Rosetta Science at Comet 67P/Churyumov-Gerasimenko

On 31 July 2014, Rosetta was in its final approach to the comet after its ten-year journey through space. The spacecraft arrived at a distance of 62 miles (100 km) on 6 August whereupon 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 deployment on 12 November occurred before Rosetta settled into longer-term science orbits. In February and March 2015 the spacecraft made several flybys as ESA confirmed in June that the mission was to be extended until the end of September 2016. The comet's increased activity in the lead up to and after perihelion in August 2015 meant that Rosetta remained well beyond 62-mile distances for several months. Following perihelion, Rosetta performed a dayside far excursion some 932 miles (1,500 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. The end of mission orbits eventually led to the final descent to the surface of the comet on September 30, 2016

All Rosetta high-resolution images and their data are since June 2018, available in ESA’s archives at ESA's Archive Image Browser or the Planetary Science Archive

.check to a description of Rosetta landing which occurred on Aug. 6, 2014. check to a description of the Philae lander landing

Arrival Data Working at Comet 67P/Churyumov-Gerasimenko

Arrival Data

Animated .gif of comet 67P/Churyumov-Gerasimenko as seen by approaching Rosetta mission! courtesy site 'Amateur Astronomy'

As soon as mission Rosetta acquired first useable pictures of comet 67P/Churyumov-Gerasimenko, it hinted to a peculiar shape. Comet 67P is obviously different from other comets visited so far. At arrival after Comet Churyumov-Gerasimenko released the equivalent of two glasses of water into space every second, as the comet began developing a coma as it came closer to the Sun. Rosetta had caught a first glimpse of its destination comet by March 2014 which is 2.5-mile (four-kilometer) wide

	That general view of comet 67P/Churyumov-Gerasimenko dated August 3rd, 2014 is showing the comet's specific shape, a seemingly assemblage of two objects. picture courtesy site 'Amateur Astronomy'
	A close up detail focusing on a smooth region shows a range of features, including boulders, craters and steep cliffs. Resolution is 7.9 ft per pixel (2.4 metres). picture courtesy site 'Amateur Astronomy'
	High cliffs, right, boulders upon a smooth terrain, center and varied terrain, left are seen in that picture. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA/Rosetta/NAVCAM

Working at Comet 67P/Churyumov-Gerasimenko

By late August 2014, information collected by Rosetta during its first two weeks at the comet allowed to five locations have been identified as candidate sites for the Philae lander's landing in mid-November 2014, about 280 million miles (450 million kilometers) from the Sun, before activity on the comet reaches levels that might jeopardise the landing. Site J (a little bit lower than represented on the picture below) was eventually chosen on Sep. 14, 2014 with minimum risk to the lander. Site C is the backup landing site as landing should occur on Nov. 12, 2014. From first data collected, both hydrogen and oxygen are extant in the comet’s coma, or atmosphere. No ice patches were seen on the comet’s surface despite it being far from the Sun. A region of jet activity began to be observable on Sept. 26, 2014

After having assisted and followed the landing of the Philae lander by mid-November 2014, the Rosetta orbiter has been moving back into a 18.5-mile (30-km) orbit around the comet. It will return to a 12.5-mile (20-km) orbit on 6 December and continue its mission to study the body in great detail as the comet becomes more active, en route to its closest encounter with the Sun on Aug. 13, 2015. Over the coming months, Rosetta will start to fly in more distant unbound orbits, while performing a series of daring flybys past the comet, some within just 5 miles (8km) of its centre

	Five landing ellipses are possible for the Philae lander at comet 67P/Churyumov-Gerasimenko. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA/Rosetta/NAVCAM
	Scientists have found that the surface of comet 67P/Churyumov-Gerasimenko can be divided into several regions, each characterized by different classes of features. Never before have a cometary surface be seen in such detail. One does not expect the borderlines identified to vary dramatically when the comet will close the Sun. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA/Rosetta/MPS for OSIRIS Team/MPS/UPD/LAM/IAA/SSO/INTA/UPM
	This fine view is showing pits on the cometary surface as seen from the Rosetta orbiter few before the lander Philae departed as the comet's activity will activate such features as it closes the Sun. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA
	A boulders' field and a high cliff is seen here as the debris might result from some collapse there. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

