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IIn a few days, a capsule containing soil samples from a distant asteroid will be released from a robotic spacecraft and launched into Earth’s upper atmosphere. Hopefully, the container will parachute safely to the Woomera test field in South Australia on 6 December, completing a mission that involved a three billion-mile journey through our solar system.
The returned information could help solve several important astronomical puzzles, scientists say, including the mystery of how water first appeared on our planet.
“Asteroids are the advanced building blocks since the formation of our solar system 4.6 billion years ago, which makes them very important to science,” said Martin Lee, professor of planetary science at the University of Glasgow. “If you want to know what the planet was made of, you have to study the asteroids.”
The Japanese probe Hayabusa 2 was launched six years ago and sent on a trajectory to the asteroid Ryugu which orbits the sun every 16 months at a distance between 90 million and 131 million miles. For 18 months, he examined this 1,100-yard piece of primeval rock before swooping close to its surface to collect a few scoops of soil. Then the spacecraft turned on its ion thrusters and began its year-long return to Earth.
Lee and his colleagues will be among the first groups of scientists to study Ryugu soil samples when they are delivered, though the team won’t have much to work on. “We expect to obtain only a few grains of material, each a few millimeters in diameter,” said geologist Luke Daly, a team member from the University of Glasgow. “However, we won’t really know how much we’re going to get until the Hayabusa capsule hits the deck – softly, let’s hope.”
Analyzing the composition of an asteroid’s surface from just a few grains of soil seems ambitious. However, the Glasgow team is confident. They plan to use a device called an atomic probe that allows researchers to identify individual atoms in a sample. Given the vast number of atoms that make up even the smallest of the samples, this will require the counting and analysis of tens of millions of individual atoms.
“Essentially, we’re going to take a piece of land and ablate its outer surface with a laser,” Lee said. “In other words, we’re going to blow up its atoms, one by one. And then each of these atoms will be measured to determine the identity of that element and its particular isotope.
‘We will also be able to reconstruct exactly where the atom was located in the sample, in order to obtain a three-dimensional image of the atomic structure of our sample.’
The engineers of the Japanese space agency, Jaxa, are still not sure how much material Hayabusa 2 has collected. Its predecessor mission, Hayabusa 1 – Hayabusa is the Japanese word for a peregrine falcon – in 2005, was plagued with engine failures and other technical problems and brought back very little material from its target, the asteroid Itokawa.
Hayabusa 2 is expected to report much more, although its champions will first have to survive their return to Earth. This will begin when the probe releases a capsule carrying soil from Ryugu. Entering the atmosphere at 27,000 miles per hour, it will plummet towards Earth until, six miles above Australia, it will deploy a parachute and glide to the ground.
The samples will then be distributed to scientists around the world. “In addition to telling us what the early solar system was made of, they will also tell us what happens to rocks when they are bombarded by the solar wind for billions of years – and this is crucial for understanding the history of water in the solar system and, above all, , on Earth, ”Lee added.
The solar wind is a stream of protons and other subatomic particles emitted by the sun. The Earth’s atmosphere protects us, but in space the particles beat without remorse the surfaces without such protection. “This bombardment could trigger the creation of water on the asteroids,” Daly added. “Protons are, essentially, hydrogen ions and could react with oxygen in rocks to create water molecules.”
Scientists are divided on the fundamental question of how water first appeared on our planet. Did it arrive with all the other materials that made up our planet 4.6 billion years ago or was it brought here much later by icy comets that crashed into our planet?
Recent space probes – such as the Rosetta mission which visited comet 67P / Churyumov – Gerasimenko between 2014 and 2016 – have found water on these bodies. However, it’s not quite like water on Earth. These extraterrestrial samples contain higher levels of deuterium, an isotope of hydrogen, than those found in Earth’s water and this has led many scientists to conclude that our stash must have been here from the start.
“However, it may be that these ancient comets were not the only source of water from other parts of the solar system and that more recent reservoirs were created by the solar wind hitting the rocks on the asteroids,” Lee said.
“The water created there may have lower levels of deuterium, which would explain how our oceans have come to contain water with a different isotopic signature. And, of course, studying the atoms of the rocks of the asteroid Ryugu, which has been hit by the solar wind for billions of years, could give us the answer. “
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