Comet 67P/Churyumov–Gerasimenko is classified as a Jupiter-family comet, meaning its orbit is primarily influenced by the massive gravitational pull of Jupiter. This icy body travels around the Sun approximately every 6.45 years, making it a regular visitor to the inner Solar System. The comet gained international scientific attention when it became the target of the European Space Agency’s Rosetta mission, which rendezvoused with it in 2014. Rosetta spent over two years studying the nucleus and surrounding environment, providing unprecedented data that allows for a precise understanding of the comet’s size, shape, and internal structure.
Precise Dimensions and Bi-Lobed Structure
The nucleus of Comet 67P is highly irregular, possessing a distinctive “bi-lobed” shape that has been frequently compared to a rubber ducky. Measurements taken by the Rosetta spacecraft reveal that the comet spans approximately 4.3 kilometers at its longest dimension. The entire nucleus is characterized by its overall size of about 4.3 by 4.1 kilometers.
This unusual structure is comprised of two distinct components, often referred to as the head and the body, or the A and B lobes. The larger lobe measures roughly 4.1 by 3.3 by 1.8 kilometers, while the smaller lobe is still substantial at about 2.6 by 2.3 by 1.8 kilometers. These two lobes are connected by a much narrower region, commonly termed the neck.
Scientists believe this shape is the result of a gentle, low-velocity merger between two separate objects early in the Solar System’s history, classifying it as a contact binary. The total volume of the nucleus has been precisely calculated to be approximately 18.56 cubic kilometers based on high-resolution imaging data.
Contextualizing the Comet’s Scale
The abstract kilometer measurements become more relatable when the comet is placed next to familiar landmarks on Earth. The maximum length of Comet 67P, at roughly 4.3 kilometers, is nearly identical to the north-to-south length of New York City’s Central Park, which measures approximately 4.0 kilometers. If the comet were placed over Manhattan, its “head” and “body” would almost perfectly stretch the entire length of the park.
A different perspective is gained by comparing the comet’s size to major infrastructure. For example, the longest runway at JFK International Airport is about 4.4 kilometers, meaning the longest dimension of the comet is about the same length as a major international airport runway. The comparison highlights that while comets are small celestial objects, their size is not insignificant in human terms.
Physical Characteristics and Density
Despite its considerable size, Comet 67P is surprisingly light, a fact directly related to its internal physical characteristics. The nucleus has a total mass of roughly \(9.982 \times 10^{12}\) kilograms, or about 10 billion tonnes. When this mass is distributed across its \(18.56 \text{ km}^3\) volume, the average bulk density is calculated to be very low, around 533 to 538 kilograms per cubic meter.
This low density suggests that the comet is not a solid, compacted body, but rather a highly porous “rubble pile.” Scientific analysis indicates the comet is composed of up to 70 to 80 percent empty space, meaning it is a loosely packed structure of ice and dust. The material making up the comet is a mixture of frozen water, carbon dioxide, and other volatile compounds, along with large amounts of dark, carbon-rich organic dust.