Halley's Comet

1P/Halley
The nucleus of Halley's Comet, imaged by the Giotto probe on 14 March 1986
Discovery
Discovered byPrehistoric (observation)
Edmond Halley (recognition of periodicity)
Discovery date1758 (first predicted perihelion)
Orbital characteristics[1]
Epoch 4 August 2061 (2474040.5)
Aphelion35.14 au[2]
(aphelion: 9 December 2023)[2][3]
Perihelion0.59278 au[4]
(last perihelion: 9 February 1986)
(next perihelion: 28 July 2061)[4]
17.737 au
Eccentricity0.96658
74.7 yr
75y 5m 19d (perihelion to perihelion)
0.07323°
Inclination161.96°
59.396°
28 July 2061[4][5]
≈27 March 2134[6][5]
Argument of perihelion
112.05°
Earth MOID0.075 au (11.2 million km)
(epoch 1968)[7]
TJupiter-0.598
Physical characteristics
Dimensions14.42 km × 7.4 km × 7.4 km (Giotto)[8]
15.3 km × 7.21 km × 7.21 km (Vega)[8]
Mean diameter
11 km[8]
Mass(2.2±0.9)×1014 kg[9]
Mean density
0.55±0.25 g/cm3[10]
0.2–1.5 g/cm3 (est.)[11]
~0.002 km/s
Synodic rotation period
2.2 d (52.8 h) (?)[12]
Albedo0.04[13]
2.1 (in 1986)[14]
28.2 (in 2003)[15]

Halley's Comet[a] is the only known short-period comet that is consistently visible to the naked eye from Earth,[16] appearing every 72–80 years,[17] though with the majority of recorded apparitions (25 of 30) occurring after 75–77 years. It last appeared in the inner parts of the Solar System in 1986 and will next appear in mid-2061. Officially designated 1P/Halley, it is also commonly called Comet Halley, or sometimes simply Halley.

Halley's periodic returns to the inner Solar System have been observed and recorded by astronomers around the world since at least 240 BC, but it was not until 1705 that the English astronomer Edmond Halley understood that these appearances were re-appearances of the same comet. As a result of this discovery, the comet is named after Halley.

In March 1986, during its latest visit to the inner Solar System, Halley's Comet became the first comet to be observed in detail by a spacecraft, ESA's Giotto mission, providing the first observational data on the structure of a comet nucleus and the mechanism of coma and tail formation. These observations supported several longstanding hypotheses about comet construction, particularly Fred Whipple's "dirty snowball" model, which correctly predicted that Halley would be composed of a mixture of volatile ices—such as water, carbon dioxide, ammonia—and dust. The missions also provided data that substantially reformed and reconfigured these ideas; for instance, it is now understood that the surface of Halley is largely composed of dusty, non-volatile materials, and that only a small portion of it is icy. It was also visited by the two spacecrafts of the Vega program, Vega 1 & 2, on March 6 and March 9, respectively. They went as close as 8,890 km (5,520 mi), and 8,030 km (4,990 mi), providing data on Halley's dimensions, shape, temperature, and surface properties.

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  2. ^ a b Cite error: The named reference Horizons2023 was invoked but never defined (see the help page).
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  4. ^ a b c Cite error: The named reference Horizons2061 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference Kinoshita was invoked but never defined (see the help page).
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  8. ^ a b c Cite error: The named reference Lamy2004 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference mass was invoked but never defined (see the help page).
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  11. ^ Cite error: The named reference Peale1989November was invoked but never defined (see the help page).
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  16. ^ Cite error: The named reference Delehanty was invoked but never defined (see the help page).
  17. ^ Cite error: The named reference Brady1987 was invoked but never defined (see the help page).


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