Asteroidal water

Nevertheless, a significant amount of water is also found inside the snow line, including in near-earth objects (NEOs).

Asteroidal water has recently been pursued as a resource to support deep space exploration activities, for example, for use as a rocket propellant, human consumption, or for agricultural production.

[12] As these include both finds (with their Earth entry and impact unobserved) and falls (meteorites from a known, recent meteor event), that water cannot be entirely terrestrial contamination.

In the late 1860s, Hubert Newton and Giovanni Schiaparelli simultaneously showed that meteor showers (and by implication, meteorites) were comet debris.

Some, such as Opik and Wetherill, hypothesized that most or all NEOs were actually extinct or dormant comets, requiring no ejection process from the main belt.

A growing understanding of Solar System dynamics, including more observations, of more bodies, replicated by faster computer models, eliminated this requirement.

The probability of impacts with this timed pattern was considered unlikely versus a model of comet-like volatile emissions.

Observations of the Geminid meteor shower linked it to (3200) Phaeton, a body in a cometary orbit but with no visible coma or tail, and thus defined as an asteroid.

Observations of (1) Ceres emitting hydroxide (OH), the product of water after exposure to the Sun's ultraviolet levels, were further evidence.

Ceres is well within the snow line, exposed to ultraviolet, and Cererean water was considered speculative, at least on its surface.

Overshadowed by Pluto was the creation of Small Solar System Body (SSSB), a category needing no comet-asteroid distinction, nor establishment/disestablishment of volatile emission.

Unfrozen water consists of molecular layers (one to possibly fifteen molecules thick[28]) bound to, and kept from crystallizing by the equal or stronger attraction of the mineral of adsorption.

Hydrogen content, as substitutions or interstitials, can react with oxygen (displacing its existing cation) to form hydroxide or water.

[36][37][38] Solar System science and asteroid mining ascribe hydrated minerals as containing water,[4][39] in a similar sense as ice giant.

[40] On a macroscopic scale, some thickness of crust may shelter water from evaporation, photolysis and radiolysis, meteoric bombardment, etc.

The phyllosilicates serpentinite, montmorillonite and saponite (clay), tochilinite,[6] chamosite, cronstedtite, and mica have been identified in meteorites.

Meteorites also sample multiple depths of their parent bodies, not just dehydrated crusts or space-weathered rinds.

C-complex bodies weather to different types and degrees than the silicate (S-type, and lunar) surfaces.

The rare CI chondrites are so severely altered by water, they consist predominantly (~90%) of phyllosilicate matrix; chondrules are entirely dissolved, or very faint.

As with the other classes and subclasses, the R chondrites show clasts of foreign materials, including phyllosilicate (water-bearing serpentinite-saponite) inclusions.

[69][70] Like ordinary chondrites, the HEDs (howardites, eucrites, and diogenites) were assumed to have formations and histories that would prevent water contents.

Actual measurements of clasts and elements indicate the HED parent body received carbonaceous chondrite materials, including their water.

Actual measurements of clasts and elements indicate the angrite parent body received carbonaceous chondrite materials, including their water.

If such a body appears as an extended object, a coma of gas and dust is suspected, especially if it shows radial falloff, a tail, temporal variation, etc.

[94] At Earth's Moon, comet impact velocities are too high for volatile materials to remain, while asteroid orbits are shallow enough to deposit their water.

[99][106] Vesta was thought to be dry; it is in an inner, warmer zone of the asteroid belt, and its minerals (identified by spectroscopy) had volcanic origins which were assumed to have driven off water.

[108] The Herschel telescope observed far-infrared emission spectra from Ceres indicating water loss.

A fourth line of evidence, relaxation of large craters, suggests a mechanically weak subsurface such as frozen volatiles.

[120] Hayabusa2, after an initial calibration adjustment, confirmed "The decision to choose Ryugu as the destination, based on the prediction that there is some water, was not wrong" (-Kohei Kitazato[121]).

(4660) Nereus, the original target of the Hayabusa mission, was selected both for its very accessible orbit, and the possibility that it is an extinct or dormant comet.