Find out how Rosetta and Philae first got inspired to visit a comet, and follow them on their incredible ten-year journey through the Solar System to their destination, flying around planets and past asteroids along the way. Watch as Philae tries to land on the comet and deals with some unexpected challenges! Learn about the fascinating observations that Rosetta made as she watched the comet change before her eyes as they got closer to the Sun and then further away again. Finally, wish Rosetta farewell, as she, too, finishes her amazing adventure on the surface of the comet. Keep watching for one last surprise!

French version:

Italian version:

Spanish version:

German version:

The animation begins on 31 July 2014, during Rosetta’s final approach to the comet after its ten-year journey through space. The spacecraft arrived at a distance of 100 km on 6 August, from where it gradually approached the comet and entered initial mapping orbits that were needed to select a landing site for Philae. These observations also enabled the first comet science of the mission.

The manoeuvres in the lead up to, during and after Philae’s release on 12 November are seen, before Rosetta settled into longer-term science orbits.

In February and March 2015 the spacecraft made several flybys. One of the closest triggered a ‘safe mode’ that forced it to retreat temporarily until it was safe to draw gradually closer again.

The comet’s increased activity in the lead up to and after perihelion in August 2015 meant that Rosetta remained well beyond 100 km for several months.

In June 2015, contact was restored with Philae again – albeit temporary, with no permanent link able to be maintained, despite a series of dedicated trajectories flown by Rosetta for several weeks.

Following the closest approach to the Sun, Rosetta made a dayside far excursion some 1500 km from the comet, before re-approaching to closer orbits again, enabled by the reduction in the comet’s activity.

In March–April 2016 Rosetta went on another far excursion, this time on the night side, followed by a close flyby and orbits dedicated to a range of science observations.

In early August the spacecraft started flying elliptical orbits that brought it progressively closer to the comet. On 24 September Rosetta left its close, flyover orbits and switched into the start of a 16 x 23 km orbit that was used to prepare and line up for the final descent.

On the evening of 29 September Rosetta manoeuvred onto a collision course with the comet, beginning the final, slow descent from an altitude of 19 km. It collected scientific data throughout the descent and gently struck the surface at 10:39 GMT on 30 September in the Ma’at region on the comet’s ‘head’, concluding the mission.

The trajectory shown in this animation is created from real data, but the comet rotation is not. Distances are given with respect to the comet centre (except for the zero at the end to indicate completion), but may not necessarily follow the exact comet distance because of natural deviations from the comet’s gravity and outgassing. An arrow indicates the direction to the Sun as the camera viewpoint changes during the animation.

We decided to collect all contributions in an e-book, to keep a long-lasting record of the mission’s impact on a variety of public audiences. This publication presents a collection of these outstanding contributions and provides a taste of Rosetta’s legacy for fellow science communicators, scientists and engineers, educators, space enthusiasts – anyone who was fascinated by the mission.

The e-book (pdf, 33MB) is available here.

Thanks again to everyone who shared with us their impressions of the mission, and to all followers of Rosetta and Philae worldwide.

This latest OSIRIS data release comprises 2423 narrow-angle camera images and 4378 wide-angle camera images from the period 11 March – 24 May 2015. You can browse through the new images in the MTP 014, 015 and 016 albums here.

Example of images from the OSIRIS narrow-angle camera albums in the latest data release. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Before we ‘retire’ the blog, we wanted to catch up with the instrument teams following this grand finale to find out how their instruments performed and if there were any surprises in Rosetta’s last ‘words’ from the comet.

Rosetta touched down just 33 m away from the target point, as indicated by the green descent trajectory line. The inner circle has a radius of 100 m and the concentric circles around the centre are spaced by increments of 100 m. Credit: ESA

First a reminder of the impact site: Rosetta was targeting a point within a 700 x 500 m ellipse, between two pits in the Ma’at region. Reconstruction of the final descent trajectory showed that the spacecraft touched down at 10:39:34 UT at the comet, only 33 metres away from the target point and just inside a shallow, ancient pit. This accuracy once again highlights the excellent work done by the flight dynamics specialists who supported the entire mission.

The touchdown site was subsequently named Sais after a town in Egypt where the Rosetta Stone, for which the mission was named, is thought to have been originally located.

Right before impact, one of Rosetta’s star trackers generated an event reporting a ‘Large Object’ in the field of view: this was the local comet ‘horizon’. Upon touchdown, the signal coming from Rosetta was lost, and mission operators believe that this was most likely caused by the high gain antenna immediately off-pointing from Earth at impact. No further telemetry was received subsequently, indicating that the planned safe mode and subsequent shut down of the spacecraft likely occurred successfully.

Rosetta’s last image was taken with the OSIRIS wide-angle camera about 20 m above the surface. Prior to that, much of the imaging campaign during the descent focused on the 130 metre-wide pit named Deir el-Medina, as shown by the blue ‘footprints’ in the plot below. As seen on 30 September, the camera succeeded in capturing detailed images of the inside of the pit and its walls. These images will be used to help understand the comet’s subsurface and thus its geological history. The trail of orange and red squares then reflects the change in pointing of the spacecraft’s camera towards the impact site at Sais.

