Comets, asteroids, and other small bodies are thought to be remnants of the original planetesimal population of the Solar System. As such, their physical, chemical, and isotopic properties hold crucial details on how and where they formed and how they evolved. Yet, placing precise constraints on the formation region of these bodies has been challenging. Data from spacecraft missions have a particularly high potential of addressing the question of the origin of the visited bodies. ESA's Rosetta mission to comet 67P/Churyumov-Gerasimenko returned data from the comet for two years on its journey around the Sun. This extensive data set has revolutionised our view on comets and still holds unsolved problems. We use the Rosetta/ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) measurement of the volatile/ice composition and the Rosetta/COSIMA (COmetary Secondary Ion Mass Analyzer) measurements of the refractory composition of comet 67P. These measurements are combined using a Monte Carlo method. The refractory-to-ice ratio is a free parameter that is constrained a posteriori. Using only the composition, we constrain the refractory-to-ice ratio to $0.5<\chi<1.7$, and derive the bulk elemental abundances for 67P of H, C, N, O, Na, Mg, Al, S, K, Ar, Ca, Cr, Mn, Fe, Kr, and Xe. We find the noble gas xenon in near solar elemental abundance in comet 67P. Krypton is slightly depleted, while argon is heavily depleted. Comet 67P is enriched in all three noble gases by up to 2.5 orders of magnitude compared to CI chondrites. We show this is consistent with a formation region between 25 and 35 au in a protoplanetary disk region with temperatures between 30 and 40 K and with the trapping of dust for a long time in rings of the protoplanetary disk.

In the plasma environment of a comet, waves are generated on vastly different temporal and spatial scales. Wave observations were carried out during the cometary flybys in the 1980s and 1990s as well as by the Rosetta spacecraft which accompanied comet 67P/Churyumov-Gerasimenko between 2014 and 2016. Waves are thought to contribute to the transfer of energy in the ionised coma. One of the fundamental plasma waves observed in space is the Langmuir wave, which appears at or above the electron plasma frequency. The Mutual Impedance Probe of the Rosetta Plasma Consortium (RPC-MIP) recorded frequency spectra of electric field fluctuations in the cometary plasma, and we used these spectra in order to detect and identify Langmuir waves. Langmuir waves were found during the part of the Rosetta mission when the comet was less than AU AU from the Sun. The Langmuir waves appear near, but always outside, the diamagnetic cavity boundary, in a region where, at much lower frequencies, steepened magnetosonic waves also are present.

In the 1990s, European scientists decided to design a much more ambitious mission that would match orbits with an incoming comet and follow it as it approached the Sun. They also proposed that a smaller spacecraft would actually try to land on the comet. The 2-ton main spacecraft was named Rosetta, carrying a dozen scientific instruments, and its 100-kilogram lander with nine more instruments was named Philae. The Rosetta mission was launched in 2004. Delays with the launch rocket caused it to miss its original target comet, so an alternate destination was picked, Comet Churyumov-Gerasimenko (named after the two discoverers, but generally denoted 67P). This comet’s period of revolution is 6.45 years, making it a Jupiter-family comet. Since the European Space Agency did not have access to the plutonium-fueled nuclear power sources used by NASA for deep space missions, Rosetta had to be solar powered, requiring especially large solar panels. Even these were not enough to keep the craft operating as it matched orbits with 67P near the comet’s aphelion.

