1P/Halley
1P/Halley is the most famous comet — the first whose return was predicted (by Edmond Halley). On its 76-year orbit it last reached perihelion in 1986 and will next return around 2061.
Key facts
Science
Physical
- Nucleus
- ≈ 15 × 8 km
- Composition
- Water ice with dust, CO, CO₂ and organics — a classic 'dirty snowball'
Orbital
- Semi-major axis
- 17.9 AU
- Eccentricity
- 0.9679
- Inclination
- 162.19 °
- Orbital period
- 75.92 years
- Perihelion
- 0.575 AU
- Aphelion
- 35.3 AU
- Mean orbital velocity
- 7.03 km/s
Activity
- Status
- Currently inactive (q = 0.575 AU, next perihelion ≈ 2061)
- Becomes active within
- 5 AU of the Sun
Radiation & temperature
- Insolation
- 0.00311 S⊕ · 1/321 of the sunlight Earth receives
- Geometric albedo
- 0.04
- Equilibrium temperature
- 65 K (-208 °C)
Discovery & history
- First known
- Known since antiquity
- By
- Periodicity recognised by Edmond Halley (1705)
- Name
- Named after Edmond Halley, who first showed it returns on a regular schedule.
Halley's Comet has been recorded for over two thousand years — Chinese astronomers noted it as early as 240 BCE, and it appears on the Bayeux Tapestry from 1066. In 1705 Edmond Halley realised that comets seen in 1531, 1607 and 1682 were the same object on a ~76-year orbit, and he correctly predicted its return in 1758, after his death. When it returned in 1986, an armada of spacecraft flew to meet it — ESA's Giotto passed just 596 km from the nucleus and took the first close-up pictures of a comet's heart. It will next return around 2061.
- 1986GiottoFlyby
Flew through Halley's coma and returned the first close-up images of a comet's nucleus.
Images
Images from open archives · credit shown per image