''Castalia'' is a proposed mission concept for a robotic spacecraft to explore the

main-belt comet Active asteroids are small Solar System bodies that have asteroid-like orbits but show comet-like visual characteristics. That is, they show comae, tails, or other visual evidence of mass-loss (like a comet), but their orbit remains within Jup ...

7968 Elst–Pizarro Comet Elst–Pizarro is a body that displays characteristics of both asteroids and comets, and is the prototype of active asteroids. Its orbit keeps it within the asteroid belt, yet it displayed a dust tail like a comet while near perihelion in 19 ...

and make the first ''in situ'' measurements of water in the asteroid belt, and thus, help solve the mystery of the origin of Earth's water. The lead is Colin Snodgrass, from

The Open University The Open University (OU) is a British public research university and the largest university in the United Kingdom by number of students. The majority of the OU's undergraduate students are based in the United Kingdom and principally study off- ...

in UK. ''Castalia'' was proposed in 2015 and 2016 to the

European Space Agency , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (1205 ...

within the Cosmic Vision programme missions M4 and M5, but it was not selected. Because of the construction time required and orbital dynamics, a launch date of October 2028 is proposed.

Overview

Main-belt comet Active asteroids are small Solar System bodies that have asteroid-like orbits but show comet-like visual characteristics. That is, they show comae, tails, or other visual evidence of mass-loss (like a comet), but their orbit remains within Jup ...

s (MBCs) are a recently discovered population of apparently icy bodies within the

main asteroid belt The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, called ...

between Mars and Jupiter, which may represent the remnants of the population which supplied the early Earth with water. The ''Rosetta'' mission to comet

67P/Churyumov–Gerasimenko 67P/Churyumov–Gerasimenko (abbreviated as 67P or 67P/C–G) is a Jupiter-family comet, originally from the Kuiper belt, with a current orbital period of 6.45 years, a rotation period of approximately 12.4 hours and a maximum velocity of . Chu ...

in 2014, indicates that Jupiter family comets cannot be the main source of Earth's water as previously thought. ''Castalia'' would rendezvous and orbit comet

and measure

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...

ratios,

plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood pla ...

and dust properties, while also mapping its interior structure with a radar. Basically, ''Castalia'' would test whether MBCs are a viable source for Earth's water, and to use MBCs as tracers of the

formation and evolution of the Solar System The formation of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a ...

. The mission architecture and spacecraft design were initially developed in 2013 by the

German Aerospace Center The German Aerospace Center (german: Deutsches Zentrum für Luft- und Raumfahrt e.V., abbreviated DLR, literally ''German Center for Air- and Space-flight'') is the national center for aerospace, energy and transportation research of Germany ...

(DLR) in Bremen and

OHB SE OHB SE is a European multinational technology corporation. Headquartered in Bremen, Germany, the corporation consists of the two business divisions Space Systems and Aerospace + Industrial Products. A key product of the corporation is fully int ...

. ''Castalia'' was proposed, in slightly different versions, to the

M4 (2015), and M5 (2016) missions within the Cosmic Vision programme. Although it was not selected, the team continues to mature the mission concept and science goals. The mission concept is named after

Castalia Castalia ( grc, Κασταλία), in Greek mythology, was a naiad-nymph, a daughter of Achelous who inhabited the Castalian spring in Delphi. In older traditions, Castalian spring already existed by the time Apollo came to Delphi searching f ...

, a nymph in Greek mythology that was turned into a fountain by a god, and she could inspire the genius of poetry to those who drank her waters or listened to their quiet sound.

Science goals

The main science goals of the mission are: *Characterise a main belt comet (MBC), by ''in situ'' investigation *Understand the physics of MBC activity *Directly detect water in the

asteroid belt The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, called ...

*Test whether MBCs are a viable source for Earth's water *Use MBCs as tracers of planetary system formation and evolution.

Science payload

The conceptual science payload includes the following instruments: *MBCCAM, vis/near-IR imager *TMC, thermal IR imager *SOURCE, deep radar *SSR, shallow radar *CAMS,

mass spectrometer Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is used ...

*DIDIMA, combined dust detector and composition *MAG,

magnetometer A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, o ...

*ChAPS,

package The mission would also include a

radio science One way of outlining the subject of ''radio science'' is listing the topics associated with it by authoritative bodies. Union of Radio Science International (URSI) The International Union of Radio Science has several commissions corresponding to ...

experiment using the spacecraft's communication system.

References

{{European Space Agency European Space Agency space probes Proposed spacecraft Missions to comets

Overview

Science goals

Science payload

See also

References