Puck (moon)

puck
Puck captured by Voyager 2
Provisional or systematic name	S / 1985 U 1
Central body	Uranus
Properties of the orbit
Major semi-axis	(86,004.44 ± 0.06) km
Periapsis	85,994 km
Apoapsis	86,015 km
eccentricity	0.00012 ± 0.00006
Orbit inclination	(0.319 ± 0.021) °
Orbital time	(0.76183287 ± 0.000000014) d
Mean orbital velocity	8.21 km / s
Physical Properties
Albedo	0.11 ± 0.015
Apparent brightness	(19.75 ± 0.05) mag
Medium diameter	(162 ± 4) km
Dimensions	≈ 2.9 · 10 18 kg
surface	≈ 80,000 km 2
Medium density	≈ 1.3 g / cm 3
Acceleration of gravity on the surface	≈ 0.029 m / s 2
Escape speed	≈ 69 m / s
Surface temperature	≈ −184 ° C to −209 ° C / 64–89 K
discovery
Explorer	Voyager 2 Stephen P. Synnott
Date of discovery	December 30, 1985
Remarks	physical data relatively imprecise
Size comparison between Uranus (left) and its largest moons, from left to right Puck, Miranda, Ariel, Umbriel, Titania and Oberon (photo montage to scale)

Puck (also Uranus XV ) is the twelfth innermost and one of the medium-sized of the 27 known moons of the planet Uranus .

Discovery and naming

Puck was discovered on December 30, 1985 by the astronomer Stephen P. Synnott on photographs taken by the Voyager 2 spacecraft . It was the first moon to be discovered by the probe's flyby. The discovery was announced on January 9, 1986 by the International Astronomical Union (IAU); the moon was initially given the provisional designation S / 1985 U 1 .

In William Shakespeare's comedy Midsummer Night's Dream, Puck is a tricky ghost who travels the world with the fairies during the night. Puck, also known as Robin Gutfreund (Robin Goodfellow), is the trusted court jester of the Elven King Oberon .

Puk , which wasborrowedfrom the Baltic popular belief (Pukis), occurs in numerous European legends, such as in Celtic ( Púca ) and Germanic mythology as well as in Nordic sagas and English folklore.

All the moons of Uranus are named after characters from Shakespeare or Alexander Pope . The first four Uranus moons discovered ( Oberon , Titania , Ariel , Umbriel ) were named after suggestions by John Herschel , the son of the Uranus discoverer Wilhelm Herschel . Later the tradition of naming was retained.

Track properties

Orbit

Hubble image of Puck and the Portia group

Puck orbits Uranus on a prograde , almost perfectly circular orbit at an average distance of around 86,000 km (approx.3.365 Uranus radii) from its center, i.e. around 60,400 km above its cloud ceiling. The orbital eccentricity is 0.00012, the orbit is 0.319 ° inclined to the equator of Uranus .

The orbit of the next inner moon Perdita is on average 9,600 km from Puck's orbit, that of the next outer moon Mab 11,700 km.

Puck is in the middle of two Uranus rings; the outer edge of the inner ν (Ny) dust ring is on average around 16,100 km from the puck orbit, and the inner edge of the outer μ (My) dust ring is almost exactly on the orbit of Puck.

Puck orbits Uranus in 18 hours, 17 minutes. Since Puck moves close to the synchronous orbit and takes a good hour longer for one orbit than Uranus rotates, it turns out that for a fictitious observer Puck only rises or sets once every 17.5 days on the horizon, which means that it can be seen in the sky for about 8.75 uranium days.

rotation

It is assumed that Puck rotates synchronously and that its axis has an inclination of 0 °.

Physical Properties

size

Puck has a mean diameter of 162 km, making it the sixth largest moon in the Uranus system . However, it is possible that this could be exceeded by the irregular moon Sycorax , discovered in 1997 , should it be darker than expected. Despite its small size, Puck appears remarkably round, the ratio of the axes is only 0.97 ± 0.04.

internal structure

Its mean density of 1.3 g / cm ^{3 is} significantly lower than the density of the earth and indicates that the moon is mainly composed of water ice . Spectral analyzes from the Hubble Space Telescope and Earth-based telescopes confirm absorptions from water ice. It appears to be made of a mixture of ice and dark material that seems to resemble what was found in the rings. This dark material could possibly be rock or organic material altered by solar radiation. The fact that Puck has no craters with bright edges suggests that it does not have a differentiated structure. On its surface, the acceleration due to gravity is 0.029 m / s ² , which corresponds to only about 3 ‰ of that on earth.

Puck has a very low albedo of 0.11; that is, 11% of the incident sunlight is reflected from the surface. It is therefore a relatively dark celestial body.

surface

The mean surface temperature of Puck is estimated to be between −184 ° C and −209 ° C (89–64  K ).

In the light spectrum , the surface of puck appears gray. The surface is severely cratered. The largest crater, Lob , is about 45 km in diameter. So far, the craters on Puck are three named, according to the USGS - nomenclature for mischievous or malicious spirits of European mythologies.

List of named craters on Puck

Crater name	Diameter (km)	Coordinates	Origin of name
Bogle	?		Bogle ( Celtic Mythology )
Butz	?		Butz ( German folk tale )
praise	45.0		Praise ( English folklore )

exploration

Since Puck was discovered early enough to be included in the observation program of the Voyager 2 space probe , it was possible to photograph it on January 24, 1986 at a minimum distance of 492,616 km and to send low-resolution images of the surface to Earth. It was the only one of the newly discovered moons during the flyby that could be explored in more detail.

Since then, the Uranus system has been studied intensively by earth-based observations as well as the Hubble Space Telescope . Puck's orbit parameters could be specified more precisely.

Web links

• IAUC 4159: Satellites of Uranus and Neptune January 9, 1986 (discovery)
• IAUC 4609: Satellites of Saturn and Uranus June 8, 1988 (numbering and naming)
• Polish moon page: Puck description and further links (English)
• Satellite Viewer Orbit simulation of the Uranus moons
• Animation of the puck track (MOV file; 749 kB)