Margaret (moon)

Margaret

Subaru 8.3 meter telescope discovery image
Discovery
Discovered by	Scott S. Sheppard, and David C. Jewitt
Discovery date	August 29, 2003[1][2]
Orbital characteristics
Mean orbit radius	14,345,000 km[3][4]
Eccentricity	0.6608[4] (mean)
Orbital period	1687.01 d
Inclination	57° (to the ecliptic)[3]
Satellite of	Uranus
Physical characteristics
Mean radius	10 km (estimate)[5]
Surface area	~1,300 km2 (estimate)
Volume	~4,200 km3 (estimate)
Mass	~5.5×1015 kg (estimate)
Mean density	~1.3 g/cm3 (assumed)
Rotation period	?
Axial tilt	?
Albedo	0.04 (assumed)[3]
Temperature	~65 K (estimate)

Margaret ( /ˈmɑrɡrɨt/ mar-grət) is the only prograde irregular satellite of Uranus. It was discovered by Scott S. Sheppard, et al. in 2003 and given the provisional designation S/2003 U 3.^[6]

Confirmed as Uranus XXIII, it was named after the servant of Hero in William Shakespeare's play Much Ado About Nothing.^[1]

Orbit

Irregular satellites of Uranus

Margaret stands out as the only prograde irregular satellite of Uranus. The diagram illustrates the orbital parameters of Margaret, unique among the irregular satellites of Uranus, with inclination on the vertical axis and the eccentricity of the orbits represented by the segments extending from the pericentre to the apocentre.

Margaret's inclination of 57° is close to the limit of stability. The intermediate inclinations 60 < i < 140 are devoid of known moons due to the Kozai instability.^[3] In this instability region, solar perturbations at apoapse cause the moons in this region to acquire large eccentricities that lead to collisions or ejection over 10 million to a billion years. Margaret's periapsis precession period (P_w) is almost 1.6 million years long.^[4]

In 2008, Margaret's current eccentricity was 0.7979.^[7] This temporarily gives Margaret the most eccentric orbit of any moon in the solar system, though Nereid's mean eccentricity is greater.

See also

• Uranus' natural satellites

References

1. ^ ^{a b} Jennifer Blue (2008-10-16). "Planet and Satellite Names and Discoverers". Working Group for Planetary System Nomenclature (WGPSN). http://planetarynames.wr.usgs.gov/append7.html#UranianSystem. Retrieved 2008-12-19. 
2. ^ Scott S. Sheppard. "New Satellites of Uranus Discovered in 2003". Institute for Astronomy at the University of Hawaii. Archived from the original on 5 May 2008. http://web.archive.org/web/20080505184616/http://www.ifa.hawaii.edu/~sheppard/satellites/uranus2003.html. Retrieved 2008-12-19. 
3. ^ ^{a b c d} Sheppard, Scott S.; David C. Jewitt, Jan Kleyna (2005). "An Ultradeep Survey for Irregular Satellites of Uranus: Limits to Completeness". The Astronomical Journal 129 (1): 518–525. arXiv:astro-ph/0410059. Bibcode 2005AJ....129..518S. doi:10.1086/426329. "Table 3 ... rⁱ (km) ... 10 ... ⁱ Radius of satellite assuming a geometric albedo of 0.04." 
4. ^ ^{a b c} Jacobson, R.A. (2003) URA067 (2007-06-28). "Planetary Satellite Mean Orbital Parameters". JPL/NASA. http://ssd.jpl.nasa.gov/?sat_elem#uranus. Retrieved 2008-01-23. 
5. ^ Sheppard 2005, p. 523
6. ^ IAU Circular 8217
7. ^ "IAU-MPC Natural Satellites Ephemeris Service". IAU: Minor Planet Center. http://www.minorplanetcenter.org/iau/NatSats/NaturalSatellites.html. Retrieved 2008-01-26.  (Select Uranian, deselect Ephemerides and select Orbital Elements)

External links

• Margaret Profile by NASA's Solar System Exploration
• David Jewitt pages
• Uranus' Known Satellites (by Scott S. Sheppard)
• Ephemeris IAU-NSES