67P/Churyumov–Gerasimenko (67P/C–G) is a pillar of studies on comets, thanks largely to its in-depth analysis by the European Space Agency’s (ESA) Rosetta mission. The Jupiter family comet provided astronomers with key details that shed more light on the processes and conditions of the formation of the early solar system.

The Astronomers Who Found It and Named It

Soviet astronomers Klim Ivanovich Churyumov and Svetlana Ivanovna Gerasimenko, in September of 1969, found 67P/C–G.

Klim Ivanovich Churyumov was sorting photographs of Comet 32P/Comas Solá taken at Alma-Ata Astrophysical Institute in Kazakhstan when he noticed a distinct different cometary object. After scrutiny, it was confirmed that it was a new comet; hence, it was named after the two discoverers.

The Motion and Orbit of Comet 67P

67P/C–G orbits in around 6.45 years, making it a Jupiter-family comet. The orbit is heavily controlled by Jupiter’s gravitative forces, which in the past altered its orbit and perihelion distance. The key orbital features:

Orbit of Comet 67P
  • Aphelion (distance of the object to the Sun): 5.704 AU
  • Perihelion (distance of the object to the Sun): 1.210 AU
  • Semi-major axis: 3.457 AU
  • Eccentricity: 0.64989
  • Orbital period: 6.45 years
  • Inclination: 3.87°

Notably, a close Jupiter approach in 1959 reduced its perihelion to 1.28 AU from a previously observed perihelion of 2.7 AU, highly increasing its activity in close proximity to the Sun. The next perihelion approach is estimated to occur on April 9, 2028.

The Unique Shape and Composition of Comet

67P/C–G’s nucleus is unique in that it has a distinct bilobed or “rubber duck” structure, indicating a contact binary origin. This is a low-velocity collision of two different bodies that merged after colliding. What are the dimensions and the structure:

Composition of Comet
  • Large lobe: Approximately 4.1 km × 3.3 km × 1.8 km
  • Small lobe: Approximately 2.6 km × 2.3 km × 1.8 km
  • Total volume: 18.7 km³
  • Density: 0.533 g/cm³
  • Porosity: High, indicating loosely packed interior structure
  • Rotational Characteristics:
  • Period of rotation: Approximately 12.4 hours
  • Axial tilt: 52°
  • Surface Temperature Range: 180 K to 230 K (-93°C to -43°C)

The surface is characterized by a dark, carbon-rich crust punctuated by bright spots indicating exposed areas of water ice. Variegated terrain, such as cliffs, pits, and smooth plains, was exposed in high-resolution imagery, indicating complex geologic processes.

The Rosetta Mission

The ESA’s Rosetta spacecraft was launched in March of 2004 to start a ten-year odyssey to rendezvous with 67P/C–G. In August 2014, Rosetta orbited a comet, providing a unique opportunity to get a close-up view of its nucleus and coma in detail. The mission was accomplished in a controlled landing on the comet’s surface on September 30, 2016. The key milestones:

  • Deployment of Philae Lander – In November of 2014, Rosetta deployed the Philae lander, making it the first landing on a comet’s surface in history. In spite of landing issues, Philae transmitted useful data before it went into hibernation.
  • Comprehensive Analysis – The instrument suite in Rosetta performed detailed analyses, indicating a complex mixture of water, ice, organic molecules, and dust.
  • Monitoring of Activity – The spacecraft monitored dynamic phenomena when the comet was heading towards perihelion, such as gas and dust emission variations, surface phenomena, and jet formation.

The findings of the mission have been instrumental in informing our knowledge of cometary structure and behaviour.

Breakthroughs and Discoveries

  • Organic Molecules – The Rosetta mission uncovered a spectrum of organic molecules, including amino acid glycine, that are crucial to life.
  • Water Vapor – The comet emits high amounts of water vapour. However, its deuterium to hydrogen ratio is distinct from that of our planet, suggesting that such comets would be unlikely to be responsible for supplying our planet’s water.
  • Geomorphology – The presence of evidence of varied phenomena on the surface, such as cliffs, pits, and boulders, shows active geologic processes.

These findings cast new light on precursors to life’s origin and processes that regulated the early solar system.

The Role of Comets in Earth’s Water Supply

One of the Rosetta mission’s key scientific objectives was to figure out whether Jupiter-family comets such as 67P are responsible for refilling our world’s oceans. The research indicated that the water vapour from 67P had a three times higher deuterium-to-hydrogen (D/H) ratio compared to the Earth’s water and, therefore, that Jupiter-family comets are perhaps not accountable for supplying most of the water in our world.

This is in opposition to existing theory and posits asteroids or objects of the Kuiper Belt as more probable water bearers.

Evidence of Active Geological Activity

  • Surface Shaping – Rosetta found evidence of surface processes, such as landslides and fracture formation.
  • Dust Jets and Gas Emissions – The mission observed active gas and dust jets erupting from the nucleus, resulting from the sublimation of volatile material.
  • Collapse of Cliffs – The cliffs on the surface of the comet were found to crack and collapse, indicating ongoing geological action.

A Mission That Made History

The Rosetta mission was one of the most ambitious and successful of all time in terms of space missions. The first to orbit a comet and land on one, it set a new path forward for studying comets.

Achievements in Technological Terms

  • First to Orbit a Comet – One of the key achievements in terms of navigating in space.
  • First Controlled Landing on a Comet’s Surface – The Rosetta spacecraft accomplished a controlled impact on the comet in September of 2016.
  • First Detection of Molecular Oxygen in a Comet’s Vicinity – Discovery that throws existing models of cometary formation into question.

Scientific Breakthroughs

  • Cometary Atmosphere Composition – Discovery of carbon dioxide, carbon monoxide, and molecular oxygen in the comet’s coma.
  • Unprecedented High-Resolution Imaging – Close-up topographic maps of the comet’s rough terrain, providing geologists with a better picture of cometary geology.
  • Detection of Noble Gases – Discovery of argon and xenon, evidence of our solar system’s formation conditions.

Conclusion

Comet 67P/Churyumov–Gerasimenko is the best-studied comet in history following the Rosetta mission. Data gathered have brought scientists novel, unprecedented insights into the composition, structure, and origin of comets, with vital evidence on our solar system’s formation early on and life on Earth’s origins.

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