As of early 2015, further knowledge of comet Churyumov-Gerasimenko has been provided by astronomers. A day at comet is about-12 hour. Jets have been spotted rising from pits and producing dune-like ripples or boulders with wind-tails. The dusty covering of the comet may be several yards- (metre)-thick in places, playing a key role in insulating the comet interior. Cliff walls are covered in randomly oriented fracture linked to the heating–cooling daily, or orbital cycles as erosion also affectes the cliffs, chunks of ice dropping and exposing the next layer of the cliff. The origine of the double-lobed shape of the comet, the coolest place of it, remains a mystery as that might result from the erosion of a larger comet, or two separate comets formed in the same part of the Solar System and then merged 4.5 billion years ago. Activity at a distance from the Sun of under 3 AU is predominantly from the neck, where jets have been seen consistently. The comet's density of 470 kg/m3 is the one of cork or wood, necessitating a fluffy texture generally with a porosity of 70 to 80 percent. Studies in April 2015 suggests that cometary grains of comet éformed at low-temperature conditions below 30°K. Astronomers found that water and carbon dioxide spewing from a comet's surface are due to electrons close to the surface and not photons from the Sun, which causes a rapid breakup of molecules

Scientists have identified more than a hundred patches of water ice a few yards (meters) in size on the surface of comet 67P/Churyumov-Gerasimenko as they likely represent boulders coated with, or made of, ice which were blasted off cliffs during a previous passage of the comet at the Sun

	Dust jets emerging from Rosetta’s comet can be traced back to active pits that were likely formed by a sudden collapse of the surface. Quasi-circular pits are a few tens to a few hundreds of yards (meters) in diameter and extend up to 210 yards (meteres) below the surface to a smooth dust-covered floor. They likely formed when the ceiling of a subsurface cavity becomes too thin to support its own weight and collapses as a sinkhole. This exposes the fractured interior of the comet. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA
	From a distance of about 16 miles from the surface and a image scale about 18" (45 cm)/pixel, a pit is seen of about 670 foot-wide (200m) near the center as the region is also providing to other pits. Young, active pits are particularly steep-sided, whereas pits without any observed activity are shallower and seem to be filled with dust, and middle-aged pits tend to exhibit boulders on their floors from mass-wasting of the sides. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA
	Imhotep region on the large lobe of comet 67P/Churyumov–Gerasimenko is seen here as spectacular roundish features are at the center-right, either bulging or depressed, which could be ancient degassing conduits. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
	Bright and bluer patches are seen here, in details in the Imhotep region. Could it be a ice sheet? picture courtesy site 'Amateur Astronomy,' based upon a picture ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Complex molecules that could be key building blocks of life, the daily rise and fall of temperature, and a assessment of the surface properties and internal structure of the comet are among data returned by Rosetta’s lander Philae last November 2014. A variation in the local temperature between about -180 degree C and -145 degree C in sync with the comet’s 12.4 hour day as a thin layer of dust, generally, lies atop a compacted dust-ice crust. Mission scientists found, by September 2015 that two fully-fledged and separately formed comets colliding at low speed in the early Solar System gave birth to comet 67P/Churyumov–Gerasimenko distinctive shape like a bilobate nucleus. The comet’s two lobes are fairly similar in composition, which suggests that they probably formed in the same environment. Molecular nitrogen, which was found for the first time at a comet, was common when the Solar System was forming, but required very low temperatures to become trapped in ice, so Rosetta’s measurements support the theory that comets originate from the cold and distant Kuiper Belt. Ammonium salts discovered on the surface of Comet 67P/Churyumov-Gerasimenko might considerably increase the amount of nitrogen that scientists had previously expected to find on the comet. A lot of molecular oxygen has been found extant by 2015 in comet 67P/Churyumov–Gerasimenko coma. Neutral gas comas of most comets are composed largely of water, carbon monoxide and carbon dioxide. Molecular oxygen should have reacted and disappear with the hydrogen in the early solar system hinting to that comet 67P/Churyumov–Gerasimenko could be a very pristine body. Molecular oxygen has been detected on icy bodies in the solar system, including the moons of Jupiter and Saturn