The European Space Agency (ESA; pronounced /ˈiːsə/ EE-sə) is a 23-member international organisation devoted to space exploration. It has its headquarters in Paris and a staff of around 3,000 people globally as of 2025. ESA was founded in 1975 in the context of European integration. Its 2026 annual budget was around €8.3 billion. The ESA human spaceflight programme includes participation in the Int The European Space Agency (ESA; pronounced /ˈiːsə/ EE-sə) is a 23-member international organisation devoted to space exploration. It has its headquarters in Paris and a staff of around 3,000 people globally as of 2025. ESA was founded in 1975 in the context of European integration. Its 2026 annual budget was around €8.3 billion. The ESA human spaceflight programme includes participation in the International Space Station (ISS) and collaboration with NASA on the Artemis programme, especially manufacturing of the Orion spacecraft's European Service Module (ESM). ESA launches and operates uncrewed missions to the Moon, Mars, Jupiter, Venus, Mercury, the Sun, and various comets and asteroids. Other activities include space telescopes, Earth observation satellites, asteroid impact avoidance, telecommunication and navigation satellites, designing launch vehicles (e.g. Ariane 6 is operated through Arianespace with ESA sharing in the costs), and maintaining Europe's spaceport (the Guiana Space Centre in Kourou, French Guiana), as well as space safety and commercialisation. At the time the ESA was formed, its main goals did not encompass human space flight; rather it considered itself to be primarily a scientific research organisation for uncrewed space exploration in contrast to its American and Soviet counterparts. It is therefore not surprising that the first non-Soviet European in space was not an ESA astronaut on a European space craft; it was Czechoslovak Vladimír Remek who in 1978 became the first non-Soviet or American in space (the first man in space being Yuri Gagarin o The European Space Agency (ESA; pronounced /ˈiːsə/ EE-sə) is a 23-member international organisation devoted to space exploration. It has its headquarters in Paris and a staff of around 3,000 people globally as of 2025. ESA was founded in 1975 in the context of European integration. Its 2026 annual budget was around €8.3 billion. The ESA human spaceflight programme includes participation in the International Space Station (ISS) and collaboration with NASA on the Artemis programme, especially manufacturing of the Orion spacecraft's European Service Module (ESM). ESA launches and operates uncrewed missions to the Moon, Mars, Jupiter, Venus, Mercury, the Sun, and various comets and asteroids. During the 2000s, ESA was considering cooperation with Russia on the proposed Kliper and CSTS crewed vehicles, but neither of these was developed. Notable deep space missions during the 2000s included the agency's first Moon, Mars, and Venus orbiters: SMART-1, Mars Express, and Venus Express. ESA's Huygens probe, launched together with the NASA's Cassini mission in 1997, reached its destination in 2005 when it successfully landed on Titan, marking the farthest landing from Earth a spacecraft has ever made. The comet orbiter Rosetta launched in 2004 and performed multiple deep space flybys and observations during the decade, but wouldn't reach its destination until 2014. In 2012, ESA committed to providing the ATV-derived European Service Module for NASA's crewed lunar spacecraft Orion. In 2014, ESA's Rosetta probe arrived at its destinatination, the Jupiter-family comet 67P/Churyumov–Gerasimenko. It became the first spacecraft ever to orbit a comet and its lander Philae performed the first ever landing on a comet. In 2016, ESA launched its second Mars orbiter mission, the ExoMars Trace Gas Orbiter (TGO), as the first ExoMars mission within the newly established Terrae Novae programme. When the spacecraft arrived at Mars later the same year, it released the Schiaparelli lander, which failed on landing. The European Robotic Arm was launched in 2021 together with the Nauka module. ESA continued contributing European astronauts to regular ISS expeditions, and also started paying private companies for short-term astronaut flights to the station. ESA also started supporting European companies in developing uncrewed space capsules for resupplying the ISS and future space stations via the LCRS initiative, as well as the Indian ISRO in developing their crewed Gaganyaan spacecraft. Rocket launches are carried out by Arianespace, which has 23 shareholders representing the industry that manufactures the Ariane 5 as well as CNES, at the ESA's Guiana Space Centre. Because many communication satellites have equatorial orbits, launches from French Guiana are able to take larger payloads into space than from spaceports at higher latitudes. In addition, equatorial launches give spacecraft an extra 'push' of nearly 500 m/s due to the higher rotational velocity of the Earth at the equator compared to near the Earth's poles where rotational velocity approaches zero. Of the applicants, 918 were chosen to take part in the first stage of psychological testing, which narrowed down the field to 192. After two-stage psychological tests and medical evaluation in early 2009, as well as formal interviews, six new members of the European Astronaut Corps were selected – five men and one woman. === Crew vehicles === In the 1980s, Following talks with Roscosmos in 2004 and June 2005, a co-operation between the ESA and Roscosmos was announced to jointly work on the Russian-designed Kliper, a reusable spacecraft that would be available for space travel beyond LEO (e.g. the moon or even Mars). It was speculated that Europe would finance part of it. A€50 million participation study for Kliper, which was expected to be approved in December 2005, was finally not approved by ESA member states. The Russian state tender for the project was subsequently cancelled in 2006.

Propriétés spectrophotométriques du noyau de la comète 67P/Churyumov-Gerasimenko observée par la sonde ROSETTA Cette thèse s'inscrit dans le cadre de la mission spatiale Rosetta et porte sur les propriétés spectrophotométriques de la comète 67P/Churyumov-Gerasimenko à l’aide de l’instrument OSIRIS. Cet instrument est composé de deux caméras pour les observations du noyau et de la coma de la comète. Elles permettent d’acquérir des images avec des filtres qui opèrent dans la gamme du proche UV au proche IR. Dans un premier temps, j'ai analysé les courbes spectrophotométriques des taches claires qui sont apparues sur le noyau de la comète. Une étude comparative de celles-ci grâce aux données du spectro-imageur VIRTIS a ainsi permis de constater que les taches claires sont liées à la glace de H2O. Dans un second temps, j’ai entrepris une étude spectrophotométrique de la région Khonsu, qui a mis en évidence les variations saisonnières de la pente spectrale de différents terrains. Par la suite, j’ai élargi mon analyse des taches à tout le noyau de la comète. J’ai détecté plus de 50 taches claires dues à la présence de glace de H2O et j’ai produit une carte pour repérer leurs emplacements sur le noyau, afin d’étudier plus en détail leur répartition et leur évolution au cours de temps. Ceci m’a permis d’identifier quatre types de taches regroupés en fonction de leur morphologie et de constater qu'elles sont dues à différentes sources d'activité cométaire.

