Irregular Moons of the Giant Planets: Potential for Observations by Spacecraft

While the first Irregular moon of a giant planet has been found on photographic plates in 1899 (Phoebe), and another ten (also through photography) until 1975, the vast majority of discoveries (now with CCDs) started no earlier than 1997, with big advances in the early noughties (almost 100 moons) and again since 2017 (well over 100 objects). Ground-based observations are important for discoveries and the determination of orbital elements and physical properties like brightness (size) and colors. However, there are geometric limits – mainly the restriction to low phase angles (25 mag), which requires large telescopes difficult to access over long periods of time. With spacecraft orbiting a giant planet, i.e. at distances at the order of 10e7 km to the Irregulars, long-duration observations to obtain lightcurves can be performed for numerous objects. Even with just one observation session over many hours and a bit of luck, a synodic rotation period at the accuracy of minutes may be deduced. With multiple observations, sidereal periods at millisecond-accuracy level, unambiguous pole solutions, and low-order convex-shape models might be obtained. Furthermore, phase curves up to >50° phase angle (for some objects even >100°, on particularly favorable geometries) can be measured. This is possible because a giant-planet orbiter revolves inside the orbits of the Irregular moons, and the Solar phase angles may in principle reach any value from 0° to 180°. Such an Irregular moons campaign has been performed for the first time with Cassini's Narrow Angle Camera while in orbit around Saturn (Denk & Mottola 2019, Icarus), providing 24 new rotation periods of Saturnian Irregulars and about a dozen sidereal periods, pole solutions, shape models, and phase curves. A similar campaign is under consideration for the Juice mission with the JANUS camera, which has the potential for an even larger sample of Jovian Irregulars. The poster will discuss the options and limits for spacecraft-based observations of Irregular moons while orbiting Jupiter or another giant planet. Beyond unresolved observations, upcoming missions to the gas and ice giant planets should also attempt close flybys of an Irregular moon, as has been done by Cassini at Phoebe in 2004. Best opportunities might occur prior to orbit insertion or during the first (large) orbits

Recommendations for Addressing Priority Io Science in the Next Decade

Io is a priority destination for solar system exploration. The scope and importance of science questions at Io necessitates a broad portfolio of research and analysis, telescopic observations, and planetary missions - including a dedicated New Frontiers class Io mission

The Science Case for Io Exploration

Io is a priority destination for solar system exploration, as it is the best natural laboratory to study the intertwined processes of tidal heating, extreme volcanism, and atmosphere-magnetosphere interactions. Io exploration is relevant to understanding terrestrial worlds (including the early Earth), ocean worlds, and exoplanets across the cosmos

DePhine - The Deimos and Phobos Interior Explorer

DePhine - Deimos and Phobos Interior Explorer - is a mission proposed in the context of ESA's Cosmic Vision program, for launch in 2030. The mission will explore the origin and the evolution of the two Martian satellites, by focusing on their interior structures and diversity, by addressing the following open questions: Are Phobos and Deimos true siblings, originating from the same source and sharing the same formation scenario? Are the satellites rubble piles or solid bodies? Do they possess hidden deposits of water ice in their interiors? The DePhine spacecraft will be inserted into Mars transfer and will initially enter a Deimos quasi-satellite orbit to carry out a comprehensive global mapping. The goal is to obtain physical parameters and remote sensing data for Deimos comparable to data expected to be available for Phobos at the time of the DePhine mission for comparative studies. As a highlight of the mission, close flybys will be performed at low velocities, which will increase data integration times, enhance the signal strength and data resolution. 10 - 20 flyby sequences, including polar passes, will result in a dense global grid of observation tracks. The spacecraft orbit will then be changed into a Phobos resonance orbit to carry out multiple close flybys and to perform similar remote sensing as for Deimos. The spacecraft will carry a suite of remote sensing instruments, including a camera system, a radio science experiment, a high-frequency radar, a magnetometer, and a Gamma Ray / Neutron Detector. A steerable antenna will allow simultaneous radio tracking and remote sensing observations (which is technically not possible for Mars Express). Additional instrumentation, e.g. a dust detector and a solar wind sensor, will address further science goals of the mission. If Ariane 6-2 and higher lift performance are available for launch (the baseline mission assumes a launch on a Soyuz Fregat), we expect to have greater spacecraft mobility and possibly added payloads

Enceladus as a potential oasis for life:science goals and investigations for future explorations

Abstract Enceladus is the first planetary object for which direct sampling of a subsurface water reservoir, likely habitable, has been performed. Over a decade of flybys and seven flythroughs of its watery plume, the Cassini spacecraft determined that Enceladus possesses all the ingredients for life. The existence of active eruptions blasting fresh water into space, makes Enceladus the easiest target in the search for life elsewhere in the Solar System. Flying again through the plume with more advanced instruments, landing at the surface near active sources and collecting a sample for return to Earth are the natural next steps for assessing whether life emerges in this active world. Characterizing this habitable world also requires detailed mapping and monitoring of its tidally-induced activity, from the orbit as well as from the surface using complementary platforms. Such ambitious goals may be achieved in the future in the framework of ESA large or medium-class missions in partnership with other international agencies, in the same spirit of the successful Cassini-Huygens mission. For all these reasons, exploring habitable ocean worlds, with Enceladus as a primary target, should be a priority topic of the ESA Voyage 2050 programme