International Cometary Explorer
The first spacecraft to meet a comet, flying through the tail of the parent of the Draconid meteors.
Key facts
- Agency
- NASA (United States), with the European Space Agency
- Type of mission
- Solar wind monitor, then comet flyby
- Target
- Comet 21P/Giacobini–Zinner
- Launched
- 12 August 1978
- Status
- Completed; contact lost 2014
This spacecraft began life as ISEE-3, one of three craft launched to study how the solar wind, the stream of charged particles from the Sun, interacts with Earth's magnetic field. It was the first spacecraft to be parked near the L1 point, about 1.5 million kilometres towards the Sun, a balance point where it could watch the solar wind before it reached Earth.
A change of plan
In 1982 and 1983 controllers used a series of close passes of the Moon to throw it onto a new path, and renamed it the International Cometary Explorer. On 11 September 1985 it flew through the tail of comet 21P/Giacobini–Zinner, about 7,800 kilometres from the nucleus. It was the first time a spacecraft had met a comet.
It carried no camera, but it measured the comet's tail directly: a stream of charged water molecules and other ions, draped in the Sun's magnetic field like a flag in the wind. That confirmed ideas about comet tails worked out from Earth. In 1986 it also measured the solar wind upstream of Halley's Comet, from tens of millions of kilometres away.
Why it matters to meteors
Comet Giacobini–Zinner is the parent of the October Draconids, a shower that is usually weak but has produced spectacular storms, as in 1933 and 1946, when Earth crossed fresh trails of its dust.
A late echo
In 2014 a team of volunteers made contact with the old spacecraft as it passed near Earth again, but its thrusters could not be fired and it drifted away.
Key dates
| Date | What happened |
|---|---|
| 12 August 1978 | Launched as ISEE-3 to study the solar wind. |
| 22 December 1983 | A final close pass of the Moon sent it towards comet Giacobini–Zinner; it was renamed ICE. |
| 11 September 1985 | Flew through the tail of comet 21P/Giacobini–Zinner, the first encounter with a comet. |
| March 1986 | Measured the solar wind upstream of Halley's Comet from afar. |
| September 2014 | Volunteers lost contact with the spacecraft after briefly bringing it back to life. |
See where this mission fits among all the others in the mission timeline.
Did you know?
The first spacecraft to reach a comet carried no camera at all.
In 1946 the Draconids briefly produced thousands of meteors an hour.
Related pages
Comets connected with this mission: Halley's Comet, Comet Giacobini–Zinner. See all comets.