67P/Churyumov–Gerasimenko

67P/Churyumov–Gerasimenko (abbreviated 67P or 67P/C–G and nicknamed "Chury") is a Jupiter-family comet. It originally came from the Kuiper belt and has an orbital period of 6.45 years. The comet spins around once every 12.4 hours and can move as fast as 135,000 kilometres per hour. Churyumov–Gerasimenko is about 4.3 by 4.1 kilometres at its longest and widest points.

It was first seen on photographic plates in 1969 by Soviet astronomers Klim Ivanovych Churyumov and Svetlana Ivanovna Gerasimenko, after whom it is named. The comet came closest to the Sun, or perihelion, on 2 November 2021, and will do so again on 9 April 2028.

Churyumov–Gerasimenko was the target of the European Space Agency's Rosetta mission, which launched on 2 March 2004. Rosetta met the comet on 6 August 2014 and began orbiting it on 10 September 2014. Its lander, Philae, landed on the comet's surface on 12 November 2014, making it the first spacecraft to land on a comet nucleus. The Rosetta spacecraft ended its mission by landing on the comet in its Maʽat region on 30 September 2016.

Discovery

The comet Churyumov–Gerasimenko was found in 1969 by Klim Ivanovich Churyumov at Kyiv University's Astronomical Observatory. He looked at a photo that had been taken for another comet, Comas Solà, by Svetlana Ivanovna Gerasimenko at the Alma-Ata Astrophysical Institute. At first, he thought it was the same comet, but later he saw it was in a different place. This showed it was a new comet.

Shape

The comet is made of two parts, called lobes, joined by a narrow neck. The bigger lobe is about 4.1 km by 3.3 km by 1.8 km, and the smaller lobe is about 2.6 km by 2.3 km by 1.8 km. Over time, the comet loses material as gas and dust are pushed away by the Sun.

The shape of the comet came from a gentle collision between two objects. Scientists have made detailed models of the comet using many images, which help us learn more about its surface and inside. These models show special places on the comet that could be important for future space missions.

Surface

There are 26 different areas on Churyumov–Gerasimenko, each named after an Egyptian deity. The areas on the larger part are named after gods, and the ones on the smaller part are named after goddesses. Nineteen areas were found in the northern part before equinox. Later, when the southern part could be seen better, seven more areas were found using the same naming rule.

Gates

Some special features on the surface look like doors and are called gates. These were named to honor people who worked on the Rosetta mission.

Surface changes

While Rosetta was studying the comet, many changes were seen on its surface, especially when the comet was close to perihelion. These changes included patterns that grew bigger each day, cracks that got longer, and big rocks moving over long distances. Some cliffs also fell down. In December 2015, Rosetta saw a bright flash from the comet, which scientists believe was caused by a large cliff falling. The comet showed a burst of activity on 14 November 2021. Researchers noted that during this time, the comet was 1.23 astronomical units from the Sun and 0.42 astronomical units from the Earth. The comet's most recent close approach to the Sun happened on 2 November 2021.

Cheops boulder

Cheops is the biggest rock on the comet’s surface, measuring up to 45 meters. It is found on the larger part of the comet and was named after the pyramid in Giza because it looks similar to a pyramid.

Orbit and rotation

Like other comets close to Jupiter, Churyumov–Gerasimenko probably started in the Kuiper belt and was pushed toward the inner part of the Solar System. Meetings with Jupiter changed its path over time. These meetings will keep happening until the comet leaves the Solar System or hits the Sun or a planet.

On February 4, 1959, a close meeting with Jupiter moved Churyumov–Gerasimenko's closest point to the Sun closer to us, and it has stayed that way since. In November 2220, the comet will pass close to Jupiter again, changing its path a little more.

Before 2009, Churyumov–Gerasimenko spun once every 12.76 hours. During 2009, its spin slowed to about 12.4 hours. This likely happened because of changes caused by heat from the Sun.

2015 perihelion

As of September 2014, Churyumov–Gerasimenko was not very bright. It reached its closest point to the Sun on August 13, 2015. From December 2014 to September 2015, it was hard to see because it was too close to the Sun. On February 10, 2015, it passed close to the Sun and was 3.3 AU (about 490 million km) from Earth. It crossed the celestial equator in May 2015 and became easier to see from the Northern Hemisphere. Even after its closest pass to the Sun, it was still not very bright and needed a telescope to see. By July 2016, it had dimmed again.

2021 perihelion

In 2021, the comet came closer to Earth than it had since 1982. It reached its closest point to the Sun on November 2, 2021, and came closest to Earth on November 12, 2021. It was bright enough to see with amateur telescopes. There were two sudden brightening events around this time, one on October 29, 2021, and another on November 17, 2021. The second brightening was stronger than the first.

Exploration

Rosetta mission

Main articles: Rosetta (spacecraft) and Philae (spacecraft)

See also: Timeline of Rosetta spacecraft

The Rosetta mission was the first to orbit a comet for several years and send a lander to collect data from its surface. It launched in 2004, reached comet 67P in 2014, and ended with a landing on the comet in 2016.

Advance work

As preparation, pictures from the Hubble Space Telescope taken in 2003 were studied to create a 3D model of the comet. In 2012, detailed observations were made with a telescope in Faulkes.

On June 6, 2014, water vapor was detected coming from the comet. Images taken later that year showed the comet had two distinct parts. Scientists decided this shape was due to the comet being made of two parts that joined together.

Rendezvous and orbit

In May 2014, Rosetta began slowing down to meet the comet. It finally reached 67P on August 6, 2014, and entered orbit on September 10, 2014.

Landing

On November 12, 2014, a small robotic lander named Philae landed on the comet’s surface. The landing site was named Agilkia. Because of the comet’s low gravity, special tools were used to keep Philae in place. However, some tools failed, and the lander bounced twice before settling down.

Contact with Philae was lost soon after landing due to low battery power. Communications were briefly restored in June 2015 but were lost again. In September 2016, Rosetta located Philae in images, showing it resting in a dark crack.

Locating Philae

Finding Philae’s exact location was difficult. Measurements helped narrow down its location. By April 2015, an image showed a possible location that matched the lander’s path and conditions. In September 2016, high-resolution images confirmed Philae was in a dark crevice.

Physical properties

The water vapor from the comet was different from Earth’s water. It contained more deuterium than hydrogen. The vapor also mixed with formaldehyde and methanol. Before Philae’s batteries died, it measured a dust layer up to 20 cm thick, with hard ice or a mix of ice and dust below.

The comet had no magnetic field, suggesting magnetism may not have been important in the early Solar System’s formation. Scientists found sixteen organic compounds on the comet, four of which were seen on a comet for the first time. Large amounts of free molecular oxygen gas were also detected around the comet, which puzzled scientists about its origin.

Future missions

CAESAR was a proposed mission to return samples from 67P to Earth. It was a finalist for NASA’s New Frontiers program but was not chosen in 2019.