[13] It was first observed on photographic plates in 1969 by Soviet astronomers Klim Ivanovych Churyumov and Svetlana Ivanovna Gerasimenko, after whom it is named.

[24][25] Churyumov–Gerasimenko was discovered in 1969 by Klim Ivanovich Churyumov of Kyiv University's Astronomical Observatory,[26] who examined a photograph that had been exposed for comet Comas Solà by Svetlana Ivanovna Gerasimenko on 11 September 1969 at the Alma-Ata Astrophysical Institute, near Alma-Ata, the then-capital city of Kazakh Soviet Socialist Republic, Soviet Union.

Churyumov found a cometary object near the edge of the plate, but assumed that this was comet Comas Solà.

Further scrutiny produced a faint image of Comas Solà at its expected position on the plate, thus proving the other object to be a different body.

[6] The two-lobe shape of the comet is the result of a gentle, low-velocity collision of two objects, and is called a contact binary.

[36][37][38] These changes included evolving patterns of circular shapes in smooth terrains that at some point grew in size by a few metres per day.

One notable example in December 2015 was captured by Rosetta's NAVCAM as a bright patch of light shining from the comet.

Rosetta scientists determined that a large cliff had collapsed, making it the first landslide on a comet known to be associated with an outburst of activity.

These interactions will continue until the comet is eventually thrown out of the Solar System or collides with the Sun or a planet.

Because of its low relative mass, landing on the comet relied on tools to anchor Philae to the surface.

The probe had an array of mechanisms designed to manage Churyumov–Gerasimenko's low gravity, including a cold gas thruster, harpoons, landing-leg-mounted ice screws, and a flywheel to keep it oriented during its descent.

While the discovery solves the question of the lander's disposition, it also allows project scientists to properly contextualise the data it returned from the comet's surface.

[74] On 22 January 2015, NASA reported that, between June and August 2014, the comet released increasing amounts of water vapor, up to tenfold as much.

[75] On 23 January 2015, the journal Science published a special issue of scientific studies related to the comet.

[78][79] The ALICE spectrograph on Rosetta determined that electrons (within 1 km or 0.6 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.

[82][83] Measurements by the COSAC and Ptolemy instruments on the Philae's lander revealed sixteen organic compounds, four of which were seen for the first time on a comet, including acetamide, acetone, methyl isocyanate and propionaldehyde.

[84][85][86] Astrobiologists Chandra Wickramasinghe and Max Wallis stated that some of the physical features detected on the comet's surface by Rosetta and Philae, such as its organic-rich crust, could be explained by the presence of extraterrestrial microorganisms.

[91] One of the most outstanding discoveries of the mission was the detection of large amounts of free molecular oxygen (O2) gas surrounding the comet.

In situ measurements indicate that the O2/H2O ratio is isotropic in the coma and does not change systematically with heliocentric distance, suggesting that primordial O2 was incorporated into the nucleus during the comet's formation.

[92] This interpretation was challenged by the discovery that O2 may be produced on the surface of the comet in water molecule collisions with silicates and other oxygen-containing materials.

[94] Detection of molecular nitrogen (N2) in the comet suggests that its cometary grains formed in low-temperature conditions below 30 K (−243 °C; −406 °F).

[95] On 3 July 2018, researchers hypothesized that molecular oxygen might not be made on the surface of comet 67P in sufficient quantity, thus deepening the mystery of its origin.