Imaging ‘footprints’ of the OSIRIS camera. The primary focus in the final descent phase was Deir el-Medina pit as shown by the blue squares, with the last images taken above the eventual impact site at Sais, as indicated by the red squares. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

ROSINA’s Comet Pressure Sensor (COPS) measured the pressure of gas in the vicinity of the spacecraft during its final hours. The surface is at a distance of roughly 2 km from the centre of the comet. The small breaks in the black line are due to internal adjustments of the COPS instrument being made during the descent to cope with the rising pressure. Image courtesy K. Altwegg.

Pressure rising

Several other Rosetta science instruments were in operation during the descent, including ROSINA’s Double Focusing Mass Spectrometer (DFMS) and Comet Pressure Sensor (COPS). Both recorded data “down to the ground”, as ROSINA Principal Investigator Kathrin Altwegg puts it. As reported on the day itself, and shown now in the plot below, ROSINA measured an increase in the surrounding gas pressure by more than a factor of 100 as the spacecraft neared the surface.

“We saw the gas velocity and ram pressure drop to zero before we reached the ground, suggesting there is an interesting acceleration of gas slightly away from the nucleus,” says Kathrin. “We also collected good data with the DFMS, and will be looking at which kind of atoms and molecules were present in the gas.”

Temperature measurements below the surface

Mark Hofstadter, Principal Investigator for the MIRO instrument, reported that good data were collected throughout the descent, with the last measurement made at 10:39:07 UT at the comet on 30 September 2016. The MIRO team think the spacecraft was about 20 m above the surface at this point.

“For the last two minutes of data, our sub-millimetre beam footprint on the surface was less than 20 cm in diameter,” says Mark.

Comet 67P/C-G viewed with Rosetta’s OSIRIS NAC on 30 September 2016, 1.2 km from the surface. In the lower right corner is the bottom of the pit, while the dark band crossing the image diagonally from right to left is the shadow of the pit wall; the terrain above the pit is visible in the upper left corner. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

During the descent, MIRO collected continuum emission data from the nucleus, providing temperature measurements ~1 and 5 cm below the surface.

“Over the last few hours, we see temperatures varying between about 80 and 160 K as our beam moved across the nucleus. We think these differences are due to topography and shadowing – but we still need to correlate the details with topographic models and OSIRIS images to confirm that.”

“We also noticed that the temperature of our telescope rose over the last couple hours of the mission. We haven’t figured out yet if that is due to the angle of the Sun changing, or if we were being heated by the nucleus as it filled more and more of the sky.”

Mark also told us that MIRO’s last spectroscopic measurement of water in the coma was made in a limb-observing mode on 27 September at 13:26 UT. This resulted in a very rough estimate of the global average water production rate at that time of about 10^24 molecules per second or the equivalent of two tablespoons (this preliminary estimate may be refined following further analysis). During its most active period in August 2015, estimates were in the region of two bathtubs’ worth of water every second.

Comet chameleon

The Alice instrument also made observations at ultraviolet wavelengths all the way to the surface. The final spectrum transmitted was an exposure that started at 10:20:16 and ended at 10:30:21 UT at the comet, about nine minutes before impact. The Alice team estimates that the final data were collected over a range of about 1000 to 500 metres altitude above the surface, with each row on the Alice instrument covering an average spatial scale of about four metres.

Final spectra from Alice, showing the reflectance of the surface at close range with ~3m resolution. Image courtesy A. Stern/J. Parker.

At the time of impact, Alice was 8.5 minutes into a 10-minute exposure. The last communication from Alice was a housekeeping packet received at 10:39:00 UT, about half a minute before impact. The housekeeping data included the count rate of the total ultraviolet flux over the Alice bandpass, which was being reported every 30 seconds, and which showed a steady increase in the UV flux during the descent.

Looking at the last hour of data from Alice as an overall averaged spectrum, the trend of the slope and lack of broad absorption features is very similar to previously published results. That is, Alice did not see significant differences in the surface composition at these high spatial resolutions when compared to observations over larger areas. There was also no obvious indication of small icy patches.

“Of course, these are very quick-look results that may change as we look more carefully at the data,” notes Joel Parker, Alice’s deputy Principal Investigator.

Data gathered from both Alice housekeeping and science telemetry indicated that the strength of a feature in the spectra nicknamed the ‘chameleon’ (the curved lines on the left side of the spectral image above) also increased throughout the descent.

“This feature has appeared throughout the mission with lots of variability, and we believe it is a result of dust and sometimes ions entering the instrument,” says Alan Stern, Alice’s Principal Investigator. “The morphology of the chameleon during this time period matches the morphologies seen during dusty time periods, indicating that there may have been an increase in nano-grain dust density as the altitude decreased.”

The last off-nucleus observation that Alice obtained of the comet’s coma was on 29 September, and was typical of limb spectra observed since the beginning of May 2016, when the comet was about 3 AU from the Sun. It showed that carbon dioxide outgassing was still on-going at the end of the mission, at greater distances from the Sun than seen when the comet was still approaching the Sun earlier in the mission.

“Overall, Alice worked exactly as planned throughout the end of mission and the descent, and provided an excellent dataset that will need much more detailed analysis,” adds Joel.

Steady solar wind and cometary plasma peak

The Rosetta Plasma Consortium sensors also enjoyed a good ride to the comet surface, with steady solar wind measurements.

