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\t\t\t\t\t\t06\/08\/2024<\/span> Exactly ten years on since Rosetta arrived at Comet 67P\/Churyumov-Gerasimenko, we dig into how the intrepid explorer has transformed our knowledge of comets, revealed some crucial pieces in the Solar System jigsaw puzzle, and shaped how we develop new missions.<\/p>\n<\/div>\n Introduction: ESA\u2019s comet chaser<\/p>\n Rosetta arrives at Comet 67P: why does it look like that?<\/p>\n A first glimpse of comet science: after ten years of waiting<\/p>\n Science that sticks: most memorable scientific discoveries<\/p>\n Most detailed study of a comet: reshaping our understanding of the Solar System<\/p>\n Comet Interceptor: ESA\u2019s next-generation comet mission<\/p>\n A fleet of Solar System explorers: Rosetta\u2019s influences on Hera, BepiColombo and Juice<\/p>\n Completing the jigsaw: how ESA missions work together to unveil the Solar System<\/p>\n Timeline<\/p>\n \u00a0<\/p>\n \nRosetta remains one of the world\u2019s most ambitious space exploration missions. It was the first spacecraft to fly alongside a comet as it headed towards the inner Solar System, watching how a frozen comet is transformed by the warmth of the Sun. It was also the first to land on a comet\u2019s surface, with its Philae lander sampling the surroundings of its landing site and snapping close-up images.<\/p>\n In this article, we speak to seven scientists who were part of team Rosetta when it arrived at Comet 67P. All of them have gone on to work in current or future ESA space science missions.<\/p>\n<\/p><\/div>\n After a ten-year voyage through space, in August 2014 Rosetta finally approaches its target comet. The team is expecting to see that the solid, central part of the comet \u2013 its \u2018nucleus\u2019 \u2013 is shaped like a potato. The images that come down showed something completely different.<\/p>\n Claire Vallat, who was planning the mission science at the time says: \u201cWhen we received the first detailed image of the nucleus I was on holiday but frenetically checking my phone for any new OSIRIS images whilst we were approaching Comet 67P.\u201d OSIRIS was Rosetta\u2019s camera, which gave us our first view of the comet.<\/p>\n<\/p><\/div>\n \u201cThis was a very exciting moment since the nucleus shape did not look at all like how we envisaged it until then: it had two lobes rather than being potato-shaped! I remember thinking that it would be extremely challenging to land Philae on such a complex object, but very exciting too.\u201d<\/p>\n For Geraint Jones, who went on to propose ESA\u2019s\u00a0Comet Interceptor\u00a0mission, the first view of Rosetta\u2019s comet came as a surprise for a different reason: \u201cIt was during the summer, I was on holiday and I had no internet access. So I actually saw the shape of the comet for the first time on a newspaper stand in Germany!\u201d<\/p>\n Geraint was amazed to see the incredible level of detail in the images, with intricate landforms and bizarre terrain.<\/p>\n Nick Thomas, who was on Rosetta\u2019s OSIRIS camera team, adds: \u201cWhat you have to recall is that Rosetta took a while to reach the comet. Data was being taken already when it was still just a distant dot. This is a rather slow process, with the comet getting bigger and bigger. It suddenly became very real when we were able to take a movie of this thing for the first time, and we saw this dual object \u2013 that was staggering, it told us we were there, and we were going to find something special.\u201d<\/p>\n The arrival of Rosetta was perfect timing for plasma scientist Charlotte G\u00f6tz, who started her PhD that same month. Charlotte was one of the first to work with data arriving from the mission. \u201cOne thing I remember was that during these first weeks and months, people were super excited \u2013 some people had waited for this data for 30 years, since Giotto!\u201d says Charlotte. Launched in 1985, Giotto was ESA\u2019s first and only previous comet mission.<\/p>\n It takes a long time to develop a space mission and get it to its final destination: 20 years passed between the first design of Rosetta and seeing the first science results. Understandably, the scientists were eager to get their hands on the data.<\/p>\n \u201cI have to say that I\u2019m a data junky,\u201d admits Nick. \u201cI get a real kick out of being the first person to see data coming down from a spacecraft \u2013 that\u2019s why I do this job.\u201d<\/p>\n For all the scientists involved, receiving the first data and seeing that a spacecraft\u2019s instruments are working as planned is equal parts thrill and relief. But it doesn\u2019t always come that easy.