Comet Grigg–Skjellerup
The second comet Giotto visited, and the parent of the southern Pi Puppids.
Key facts
- Designation
- 26P/Grigg–Skjellerup
- Type
- Jupiter-family comet
- Orbital period
- about 5.2 years
- Closest to the Sun
- about 1.1 AU (about 165 million km) at present
- Farthest from the Sun
- about 5 AU, at Jupiter's distance
- Tilt of orbit
- about 22°
- Nucleus
- about 2.6 km across
- Discovered
- by John Grigg in New Zealand on 23 July 1902; found again by John Skjellerup in South Africa in 1922
- Returns
- at perihelion in 2023; next around 2028
Orbit
Grigg–Skjellerup goes round the Sun every five years or so. Over the past century close passes of Jupiter have pushed its nearest point to the Sun outward, from just inside Earth's orbit to just beyond. That shift matters for its meteor shower.
Size and nature
It is a small, weakly active comet with a nucleus about 2.6 km across. Its faintness made it a test of how close a spacecraft could fly to a quiet comet and still learn something.
History
John Grigg, a music teacher in Thames on New Zealand's North Island, found it in 1902. John Skjellerup, an Australian telegraphist working in South Africa, found it again in 1922, and the two sightings were shown to be the same comet.
Meteor showers
The Pi Puppids are a southern shower in late April, from a radiant in the constellation Puppis. They are normally almost absent, but in 1977 and 1982, years when the comet was near the Sun, observers in the southern hemisphere saw around 40 meteors an hour. Now that the comet's orbit has moved away from Earth's, strong displays are less likely.
Missions
After its encounter with Halley's Comet in 1986, the European spacecraft Giotto was put into hibernation and later steered back past Earth. On 10 July 1992 it flew within about 200 km of Grigg–Skjellerup, closer than it had passed Halley. Its camera had been damaged at Halley, but its other instruments measured the comet's gas and recorded a few impacts of its dust. It was the first time a spacecraft had visited two comets.
Its meteor showers
- The Pi Puppids peak around 23–24 April; about variable: usually low, with bursts near 40 when the comet is close to the Sun an hour at best; 18 km/s
Space missions
- Giotto Europe's first deep-space mission flew within 600 kilometres of Halley's Comet.
Key dates
| Date | What happened |
|---|---|
| 23 July 1902 | John Grigg discovered the comet now called Grigg–Skjellerup. |
| 10 July 1992 | Giotto passed about 200 km from Comet Grigg–Skjellerup. |
Did you know?
Giotto reached Grigg–Skjellerup six years after Halley, having travelled round the Sun several times.
The Pi Puppids are best seen from Australia, New Zealand and South Africa.
Grigg was an amateur astronomer who also composed songs.