	Another landscape as photographied from 10.8 miles from the comet's center. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA
	This image was acquired at a distance of 11.4 miles from the comet center and provides an oblique view of the Imhotep region on the underside of the comet, with the image 1 mile across. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA
	That diagram is a summary to Rosetta's approach, orbit and work at comet 67P/Churyumov-Gerasimenko. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA
	This image measures 9.7-yard across as it reveals for the first time that close a comet’s surface. The regolith in this region is thought to extend to a depth of 2 yards in places, but seems to be free from very fine-grained dust deposits like seen here. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA/Rosetta/Philae/ROLIS/DLR
	This image is showing a detailed view of comet soil, was taken by landing Philae during its descent to the surface, by 193ft (57.9m) only of altitude. The image measures 208-foot (62.3m) across. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA/Rosetta/Philae/ROLIS/DLR
	A daily water-ice cycle is extant on and near the surface of comets. At comet 67P/Churyumov–Gerasimenko, for example, a mechanism replenishes the comet's surface with fresh ice at every 12-hour rotation like explained by that diagram. Comet 67P/Churyumov–Gerasimenko thus allowed scientists to confirm theoretical models of a cometary daily cycle. Down to a few cm deep over the region of the portion of the comet nucleus that was surveyed, water ice accounts for 10–15% of the material and appears to be well-mixed with the other constituents. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA

Comet 67P/Churyumov–Gerasimenko made its closest approach to the Sun, or perihelion at 02:03 GMT on August 13th, 2015, within 116 million miles from the Sun, as Rosetta had traveled 463 million miles towards along with the comet. The cometary activity is expected to reach its peak intensity around perihelion and in the weeks following. Flight controllers were forced to move Rosetta further on the orbit, up to 201-211 miles to get distant from the material emitted. Surface temperatures of around minus 70 degree C were recorded as highs of a few tens of degrees above zero are forecast next month. Comet's tail now is extending more than 74,600 miles. In the months leading to the perihelion, dramatic and rapid surface changes occurred on the Imhotep region. The swiftness of change might hint to that the surface material is very weak or that there is a crystallisation of amorphous ice, or a destabilisation of so-called 'clathrates' (a lattice of one kind of molecule containing other molecules). That could liberate energy and thus drive changes. The erosion could be accompanied by increased rates of gas outflow, including H2O, CO2, or CO. During passage to Sun's closest, loose debris have been seen all over the comet, but sometimes boulders have been caught in the act of being ejected into space, or rolling across the surface. Boulders at a comet on the other hand, have a density around one hundred times weaker than freshly packed snow. Also collapses of cliff have been observed along lines of weakness. Due to the specificities of the comet’s orbit, its northern hemisphere experiences a very long summer, lasting over 5.5 years, while the southern hemisphere undergoes a long, dark and cold winter. However, a few months before the comet reaches perihelion the situation changes, and the southern hemisphere transitions to a brief and very hot summer. The 'dark side' might thus feature larger quantities of water and carbon-dioxyde ice. Observations made shortly after Rosetta’s arrival at its target comet in 2014 have provided definitive confirmation of the presence of water ice. Water vapour is the main gas seen flowing from comet as most of ice is believed to come from under the comet’s crust, as very few examples of exposed water ice have been found on the surface. The comet’s topmost layer however is primarily coated in a dark, dry and organic-rich material but with a small amount of water ice mixed in. A varied populations of icy grains on the surface of the comet implies different formation mechanisms, and different formation's time scales. Very small grains, for example, are associated with a thin layer of 'frost' that forms as part of the daily ice cycle. Larger grains have a more complex history as they likely formed slowly over time and they are only occasionally exposed through erosion. Such large grains can also be explained by the growth of 'secondary ice crystals,' be ice grains compacted together, a process called sintering, or enduring sublimation, with heat from the Sun penetrating the surface and triggering evaporation of buried ice. A significant fraction of the ice, on a other hand, recondenses in layers beneath the surface. Ice-rich subsurface layers several yards (metres) thick can affect the structure, porosity and thermal properties of a comet's nucleus

