start descending.
On Monday, another manoeuvre will circularise the orbit at 20 km along the terminator plane.After a week at 20 km, a decision will be made as to whether it is safe to proceed to just 10 km.
Quelle: ESA.
Update: 27.09.2014
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COMETWATCH – 21 & 24 SEPTEMBER
Today’s lead CometWatch image is a four-image NAVCAM mosaic taken on 24 September from a distance of 28.5 km from the centre of comet 67P/C-G (the four 1024 x 1024 pixel images making up the mosaic are provided at the end of this post). The images are background subtracted to remove some striping and fixed noise patterns.
Note that at these closer distances, it is harder to create accurate mosaics due to combined effect of the comet rotation between the first and last images taken in the sequence (about 10 degrees over 20 minutes), and the fact that the spacecraft has moved some 1-2 km in the same time. The mosaicking programme we are using (Microsoft ICE) seems to have done a nice job of stitching the images together, but if you refer to the four separate images you will see some differences in illumination and shadows due to this rotation and motion.
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Four image mosaic of Comet 67P/C-G using images taken on 24 September. Credits: ESA/Rosetta/NAVCAM
Nevertheless, we can enjoy this very impressive view from NAVCAM, and can point out some interesting features. However, please remember that thorough scientific analyses of what 67P/C-G’s features are, how they came to be, and what they mean for this comet’s history and evolution will come in the form of scientific papers in the fullness of time.
Some obvious features that stand out are the large boulders, several metres across, lying in the smooth ‘neck’ region. Boulders are also seen at the base of exposed cliff faces, for example towards the top left in this image, and on the ‘head’ of the comet.
Other notable features include a variety of DEPRESSIONS with differing morphologies. One prominent example of a crater-like DEPRESSION is located on the larger lobe (or the ‘body’), to the far left centre of the image. It is about 350 metres across with quite a well-defined rim from this viewing angle, and a mixture of ‘rubble’ and smooth terrain inside. Although the rubble is in shadow in the 23 September mosaic, it is clearly seen in other images, for example in the frame shown below, which was captured on 21 September.
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Single frame (and slightly cropped) NAVCAM image taken on 21 September. Note this image shows the BACKUP landing site C. Credits: ESA/Rosetta/NAVCAM
In the same image (towards the left in the 21 September view) another family of DEPRESSIONScan be seen; these are characterised by both irregular and near-circular shapes, steep walls and smooth floors.
Another very different type of crater-like feature again can be seen to the upper right of the large depression in the main image (slightly to the lower right of it in the 21 September image), about 1.5 times the large feature’s diameter away. This one appears to be a rather fresh-looking small ‘dimple’, about 20 metres across.
As discussed during the EPSC conference earlier this month, the majority of the depressions on 67P/C-G have likely formed as a result of activity; that is, through surface collapse either as subsurface ice sublimates out through a porous crust, or as pockets of trapped gases are expelled.
But of course that doesn’t exclude impacts by external sources as a method of crater formation, although in general, due to the active nature of comet surfaces, impact craters that formed billions of years ago have likely long since been erased.
The origin of craters has been debated for other comet nuclei seen in brief flybys of other spacecraft. Fortunately, ROSETTA is perfectly placed to determine the origin of these features on 67P/C-G, and if and how they may change over the course of the mission.
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The European Space Agency’s ROSETTA mission will deploy its lander, Philae, to the surface of Comet 67P/Churyumov–Gerasimenko on 12 November.
Philae’s landing site, currently known as Site J, is located on the smaller of the comet’s two ‘lobes’, with a BACKUP site on the larger lobe. The sites were selected just six weeks after ROSETTAarrived at the comet on 6 August, following its 10-year journey through THE SOLAR SYSTEM
In that time, the ROSETTA mission has been conducting an unprecedented scientific analysis of the comet, a remnant of the Solar System’s 4.6 billion-year history. The latest results from ROSETTAwill be presented on the occasion of the landing, during dedicated press briefings.
The main focus to date has been to survey 67P/Churyumov–Gerasimenko in order to prepare for the first ever attempt to soft-land on a comet.