“These data are actually very useful, providing us with a ‘quiet’ time reference profile covering a large altitude interval for a steady solar wind, which will help us calibrate the datasets that were took throughout the whole comet phase,” comments Hans Nilsson, Principal Investigator for the RPC-ICA sensor.

Artist impression of Rosetta arriving on the surface of the comet. Credit: ESA/ATG medialab

RPC-LAP and RPC-MIP both reported very low plasma densities through the descent, though slowly and evenly increasing, similar to that seen by ROSINA-COPS for neutral gas. However, the plasma reached a broad peak of up to about 100–150 cm^-3 (preliminary measurement) at about 2 km from surface, before dropping off again. This is as expected for a plasma originating from the neutral gas released by the comet: its density must be low at the surface since the molecules found there have just left the nucleus and have not had any time to become ionised.

“There is some plasma structure to be seen, but not much: this counts among the weakest ionospheres we have seen at the comet, but as may be expected in the northern hemisphere, which was winter at the time,” adds Anders Eriksson, Principal Investigator of the RPC-LAP sensor. “If there was any local outgassing from the Ma’at pits, it is at least not immediately striking in our data.”

RPC-IES demonstrated that the ions in the coma showed a modest increase in energy while the total flux of electrons decreased very near the comet, as expected and in line with the reduced coma density observations. The increase in observed coma ion energy could have been caused by an increase in negative spacecraft potential as the density decreased – something that is being looked into.

Finally, RPC-MAG made measurements down to a distance of about 11 m above the surface, showing no increase in the magnetic field with proximity. This confirms the finding, made during Philae’s landing in November 2014, that the comet is non-magnetic.

A dust free descent?

Of Rosetta’s three dust instruments, only GIADA was on during the descent, with MIDAS and COSIMA completing their missions in the days before. As it turns out, GIADA did not detect any dust, but this non-detection is itself an interesting observation.

“During the final descent, the environment was like a clean room!” remarked GIADA Principal Investigator, Alessandra Rotundi.

ROSINA, MIRO, and Alice team members confirmed the GIADA view. For example, the water production rate observed by MIRO over the region where Rosetta impacted was likely far too low to lift dust particles detectable by GIADA off the surface. Any dust grains present must have been very small indeed to evade detection, below GIADA’s limit of 50 micrometres diameter.

The very last COSIMA particle – named Yaman Evijarvi – was collected on 27 September 2016 between 01:51:55 and 14:08:11 UT on target 2C3, about 20 km away from the comet. Image courtesy M. Hilchenbach.

One last dust particle…

Even though COSIMA was off during the final descent, the instrument’s Principal Investigator, Martin Hilchenbach, told us that one last dust particle was collected during their final day of operations, on 27 September. At that time, Rosetta was about 20 km from the comet centre.

The particle has the name ‘Yaman Evijarvi’. Earlier in the mission, COSIMA particles were named for COSIMA team members, but with thousands of particles collected, this list was soon exhausted. Instead, ‘Yaman’ was the next name on a random list of international names (this one from Turkey), and ‘Evijarvi’, the name of a Finnish lake, comes from the theme used by the team to identify time periods of dust collection.

The last secondary ion mass analysis, around dust particle ‘Lou’ on target C3, zoomed to a mass range including aluminium and organic molecules. Image courtesy M. Hilchenbach.

Martin commented that the last days of Rosetta were as busy as ever for their team, as the COSIMA primary ion source parameters had to be adjusted in the very last minutes to acquire the last secondary ion spectra. “I was really impressed that after 26 months of operations, the motivation was just as high as on the first day,” he said. “In the end, our primary ion beam source outlived the total predicted hours of operation by a factor of two.”

Martin adds “And as planned, we returned all of the dust particles we collected back to the surface of the comet on 30 September – cosmic recycling, over 700 million km from Earth!”

“It’s great to have these first insights from Rosetta’s last set of data,” says Matt Taylor, ESA’s Rosetta project scientist. “Operations have been completed for over two months now, and the instrument teams are very much focused on analysing their huge datasets collected during Rosetta’s two-plus years at the comet.

“Data from this period will eventually be made available in our archives in the same way as all Rosetta data.”

And finally… from the blog editors to the Rosetta teams all around the world: thank you for sharing your stories and discoveries with us, to make this blog such a rich source of information for everyone to enjoy. We’re looking forward to the discoveries to come and continuing our science coverage on esa.int and sci.esa.int.

Artist’s impression of Rosetta’s descent on the comet on 30 September 2016. Credit: ESA/ATG medialab

Some ten weeks have passed since Rosetta ended its mission on the surface of Comet 67P/Churyumov–Gerasimenko, and it is time for a little reflection here on the Rosetta blog…

Over the past three years, we have written over 670 posts covering mission operations, science highlights, special events, images of the comet, and so much more. The blog has become a reference for a wide audience, ranging from science journalists to space enthusiasts, from casual readers to educators and even Rosetta mission scientists and operators.

Beyond that, it has become a place for people to share their ideas and concerns. When we re-launched the blog in 2013, we did not expect the huge number of comments that came in – almost 18,600 to date – and certainly we didn’t envision the considerable amount of time needed to moderate them! But we learned a lot from the comments, some of which became lengthy discussions, and which on occasion triggered new blog posts or direct engagement between readers and mission experts.