	A outburst seen on July 29th, 2015 as a result that the comet is nearing perihelion. The ouburst made the amount of carbon dioxide increased by a factor of two, methane by four, and hydrogen sulfide by seven, while the amount of water stayed almost constant. Jet was traveling at 33 feet per second (10 meters per second), at least. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA
	Views of comet 67P/Churyumov–Gerasimenko during its most active period in August 2015, with thirty-four no less outbursts in the three months centered around the comet’s closest approach to the Sun on Aug. 13, 2015. Outbursts were traced back to their origins on the surface as some linked to changes in local temperatures, perhaps in the early morning after many hours of darkness, or later in the day after several hours of heating, while others from areas associated with pits or steep cliffs. Outbursts typically only lasted a few minutes expelling some 60–260 tons of material each. Such transient events occurred over and above regular jets and flows of material which already existed streaming from the comet’s nucleus, and were much brighter. Some outbursts were long, narrow jets extending far from the comet nucleus, while others had a broader base that expanded more laterally. Others seem to be a hybrid of the two. By the summer of 2015, the comet was so active that Rosetta could only observe it from a safe distance of 124-186 miles (200–300 km). picture courtesy site 'Amateur Astronomy,' based upon pictures OSIRIS: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; NavCam: ESA/Rosetta/NavCam
	That image, taken on 21 January 2016, 6 months after Comet 67P/Churyumov–Gerasimenko left perihelion shows how the environment was still extremely chaotic with dust grains moving. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA
	That image of Comet 67P/Churyumov–Gerasimenko was taken on 18 December 2015, when Rosetta was 59.6 miles away, with a scale 1.73 m/pixel. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
	That is a stunning view across the Imhotep region on Comet 67P/Churyumov–Gerasimenko, measuring 2 miles (3.2 km) across, as it captures one of the most geologically diverse areas of the comet. The smooth dusty terrain at the area's center is etched with curvilinear features stretching hundreds of yards (metres) and which have been found to change in appearance over time, with many large boulders also scattered. Layers like those seen at top left of the scenery are still unknown in terms of how they formed as layers like that are also seen elsewhere on the comet. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
	That fountain of dust is a cometary outburst seen on Jul. 3, 2016, as the origins of such phenomenons are still unclear. They might be outbursts from inside the comet and pressurised gas bubbles, or stores of ice reacting violently to sunlight. The plume lasted for roughly one hour, flowing dust particles and water ice grains. Collapsing cliffs are also a usual phenomenon on a comet. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA

Rosetta demonstrated that there are no large caverns inside Comet 67P/Churyumov-Gerasimenko, solving a long-standing mystery. That study was made building a gravity map of the comet. In September 2016, Rosetta will be guided to a controlled impact on the surface of the comet as when the craft will get nearer and nearer the complex gravity field of the comet will make navigating harder and harder. Comet 67P/Churyumov-Gerasimenko has been seen changing colour and brightness since Rosetta arrival as the Sun’s heat strips away the older surface to reveal fresher material. As the comet was a extremely dark body, with a albedo of about 6 percent due to surface covered with a layer of dark, dry, dust made out of mixture of minerals and organics, those old dust layers were slowly ejected due to gaseous activity and fresher with new material gradually exposed, more reflective, making the comet brighter, and richer in ice. Albedo at the Imhotep region increased from 6.4 to 9.7 percent over three months

The path of Comet 67P/Churyumov–Gerasimenko. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA

