Astronomy Earth Science

How Solar Winds and Interplanetary Dust Combine to Form Water

Water can be considered special for any number of reasons. Water provides a foundation for all life on this planet. Water’s solid state that is less dense than its liquid state. Water remains a liquid up to 100 degrees Celsius whereas similarly sized molecules would become a gas long before that point. Water can be found in the solid, liquid, and gas state simultaneously in nature…it’s the only known substance that naturally occurs in all three phases.

Image sourced from Lawrence Livermore National Laboratory
Image sourced from Lawrence Livermore National Laboratory

Water is also rather difficult to make. The process takes a fair amount of energy and it can be dramatically explosive. Place gaseous hydrogen and oxygen in a container and the two substances are perfectly content swirling around one another and keeping their conspecific bonds.

Provide that mixture with spark or flame, however, and boom! The hydrogen is oxidized as it explosively reacts with the oxygen. Before you can blink, 2 H2(g)  +  O2(g)  →  2 H2O(g).

Polar jets blast outward from this protostar
Polar jets blast outward from this proto-star. Illustration: NASA/JPL.
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Given the energetic and explosive nature of water synthesis, it is unsurprising that most water formation in the universe occurs in close proximity to stars. Both stellar death and proto-star formation have both been shown to provide the energy and material necessary to produce massive amounts of H2O through spectacular, violent processes.

While those phenomena are probably the primary generators of water in the universe, researchers from the University of Hawaiʻi at Mānoa’s School of Ocean and Earth Science and Technology (SOEST), Lawrence Livermore National Laboratory, Lawrence Berkeley National Laboratory, and the University of California Berkeley have pointed to another source of water formation in space: interplanetary dust.

Dust rich in silicates travels through space where it is constantly irradiated by solar wind. Eventually, the constant barrage of particles erodes the edges of the silicate-rich dust, causing deformations. This phenomenon is known as “space weathering” and such erosion also occurs on large bodies like the moon which lack an atmosphere to protect its surface.

As the silicate-rich dust erodes and chips, some of the oxygen atoms begin to lose their bond strength and become susceptible to reactions with the high energy hydrogen ions traveling in the solar wind. The result is water.

(A) Secondary electron image of CP IDP U220A19. (B) Dark-field image of a pyroxene crystal on the surface of U220A19 with an ∼100-nm thick amorphous rim resulting from SW irradiation. The linear features (arrows) in the pyroxene crystal are SF tracks. (C) High-angle annular dark-field (HAADF) density contrast image of the SW rim on the pyroxene showing vesicles within the amorphous silicate rim. (D) HAADF image of a vesiculated rim on a lunar soil anorthite crystal. Water was not detected in the vesicles. HAADF images of the amorphous rims on the surfaces of olivine (E) and anorthite (F) crystals following exposure to 5-keV He+ (7.5 × 1018 He+ per square centimeter) and 5-keV H+ (1.0 × 1019 H+ per square centimeter), respectively.
(A) Secondary electron image of CP IDP U220A19. (B) Dark-field image of a pyroxene crystal on the surface of U220A19 with an ∼100-nm thick amorphous rim resulting from SW irradiation. The linear features (arrows) in the pyroxene crystal are SF tracks. (C) High-angle annular dark-field (HAADF) density contrast image of the SW rim on the pyroxene showing vesicles within the amorphous silicate rim. (D) HAADF image of a vesiculated rim on a lunar soil anorthite crystal. Water was not detected in the vesicles. HAADF images of the amorphous rims on the surfaces of olivine (E) and anorthite (F) crystals following exposure to 5-keV He+ (7.5 × 1018 He+ per square centimeter) and 5-keV H+ (1.0 × 1019 H+ per square centimeter), respectively.  Source: PNAS

The team of researchers was able to replicate this phenomenon in the laboratory and consistently produced water. While this probably isn’t how most of the universe’s water came to exist, it may provide another potential explanation for how life came to exist on Earth.

As stated by Hope Ishii, Associate Researcher in HIGP and co-author of the study, “interplanetary dust, especially dust from primitive asteroids and comets, has long been known to carry organic carbon species that survive entering the Earth’s atmosphere, and we have now demonstrated that it also carries solar-wind-generated water. So we have shown for the first time that water and organics can be delivered together.

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