However, with the flight phase of the mission now over there are obviously no longer any news updates to share about current operations, and so we have decided to close the blog. We will soon publish our last post and close the comments section for good, although naturally, all of the material will remain online for the foreseeable future.

And of course, we will keep writing about new scientific results based on data from the mission as they are published, and news such as updates on the availability of data in the public archives. These will be reported via our websites (Space Science Portal and Science & Technology) and on social media, especially via our @esascience Twitter account.

It’s been an amazing and intense three years for us, and we hope that you also enjoyed the ride. It has been our pleasure to have you join in. As a final farewell, we would like to invite all blog readers to tell us a little about yourselves – after all, many of the contributors to the comment section are long since familiar to us by their names and nicknames, but in many cases, we don’t know a lot more.

So, make a comment to this post and feel free to tell us when, how, and why you became interested in Rosetta/comets/space science in general, how you found out about the blog, whether you followed it regularly, and what you enjoyed (or disliked!) most about it.

As ever, there are rules: only one comment allowed per contributor and, as usual, off-topic posts will not be published

The comment function of the blog will be deactivated before the holiday break, so please post your comments before then.

We are looking forward to reading your contributions!

Best wishes,

– The Rosetta blog team

Rosetta’s comet approached its most active period last year, the spacecraft spotted carbon dioxide ice – never before seen on a comet – followed by the emergence of two unusually large patches of water ice.

The carbon dioxide ice layer covered an area comparable to the size of a football pitch, while the two water ice patches were each larger than an Olympic swimming pool and much larger than any signs of water ice previously spotted at the comet.

The three icy layers were all found in the same region, on the comet’s southern hemisphere.

Sequence of 23 images of Comet 67P/Churyumov–Gerasimenko taken with Rosetta’s OSIRIS narrow-angle camera on 4 July 2015, about a month before the comet’s closest approach to the Sun. The three-colour images are made from observations at 480, 649 and 882 nm. The images are taken at 30 minute intervals and span a full day at the comet, which spins around its axis in about 12.4 hours. The Sun is towards the top of the frame. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; Reprinted with permission from S. Fornasier et al., Science 10.1126/science.aag2671 (2016)

A combination of the complex shape of the comet, its elongated path around the Sun and the substantial tilt of its spin, seasons are spread unequally between the two hemispheres of the double-lobed Comet 67P/Churyumov–Gerasimenko.

When Rosetta arrived in August 2014, the northern hemisphere was still undergoing its 5.5 year summer, while the southern hemisphere was in winter and much of it was shrouded in darkness.

However, shortly before the comet’s closest approach to the Sun in August 2015, the seasons changed and the southern hemisphere experienced a brief but intense summer, exposing this region to sunlight again.

In the first half of 2015, as the comet steadily became more active, Rosetta observed water vapour and other gases pouring out of the nucleus, lifting its dusty cover and revealing some of the comet’s icy secrets.

In particular, on two occasions in late March 2015, Rosetta’s visible, infrared and thermal imaging spectrometer, VIRTIS, found a very large patch of carbon dioxide ice in the Anhur region, in the comet’s southern hemisphere.

This is the first detection of solid carbon dioxide on any comet, although it is not uncommon in the Solar System – it is abundant in the polar caps of Mars, for example.

Comet images and spectra taken by VIRTIS on 21–22 March, with the unmistakable signature of carbon dioxide ice: a series of three absorption lines at wavelengths around 2 microns, and two additional absorption lines at 2.7 and 2.78 microns. These characteristic features are not present in the spectrum of water ice. Later images and spectra, taken by VIRTIS on 12–13 April, show that the signature of carbon dioxide ice had disappeared. Credit: ESA/Rosetta/VIRTIS/INAF-IAPS/OBS DE PARIS-LESIA/DLR; Reprinted with permission from G. Filacchione et al., Science 10.1126/science.aag3161 (2016); context image: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0

“We know comets contain carbon dioxide, which is one of the most abundant species in cometary atmospheres after water, but it’s extremely difficult to observe it in solid form on the surface,” explains Gianrico Filacchione from Italy’s INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, who led the study.

In the comet environment, carbon dioxide freezes at –193ºC, much below the temperature where water turns into ice. Above this temperature, it changes directly from a solid to a gas, hampering its detection in ice form on the surface.

By contrast, water ice has been found at various comets, and Rosetta detected plenty of small patches on several regions.

“We hoped to find signs of carbon dioxide ice and had been looking for it for quite a while, but it was definitely a surprise when we finally detected its unmistakable signature,” adds Gianrico.

The patch, consisting of a few percent of carbon dioxide ice combined with a darker blend of dust and organic material, was observed on two consecutive days in March. This was a lucky catch: when the team looked at that region again around three weeks later, it was gone.

Assuming that all of the ice had turned into gas, the scientists estimated that the 80 x 60 m patch contained about 57 kg of carbon dioxide, corresponding to a 9 cm-thick layer. Its presence on the surface is likely an isolated rare case, with the majority of carbon dioxide ice being confined to deeper layers of the nucleus.

Gianrico and his collaborators believe the icy patch dates back a few years, when the comet was still in the cold reaches of the outer Solar System and the southern hemisphere was experiencing its long winter. At that time, some of the carbon dioxide still outgassing from the interior of the nucleus condensed on the surface, where it remained frozen for a very long while, and vaporised only as the local temperature finally rose again in April 2015.