Philae’s descent and science on the surface
Access the video
Site J was chosen unanimously over four other candidate sites as the primary landing site because the majority of terrain within a square kilometre area has slopes of less than 30º relative to the local vertical and because there are relatively few large boulders. The area also receives sufficient daily illumination to recharge Philae and continue surface science operations beyond the initial 64-hour battery-powered phase.
Over the last two weeks, the flight dynamics and operations teams at ESA have been making a detailed analysis of flight trajectories and timings for Rosetta to deliver the lander at the earliest possible opportunity.
Two robust landing scenarios have been identified, one for the primary site and one for the BACKUP. Both anticipate separation and landing on 12 November.
For the primary landing scenario, targeting Site J, Rosetta will release Philae at 08:35 GMT/09:35 CET at a distance of 22.5 km from the centre of the comet, landing about seven hours later. The one-way signal travel time between Rosetta and Earth on 12 November is 28 minutes 20 seconds, meaning that confirmation of the landing will arrive at Earth ground stations at around 16:00 GMT/17:00 CET.
If a decision is made to use the backup Site C, separation will occur at 13:04 GMT/14:04 CET, 12.5 km from the centre of the comet. Landing will occur about four hours later, with confirmation on Earth at around 17:30 GMT/18:30 CET. The timings are subject to uncertainties of several minutes.
Quelle: ESA
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Update: 28.09.2014
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Rosetta to Deploy Lander on November 12
The European Space Agency’s Rosetta mission will deploy its lander, Philae, to the surface of comet 67P/Churyumov–Gerasimenko on Nov. 12.
Rosetta is an international mission spearheaded by the European Space Agency with support and instruments provided by NASA.
Philae’s landing site, currently known as Site J, is located on the smaller of the comet’s two "lobes," with a backup site on the larger lobe. The sites were selected just six weeks after Rosetta's Aug. 6 arrival at the comet, following the spacecraft's 10-year journey through the solar system.
In that time, the Rosetta mission has been conducting an unprecedented scientific analysis of the comet, a remnant from early in the solar system’s 4.6-billion-year history. The latest results from Rosetta will be presented when Philae lands, during dedicated press briefings.
The main focus to date has been to survey 67P/Churyumov–Gerasimenko in order to prepare for the first-ever attempt to soft-land on a comet.
The descent to the comet is passive and it is only possible to predict that the landing point will be within a "landing ellipse" (typically a few hundred yards or meters in size). For each of Rosetta's candidate sites, a larger area -- four-tenths of a square mile (one square kilometer) -- was assessed. Site J was chosen unanimously as the primary landing site because the majority of terrain within an area that size has slopes of less than 30 degrees relative to the local vertical and because there are relatively few large boulders. The area also receives sufficient daily illumination to recharge Philae and continue surface science operations beyond the initial 64-hour battery-powered phase.
Over the last two weeks, the flight dynamics and operations teams at ESA have been making a detailed analysis of flight trajectories and timings for Rosetta to deliver the lander at the earliest possible opportunity.
Two robust landing scenarios have been identified, one for the primary site and one for the backup. Both anticipate separation and landing on Nov. 12.
For the primary landing scenario, targeting Site J, Rosetta will release Philae at 08:35 UTC (12:35 a.m. PST; 9:35 a.m. Central European Time) at a distance of 14 miles (22.5 kilometers) from the center of the comet, landing about seven hours later. The one-way signal travel time between Rosetta and Earth on Nov. 12 will be 28 minutes and 20 seconds, meaning that confirmation of the landing will arrive at Earth ground stations at around 16:00 UTC (8 a.m. PST; 5 p.m. CET).
If a decision is made to use the backup site, Site C, separation will occur at 13:04 UTC (5:04 a.m. PST; 2:04 p.m. CET) at a distance of 7.8 miles (12.5 kilometers) from the center of the comet. Landing will occur about four hours later, with confirmation on Earth at around 17:30 UTC (9:30 a.m. PST; 6:30 p.m. CET). The timings are subject to uncertainties of several minutes.
Final confirmation of the primary landing site and its landing scenario will be made on October 14 after a formal Lander Operations Readiness Review, which will include the results of additional high-resolution analysis of the landing sites conducted in the meantime. Should the backup site be chosen at this stage, landing can still occur on Nov. 12.
A competition for the public to name the primary landing site will also be announced during the week of Oct. 14.
