What Rosetta found at Comet 67P
A duck-shaped contact binary, oxygen, glycine and a twist in the story of Earth's water.
Published 2026-10-23
Rosetta spent more than two years alongside Comet 67P, watching it warm up, erupt and change.[5] Here are some of the highlights.
A contact binary
The first close images in July 2014 revealed two distinct lobes.[4] Layered “terraces” point in different directions in each lobe, indicating that two objects merged in a gentle, low-speed collision.[4] The comet's 26 regions are named after Egyptian deities.[4]
Fluffy and dusty
67P has a density of only about 0.53 g/cm³ — about half that of water — so its nucleus is thought to be very porous.[3][1] When heated by the Sun, it is thought to emit about twice as much dust as gas.[1]
Firsts in comet chemistry
NASA lists among Rosetta's key findings:[1]
- The first detection of molecular nitrogen and molecular oxygen at a comet.
- Exposed water ice on the comet's surface.
- The amino acid glycine, commonly found in proteins.
- Phosphorus, a component of DNA and cell membranes.
On the surface, Philae added sixteen organic compounds, four never seen on a comet before.[6]
A twist in the story of Earth's water
Early Rosetta results suggested that the water in 67P had a ratio of deuterium to hydrogen about three times that of Earth's water — evidence against comets like 67P supplying Earth's oceans.[5][1] But a re-analysis published in 2024 identified a significant measurement error; once corrected, 67P's water turned out to be similar to Earth's, so it remains plausible that some of Earth's water came from comets like it.[5]
A changing world
Rosetta saw many surface changes, especially near perihelion.[4] The comet's spin even changed: its rotation period dropped from 12.76 hours before 2009 to about 12.4 hours, likely because of jets of escaping gas.[4]
Numbered citations link to the sources list on the Comet 67P/Churyumov–Gerasimenko overview page.