This reveals a seasonal cycle of carbon dioxide ice, which unfolds over the comet’s 6.5 year orbit, as opposed to the daily cycle of water ice, also spotted by VIRTIS shortly after Rosetta’s arrival.

Interestingly, shortly after the carbon dioxide ice had disappeared, Rosetta’s OSIRIS narrow-angle camera detected two unusually large patches of water ice in the same area, between the southern regions of Anhur and Bes.

The appearance of two bright patches of water ice (indicated as A and B) in the Anhur and Bes regions of Comet 67P/C–G. The patches were first observed in April 2015 and persisted for about 10 days before they completely disappeared. The water ice patch indicated as A was likely lurking underneath the carbon dioxide ice sheet revealed by Rosetta’s VIRTIS instrument about a month before. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; Reprinted with permission from S. Fornasier et al., Science 10.1126/science.aag2671 (2016)

“We had already seen many metre-sized patches of exposed water ice in various regions of the comet, but the new detections are much larger, spanning some 30 x 40 m each, and they persisted for about 10 days before they completely disappeared,” says Sonia Fornasier from LESIA–Observatoire de Paris and Université Paris Diderot, France, lead scientist of the study focusing on seasonal and daily surface colour variations.

These ice-rich areas appear as very bright portions of the comet surface reflecting light that is bluer in colour compared with the redder surroundings. Scientists have experimented with mixtures of dust and water ice to show that, as the concentration of ice in them increases, the reflected light becomes gradually bluer in colour, until reaching a point where equal amounts of light are reflected in all colours.

The two newly detected patches contain 20–30% of water ice mixed with darker material, forming a layer up to 30 cm thick of solid ice. One of them was likely lurking underneath the carbon dioxide ice sheet revealed by VIRTIS about a month before.

“On a global scale, we also found that the entire comet surface turned increasingly bluer in colour as it approached the Sun and the intense activity lifted off large amounts of dust, exposing more of the ice-rich terrain underneath,” explains Sonia.

As the comet moved away from the Sun, the scientists observed the overall colour of the comet surface gradually turning redder again.

The colour of visible light reflected by Comet 67P/Churyumov–Gerasimenko on 1 August 2014 (left), shortly before Rosetta arrived at the comet, and a year later, on 30 August 2015 (right), shortly after the comet’s closest approach to the Sun. The maps are derived from the comparison of images taken at wavelengths between 535 and 882 nm with Rosetta’s OSIRIS narrow-angle camera. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; Reprinted with permission from S. Fornasier et al., Science 10.1126/science.aag2671 (2016)

They also revealed local variations of colour, indicative of the daily cycle of water ice. Quickly turning into water vapour when exposed to sunlight during the local daytime, it condensed back into thin layers of frost and ice as the temperature decreases after sunset, only to vaporise again on the following day.

The distribution of water ice beneath the dusty surface of the comet seems widely but not uniformly spread, with small patches punctuating the nucleus, appearing and disappearing as a result of the comet’s activity.

Occasionally, larger and thicker portions of ice are also uncovered, dating back to a previous approach to the Sun.

“These two studies of the comet’s icy content are revealing new details about the composition and history of the nucleus,” says Matt Taylor, ESA Rosetta project scientist.

“While the flight part of the mission is now over, the scientific exploitation of the enormous quantity of data collected by Rosetta continues.”

—

“Seasonal exposure of carbon dioxide ice on the nucleus of comet 67P/Churyumov–Gerasimenko” by G. Filacchione et al and “Rosetta’s comet 67P/Churyumov–Gerasimenko sheds its dusty mantle to reveal its icy nature” by S. Fornasier et al are published in the journal Science.

About VIRTIS
The Visible, InfraRed and Thermal Imaging Spectrometer VIRTIS was built by a consortium of Italy, France and Germany, under the scientific responsibility of IAPS, Istituto di Astrofisica e Planetologia Spaziali of INAF, Rome (IT), which lead also the scientific operations. The VIRTIS instrument development for ESA has been funded and managed by ASI, with contributions from Observatoire de Meudon financed by CNES and from DLR. The VIRTIS instrument industrial prime contractor was former Officine Galileo, now Leonardo (Finmeccanica Group) in Campi Bisenzio, Florence, IT.

About OSIRIS
The scientific imaging system OSIRIS was built by a consortium led by the Max Planck Institute for Solar System Research (Germany) in collaboration with CISAS, University of Padova (Italy), the Laboratoire d’Astrophysique de Marseille (France), the Instituto de Astrofísica de Andalucia, CSIC (Spain), the Scientific Support Office of the European Space Agency (The Netherlands), the Instituto Nacional de Técnica Aeroespacial (Spain), the Universidad Politéchnica de Madrid (Spain), the Department of Physics and Astronomy of Uppsala University (Sweden), and the Institute of Computer and Network Engineering of the TU Braunschweig (Germany). OSIRIS was financially supported by the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), and Sweden (SNSB) and the ESA Technical Directorate.

During the last few weeks of its mission at Comet 67P/C–G, the Rosetta spacecraft ventured closer than it had ever been to the surface of the nucleus. Eventually, it came to rest on the small lobe of the comet in a daring descent on 30 September 2016. No navigation images were taken during the descent; the last five NAVCAM images were taken several hours earlier, between about 20 and 17 km from the comet centre.

