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
- From catalogued orbital elements (MPC)
- Eccentricity
- 0.968
- From catalogued orbital elements (MPC)
- Inclination
- 162.19 °
- From catalogued orbital elements (MPC)
- Orbital period
- 75.48 years
- From catalogued orbital elements (MPC)
- Perihelion
- 0.571 AU
- Computed from the orbital elements
- Aphelion
- 35.1 AU
- Computed from the orbital elements
- Mean orbital velocity
- 7.05 km/s
- Computed from the orbital elements
Activity
- Status
- Currently inactive (q = 0.571 AU, next perihelion ≈ 2061)
- Becomes active within
- 5 AU of the Sun
Radiation & temperature
- Insolation
- 0.00314 S⊕ · 1/319 of the sunlight Earth receives
- Computed from the distance to the Sun (inverse-square; Earth's sunlight = 1), before any atmosphere.
- Geometric albedo
- 0.04
- Nucleus geometric albedo ≈ 0.04 — one of the darkest objects known (Giotto, 1986).
- Equilibrium temperature
- 65 K (-208 °C)
- Computed from albedo + distance from the Sun (airless black body); uses the geometric albedo as an estimate
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.
The first spacecraft to image Halley's nucleus; its position measurements helped steer Giotto closer.
Imaged the comet's hydrogen cloud in ultraviolet and passed 151,000 km from the nucleus (152,400 km in NASA's history).
Three days after Vega 1; together they showed the nucleus to be dark and about 14 km long.
Japan's first interplanetary probe passed 6.99 million km from the comet, on its sunward side.
- 1986GiottoFlyby
Flew through Halley's coma and returned the first close-up images of a comet's nucleus.
Measured the solar wind 40.2 million km sunward of the comet, before it reached Halley.
Images
Images from open archives · credit shown per image