Comet Tuttle
A double-lobed comet whose dust brings the Ursids just before Christmas.
Key facts
- Designation
- 8P/Tuttle
- Type
- Halley-type comet
- Orbital period
- 13.6 years
- Closest to the Sun
- about 1.03 AU (about 154 million km)
- Farthest from the Sun
- about 10.4 AU, near Saturn's orbit
- Tilt of orbit
- about 55°
- Nucleus
- two joined lobes, together equal to a ball about 4.5 km wide
- Discovered
- first seen by Pierre Méchain in January 1790; rediscovered by Horace Tuttle on 5 January 1858
- Returns
- last at perihelion 27 August 2021; next due April 2035
Orbit
Tuttle goes round the Sun every 13.6 years, reaching from just outside Earth's orbit to near Saturn's. Its orbit is steeply tilted, and the dust it leaves meets Earth each December at about 33 km/s, from a radiant near the Little Bear, close to the Pole Star.
Size and nature
In January 2008 the giant radio telescope at Arecibo bounced radar off the comet and found that the nucleus is a contact binary: two rounded bodies resting against each other. Together they are about the volume of a ball 4.5 km wide. Many comets seen up close since, such as 67P, have the same double shape, which suggests that small bodies often formed by two pieces gently merging.
History
Pierre Méchain saw the comet in 1790, but it was not seen again until Horace Tuttle found it in 1858. Tuttle realised it matched Méchain's comet. In the twentieth century the Czech astronomer Antonín Bečvář noticed a strong burst of meteors from near the Little Bear in December 1945, and the link with Comet Tuttle was confirmed.
Meteor showers
The Ursids peak around 22 December, usually with 5 to 10 meteors an hour. Because the radiant is so far north, the shower can be watched all night from Britain and other northern countries, though the long nights are often cloudy. Outbursts of around 50 an hour or more were seen in 1945 and 1986, and smaller ones in 2000 and 2014. Strong years tend to come when the comet is far away near the outer end of its orbit, from dust trails laid down centuries ago.
Its meteor showers
- The Ursids peak around 21–22 December; about 10 (occasional outbursts) an hour at best; 33 km/s
Key dates
| Date | What happened |
|---|---|
| 5 January 1858 | Horace Tuttle rediscovered the comet behind the Ursid meteors. |
| 27 August 2021 | Comet Tuttle passed closest to the Sun. |
Did you know?
Horace Tuttle co-discovered three comets that feed meteor showers: Swift–Tuttle, Tempel–Tuttle and this one.
The Ursid radiant never sets as seen from Britain.
Radar showed the comet's double shape in 2008 without any spacecraft visiting it.