This montage features the three closest images of the comet’s surface taken by Rosetta’s navigation camera – acquired in the first half of September. 

The left image in the composite (also shown below) was taken on 8 September, some 2.6 from the comet surface.

Enhanced NAVCAM image of Comet 67P/C-G taken on 8 September 2016, 4.3 km from the comet centre and about 2.6 km from the surface. The distance from Rosetta to the closest pixel in this image is 2.3 km. The scale is 0.2 m/pixel and the image measures about 225 m across. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Context view for the 8 September NAVCAM image. Credit: ESA

The image shows a portion of the large comet lobe, portraying the boundary between the Ash and Seth regions. A context view is provided in the image on the right.

This view reveals the dust-covered terrains of Ash in the lower right part of the frame, declining towards Seth in the upper left, where part of one of the many round features present in this region is visible.

The central frame in the composite (also shown below) was taken on 14 September, about 2.6 km from the comet surface.

Enhanced NAVCAM image of Comet 67P/C-G taken on 14 September 2016, 4.2 km from the comet centre and about 2.6 km from the surface. The distance from Rosetta to the closest pixel in this image is 2.4 km. The scale is 0.2 m/pixel and the image measures about 225 m across. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Context view for the 14 September NAVCAM image. Credit: ESA

This image provides a detailed view of small and large boulders scattered in the Anubis region, which is also located on the large comet lobe and separated by a scarp from Seth. A context view is provided in the image on the right.

On the right in the composite (and shown below), an image from 11 September shows another view of the Seth region.

Enhanced NAVCAM image of Comet 67P/C-G taken on 8 September 2016, 4.5 km from the comet centre and about 3.5 km from the surface. The distance from Rosetta to the closest pixel in this image is 3.2 km. The scale is 0.3 m/pixel and the image measures about 310 m across. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Context view for the 8 September NAVCAM image. Credit: ESA

Taken about 3.5 km from the comet surface, the view reveals a terrace casting dramatic shadows on the underlying terrain, covered in dust and boulders. A context view is provided in the image on the right.

Comet 67P/Churyumov–Gerasimenko is now moving along the part of its orbit that is farthest from the Sun, in the outer Solar System, between the orbits of Mars and Jupiter. Today, it is over 600 million km from the Sun and over 740 million km from Earth.

All images from Rosetta’s navigation camera are available online via the Archive Image Browser.

The three original NAVCAM images are provided below.

Artist’s impression of Philae landing on Comet 67P/Churyumov-Gerasimenko. Credit: ESA/ATG medialab

Two years ago this week, the entire world was getting ready for a historic endeavour in space: the first soft landing of a human-made probe on a comet.

On 12 November 2014, Rosetta’s lander Philae landed on Comet 67P/Churyumov–Gerasimenko, and while the landing didn’t go exactly as planned, Philae finally managed to secure itself to the nucleus and to conduct a series of scientific experiments in situ, while Rosetta kept observing the comet from a distance until the mission’s end last September.

As communicators of ESA’s science missions, we gathered at the European Space Operations Centre (ESOC) in Darmstadt, Germany, to follow Philae’s landing and report it via ESA’s web and social media. During the week, ESOC was packed with scientists and engineers from the Rosetta and Philae teams, members of the international press and a number of special guests. Among them was also Professor Klim Churyumov, who together with Svetlana Gerasimenko had discovered the comet back in 1969, and who sadly passed away last month.

Professor Churyumov and his interpreters with a 3D model of Comet 67P/Churyumov-Gerasimenko at ESOC on 11 November 2014. Credit: ESA/C.Carreau

The day before landing – two years ago today – I had the pleasure to briefly meet Professor Churyumov and even asked him a few questions, taking down notes with the help of his interpreters. Back then, I was planning to write down a transcript of that conversation for this blog, but in the end the chance did not materialise at the time. Then recently, while going through my old notebooks, I found the notes from that brief interview and finally had some time to share them with the readers of the blog.

At the time, in November 2014, Rosetta had been at the comet for only three months, during which it had taken many striking pictures of this incredible little world. I asked Klim what were his expectations of how “his” comet would look like, and the reaction to Rosetta’s first close-up images. He said he was very amazed to discover that 67P/C-G consists of two lobes. Of course, he was not surprised that it had an irregular shape, as most comets do because of their small mass.

According to my notes and to the translation, Klim had compared Comet 19P/Borrelly to a potato, Comet 81P/Wild (also known as Wild 2) to an elongated grapefruit, and Comet 67P/C-G… well, to him it looked like a shoe! Indeed, he said the unexpected and beautiful shape of the comet nucleus reminded him of some traditional Ukranian shoes made of straw and used by local farmers. We all joked of how “his” comet was in fact a “cosmic slipper”.

Klim Churyumov at ESOC on 11 November 2014. Credit: ESA/C.Carreau

He added that the landscapes of the comet reminded him of mountain ranges on Earth, with peaks and valleys, like in the Alps or in the Carpathians, but smaller.

He also pointed out that this comet has spent most of its lifetime much farther away from the Sun than it currently does, as it was an encounter with Jupiter in 1959 that reduced the comet’s perihelion and led it to its present orbit, incidentally making it possible for Svetlana Gerasimenko and himself to discover it ten years later. As such, he thought of the comet as a time capsule, a “Greetings from the Past” message for scientists to investigate.

