Methone (moon)

Methone
Methone captured by the Cassini spacecraft on May 21, 2012
Provisional or systematic name	S / 2004 S 1
Central body	Saturn
Properties of the orbit
Major semi-axis	194,440 ± 20 km
Periapsis	194,420 km
Apoapsis	194,460 km
eccentricity	0.0001
Orbit inclination	0.007 ± 0.003 °
Orbital time	1.009573975 d
Mean orbital velocity	13.97 km / s
Physical Properties
Albedo	?
Apparent brightness	25.0 mag
Medium diameter	3.2 ± 1.2 km
Dimensions	8.9920 · 10 12 kg
surface	32.2 km 2
Medium density	0.5 g / cm 3
Sidereal rotation	1.009573975
Axis inclination	0 °
Acceleration of gravity on the surface	0.00023 m / s 2
Escape speed	0.83333 m / s
discovery
Explorer	Sébastien Charnoz
Date of discovery	August 16, 2004

Methone (also Saturn XXXII ) is the eleventh and one of the smallest of the 82 known moons of the planet Saturn . Their orbit lies between those of the great moons Mimas and Enceladus, and the moons of this section, which also includes Anthe and Pallene , are called the Alkyonid group .

discovery

Methone was discovered on August 16, 2004 by the astronomer Sébastien Charnoz together with Pallene in photographs taken on June 1, 2004 by the Cassini-Huygens space probe . Charnoz is a member of the scientific team (headed by Carolyn C. Porco , Charnoz, André Brahic and Luke Dones) at Cassini-Huygens and works at the University of Paris . Since the smaller, so far undiscovered moons are extremely faint objects, the Cassini probe had taken 75 pairs of long-exposure images around Saturn. Charnoz had the recordings examined using software he developed . He found the moons Methone and Pallene. Charnoz reports: “I had been looking for objects like this in my Paris office for weeks, but it wasn't until I was on vacation using my laptop that I found it. That told me that I should take more vacation. "

Methone may have been observed by the Voyager 2 spacecraft as early as the 1980s . At that time it was named S / 1981 S14 . It is possible, however, that the observed moon was Pallene.

Methone was initially given the provisional designation S / 2004 S 1 . On January 21, 2005, the moon was named after one of the seven daughters of the giant Alkyoneus from Greek mythology (Alkyoniden). Alkyoneus was a son of Gaia and the blood of Uranus . The giant was killed in the giant battle by Herakles . Methone and her six sisters (including Anthe and Pallene) were so grieved over their father's death that they threw themselves from the Canastra promontory into the sea. But out of pity, the Oceanid (or Nereid ) Amphitrite saved their lives and turned them into kingfishers .

Track properties

Animation of Methone's orbit

Orbit

Methone orbits Saturn on a prograde , almost perfectly circular orbit at an average distance of 194,440 km (approx. 3,226 Saturn radii) from its center, i.e. about 134,172 km above its cloud ceiling. The orbit eccentricity is 0.0001, the orbit is inclined 0.007 ° to the equator of Saturn , so it lies almost in the equatorial plane of the planet. Due to the low eccentricity, the orbit varies by about 40 km in the distance to Saturn.

The orbits of the next inner moon Mimas is on average about 8920 km from the orbit of Methone, the distance of the orbit of the next outer moon Anthe is on average about 3260 km.

Methone orbits Saturn in 1 day, 0 hours, 13 minutes and 47.2 seconds. It takes 3 hours and 36.7 minutes longer than its inner neighbor Mimas to complete one cycle. Methone's orbit is the closest of any moons in the solar system on an earthly day; it covers a distance of 356 ° in 24 hours.

Methone is in a 15:14 orbit resonance with its closest neighbor, Mimas, with a 450-day libration time. This severely disrupts their orbit of mimas . The much larger Mimas causes deviations in the Methone orbit of about 20 km due to its gravity. The influence of the orbital resonance also means that methone moves back and forth on its orbit at a length of 5 °. The eccentricity varies at certain time intervals between 0.0011 and 0.0037, the inclination between 0.003 ° and 0.020 °.

The ring arches by Anthe (top left) and Methone (bottom right), Cassini , October 29, 2007.

Methone ring arch

Despite the small size of methone, a ring system was discovered in front of and behind it in September 2006. However, this does not form a closed system around Saturn, but extends only a few thousand kilometers in front of and behind Methone and moves with it. It is assumed that the ring arcs of Methone and Anthe were probably formed from material that was knocked out of these two moons by micrometeorites and, due to the low gravity, are not so strongly attracted by the moons that they fall on the surface and could stay there (and enlarge the moon). The gravitational resonance with mimas keeps them in their shape; Mimas prevents the ring material from spreading over the entire orbit like the other Saturn rings and forming a uniform ring.

rotation

The rotation time is the same as the orbital time and Methone shows, like the earth's moon , a synchronous rotation , which also takes place within one day, 0 hours, 13 minutes and 47.2 seconds. The axis of rotation is inclined at 0 ° with respect to the orbit.

Physical Properties

Methone next to overexposed Saturn

Methone is about 3.2 km in diameter. An average density of 0.5 g / cm ³ results in a mass of 8.9920 · 10 ¹²  kg. On its surface, the acceleration due to gravity is 0.00023 m / s ² , which corresponds to only about 0.025 ‰ of that on earth.

So far there have been two theories about the origin of the three closely spaced moons Methone, Anthe and Pallene : First, they were broken out by either Mimas or Enceladus through a collision with a comet or asteroid , and second , all of these five moons could even be residues of a larger swarm, who wandered to this near region of Saturn.

exploration

Methone has an apparent magnitude of 25.0 ^m , which is 1: 5,000,000,000 of the central planet. Methone has been visited by four spacecraft so far , namely the flyby probes Pioneer 11 on September 1, 1979, Voyager 1 on November 12, 1980 and Voyager 2 on August 25, 1981 and finally Cassini-Huygens . However, the discovery by the Voyager probes could not be confirmed, as the moon could most likely be seen on only a single image from Voyager 2 from August 23, 1981. The distance was then estimated to be around 200,000 km and therefore applies to Methone and Pallene.

Since its discovery in 2004, its orbital parameters have been made more precise by the Cassini probe, which has been orbiting Saturn since July 1, 2004. Cassini's next flyby occurred on September 9, 2006, when the Methone probe passed at a distance of 12,272 km. However, no targeted flyby has taken place so far.

Web links

Commons : Methone (moon)  - collection of images, videos and audio files

• IAUC 8389: S / 2004 S 1 and S / 2004 S 2 August 16, 2004 (discovery)
• IAUC 8471: Satellites of Saturn January 21, 2005 (numbering and naming)

Individual evidence

1. ↑ Paul Rincon: Saturn overtakes Jupiter as planet with most moons. BBC , October 7, 2019, accessed March 20, 2020 . 
2. ↑ astronews.com
3. ↑ solarsystem.nasa.gov ( Memento from August 1, 2007 in the Internet Archive )
4. ↑ iopscience.iop.org

further inside	Saturn moons	further outside
Mimas	Semi-major axis  (km) Methone 194,000	Anthe