Langmuir waves are fundamental waves in plasmas, and they appear at or above the electron plasma frequency. We have observed Langmuir waves in the plasma environment of comet 67P/Churyumov-Gerasimenko [1]. Waves on electron timescales were observed around the plasma frequency, using the passive mode of the mutual impedance probe (RPC-MIP) on board the Rosetta spacecraft as seen in Fig 1(a). These waves could be observed during the phase of the Rosetta mission when the comet was within a few months from its perihelion passage. The vast majority of the Langmuir waves were seen at heliocentric distances less than 2.6 AU [1].

67P/Churyumov-Gerasimenko - potential target for the Rosetta mission An influence of the non-gravitational effects on the motion of short-period comet 67P/Churyumov-Gerasimenko is investigated. It was found that the normal component of the non-gravitational force exceeds the transverse one and a model of the motion including A_1, A_2, A_3 better fits the observations than model neglecting A_3. Assuming asymmetry in g(r) with respect to the perihelion the large value of displacement \tau was derived (about 34 days), and very small negative value of transverse component A_2 was obtained. The models of rotating non-spherical nucleus also suggest the large shift of light curve with respect to perihelion (\tau greater than 30 days). The forced precession model of 67P with \tau = 34 days gives a prolate spheroidal shape of the rotating nucleus with axial ratio R_b/R_a = 1.16, rotational period to equatorial radius P_{rot}/R_a = 4.6\pm 1.4 hrs/km, and torque factor f_{tor}=3\cdot 10^5 day/AU. The much larger \tau = 54 days gives distinctly prolate shape of nucleus with axial ratio R_b/R_a = 1.71. The orientation of spin axis of the nucleus and its evolution are presented.

A Spitzer Study of Comets 2P/Encke, 67P/Churyumov-Gerasimenko, and C/2001 HT50 (LINEAR-NEAT) We present infrared images and spectra of comets 2P/Encke, 67P/Churyumov-Gerasimenko, and C/2001 HT50 (LINEAR-NEAT) as part of a larger program to observe comets inside of 5 AU from the sun with the Spitzer Space Telescope. The nucleus of comet 2P/Encke was observed at two vastly different phase angles (20 degrees and 63 degrees). Model fits to the spectral energy distributions of the nucleus suggest comet Encke's infrared beaming parameter derived from the near-Earth asteroid thermal model may have a phase angle dependence. The observed emission from comet Encke's dust coma is best-modeled using predominately amorphous carbon grains with a grain size distribution that peaks near 0.4 microns, and the silicate contribution by mass to the sub-micron dust coma is constrained to 31%. Comet 67P/Churyumov-Gerasimenko was observed with distinct coma emission in excess of a model nucleus at a heliocentric distance of 5.0 AU. The coma detection suggests that sublimation processes are still active or grains from recent activity remain near the nucleus.

Cometary outgassing produces a back-reaction force on a nucleus that can alter its trajectory and rotation state. Understanding this activity is key to exploring the physics of the upper layers of cometary surfaces, with implications for their formation and subsequent evolutionary history, and can be constrained by observing the orbit and rotation changes. For comet 67P/Churyumov-Gerasimenko, detailed measurements have been made by the Rosetta spacecraft and various attempts have been made to model the activity (see, e.g. [1,2]).Here we will present updated work using the activity model of [2] to fit to Rosetta outgassing, trajectory, and rotation data. We test a number of different activity distributions over the surface of the comet by varying the Effective Active Fraction (EAF), relative to pure water ice, of facets on a shape model. The previous work has shown that, in order to fit the fast ramp-up and fall-off in outgassing either side of perihelion, 67P&amp;#8217;s EAF must vary with time. We therefore investigate a number of different EAF curves to see if different parametric models can be ruled out. The objective here is to constraint the shape of the activity curve that a more advanced thermo-physical model (see, for example [3,4]) must produce in order to fit the data. We also investigate different spatial patterns in EAF, and attempt to correlate them to physical features on the cometary surface. Here we are able, for the first time, to achieve a good fit to the Rosetta data by parameterizing EAF in terms of the different geological unit types on 67P (Fig. 1). This may have important implications for understanding how activity works on the different types of surface observed on cometary nuclei, including &amp;#8216;rough&amp;#8217;, &amp;#8216;smooth&amp;#8217;, &amp;#8216;dusty&amp;#8217; and &amp;#8216;rocky&amp;#8217; surface morphologies. Finally, in addition to the changes in rotation period examined in [2], we also compute changes in the rotation axis in order to compare with the observations.References