- Cosmochemists discover water in fragments of an asteroid named Itokawa.
- Impacts by similar asteroids may have delivered almost half of the Earth’s ocean water.
More than 332,519,000 cubic miles of water is present on Earth and 96.5% of this volume is in the ocean. Earth contains massive amounts of water in its crust [20,000 ppm (parts per million) and mantle (2,560 ppm).
But how did water come to our planet? There are many theories explaining the origin of water on Earth and each of them provides a different explanation. Among these theories, there exist large uncertainties in source regions, timings, and amounts of water delivered to terrestrial planets.
Recently, cosmochemists at Arizona State University discovered water in fragments of an asteroid named Itokawa. The asteroid samples were captured by a robotic spacecraft Hayabusa developed by the Japan Aerospace Exploration Agency (JAXA).
The sample contained more water than what was found in inner solar system objects. The findings show that impacts by similar asteroids (billions of years ago) may have delivered almost half of the Earth’s ocean water.
What Exactly They Discovered?
JAXA found 5 particles in the samples of Itokawa, out of which two contain mineral pyroxene. On Earth, these minerals are found in the crystal structure that consists of water. The researchers anticipated that particles of Itokawa could also feature traces of water but they had no idea about the amount of such traces.
Therefore, they analyzed the samples using a special technique called Nanoscale Secondary Ion Mass Spectrometer, which precisely measures extremely small mineral grains.
The outcomes showed the fragments of Itokawa were surprisingly rich in water. In fact, similar asteroids (including the nominally dry ones) could harbor more water than previously estimated.
Itokawa is a near-Earth object and a potentially hazardous asteroid discovered in 1998 by the LINEAR program. It’s an odd peanut-shaped S-type asteroid with high porosity and low density.
It is about 548 meters long and 300 meters wide. It orbits the Sun every 1.5 years at an average distance of 195 million kilometers. Its orbit has 0.28 eccentricity and 2-degree inclination.
S-type asteroids are moderately bright and mostly contain iron- and magnesium-silicates. They are mostly situated in the inner part of the asteroid belt and have kept water and other volatile substance they formed with.
The asteroid has a bumpy history that involves several massive impacts and fragmentation. Rather than a single solid body, it consists of various boulders of different sizes.
The sample examined in this study came from a large region of Itokawa named Muses-C. It’s a smooth and dust-covered area. Despite being exposed to harsh radiation and multiple impacts, the samples still show signs of water.
2 Itokawa particles (each half as thick as a human hair) analyzed in this study | Credit: JAXA/ASU
Hydrogen isotopic constituents of the minerals are indistinguishable from our planet. This indicates that similar asteroids and their parent bodies are likely the main source of water and numerous other substance for the terrestrial planets, which makes them prime targets for further research.
Overall, this asteroid has helped researchers understand how volatile contents came to Earth. It’s possible that planets outside our solar system have produced water via a similar mechanism.
JAXA’s succeeding mission, Hayabusa2, will collect the samples of another near-Earth asteroid called Ryugu and bring them back to Earth in 2020. NASA has also planned a mission to collect fragments of a carbonaceous asteroid named Bennu and bring them back to Earth in 2023.