Following the Philae landing, the Rosetta orbiter will continue to study the comet and its environment using 11 science instruments for another year as the spacecraft and comet orbit the sun together. The comet is on an elliptical 6.5-year orbit that takes it from beyond Jupiter at its farthest point, to between the orbits of Mars and Earth at its closest to the sun. Rosetta will accompany the comet for more than a year as they swing around the sun and back to the outer solar system again.
The analyses made by the Rosetta orbiter will be complemented by the measurements performed on the comet by Philae's 10 instruments.
Comets are time capsules containing primitive material left over from the epoch when the sun and its planets formed. By studying the gas, dust and structure of the nucleus and organic materials associated with the comet, the Rosetta mission should become key to unlocking the history and evolution of our solar system, as well as answering questions regarding the origin of Earth’s water and perhaps even life.
Rosetta is an ESA mission with contributions from its member states and NASA. Rosetta's Philae lander is provided by a consortium led by the German Aerospace Center, Cologne; Max Planck Institute for Solar System Research, Gottingen; National Center of Space Studies of France (CNES), Paris; and the Italian Space Agency, Rome. NASA's Jet Propulsion Laboratory in Pasadena, California, a division of the California Institute of Technology, manages the U.S. participation in the Rosetta mission for NASA's Science Mission Directorate in Washington.
Quelle: NASA
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Update: 2.10.2014
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COMETWATCH – 26 KM ON 26 SEPTEMBER
Montage of four images of Comet 67P/C-G taken on 26 September, from a distance of 26.3 km from the centre of the comet. The four 1024 x 1024 pixel images MAKING UP the montage are provided at the end of this post.
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Four image montage of 67P/C-G on 26 September from a distance of 26.3 km. CREDIT: ESA/Rosetta/NAVCAM
The individual images have been background subtracted to REMOVE some striping and fixed noise patterns. In making the montage, the background levels have then been adjusted in order to make the images more or less equivalent, the vignetting in the corners of the images has been reduced, and some processing of the overall brightness and contrast has been applied using Adobe Lightroom. Finally, the montage has been rotated by 180°.
We have not made a proper mosaic on this occasion, because it is becoming extremely difficult at these close distances due to the combined effect of the comet rotating between the first and last images taken in the sequence (about 10 DEGREES over 20 minutes) and the spacecraft moving by some 1–2 km in the same time.
While the two images on the right of the montage could perhaps be joined seamlessly, the problem becomes much harder between the lower-right and lower-left images. Careful inspection makes it clear that the perspective has shifted considerably between them and that some of the shadows have changed a lot as WELL.
It’s not easy to bring these images into alignment and thus we leave the challenge of making a reasonable mosaic from them to you!
That aside, it goes without saying that the main talking point of this image is the spectacular region of activity at the neck of 67P/C-G. What we’re seeing is the product of ices sublimating and gases escaping from inside the comet, carrying STREAMS of dust out into space. Zooming in close to the surface and to the source of this activity and it is apparent that it is originating from several discrete locations.
You might also like to try increasing the exposure of the montage to bring out some faint details of the comet’s ‘head’, and even some boulders in the neck region.
As the comet gets progressively closer to the Sun along its orbit, the surface will become warmer, and the level of activity will increase, producing a vast coma around the nucleus, along with a tail. It’s perhaps hard to believe looking at images like this at less than 30 km distance from the surface, but recent ground-based images have revealed that 67P/C-G’s coma already extends at least 19 000 km from the nucleus!
Quelle: ESA.
Update: 6.10.2014
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MEASURING COMET 67P/C-G
This post provides a summary of some of the essential physical parameters of Comet 67P/Churyumov-Gerasimenko, as measured by Rosetta ahead of and since its 6 August rendezvous. This is an on-going process and the numbers will be updated as newer data are obtained, analysed, and made available.
Shape model of 67P/C-G. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
One of the key things is the so-called “shape model”, meaning a 3D model of the comet based on images from the OSIRIS and NAVCAM cameras. In a previous post we showed a render of one of the first shape models derived from OSIRIS data. Here we are releasing a more recent OSIRIS shape model in .wrl and .obj format, suitable for loading into 3D graphics applications (click the links to download).