I also asked him about the next steps and what he’d be most looking forward to in terms of the scientific exploitation of the data from Rosetta. He was eagerly waiting for Philae’s descent and the first measurements to be performed on the surface of a comet.

He also mentioned that comets might have brought to our planet water and other molecules crucial to the emergence of life as we know it on Earth, and recalled the findings of NASA’s Stardust mission, which detected the amino acid glycine at Comet Wild 2. He was hoping Rosetta would find amino acids at “his” comet too… and many months later, it actually happened, as Rosetta detected glycine at Comet 67P/C-G.

As for water, Klim said he had no doubts that Earth’s water comes from space, and was looking forward to Rosetta’s measurements of the isotopic composition of water at the comet. In fact, that result was published only a month after our conversation, demonstrating that water at Comet 67P/C-G contains three times more deuterium than water on Earth, and fuelling once again the debate on the main carriers of water to our planet’s oceans – comets or asteroids?

Klim Churyumov (left) with Sam Gulkis (right), principal investigator of the MIRO instrument on Rosetta, at Philae’s comet landing event in ESOC. Credit: ESA/C.Carreau

Klim said he was also looking forward to the measurements of the electric and magnetic field by the Rosetta Plasma Consortium suite of sensors on the orbiter and the ROMAP instrument on Philae, as well as to the results of the Radio Science Experiment (RSI) and of the CONSERT radar experiment to probe the comet’s interior. Several studies based on data from these instruments were published on scientific journals in the past couple of years, and I hope that he had a chance to read about these interesting results.

As a final remark, he mentioned having a dream: he would have loved to be an astronaut, travel to the comet to have a walk on the surface, take some pictures and safely come back to Earth. And he was sure something like this would become possible in the future.

The authenticity and ingenuity of the submitted entries was overwhelming, and it has been challenging to pick one top prize winner (apologies for the delay!).

One entry in particular caught the attention of the ESA judges for the combination of creative effort and motivation, so we selected Cristina Romero from Spain as the top prize winner. The prize consists in a special visit to ESTEC, ESA’s technical heart in Noordwijk (The Netherlands).

Below is Cristina’s winning entry (translated into English):

“Missions like the one of Rosetta have allowed me to discover the wonderful world of space, and as a result I started to look for more information about these topics and I discovered my passion: space.

Since then, every day I need to learn something new, to read the news about advances in aerospace industry and follow the current missions.

I ended up with such a fascination with all this, that my big dream is to be able one day to study Aerospace Engineering, in order to take part to wonderful missions like this one. This is what’s pushing me to keep working hard every day, to save up to accomplish my dream, and every time it takes a little less effort to achieve it.

Cristina Romero’s pendant inspired by Rosetta, Philae and Comet 67P.

On September 30, the day Rosetta landed on the comet, while I was watching the webcast, I created this pendant-shaped piece to remember everything that this mission has meant to me. It is entirely handmade with polymer clay, crafted while Rosetta was landing to finally rest on Comet 67P, together with Philae.

Many thanks to ESA and the entire team for sharing this mission with us.

Cristina”

We wish to thank again everyone who shared with us what the mission meant to them, and all followers of Rosetta and Philae worldwide. It is also thanks to you that the legacy of this extraordinary mission will live on forever.

One of the responsibilities of the engineers on any mission’s Flight Control Team is to monitor the spacecraft and react immediately in case of trouble.

The Rosetta phone Credit: ESA

There are two levels of support for this:

1. The Spacecraft Controllers (‘Spacons’), who sit in the dedicated control room on shift and perform routine spacecraft control actions (monitor ground station passes, upload commands, etc.) as well as a undertake some contingency recovery activities
2. The Spacecraft Operation Engineers (SOEs), who take turns being ‘on-call’ and who can be called by the Spacon in case an anomaly must be further investigated or if a critical problem is detected beyond the expertise of the Spacon

Typically, SOEs must remain within one hour travel time to ESOC when on call.

In order to make the Spacon’s life easier (give them just a single number to call) and avoid that engineers must make calls via their personal mobile phones when having to call abroad in the middle of the night (in case of an on-board instrument failure requiring the intervention of the instrument teams, which can be anywhere in Europe or overseas), ‘on-call phones’ are available for all missions.

In 2004, we got a phone that was quite modern at the time – it had a colour display and rear-lit keyboard – and selected the only available ringtone that was not a beep or a ring, called ‘Luminaa’.

This phone has followed us through the whole mission, its battery still holding almost the whole week (when not being called) even after 10 years. Its ringtone was literally engraved in our psyches, such that whenever it would ring, anywhere within earshot, the whole team would jump up and start looking around (until we remembered who was actually on call).

When on call, it also happened to several of us that we would hear the phone ring and we’d start frantically looking for it, before realising it was just a similar sound via the TV – with some of us then realising, ‘Oh, I’m not the one having it this week anyway!’.

So when did the phone ring, for real?

Countless times! We all recall being rung up by the Spacon to tell us that a Safe Mode had happened (inevitably in the middle of the night), or that instrument temperatures were running through the roof (usually on Sundays), that ground stations were snowed in and had lost contact with the spacecraft while it was still busy downloading recorded science data (which  – unavoidably – was then lost).

