67P/Churyumov–Gerasimenko.space

Jupiter-family comet · Between Mars and Jupiter · perihelion near 1.24 AU

67P/Churyumov–Gerasimenko

Comet 67P · Jupiter-family comet · found on a 1969 photographic plate

A two-lobed comet that loses roughly a metre of its surface every trip around the Sun — and whose orbit Jupiter rewrote in 1959.

Key factsComet & night-sky camera picker
67P/Churyumov–Gerasimenko at a glance
Object typeJupiter-family comet; a contact binary with two lobes[2]
FoundOct. 22, 1969, on a plate exposed Sept. 11, 1969 at Alma-Ata[3]
Mean diameter≈ 3.4 km[1]
Lobes≈ 4.1 × 3.3 × 1.8 km and ≈ 2.6 × 2.3 × 1.8 km[2]
Bulk density≈ 0.53 g/cm³ — about half that of water[1]
Rotation period12.76 h before 2009; ≈ 12.4 h after[2]
Distance from Sun1.24–5.68 AU[1]
Orbital period≈ 6.4 years (2,350 days)[1]
Inclination≈ 7.0°[1]
Recent periheliaAug. 13, 2015 and Nov. 2, 2021[2]
Surface lost per orbit≈ 1 ± 0.5 m on average (2015 estimate)[2]

Found on someone else’s photograph

On September 11, 1969, Svetlana Gerasimenko photographed comet 32P/Comas Solà from the Alma-Ata Astrophysical Institute in Kazakhstan. Back in Kyiv, Klim Churyumov examined the plate and noticed a comet near its edge — but assumed it was Comas Solà.[3]

On October 22 he realised the object sat 2–3 degrees from where Comas Solà should be. A fainter image of the real Comas Solà was found in the right place, so the other smudge was a new comet.[3] It now carries both discoverers’ names.

Two comets stuck together

67P is a contact binary: a large lobe about 4.1 × 3.3 × 1.8 km joined by a narrow neck to a smaller one about 2.6 × 2.3 × 1.8 km.[2] Layered terraces exposed on the two lobes point in different directions, which is why scientists think two separate bodies met in a gentle, low-speed collision and fused.[2]

The whole nucleus is remarkably light. JPL lists a bulk density of about 0.53 g/cm³ — it would float in water if you could find a big enough bath.[1]

A map written in Egyptian gods

Mapping teams divided the surface into 26 regions, each named after an Egyptian deity: gods on the big lobe, goddesses on the small one. Nineteen were defined in the north; seven more were added once the southern hemisphere came into sunlight.[2]

The largest boulder, up to 45 m across, is called Cheops after the Giza pyramid it resembles.[2]

An orbit Jupiter keeps editing

Like other Jupiter-family comets, 67P probably came from the Kuiper belt and was nudged inward by encounters with the giant planet.[2] On February 4, 1959 it passed 0.0515 AU from Jupiter, which dragged its closest point to the Sun from about 2.7 AU to about 1.28 AU.[2] Today JPL gives a perihelion of 1.24 AU and an aphelion of 5.68 AU — just beyond Jupiter’s orbit — and a period of about 6.4 years.[1]

The next big edit is scheduled: in November 2220 the comet should pass about 0.14 AU from Jupiter, pulling perihelion in to roughly 0.8 AU.[2]

Sun Earth (1 AU)Jupiter (5.2 AU) aphelion ≈ 5.68 AU perihelion ≈ 1.24 AU
Top-down orbit of 67P/Churyumov–Gerasimenko to scale, computed from JPL orbital elements (a ≈ 3.46 AU, e ≈ 0.641).[1] Earth and Jupiter orbits shown for comparison.[7]

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Shrinking a little every lap

Each pass near the Sun warms the ices, and gas and dust stream away. A 2015 estimate puts the average loss at about 1 ± 0.5 m of surface per orbit.[2] Close to perihelion, observers saw circular patterns in smooth terrain grow by metres a day, a fracture in the neck widen, and boulders tens of metres wide shift more than 100 m.[2]

Outgassing even changes the spin: 67P’s rotation shortened from 12.76 hours to about 12.4 hours during its 2009 perihelion, likely from jet torques.[2]

Catching a comet on camera

In 2021, 67P made its closest approach to Earth since 1982 — about 61 million km on November 12 — and brightened to around magnitude 9, within reach of amateur telescopes.[2] That is typical of periodic comets: faint, fuzzy and slowly moving against the stars, so a camera stacking many exposures often shows more than the eye. Our astrophotography picker suggests starter setups for comets, the Moon and deep-sky targets.

Read more

How Jupiter rewrote comet 67P’s orbit

A 1959 close pass moved 67P’s perihelion from 2.7 AU to 1.28 AU — and another encounter is due in 2220.

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The Egyptian map of comet 67P

Twenty-six regions named for gods and goddesses, a 45-metre “pyramid” boulder and a surface that changed while we watched.

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Watching comet 67P come back

What the 2015 and 2021 returns looked like from Earth, and what to expect when periodic comets come round again.

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Sources

  1. Small-Body Database Lookup: 67P/Churyumov-Gerasimenko — NASA JPL Solar System Dynamics
  2. 67P/Churyumov–Gerasimenko — Wikipedia
  3. Svetlana Gerasimenko — Wikipedia
  4. Comet (Jupiter-family comets) — Wikipedia
  5. Comet nucleus — Wikipedia
  6. Contact binary (small Solar System body) — Wikipedia
  7. Planetary Fact Sheet (orbit comparison) — NASA NSSDCA

Figures are rounded; where sources differ we note it. Spotted an error? Tell us.