Scientists have analyzed one of the oldest space rocks ever discovered. The data could reveal secrets about the early solar system during the birth of planets, and help scientists better determine the ages of the oldest meteorites to fall to Earth.
The 4.6-billion-year-old Erg-Shish 002 meteorite, studded with green crystals, was discovered in the Erg-Shish region of the Sahara Desert in Algeria in 2020.
It is believed that such meteorites formed from material contained in a disk of gas and dust around the newborn sun. The cold, dense patches of this “solar nebula” collapsed to give birth to the planets, but the remaining material formed comets and asteroids that are separated from meteorites, and often find their way to Earth’s surface in the form of meteoroids. This means that meteorites can paint a picture of the elements that served as the building blocks of planets.
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Erg Sheesh 002 had the radioactive isotope aluminum-26 when it formed, which is significant because this unstable form of aluminum is thought to have been important in a later phase of Earth’s evolution, called “planetary melting,” the team led by Kutub. Australian National University scientist Evgeny Christianinov, in a paper published in Nature Communications.
Planetary melting is thought to be the process by which rocky planets like ours “differentiated” or formed different compositions in different layers. This is because melting allows denser material to descend into the planets’ cores. So, for Earth, an example of such differentiation is the formation of a dense metallic core, above which is a less dense rocky layer.
Understanding how aluminum-26 was distributed during planet formation about 4.6 billion years ago is important for building a picture of how the solar system’s rocky inner planets evolved. Additionally, because aluminum-26 decays into magnesium-26, which is a stable form of magnesium, it can be used as a dating system for space rocks.
To determine the age of Erg Chech 002 at 4.566 billion years, the team measured the amounts of lead isotopes within it, but ironically this could have provided scientists with a way to improve another dating strategy for similar meteorites.
“Aluminium-26 is a very useful material for scientists who want to understand how the solar system formed and evolved,” Kristianinov told Live Science. “Because it decays over time, we can use it to date events, especially during the first four or five million years of the life of the solar system.”
Meteorite dating made easy
Aluminum-26 has a half-life of about 717,000 years, which means it is too short-lived to be found directly in significant quantities in a 4.6-million-year-old space rock. However, when it decays, this radioactive isotope of aluminum leaves behind magnesium 26, which is a stable, non-radioactive isotope of magnesium.
This means that magnesium-26 can be used to determine the initial amount of aluminum-26 in a space rock such as Erg Chech 002, and this can be used as a dating system (also known as a chronometer) for space rocks. But there’s something scientists need to know first.
“The aluminum-26-magnesium-26 decomposition system also serves as a high-accuracy relativistic chronometer,” the authors write, adding that to do this, it is important to determine whether aluminum-26 is unevenly or evenly distributed throughout the solar nebula. That spawned planets, asteroids and comets in the solar system.
The researchers’ study of Erg Chech 002, a chondrite rock formed by the melting of planetesimals, has been combined with existing data on ingrete meteorites – a rare group of chondrites. Chondrites are meteorites that show signs of melting and have similar features to igneous rocks here on Earth.
“We found that the original body of Erg Chech 002 must have formed from a material containing three or four times as much aluminum-26 as the original body source of the angrites,” Kristianinov said. “This indicates that aluminum-26 was unevenly distributed throughout the cloud of dust and gas that formed the solar system.”
This modifies our picture of Al-26 in the early solar system, and could indicate that the ages of meteorites dated using this method alone in the past may need revision.
However, the team’s findings also indicate that the decay of aluminum-26 and magnesium-26 is the most effective chronometer for meteorites.
“Developing a general approach to isotopic dating using aluminum-26, magnesium-26, and other extinct isotopic time instruments that account for the heterogeneous distribution of the original radionuclides would allow us to produce more accurate and reliable age data for meteorites and asteroid and planetary material. The authors conclude, offering an understanding Best for the formation of our solar system.
The team’s research is published August 29 in the journal Nature Communications.