Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer).
Rings and moons are the matter that orbit a celestial body other than a star. Rings are a collection of dust or small particles that form into a flat disk. Moons, or natural satellites, are much larger single bodies. Large moons can themselves support rings.
Cassini’s camera observed Titan from orbit at different angles (0–166°) and found that the planet looks brighter towards the night than at midday. This effect, linked to the scattering properties of Titanian haze, can also be present in exoplanets.
Liquid methane lakes dot Titan’s polar regions. Numerical models reveal that the creation of buoyant bubbles through nitrogen exsolution near the bed of the Ligeia Mare lake can explain transient brightenings observed by Cassini on the lake’s surface.
Frictional charging of granular materials may readily occur on Saturn’s moon Titan. Laboratory experiments under Titan-like conditions suggest that the resulting electrostatic forces are strong enough to affect sand transport on Titan.
The moon Phobos is spiralling inwards towards its disintegration to eventually form a ring around Mars from which new moons may form. Simulations suggest that this is just the latest of multiple ring–moon cycles over the history of Mars.
Cassini’s RADAR has surveyed a region close to Enceladus’s ‘tiger stripes’. It finds a temperate subsurface with warm cracks, indicating that the moon’s icy crust is only a few kilometres thick at these points. A dormant crack hints at episodic geological activity.
The seabed of Ligeia Mare, a hydrocarbon sea at the north pole of Titan, may be a favourable place for the separation of nitrogen and the creation of bubbles that then buoyantly rise to the sea's surface.
The twin isotopic signatures of the Moon and Earth are difficult to explain by a single giant impact. Impact simulations suggest that making the Moon by a combination of multiple, smaller moonlet-forming impacts may work better.
The two small satellites of Mars are thought to have accreted from a debris disk formed in a giant impact. Simulations suggest the moons were shepherded into formation by the dynamical influence of one or more short-lived massive inner moons.
After more than a decade exploring Saturn and its moons, the Cassini mission is in its closing act. Cassini's last year is an encore performance stuffed with science, including a final plunge into Saturn's atmosphere.
Compared to Earth, the Moon is depleted in volatile species like water, sodium and potassium. Simulations suggest that much of the Moon formed from hot, volatile-poor melt in a disk of debris after initially amassing cooler, volatile-rich melt.