Cassini–Huygens
What is Cassini–Huygens?
Probes & telescopes· 1997-10-15 – 2017-09-15 (20-year mission complete). A NASA–ESA spacecraft that orbited Saturn for 13 years, studying the planet, its rings and moons. Its companion Huygens landed on Titan in 2005, and Cassini ended its mission by plunging into Saturn in 2017.
Spacecraft specs
| Launch | 1997-10-15 |
|---|---|
| Saturn arrival | 2004-07-01 |
| Huygens landing | 2005-01-14 |
| End | plunged into Saturn |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
How Cassini used the rings to time Saturn's day
Saturn was a planet whose day was hard to pin down. It has no solid surface whose markings could be timed. Its magnetic field is also lined up almost exactly with its spin axis, so the wobble in the field that reveals other planets' rotation was missing. Voyager gave 10 hours 39 minutes and early Cassini measurements 10 hours 47 minutes, a difference of eight minutes.
The answer lay in the rings. When Saturn's interior vibrates, its gravity changes very slightly, and this carves faint spiral ripples into the C ring. By reading those ripples in Cassini's ring images, scientists found in 2019 that Saturn's day lasts 10 hours 33 minutes 38 seconds. Just as earthquake waves reveal Earth's interior, the rings revealed Saturn's.
The same method showed that Saturn's core has no sharp edge but fades gradually into the layers around it. Over 13 years Cassini sent back more than 450,000 images and discovered several small moons, including Daphnis and Methone. The orbiter is named after astronomer Giovanni Cassini, who discovered four of Saturn's moons and the main gap in its rings.
The mission in depth
Cassini–Huygens combined NASA's Cassini orbiter with the European Space Agency's Huygens lander. It was launched on 15 October 1997 and, at 5.7 tonnes, was one of the largest planetary spacecraft of its time. It lacked the power to fly straight to Saturn, so it gained speed by passing Venus twice and Earth and Jupiter once each. It entered orbit around Saturn on 1 July 2004.
On 14 January 2005 Huygens landed on Titan, Saturn's largest moon. It was the first landing ever made in the outer solar system. Pictures taken on the way down through the thick orange haze showed channels like riverbeds carved by liquid methane, and rounded pebbles of ice.
Cassini discovered jets of water shooting from the south pole of the small moon Enceladus. When it flew through the jets and measured what was in them, it found salt and organic molecules. This was strong evidence for an ocean beneath the ice, and it made Enceladus a leading place to look for conditions that could support life.
As its fuel ran low, Cassini flew 22 times through the narrow gap between Saturn and its rings in 2017. On 15 September it dived into Saturn's atmosphere and burned up. This ending was chosen so that it could never crash onto Enceladus or Titan and carry microbes from Earth there.
Frequently asked
- When did Cassini–Huygens launch?
- Cassini–Huygens was launched on 1997-10-15.
- In one line, what is Cassini–Huygens?
- Probes & telescopes — A NASA–ESA spacecraft that orbited Saturn for 13 years, studying the planet, its rings and moons.
- What can I see of Cassini–Huygens here?
- You can see the figures and story on this page.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.