67P/Churyumov–Gerasimenko in the context of Photographic plate

The nucleus is the solid, central part of a comet, formerly termed a dirty snowball or an icy dirtball. A cometary nucleus is composed of rock, dust, and frozen gases. When heated by the Sun, the gases sublime and produce an atmosphere surrounding the nucleus known as the coma. The force exerted on the coma by the Sun's radiation pressure and solar wind cause an enormous tail to form, which points away from the Sun. A typical comet nucleus has an albedo of 0.04. This is blacker than coal, and may be caused by a covering of dust.

Results from the Rosetta and Philae spacecraft show that the nucleus of 67P/Churyumov–Gerasimenko has no magnetic field, which suggests that magnetism may not have played a role in the early formation of planetesimals. Further, the ALICE spectrograph on Rosetta determined that electrons (within 1 km (0.62 mi) above the comet nucleus) produced from photoionization of water molecules by solar radiation, and not photons from the Sun as thought earlier, are responsible for the degradation of water and carbon dioxide molecules released from the comet nucleus into its coma.

Rosetta was a space probe built by the European Space Agency that launched on 2 March 2004. Along with Philae, its lander module, Rosetta performed a detailed study of comet 67P/Churyumov–Gerasimenko (67P). During its journey to the comet, the spacecraft performed flybys of Earth, Mars, and the asteroids 21 Lutetia and 2867 Šteins. It was launched as the third cornerstone mission of the ESA's Horizon 2000 programme, after SOHO / Cluster and XMM-Newton. The total cost of the mission was about €1.3 billion (US$1.8 billion).

On 6 August 2014, the spacecraft reached the comet and performed a series of manoeuvers to eventually orbit the comet at distances of 30 to 10 kilometres (19 to 6 mi). On 12 November, its lander module Philae performed the first successful landing on a comet, though its battery power ran out two days later. Communications with Philae were briefly restored in June and July 2015, but due to diminishing solar power, Rosetta's communications module with the lander was turned off on 27 July 2016. On 30 September 2016, the Rosetta spacecraft ended its mission by hard-landing on the comet in its Ma'at region.

Philae (/ˈfaɪliː/ or /ˈfiːleɪ/) was a robotic European Space Agency lander that accompanied the Rosetta spacecraft until it separated to land on comet 67P/Churyumov–Gerasimenko, ten years and eight months after departing Earth. On 12 November 2014, Philae touched down on the comet, but it bounced when its anchoring harpoons failed to deploy and a thruster designed to hold the probe to the surface did not fire. After bouncing off the surface twice, Philae achieved the first-ever "soft" (nondestructive) landing on a comet nucleus, although the lander's final, uncontrolled touchdown left it in a non-optimal location and orientation.

Despite the landing problems, the probe's instruments obtained the first images from a comet's surface. Several of the instruments on Philae made the first in-situ analysis of a comet nucleus, sending back data regarding the composition of the surface and outgassing from the subsurface. In October 2020, scientific journal Nature published an article revealing what Philae had discovered while it was operational on the surface of 67P/Churyumov–Gerasimenko.

Hibernation of spacecraft is an operating mode used when regular operations are suspended for an extended period of time but restarting is expected (unlike termination). On long duration and deep space missions it saves power or other limited resources and extends mission life. The term is substantially similar to the hibernation mode used in computer power saving.

• Rosetta, a mission to study comet 67P/Churyumov–Gerasimenko (67P), was placed into hibernation for 31 months to conserve its limited resources when it ventured near the orbit of Jupiter while en route to its rendezvous.
• The New Horizons mission entered hibernation mode many times on its way to Pluto and then again while en route to the Kuiper belt object 486958 Arrokoth. Its hibernation mode provides some amount of health and status monitoring and occasional wake-ups to check and calibrate instruments.
• NASA's Wide-field Infrared Survey Explorer mission, originally operated by the agency's astrophysics division for an infrared all-sky survey, was placed into hibernation in 2011 and then reawakened in 2013 to conduct an asteroid survey by the planetary science division.

Agilkia Island (also called Agilika; Arabic: أجيليكا, from Old Nubian: ⲁ̅ⲅⲗ̅, romanised: agil, "mouth") is an island in the reservoir of the Old Aswan Dam along the Nile River in southern Egypt; it is the present site of the relocated ancient Egyptian temple complex of Philae. Partially to completely flooded by the old dam's construction in 1902, the Philae complex was dismantled and relocated to Agilkia island, as part of a wider UNESCO project related to the 1960s construction of the Aswan High Dam and the eventual flooding of many sites posed by its large reservoir upstream. To allow Agilkia island to accommodate the relocated temple, the island was leveled to match the old contours of Philae island as best as possible, which required the removal of the top of the island.

Agilkia, like the island, was the name chosen for the planned landing site on a comet by the Rosetta spacecraft mission's Philae lander. Upon initial touchdown, however, the lander took a large bounce followed by a smaller one before finally coming to rest perhaps a kilometre away from Agilkia, at a site named Abydos, after the ancient Egyptian city.

Svetlana Ivanovna Gerasimenko (Russian: Светлана Ивановна Герасименко; Ukrainian: Світлана Іванівна Герасименко; 23 February 1945 – 8 April 2025) was a Soviet and Tajikistani astronomer and discoverer of comet 67P/Churyumov–Gerasimenko.