Trinculo (moon)
Trinculo, also known as Uranus XXI and previously as S/2001 U 1, is a small irregular satellite or moon of Uranus on a very wide and elliptical orbit. It was discovered on 13 August 2001 by Matthew J. Holman, John J. Kavelaars, and Dan Milisavljevic using the 4.0-meter Víctor M. Blanco Telescope at Cerro Tololo Observatory, Chile. It was named after Trinculo, a jester from William Shakespeare's play The Tempest. Trinculo orbits Uranus in the retrograde direction at an average distance of and takes about 749 Earth days to complete one orbit. Trinculo is estimated to be about in diameter and its surface might be dark and gray in color.
Discovery
Trinculo was discovered on 13 August 2001 by a group of astronomers consisting of Matthew J. Holman, John J. Kavelaars, and Dan Milisavljevic, who at the time were searching for distant moons of Uranus. Trinculo was the sixth irregular moon discovered around Uranus. The discovery observations were made at Cerro Tololo Observatory, Chile, using the 4.0-m Víctor M. Blanco Telescope equipped with a wide-field camera. The group discovered Trinculo and three other Uranian irregular moons in the telescope images by using a computer algorithm that followed the motion of Uranus and then combined the images to enhance the faint moons—a technique known as shift-and-adding. Later images obtained by Kavelaars using the Canada–France–Hawaii Telescope on 25 August 2001 confirmed that Trinculo was orbiting Uranus.To determine the orbit of Trinculo, the group continued observing the moon from different observatories, including the 200-inch Hale Telescope at Palomar Observatory and 8.2-m Very Large Telescope at Paranal Observatory. Brian G. Marsden, director of the Minor Planet Center, helped compute the orbit of Trinculo and provided predictions for its location in 2002. Marsden's predictions allowed Gladman to identify a Uranian moon candidate detected in VLT images taken by Philippe Rousselot and Olivier Mousis on 5 September 2002, which was then confirmed to be Trinculo after Gladman and Tommy Grav investigated images taken earlier by the Blanco telescope on 13 August 2002. The Minor Planet Center announced the discovery of Trinculo on 30 September 2003.
Name
When the discovery of Trinculo was announced, it was given the temporary provisional designation S/2001 U 1 by the Minor Planet Center. It was later named and given the Roman numeral designation Uranus XXI by the International Astronomical Union's Working Group for Planetary System Nomenclature on 29 December 2005. The moon was named after the drunken jester Trinculo from William Shakespeare's play, The Tempest.Orbit
Trinculo is an irregular moon of Uranus, which have very wide, elliptical, and inclined orbits in contrast to the regular moons of Uranus. Irregular moons like Trinculo are thought to be former asteroids that were captured by their planet during the Solar System's formation. The Uranian irregular moons are loosely bound by Uranus's gravity because of their great distance from the planet, so their orbits are frequently perturbed by the gravity of the Sun and other planets. This results in significant changes in the orbits of irregular moons over short periods of time, so a simple Keplerian elliptical orbit cannot accurately describe the long-term orbital motions of irregular moons. Instead, proper or mean orbital elements are used to describe the long-term orbits of irregular moons more accurately, since these are calculated by averaging out the perturbed orbit over a long period of time.Over a 10,000-year time period, Trinculo's average semi-major axis or orbital distance from Uranus is, with an average orbital period of. Trinculo has an average orbital eccentricity of 0.22 and an average inclination of 167° with respect to the ecliptic, or the plane of Earth's orbit. Since Trinculo's orbital inclination is greater than 90°, the moon has a retrograde orbit, meaning it orbits in the opposite direction of Uranus' orbit around the Sun. Trinculo's orbital elements fluctuate over time due to perturbations: its semi-major axis varies by up to ±, eccentricity varies by ±0.02, and inclination varies by ±1°. Trinculo's orbit exhibits nodal and apsidal precession with average periods of several thousand Earth years.
The eccentric orbits of Trinculo and other Uranian irregular moons overlap in distance, which leads to the possibility of Trinculo passing close to another irregular moon. Orbit simulations performed by Marina Brozović and Robert Jacobson in 2022 found that Trinculo had approached Sycorax within several tens of thousands of kilometers 9,700 years ago. Trinculo is not known to be part of a collisional family or group; its orbit is apparently unique among the known Uranian irregular moons. If there is a collisional family associated with Trinculo, then any Uranian irregular moons related to it are likely undiscovered because they are presumably small and faint.
Physical characteristics
Trinculo is very faint with an average apparent magnitude of 25.4, so it could only be observed with long-exposure imaging by large-aperture telescopes. Trinculo is expected to have a dark surface composed of water ice, hydrated silicates, and organic compounds, similar to other irregular moons. Observations by the Herschel space telescope did not find any significant infrared thermal emission coming from Trinculo, indicating the moon must have a geometric albedo higher than 0.03 and a diameter smaller than. Assuming an absolute magnitude of 12.7 and a generic irregular moon geometric albedo range of 0.04–0.10, Trinculo should have a diameter between. Scott Sheppard, who has discovered many irregular moons around other giant planets, estimates Trinculo's diameter to be.Observations by the Keck II telescope in 2003 suggest that Trinculo might have a "neutral" or gray color, similar to the larger Uranian irregular moons Prospero and Setebos. Astronomers have attempted to measure Trinculo's rotation period in 2005 by using the Very Large Telescope, but were unable to find any periodic variation in the moon's brightness.