It is inferred from the empirical study of natural satellites in the Solar System that subsatellites may be elements of planetary systems. In the Solar System, the giant planets have large collections of natural satellites. The majority of detected exoplanets are giant planets; at least one, Kepler-1625b, may have a very large exomoon, named Kepler-1625b I, with speculations of a subsatellite. Nonetheless, aside from human-launched satellites in temporary lunar orbit, no notable "moon of a moon" or subsatellite is known in the Solar System or beyond. In most cases, the tidal effects of the planet would make such a system unstable.
Terms used in scientific literature for moons of moons include "submoons" and "moon-moons". Other terms that have been suggested include moonitos, moonettes, and moooons.
Possible natural instancesEdit
The possible detection of a ring system around Saturn's natural satellite Rhea led to calculations that indicated that satellites orbiting Rhea would have stable orbits. Furthermore, the suspected rings are thought to be narrow, a phenomenon normally associated with shepherd moons. However, targeted images taken by the Cassini spacecraft failed to detect any subsatellites or rings associated with Rhea, at least no particles larger than a few millimeters.
It has also been proposed that Saturn's satellite Iapetus possessed a subsatellite in the past; this is one of several hypotheses that have been put forward to account for its unusual equatorial ridge.
Many spacecraft have orbited the Moon, including crewed craft of the Apollo program. As of 2020[update], none have orbited any other moons. In 1988, the Soviet Union unsuccessfully attempted to put two robotic probes on quasi-orbits around the Martian moon Phobos.
Launched June 18, 2009, the Lunar Reconnaissance Orbiter (LRO) is a NASA robotic spacecraft currently orbiting Earths moon Luna in an eccentric polar mapping orbit. Data collected by LRO have been described as essential for planning NASA's future human and robotic missions to the Moon. Its detailed mapping program is identifying safe landing sites, locating potential resources on the Moon, characterizing the radiation environment, and demonstrating new technologies.
Future planned artificial moon satellitesEdit
Additionally, the multi-agency supported Lunar Gateway human-rated space station is due to begin construction in 2024 in a near-rectilinear halo orbit (NRHO), primarily in support of the later stage NASA Artemis program missions to Earth's moon. Lunar Gateway will also potentially support future missions to Mars and outlying asteroids.
With a projected November 2021 launch, the Lunar Flashlight is planned low-cost CubeSat lunar orbiter mission to explore, locate, and estimate size and composition of water ice deposits on Luna for future exploitation by robots or humans from a polar orbit.
In Planet 51 the titular planet is orbited by a moon with a Saturn-like ring system.
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- Media related to Extrasolar moons at Wikimedia Commons
- Shadow Moons: The Unknown Sub-Worlds that Might Harbor Life
- Likely First Photo of Planet Beyond the Solar System
- Working Group on Extrasolar Planets – Definition of a "Planet" Position statement on the definition of a planet. (IAU)
- The Hunt for Exomoons with Kepler (HEK): I. Description of a New Observational Project