Ingredients regarded as crucial for the origin of life, including the amino acid glycine, which is commonly found in proteins, and phosphorus, a key component of DNA and cell membranes have been unambiguously ascertained at Comet 67P/Churyumov–Gerasimenko as repeated detections were made in the comet's coma. That constitutes a first in terms of cometary exploration. Also detected were certain other organic molecules that can be precursors to glycine, hinting at the possible ways it may have formed. Recent studies of Rosetta data brought astronomers to state that comets are ancient, accreted leftovers of the early solar system formation, and not younger fragments resulting from subsequent collisions. It looks like that icy trans-Neptunian objects or TNOs first gently grew and some even turned objects like Triton or Pluto. After TNOs, more grains and pebbles of icy material remained as they came together at low velocity. It was that process which produced comets roughly 3.1 miles (5km) in size and, because it was done at low speed, that made that comets have a fragile nucleus with high porosity and low density. TNOs then stirred comets' orbits making that more material accreted unto those at a higher speed during the next 25 million years, as that yielded comets' outer layers. In the case of Comet 67P/Churyumov–Gerasimenko, some objects even bumped slowly into each other and bringing the observed bi-lobe nature. The low mass of comets also likely made that they released their radioactive decay-generated heat without heating too much. That slow eventually growth allowed comets to preserve some of the oldest volatile-rich material from the solar nebula

By the summer of 2016, Rosetta unexpectedly captured a dramatic comet outburst that may have been triggered by a landslide. Thermal stresses in the surface material might have triggered a landslide that exposed fresh water ice to direct solar illumination, the ice immediately sublimating, and dragging surrounding dust with it. In the three months centred around the comet’s closest approach to the Sun 34 outbursts were observed by Rosetta. Such jets were observed over and above regular jets, and triggered by the 'daily' rotation of the comet. They were typically brighter and with a very short lifetime. A typical outburst is thought to release 60–260 tonnes of material in a few minutes. On average, the outbursts around the closest approach to the Sun occurred once every 30 hours – about 2.4 comet rotations as three types of them have been categorized. Long, narrow jets extending far from the nucleus, broad, wide-base ones expanding more laterally and the third category a complex hybrid of the other two. Astronomers can’t tell however whether these three types of plume correspond to different mechanisms or just different stages of a single process (beginning with a narrow jet and then broadening at its base when its exit point is modified). Outbursts also occur function of the time of the day, with thermal stress with explosive events occurring at dawn, after hours of darkness and explosion from pockets of volatiles due to the cumulative heat accumulated when it's noon at the comet. Some outbursts, further, likely are due to regional boundaries on the comet with changes in texture or topography in the local terrain, such as steep cliffs, pits or alcoves (as boulders and other debris are also seen there, they hint to areas particularly susceptible to erosion, like cliffs)

By early September 2016, Rosetta’s high-resolution camera has revealed the Philae lander wedged into a dark crack on Comet 67P/Churyumov–Gerasimenko. The images provide proof why establishing communications was so difficult. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA

The final descent to the comet's surface, on Sept. 30, 2016, gave Rosetta the opportunity to study the comet's gas, dust and plasma environment very close to its surface, as well as take very high-resolution images. The final image was acquired about 20 m above the impact point. A increase in very small dust grains occurred close to the surface. Comet was also confirmed like as a non-magnetic body

	That series of pictures is showing varied views during the descent of the Rosetta probe towards the surface of Comet 67P/Churyumov-Gerasimenko. Data above and below are showing the altitude at which the pictures were taken and what the dimensions of the terrain viewed are. The picture right is the last taken, shortly before impact. picture courtesy site 'Amateur Astronomy,' based upon pictures ESA and NASA
	Several sites of cliff collapse on comet 67P/Churyumov–Gerasimenko were identified during Rosetta’s mission. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA
	That final image from Rosetta, shortly before it made a controlled impact onto Comet 67P/Churyumov–Gerasimenko on 30 September 2016, was reconstructed from residual telemetry. The image measures about 1 yard across. picture courtesy site 'Amateur Astronomy,' based upon a picture ESA

During its trip through the inner solar system, the surface of comet 67P/Churyumov-Gerasimenko was a very active place full of growing fractures, collapsing cliffs and massive rolling boulders. Comet 67P/Churyumov-Gerasimenko's spin sped up by two minutes as it approached the Sun, and then slowed by 20 minutes as it receded as such changes were produced by the interplay between the comet's shape and the location and activity of its jets. The warming of 67P also caused the comet’s rotation rate to speed up which in turn caused a fracture to increase in size and maybe leading one day to the comet to split