Castalia (spacecraft)

Overview

Main-belt comets are a recently discovered population of apparently icy bodies within the main asteroid belt between Mars and Jupiter. They may represent remnants of the population that supplied early Earth with water. The Rosetta mission to comet 67P/Churyumov–Gerasimenko in 2014 indicated that Jupiter family comets cannot be the main source of Earth's water as previously thought. Castalia would rendezvous and orbit comet 7968 Elst–Pizarro, measuring isotope ratios, plasma and dust properties, and mapping its interior structure with a radar. The mission would test whether main-belt comets are a viable source for Earth's water and use them as tracers of Solar System formation and evolution. The spacecraft would orbit from 20 km and perform close approaches and hovering for 100 hours as close as 5 km to collect dust and gas samples. The mission architecture was initially developed in 2013 by the German Aerospace Center (DLR) in Bremen and OHB SE. Castalia was proposed to the European Space Agency M4 (2015) and M5 (2016) missions within the Cosmic Vision programme but was not selected; the team continues to mature the concept. The mission is named after Castalia, a nymph in Greek mythology turned into a fountain who could inspire poetry to those who drank her waters. The main science goals include characterizing a main-belt comet by in situ investigation, understanding the physics of main-belt comet activity, directly detecting water in the asteroid belt, testing whether main-belt comets are a viable source for Earth's water, and using main-belt comets as tracers of planetary system formation and evolution.