<\/p>\n Johannes Benkhoff had been working on two of Rosetta\u2019s 21 science instruments: VIRTIS and MUPUS:<\/p>\n \u201cVIRTIS was working very nicely and as expected, but unfortunately since the Philae lander didn\u2019t land as we had hoped, the operation of MUPUS was different to what we expected; it should have dug straight down into the comet\u2019s surface, but instead it went sideways. We did still get some data, but it was a little bit disappointing.\u201d<\/p>\n<\/p><\/div>\n \u201cAs a scientist, you work on something for years, and then you finally get to harvest,\u201d he adds. \u201cSometimes you get your reward very late, and sometimes not at all.\u201d<\/p>\n Nick gives an impression of just how much work goes into preparing an instrument, long before the data reward arrives: \u201cThere are upwards of 120 people working on these systems, it\u2019s a full team effort. For example, during the instrument calibration in 2001\u20132002 I worked nights for about four months, figuring out issues at night so that engineers could fix them during the day. Seeing that an instrument functions correctly and produces valid scientific data is absolutely necessary and an important part of the scientist\u2019s work.\u201d<\/p>\n These first glimpses of science were just a teaser of what was to come. Rosetta changed our view of how the Solar System formed, how the planets were made, and how life began. What scientific discoveries stick in the mind of our team?<\/p>\n \u201cThere were so many science results that it\u2019s hard to pick one!\u201d says Claire. A few seconds later, she adds: \u201cThe shape of the nucleus was a real surprise, and it raised the question of whether this was the result of specific erosion processes or of a collision between two distinct bodies. Analysis of data from multiple instruments confirmed the latter, and provided key information on the formation of the Solar System.\u201d<\/p>\n Nick gives two examples: \u201cOne thing that we were not expecting was just how important dust particles falling back onto the nucleus is. This was described in the nineties as a \u2018dust hail\u2019 but at the time nobody appreciated just how important it really is, how much material falls back onto the nucleus and makes this dust covering, which reduces the activity of the comet.\u201d<\/p>\n \u201cThe other thing that was really shocking in those first images was how diverse the nucleus surface is,\u201d he adds. \u201cThere are places that you would expect to have been affected by the same heat and radiation from the Sun, but the surface texture is totally different.\u201d<\/p>\n<\/p><\/div>\n Michael K\u00fcppers, who worked with Claire on Rosetta mission science and is now Project Scientist for ESA\u2019s Hera and Comet Interceptor missions, also finds it hard to settle on one scientific discovery.<\/p>\n \u201cRosetta revealed the importance of the transport of material from the illuminated side of the nucleus to the dark side, which partly shapes the surface of the nucleus. But it also found lots of organic material, saw cliffs collapsing, and provided data that suggests that some noble gases in Earth\u2019s atmosphere actually come from comets.\u201d<\/p>\n Zooming out from the nucleus, Geraint explains that he found the discoveries on the interaction between Comet 67P and the\u00a0solar wind\u00a0fascinating: \u201cThe comet releases gas into fast plasma coming from the Sun. It\u2019s like throwing paint into a stream and the paint mixes with the water. Rosetta sitting in this flow was a very important part of the mission, it informed our understanding of how comet plasma tails form.\u201d<\/p>\n<\/p><\/div>\n Charlotte also works on plasma, a charged state of matter that makes up 99.9% of the visible Universe, including the Sun and other stars. Looking through the Rosetta data, she found that a powerful outburst from Comet 67P had pushed away the solar wind, creating a region of zero magnetic field:<\/p>\n \u201cWe knew this happened at comets thanks to Giotto \u2013 but with Rosetta we were quite far away from the nucleus and we didn\u2019t think we would be close enough to see it \u2013 it actually became the focus of my PhD to analyse the Rosetta data and find out why this \u2018cavity\u2019 was so much bigger than expected.\u201d<\/p>\n The Rosetta mission officially ended in 2016, but the scientific discoveries keep coming. It was only after the mission, once the hectic work of actually operating the spacecraft was over, that scientists could focus on digging deeper into the data.<\/p>\n Charlotte explains why so many people are still working on Rosetta data: \u201cThis mission is so unique, and the instruments are so unique in their properties and how they react to the environment; for years after mission end, our team spent a lot of time figuring out how to treat the data and improve it.