Interplanetary dust points to primordial water reserves beyond Saturn's orbit, study finds
Analysis of 12 interplanetary dust particles points to a water reservoir enriched in heavy oxygen far beyond Saturn. The water itself was not measured directly.
An analysis of 12 microscopic particles of interplanetary dust suggests that a large reservoir of water with a distinct isotopic composition may be preserved far beyond Saturn's orbit, possibly in the Kuiper belt, Universe Magazine reports, citing phys.org. The work was published in Science Advances. universemagazine.com
Universe Magazineuniversemagazine.comOpen source ↗ Calculations showed that the original ratio of oxygen-18 to oxygen-16 in this water was about 15% higher than in Earth's ocean water. The authors note that this is an upper-limit estimate obtained by modeling. The water could not be measured directly.
Water isotopes and the question of origin
A water molecule consists of two hydrogen atoms and one oxygen atom, but both elements exist in several isotopic forms. Besides the heavy hydrogen isotopes, deuterium and tritium, oxygen has a light variant with 8 protons and 8 neutrons and two heavy ones, with 9 and 10 neutrons. Ordinary water is a mixture of all these isotopes.
Samples of cometary ice have long hinted that the outskirts of the Solar System hold a reservoir of water left from the time of its formation and different in isotopic composition. The Genesis experiment, in 2011, showed that the Sun contains considerably more light oxygen than the Earth does.
What the particles showed
The researchers studied solid particles that, in their view, came from the Kuiper belt, where water with more of the heavy oxygen isotope should be found. Spectroscopic analysis found traces of high-energy particles indicating that the grains formed far from the Sun. universemagazine.com
Universe Magazineuniversemagazine.comOpen source ↗ Where exactly, the scientists are not certain: at least farther than Saturn, but how much farther remains an open question.
The particles themselves are not water but various minerals. They show signs of hydration and resemble clays in their state. The hydrated clay minerals indicate that reactions between "heavy" water and rock took place at low temperatures inside the parent bodies of these particles. The authors propose that amorphous silicate grains with nanophase inclusions of iron-nickel alloys (FeNi) and sulfides were the main precursors of the clay minerals. This is supported by observations of the mineral composition of the dust particles and of Antarctic micrometeorites, and by hydration experiments on anhydrous particles.
According to the researchers, when the Solar System was forming, this reservoir of primordial water was not significantly mixed with water closer to the Sun. Where exactly it resides, in the Kuiper belt or inside Uranus and Neptune, is still undecided.
