13 August 2015
Perihelion Distance (q)
Aphelion Distance (Q)
Click for NASA orbit diagram
Hills Observatory: 1 January 2013 to 5 January 2019
The comet was discovered in 1969 by Klim Ivanovych Churyumov of the Kiev University's
Astronomical Observatory, 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 (now Almaty), 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.
After returning to his home institute in Kiev, Churyumov examined all the photographic plates
more closely. On 22 October, about a month after the photograph was taken, he discovered that
the object could not be Comas Solà, because it was about 1.8 degrees off the expected position.
Further scrutiny produced a faint image of Comas Solà at its expected position on the plate, thus
proving that the other object was a different comet.
In February 1959, a close encounter with Jupiter moved Churyumov-Gerasimenko's perihelion
inward to about 1.3 AU (190,000,000 km), where it remains today. Before that, its perihelion
distance was approximately 2.7 AU (400,000,000 km).
Before Churyumov-Gerasimenko's perihelion passage in 2009, its rotational period was 12.76
hours. During this perihelion passage, it decreased to 12.4 hours, which likely happened due to
Churyumov-Gerasimenko was the destination of the Rosetta mission, launched in 2004, which
rendezvoused with it in 2014 and was the first mission to land a space probe on a comet.
Descent of a small lander occurred on 12 November 2014. Philae is a 100 kg (220 lb) robotic
probe that set down on the surface with landing gear. The landing site has been christened
Agilkia in honour of Agilkia Island, where the temples of Philae Island were relocated after the
construction of the Aswan Dam flooded the island. The acceleration due to gravity on the surface
of Churyumov-Gerasimenko has been estimated for simulation purposes at 10−3 m/s2, or about
one ten-thousandth of that on Earth.
Due to its low relative mass, landing on the comet involved certain technical considerations to
keep Philae anchored. The probe contains 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. During the event, the
thruster and the harpoons failed to operate, and the ice screws did not gain a grip. The lander
bounced twice and only came to rest when it made contact with the surface for the third time,
two hours after first contact.
Contact with Philae was lost on 15 November 2014 due to dropping battery power. The European
Space Operations Centre reestablished communications on 14 June 2015.
The composition of water vapor from Churyumov-Gerasimenko, as determined by the Rosetta
spacecraft, is substantially different from that found on Earth. The ratio of deuterium to hydrogen
in the water from the comet was determined to be three times that found for terrestrial water.
This makes it unlikely that water found on Earth came from comets such as Churyumov-
Gerasimenko. 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. On 23 January 2015,
the journal Science published a special issue of scientific studies related to the comet.
Measurements carried out before Philae's batteries failed indicate that the dust layer could be as
much as 20 cm (7.9 in) thick. Beneath that is hard ice, or a mixture of ice and dust. Porosity
appears to increase toward the center of the comet.
The nucleus of Churyumov-Gerasimenko was found to have no magnetic field of its own after
measurements were taken during Philae's descent and landing by its ROMAP instrument and
Rosetta's RPC-MAG instrument. This suggests that magnetism may not have played a role in the
early formation of the Solar System, as had previously been hypothesized.
The ALICE spectrograph on Rosetta determined that electrons (within 1 km (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. Also, active pits, related to
sinkhole collapses and possibly associated with outbursts are present on the comet.
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. 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. Rosetta program scientists dismissed the claim as "pure speculation". Carbon-
rich compounds are common in the Solar System. Neither Rosetta nor Philae is equipped to
search for direct evidence of organisms.
One of the most outstanding discoveries of the mission so far is the detection of large amounts
of free molecular oxygen (O2) gas surrounding the comet. Current solar system models suggest
the molecular oxygen should have disappeared by the time 67P was created, about 4.6 billion
years ago in a violent and hot process that would have caused the oxygen to react with hydrogen
and form water. Molecular oxygen has never before been detected in cometary comas. 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. Detection of molecular nitrogen (N2) in the comet
suggests that its cometary grains formed in low-temperature conditions below 30 K (−243.2 °C).
The two-lobe shape of the comet is the result of a gentle, low-velocity collision of two objects.
The "terraces", layers of the interior of the comet that have been exposed by the partial stripping
of outer layers during its existence, are oriented in different directions in the two lobes, indicating
that two objects fused to form Churyumov-Gerasimenko.
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