2023-10-30 14:11:00
Minerals in ancient meteorites offer insights into the origins of nearly three-quarters of Earth’s surface.
Dr. Alice Stephant, an astrophysicist, is helping to solve a long-standing mystery regarding Earth’s water: its origin.
Scientists have long believed that water, which covers 70% of the Earth, was probably rare or non-existent on other planets. The assumption was that water on Earth arose from a unique series of galactic events billions of years ago.
Far away
Stephant, who works at the National Institute of Astrophysics in Italy’s capital Rome, questions these long-standing assumptions.
Their research suggests that the chemical components of water, namely hydrogen and oxygen, may come from the vast cloud of dust and gas that formed Earth’s solar system.
If the water from this cloud went directly into the formation of planets, it might be present anywhere in the universe.
“Perhaps this way of bringing water to a planet can happen in any other solar system,” said Stephant, a French native who has also worked in Britain and the United States.
She led a research project calledPOSEIDON, funded by the EU to research the origins of water on Earth. The team studied the chemical components of hydrogen and oxygen in a specific type of meteorite: primitive achondrites.
The project was completed in January 2023 following 29 months.
Sun birth
Earth’s solar system formed regarding 4.5 billion years ago from a swirling cloud of dust and gas known as the solar nebula. Over time, gravity pulled this material together into the center of the nebula.
When almost everything – more than 99% – had accumulated in the center, the resulting pressure and heat from compression led to nuclear fusion and the sun was born.
The remaining material orbited the Sun and eventually began to coalesce into larger objects. Some of these evolved into the planets and moons we see today.
Others did not and instead became meteorites, comets and asteroids. These rocks are important to scientists because they represent relics from the early history of the solar system.
Primitive achondrites are of particular interest because they come from asteroids, which were among the very first building blocks of planets in the solar system.
New group of meteorites
Stephant has identified a new group of primitive achondrites that provide important clues to the origin of water on Earth and other planets in the solar system.
Until now, only two groups of primitive achondrites were known. Stephant has identified a third one, which is characterized by a so-called isotypic composition of oxygen.
This means that these meteorites come from different materials from the early solar system.
They also contain another isotope of hydrogen. This means that the hydrogen has a different number of neurons in its nucleus. “There were probably multiple water sources, not just one,” Stephant said.
One of the possible sources is primordial hydrogen, which probably comes from nebulous gases in the early formation of the solar system.
The components of water might have been contained in the earliest building blocks of the planets. If so, it is more likely that the components of water have been incorporated into the chemical composition of many planets.
And that greatly increases the likelihood that there is water on the surfaces of other planets in the universe.
“It used to be said that the water on Earth was made up of a combination of many events that made it unique,” says Stephant. “But maybe that’s not the case in reality.”
Time test
While Stephant searches for further evidence of the water’s origin, Dr. Sandrine Péron explores the elements that came to Earth with water to learn more regarding the early solar system.
Péron is a geochemist at ETH Zurich, a university in Switzerland, and comes from France. She leads an EU-funded research project called VolatileOriginwhich runs for 29 months until April 2024.
It focuses on two noble gases in the earth’s crust: krypton and xenon. Krypton and xenon isotopes help scientists understand the origins of Earth’s volatile elements such as carbon, nitrogen and water.
That’s because these isotopes were brought to Earth along with volatile elements like water. Because the isotopes are much less reactive, they retain the ancient chemical fingerprints that indicate their origins in the early solar system.
The chemical signatures of krypton and xenon in a class of primitive meteorites known as carbonaceous chondrites match those of Earth’s mantle. This shows that these meteorites were built into the Earth’s mantle.
Kryptonian anomaly
A few years ago, Péron and her colleagues took samples of krypton in the Earth’s mantle at geological hotspots in Iceland and the Galapagos Islands, where magma rises from the Earth’s interior.
The researchers discovered a relative scarcity of krypton with isotope number 86. “We found that we have a deficit of krypton 86 in the deep mantle compared to the average composition of carbonaceous chondrites,” said Péron.
If the Krypton-86 deficit is due to an anomaly in the formation of atomic nuclei in the early solar system, it would indicate that water – and other volatile elements – were brought to Earth before the nebula material was fully mixed.
Museum pieces
The Kryptonian anomaly suggests that in addition to the carbonaceous chondrites, other meteorites also contributed to the Earth’s mantle.
In VolatileOrigin, Péron examines meteorites that fell to Earth and are now in museums to determine whether some of them exhibit the same Kryptonian anomaly as Earth’s deep mantle.
The project is also looking for krypton deficits in the upper mantle. Such anomalies occurred before the formation of the solar system and show that the different isotopes were not well mixed, says Péron.
“These different isotopes are produced by different types of stars or supernovas,” she said. “If this material is integrated into the solar system, we might have some pieces that preserve more of a particular isotope or another.”
The chemical signatures left by these ancient cosmic events provide clues to the path that materials took between different parts of the solar system during their early evolution.
“When we see these anomalies, either in meteorites or in the Earth, it gives us information regarding the processes that took place during the early stages of the formation of the solar system,” adds Péron.
Further information
Article by Michael Allen
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