\u201d<\/p>\n During the active mission phase, scientists focused on publishing science based on data collected by individual instruments. But since then, there\u2019s been time to focus on making it easier to combine and compare datasets from different instruments, allowing them to delve even further into comet science.<\/p>\n Charlotte gives an example: \u201cThere was a recent paper about ultraviolet auroras at Comet 67P, this was the first time that auroras were detected at a comet. The discovery needed to combine data from multiple instruments, which was only possible once the data had been calibrated and understood. This leads to discoveries that are not immediately obvious!\u201d<\/p>\n \u201cFor me the post-mission phase never ends, we\u2019re always trying to improve things and the really exciting science happens in the years after,\u201d Charlotte adds. \u201cThere\u2019s still so much data that we haven\u2019t really looked at \u2013 the instrument I worked on produced 20 measurements each second, for example, so I\u2019m sure there will be something that we still find.\u201d<\/p>\n Remaining mysteries include how changes in the plasma near a comet\u2019s nucleus affect its distant tail, and the relationship between the ice-dust material that makes up the surface and the gas just above the surface.<\/p>\n Whilst scientists are still wading through data from Rosetta, ESA is planning its next mission to visit a comet \u2013 Comet Interceptor.<\/p>\n Michael leads on its scientific goals: \u201cComet Interceptor is perceived on a completely different philosophy. The real star of the mission is the target \u2013 we are aiming for a new comet coming into the inner Solar System for the first time.\u201d<\/p>\n<\/p><\/div>\n Broadly speaking, there are two main types of comets. Short-period comets, like those visited by Rosetta and Giotto, whizz around the Sun in less than 200 years; every time they pass close to the Sun, they are transformed by the Sun\u2019s heat and radiation. Long-period comets, on the other hand, have visited the inner Solar System only very rarely, in some cases never.<\/p>\n Geraint tells us more about Comet Interceptor\u2019s science ambitions: \u201cThe overall aims of Comet Interceptor are to see the surface of a comet before it\u2019s sculpted by the heat of the Sun and before the most exotic ices have turned to gas. We want to go to a different type of comet \u2013 a really, really pristine comet, that\u2019s a real time capsule from when the Solar System was formed.\u201d<\/p>\n Michael points out: \u201cBy visiting an unchanged \u2013 or \u2018dynamically new\u2019 \u2013 comet, Comet Interceptor will help us determine which of the larger features seen by Rosetta are original, and which were formed as the comet passed around the Sun.\u201d<\/p>\n \u201cIf we get really good resolution images of the nucleus of a dynamically new comet, we can compare the images of the two and ask ourselves how they look different,\u201d adds Nick. \u201cA significant fraction of the science comes in that moment, the first result in 30 seconds.\u201d<\/p>\n One thing that scientists will be looking into is whether the surface of Comet Interceptor\u2019s comet looks different to the short-period ones we have encountered before. Will it also be as dark as coal, and if not, can we tell why not?<\/p>\n What\u2019s more, Rosetta has taught us valuable lessons that those working on Comet Interceptor are using to plan the mission.<\/p>\n Charlotte is ready with an example: \u201cWe realised with Rosetta that one spacecraft is not enough to study plasma around a comet, we need measurements from multiple angles and so we designed Comet Interceptor to consist of three spacecraft.\u201d<\/p>\n<\/p><\/div>\n By making measurements from three different locations in space, scientists will be able to build a 3D map of the magnetic field around a comet, making a huge difference to our understanding of how the solar wind interacts with a comet.<\/p>\n Nick adds: \u201cOne thing that\u2019s really important to mention is that so many good young people working on Rosetta moved on to become more senior people in Comet Interceptor. Others have gone off to do something else, and they do it well because they were inspired by Rosetta, they saw what an impact one can make to these missions.\u201d<\/p>\n Comets are only one type of object in a Solar System full of planets, dwarf planets, moons and asteroids (see comets vs. asteroids). Rosetta\u2019s significant impact on ESA missions heading to these other objects may come as a bigger surprise.<\/p>\n Hera, due to launch in October 2024, is the first planetary defence mission developed under ESA’s Space Safety Programme. Hera will visit a double asteroid as part of the world\u2019s first ever asteroid deflection experiment. Hera will carry two smaller satellites; one with a radar instrument based on Rosetta\u2019s CONCERT, and the other with a dust measuring instrument based on Rosetta\u2019s GIADA.