A render of this shape model is shown at the top of this page, while the image below shows a pair of NAVCAM images to illustrate the sizes.
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Comet 67P/C-G dimensions. Images: NAVCAM (19 August image); dimensions: OSIRIS
Because roughly 30% of the ‘dark side’ of 67P/C-G has not been resolved and analysed fully yet, the shape model is very incomplete over those regions. As a result, some of the derived parameters for the comet are only best estimates at present. These include the volume and the global density, the latter depending on the mass and the volume.
The table below summarises the approximate dimensions of 67P/C-G and other known parameters derived from observations made by Rosetta, with the instrument with which the measurement was made also indicated. Links are provided to earlier posts where some of these numbers have been previously presented.
Again, these values are preliminary and will likely change as the mission progresses and more data are available, and as the comet itself changes as it moves closer to the Sun. Similarly, other parameters such as the albedo of the comet will be added to this table, as they are made available by the instrument science teams.
Dimensions (small lobe) 2.5 x 2.5 x 2.0 km OSIRIS
Dimensions (large lobe) 4.1 x 3.2 x 1.3 km OSIRIS
Rotation 12.4043 hours OSIRIS
Spin axis Right ascension: 69 degrees; Declination: 64 degrees OSIRIS
Mass 10^13 kg RSI
Volume 25 km^3 OSIRIS
Density 0.4 g/cm^3 RSI / OSIRIS
Water vapour production rate 300 ml/sec (Jun 2014); 1–5 l/sec (Jul-Aug 2014) MIRO
Surface temperature 205–230K (Jul-Aug 2014) VIRTIS
Subsurface temperature 30–160K (Aug 2014) MIRO
Gases detected Water, carbon monoxide, carbon dioxide, ammonia, methane, methanol ROSINA
Dust grains A few tens of microns to a few hundreds of microns COSIMA
(detections also by GIADA)
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COMETWATCH – SITE J FROM 18 KM
Montage of four images of Comet 67P/C-G taken on 30 September, from a distance of 18.1 km from the centre of the comet – our closest image yet.
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Four image montage of 67P/C-G taken on 30 September from 18.1 km, and featuring primary site J. Note that a "feature" can be seen against the dark sky in the centre of the upper two images of the montage, namely a broad, diffuse region of low-level brightness. Our current thinking is that this is likely due to internal scattering of off-axis light (i.e. the comet itself) in the NAVCAM optics, rather than comet coma emission, but we'll making further checks.
Credits: ESA/Rosetta/NAVCAM
The four 1024 x 1024 pixel images making up the montage are provided at the end of this post: for processing details please see the previous post. The image scale at this distance is about 1.4 metres per pixel, so each 1024 pixel frame measures about 1.4 kilometres across.
The image features Site J, the primary landing site for Rosetta’s lander Philae. A context image is provided below.
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Site J, Philae's primary landing site.
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The effect of the comet’s rotation and movement of the spacecraft in the twenty minutes spanned by the imaging sequence can clearly be seen by comparing the first (bottom left) and last (bottom right) image of the montage. Features visible in the first image, such as the depressions close to the right of the first image, are cast into shadow twenty minutes later.
This makes mosaicking the four images together very challenging in 2D, although we know that some of you out there are doing great work in ‘draping’ the images over 3D shape models, similar to the one from OSIRIS which we released last week. Mattias Malmer’s impressive work with our NAVCAM images caught our attention in particular (thanks Mattias!)
Once again, these four frames contain a stunning array of features. In the upper frames, there are steep cliffs, exhibiting clear horizontal layering with several vertical grooves or fractures. Other exposed faces, such as those seen most clearly in the lower left frame, resemble more of a rubble pile with discrete boulders of varying sizes.
Towards the middle of the lower left frame, there are also the beginnings of exposed ledges, again with rubble at their bases as they become more eroded. Interspersed is much smoother, fine-grained material, seemingly sculpted into ripples in some places, reminiscent of some wind-swept features seen on Mars (and Earth for that matter), but which on 67P/C-G are presumably linked to activity and the result of differential erosion as material is lifted from the surface.
The entire scene disappears into shadow at the bottom of this image, corresponding to the steep walls of the large depression that define the previously considered candidate landing Site B.
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Quelle: ESA
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