Mab (moon)

from Wikipedia, the free encyclopedia
S2003U1 zoom.png
Mab on a photo taken by the Hubble Space Telescope
Provisional or systematic name S / 2003 U 1
Central body Uranus
Properties of the orbit
Major semi-axis 97,736 km
Periapsis 97,492 km
Apoapsis 97,980 km
eccentricity 0.0025
Orbit inclination 0.1335 °
Orbital time 0.9228 d
Mean orbital velocity 7.68 km / s
Physical Properties
Albedo ≈ 0.103
Apparent brightness 26.0 likes
Medium diameter ≈ 16 km
Dimensions 4 x 10 15 kg
Medium density 1.3 g / cm 3
Acceleration of gravity on the surface ≈ 0 m / s 2
Escape speed ≈ 0 m / s

Mark R. Showalter ,
Jack J. Lissauer

Date of discovery August 25, 2003
Remarks Physical data relatively imprecise.

Mab (also Uranus XXVI ) is the thirteenth-innermost and one of the smaller of the 27 known moons of the planet Uranus .

Discovery and naming

Mab was discovered on August 25, 2003 by astronomers Mark R. Showalter and Jack J. Lissauer using the Hubble Space Telescope . It was the first moon in the solar system to be discovered with this telescope. The moon was then seen on old photos from the Voyager-2 probe. The discovery was announced on September 25, 2003 by the International Astronomical Union (IAU); the moon was initially given the provisional designation S / 2003 U 1 .

The moon got the official name Mab after a Queen Mab, the midwife of the fairy queens, mentioned in Shakespeare's Romeo and Juliet . The figure comes from 17th century English folklore. She was probably inspired by Medb , the legendary Queen of Connacht.

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. The provisional designation S / 2003 U 1 corresponds to the IAU system .

Track properties


Mab orbits Uranus on a prograde , almost perfectly circular orbit at an average distance of around 97,736 km (approx. 3.824 Uranus radii) from its center, i.e. around 72,200 km above its cloud ceiling. The orbital eccentricity is 0.0025, the web is 0.1335 ° relative to the equator of Uranus inclined .

The orbit of the nearest inner moon Puck is on average 11,700 km from Mabs orbit, that of the next outer moon Miranda 31,650 km. Mab is the outermost of the group of inner 13 regular small moons of Uranus, and together with Puck it forms a separate subgroup.

Mab is located in the middle of the μ (My) dust ring , from the inner and outer edges of which it is about 11,700 km and 5,200 km, respectively. The brightest and densest part of this outermost Uranus ring coincides almost exactly with the orbit of the moon and is believed to be the source of the ring particles.

Mab orbits Uranus in 22 hours 8 minutes.


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

Physical Properties


The size of the moon is not well known, it is about 16 km. There are data from 10 to 24 km, which is probably based on the uncertainty of the albedo , which is given as 0.07 to 0.103 (ie 7 or 10% of the incident sunlight is reflected by the surface; it is therefore a relatively dark one Celestial bodies). Should Mab be brighter than expected, the lower value of 10 km is more likely, which would make it the smallest known Uranus moon .


The surface of the moon is badly cratered. The source of the heavy bombardment is unknown, but it is believed that one or two neighboring moons are responsible. Mab seems to be the source of the μ (My) dust ring , for which it would be the optimal size. More massive moons would collect the dust again, while less massive moons would be too small to feed such a ring through collisions or micrometeorite impacts. No dust rings were found around Perdita and Cupid , possibly due to the moon Belinda , which limits the lifespan of the dust produced by these moons.

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

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 . On its surface, the acceleration due to gravity is 0.0032 m / s 2 , which corresponds to only about 0.03% of that on earth.


Since the Voyager 2 space probe flew by, in which Mab could not be found due to its small size and brightness, the Uranus system has been intensively studied by earth-based observations as well as the Hubble space telescope . The orbit parameters could be specified more precisely by Mab.

Web links

Individual evidence

  1. ^ Showalter, Mark R .; Lissauer, JJ; French, RG et al .: The Outer Dust Rings of Uranus in the Hubble Space Telescope . In: American Astronomical Society, DDA meeting # 39, id . 16.02 . 2008, bibcode : 2008DDA .... 39.1602S (English).