<\/p>\n Hera Project Scientist Michael K\u00fcppers explains how else the mission has benefitted from Rosetta: \u201cHera builds upon Rosetta operations, with the orbit scheme borrowed directly from the comet mission. Though Hera has more autonomy, the navigation scheme in the early phases is the same as Rosetta\u2019s.\u201d<\/p>\n<\/p><\/div>\n ESA\u2019s Mercury mission BepiColombo also benefits from lessons learned from Rosetta, with aerospace manufacturer Astrium (later merged to form Airbus Defence and Space) building both missions. Like Hera, some of BepiColombo\u2019s instruments are similar to Rosetta\u2019s.<\/p>\n \u201cThere are entire teams that worked on Rosetta now working on BepiColombo,\u201d explains BepiColombo co-Project Scientist Johannes. \u201cFor example, many involved in Rosetta\u2019s VIRTIS imaging spectrometer instrument are now working on BepiColombo\u2019s similar SIMBIO-SYS, and the magnetometer teams are similar on both missions. The planetary science community is quite small!\u201d<\/p>\n Claire tells us about how Rosetta has helped prepare ESA for its Jupiter Icy Moons Explorer (Juice) mission, currently on its way to Jupiter.<\/p>\n \u201cRosetta is one of the most ambitious and challenging missions, also from a human perspective. It was a long project involving people spread all over the world, sometimes belonging to different generations, all learning to work together towards a common\u00a0scientific goal. This was really inspiring and very good preparation for Juice, which will, like Rosetta, have a long cruise phase and will require similar interactions and preparation.\u201d<\/p>\n Each of our Solar System explorers has different goals and carries different instruments. They ask different questions and give different answers. But ultimately, they each provide a piece of the puzzle in revealing the Solar System.<\/p>\n \u201cRosetta, Comet Interceptor and Hera are all missions to small bodies, which are kind of the leftovers of the formation of the Solar System. These bodies have not changed much since the Solar System formed,\u201d says Michael. \u201cOther missions investigate planets \u2013 the outcome of the formation process. They\u2019re at the other end of the scale, seeing the most processed parts of the Solar System. Putting all of this together, we better understand how the Solar System formed and evolved.\u201d<\/p>\n Johannes adds: \u201cIf you look at a comet, you get some information from far out of the Solar System. Then looking at Mercury, you see the planet closest to the Sun. So with both a comet and Mercury, we have the two ends of the spectrum \u2013 closest to and furthest from the Sun.\u201d<\/p>\n \u201cIt\u2019s important to study the extreme cases in order to understand the physics and what\u2019s going on \u2013 it\u2019s not enough to look only to Mercury, not enough to look only at comets \u2013 we need both to get the bigger picture.\u201d<\/p>\n Patrick Martin has worked on two of ESA\u2019s Mars missions since being Rosetta Mission Manager \u2013 Mars Express and ExoMars Trace Gas Orbiter (TGO). \u201cThese three missions contribute to the study of our Solar System as a whole, maintaining ESA\u2019s presence and leadership in space science. Rosetta was a pioneering cometary science mission following in the footsteps of Giotto, while Mars Express and ExoMars TGO enable and foster ESA\u2019s presence at Mars as part of the robotic exploration of the planet, before crewed flights become a reality.\u201d<\/p>\n \u00a0<\/p>\n 2 March 2004 \u2013 Rosetta launch<\/i><\/p>\n 20 January 2014 \u2013 Rosetta wakes up<\/i><\/p>\n 6 August 2014 \u2013 Rosetta arrives at Comet 67P<\/i><\/p>\n 12 November 2014 \u2013 Rosetta\u2019s Philae lander lands on Comet 67P<\/i><\/p>\n 30 September 2016 \u2013 Rosetta mission complete<\/i><\/p>\n 19 June 2019 \u2013 Comet Interceptor selected as ESA mission<\/i><\/p>\n 8 June 2022 \u2013 Comet Interceptor approved for construction<\/i><\/p>\n<\/p><\/div>\n
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\n\t\t\t\t\t\t\t\t\t\t1<\/span> likes<\/small><\/span><\/p>\n<\/header>\n\nAugust 2014: Rosetta arrives at Comet 67P<\/h3>\n
\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\n\nA first glimpse of comet science<\/h3>\n<\/p><\/div>\n
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\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\n\nScience that sticks<\/h3>\n
\nMost detailed study of a comet<\/h3>\n
\nComet Interceptor: ESA\u2019s next-generation comet mission<\/h3>\n
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\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\n\nA fleet of Solar System explorers<\/h3>\n
\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\n\nCompleting the jigsaw<\/h3>\n
\nTimeline<\/b><\/i><\/h3>\n