Inside Enceladus: Saturn's moon Enceladus has often been the focus of flybys of the Cassini spacecraft. Although small—Enceladus is roughly 10 times smaller than Saturn's largest moon, Titan—Enceladus has shown hints of having a complex internal structure rich in liquid water. Iess et al. (p. 78 ) used long-range data collected by the Cassini spacecraft to construct a gravity model of Enceladus. The resulting gravity field indicates the presence of a large mass anomaly at its south pole. Calculations of the moment of inertia and hydrostatic equilibrium from the gravity data suggest the presence of a large, regional subsurface ocean 30 to 40 km deep.

Getting to Know Titan: Gravity-field measurements provide information on the interior structure of planets and their moons. Iess et al. (p. 457 ; published online 28 June) analyzed gravity data from six flybys of Saturn's moon, Titan, by the Cassini spacecraft between 2006 and 2011. The data suggest that Titan's interior is flexible on tidal time scales with the magnitude of the observed tidal deformations being consistent with the existence of a global subsurface water ocean.

Juno swoops around giant Jupiter: Jupiter is the largest and most massive planet in our solar system. NASA's Juno spacecraft arrived at Jupiter on 4 July 2016 and made its first close pass on 27 August 2016. Bolton et al. present results from Juno's flight just above the cloud tops, including images of weather in the polar regions and measurements of the magnetic and gravitational fields. Juno also used microwaves to peer below the visible surface, spotting gas welling up from the deep interior. Connerney et al. measured Jupiter's aurorae and plasma environment, both as Juno approached the planet and during its first close orbit. Science , this issue p. 821 , p. 826

Cassini's last look at Saturn's rings: During the final stages of the Cassini mission, the spacecraft flew between the planet and its rings, providing a new view on this spectacular system (see the Perspective by Ida). Setting the scene, Spilker reviews the numerous discoveries made using Cassini during the 13 years it spent orbiting Saturn. Iess et al. measured the gravitational pull on Cassini, separating the contributions from the planet and the rings. This allowed them to determine the interior structure of Saturn and the mass of its rings. Buratti et al. present observations of five small moons located in and around the rings. The moons each have distinctive shapes and compositions, owing to accretion of ring material. Tiscareno et al. observed the rings directly at close range, finding complex features sculpted by the gravitational interactions between moons and ring particles. Together, these results show that Saturn's rings are substantially younger than the planet itself and constrain models of their origin. Science , this issue p. 1046 , p. eaat2965 , p. eaat2349 , p. eaau1017 ; see also p. 1028

We present in detail the scientific objectives in fundamental physics of the Space–Time Explorer and QUantum Equivalence Space\ud Test (STE–QUEST) space mission. STE–QUEST was pre-selected by the European Space Agency together with four other missions\ud for the cosmic vision M3 launch opportunity planned around 2024. It carries out tests of different aspects of the Einstein Equivalence\ud Principle using atomic clocks, matter wave interferometry and long distance time/frequency links, providing fascinating science at the\ud interface between quantum mechanics and gravitation that cannot be achieved, at that level of precision, in ground experiments. We\ud especially emphasize the specific strong interest of performing Equivalence Principle tests in the quantum regime, i.e. using quantum\ud atomic wave interferometry. Although STE–QUEST was finally not selected in early 2014 because of budgetary and technological reasons, its science case was very highly rated. Our aim is to expose that science to a large audience in order to allow future projects and\ud proposals to take advantage of the STE–QUEST experience