It also rang to tell to us that Philae had called home in June 2015, after we all thought we’d never hear from it again (see: How we heard from Philae).

We were also rung up for a multitude of smaller, less dramatic issues – things that needed an explanation or a just quick look. On a normal on-call shift, at least a few calls were to be expected.

I am quite certain that many years from now, we will still pause and look around, startled, if we happen to hear that ‘Luminaa’ ringtone or anything that sounds even close.

The ringtone @ESA_Rosetta engineers have been dreading for 10 years. Phone is now off too… pic.twitter.com/5OH923eShI

— Armelle Hubault (@Marmelleade) October 6, 2016

The image set covers the period 2-30 September when the spacecraft was on elliptical orbits that sometimes brought it to within 2 km of the comet’s surface (watch this video for a reminder of Rosetta’s ‘end of mission’ orbits).

The archive release also includes the final five NAVCAM images that were published on 30 September, taken shortly after the spacecraft’s collision manoeuvre was executed on 29 September.

The new image sets can be found in folders MTP034 and MTP035.

Klim Churyumov and a 3D model of Comet 67P/Churyumov-Gerasimenko, at Philae’s comet landing event in ESOC, Germany, in November 2014. Credit: ESA/C.Carreau

We were saddened to learn the news yesterday that Klim Churyumov, who discovered Rosetta’s comet together with Svetlana Gerasimenko in 1969, has passed away.

Many of us had the pleasure to meet him at various Rosetta Mission events held at ESOC, and we are certainly very glad that he could see ‘his’ comet up close, and follow the mission right through until its conclusion just a couple of weeks ago.

Our condolences to his family and friends in this time.

Comet 67P/Churyumov-Gerasimenko observed by A. Baransky and K. Churyumov from Kiev on 26 January 2016. Image credit: A. Baransky, K. Churyumov. Kindly provided by Padma Yanamandra-Fisher on behalf of the PACA_Rosetta67P group.

This is an image of Comet 67P/C-G that Klim Churyumov took in January 2016 and shared in the Amateur Observing Group, PACA_Rosetta67P. Professor Churyumov encouraged the participation of amateur astronomers to observe the comet.

Read more about Klim Churyumov in this interview from 2014.

A series of 15 images of Comet 67P/C-G taken with the Kepler space observatory between 17 and 18 September 2016. The comet is seen passing through Kepler’s field of view from top right to bottom left, as outlined by the diagonal strip. The white dots represent stars and other regions in space studied by Kepler. Credit: C. Snodgrass (The Open University) and E. Ryan (SETI Institute)

A world-class exoplanet hunter, Kepler is now in its second mission, called K2, which started on 30 May 2014. While still looking for exoplanets, it is now performing observations along the ecliptic and so observing a wealth of Solar System objects, from large bodies like Neptune and Pluto to smaller ones, like comets. For example, it took images of Comet Siding Spring (C/2013 A1) in October 2014.

“Observing Comet 67P/C-G with Kepler was a unique opportunity to get a global perspective of the gas and dust in the comet’s environment while Rosetta was getting closer and closer to the nucleus,” says Colin Snodgrass of the Open University, UK, who coordinates a consortium of professional astronomers that observed the comet remotely during the time of Rosetta’s mission.

“Together with the many ground-based observations of the comet performed over the last couple of years, these images will be instrumental to understand the link between the activity observed locally by Rosetta and remotely from Earth (or near Earth), providing crucial information for the study of other comets that we cannot visit with spacecraft.”

The replica Rosetta had been used in the past decade to test and validate software and procedures before being uploaded to space. Switch-off was done by Rosetta Spacecraft Operations Manager Sylvain Lodiot on 6 Oct 2016, at ESOC.

This Flickr set records the occasion: https://www.flickr.com/photos/esa_events/sets/72157674885552235

Rosetta’s last image, taken 20 m from the surface of the comet. ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

In case you missed it during our live coverage on Friday, Rosetta’s impact site has been named Sais.

Mission Manager Patrick Martin announced the name of the impact site after contact with the comet’s surface was confirmed and the mission declared complete.

He said: “The Rosetta Stone was originally located in Sais, and we shall name the impact point as such so we can finally say that Rosetta has come home to Sais.”

The mission was named after the Rosetta Stone, itself so named because it was found in a town called Rashid (Rosetta), having thought to have been moved there from a temple in a town called Sais.

Rosetta’s last image of the comet surface is highlighted today as Space Science Image of the Week.

Heading bk from Germany & the end of Rosetta's flight mission. Our Alice UV spectrograph's final image: made minutes b4 touchdown. #Proud pic.twitter.com/dLtvhtrKRl

— Alan Stern (@AlanStern) October 1, 2016

We exchanged a brief email with Alan yesterday, who confirmed: “The spectrum shows the reflectance of the surface at close range with ~3m resolution — which is unprecedented for ultraviolet studies of comets.”

Congratulations Alice!

We’re looking forward to hearing more from the various instrument teams in due course as to what exciting measurements they achieved in the final hours of the mission.

ESA’s historic Rosetta mission has concluded as planned, with the controlled impact onto the comet it had been investigating for more than two years.

Read the press release on the ESA website.

Watch how the final stages of Rosetta’s descent to the surface of the comet played out at ESA’s mission control: Rosetta’s final hour