The famous meteorite reveals the first presence of water on Mars and a first bombardment in outer space | Science

By Paul Voosen16 November 2020, 15:00

It was a tough fundraiser: Martin Bizzarro, a cosmochemist from the University of Copenhagen, needed around $ 500,000 to buy – and then grind – material from one of the world’s oldest and most precious rocks. Only this rock was not native to Earth. It came from Mars.

Bizzarro’s bet has now paid off handsomely. With just 15 grams of the 4.4 billion-year-old “Black Beauty” meteorite discovered in 2011 in Western Sahara, his team has revealed a record of asteroid impacts and volcanic eruptions spanning nearly the entire history of Mars.

One of the most surprising discoveries: After Mars suffered a beating early in its life, everything calmed down, even during a period, almost 4 billion years ago, when our Solar System was thought to have suffered an attack cataclysmic. This is based on the age of 51 zircon crystals found inside the meteorite that likely formed under the extreme heat of an impact. The age of zircons largely clusters around 4.5 billion years ago, indicating a period of planetary assault, but the planet seems relatively calm afterward, Bizzarro and colleagues report today in the Proceedings of the National Academy of Sciences.

The finding aligns with recent work that questions the so-called Late Heavy Bombardment. When scientists first analyzed the rocks reported by Apollo astronauts, they seemed to indicate multiple devastating impacts on the moon nearly 4 billion years ago. Solar System models suggested fluctuations in the orbits of Jupiter and Saturn at that time, causing asteroids and causing them to crash into the inner Solar System.

But the new analysis has since made it clear that many of the moon rocks came from a single impact, and other attacks date back 4.3 billion years. This did not suggest any spikes in impacts, but rather a gradual decline in bombing over time.

Meanwhile, updated computer models have suggested that the migration of giant planets to their current orbits also occurred earlier, near the start of the Solar System 4.56 billion years ago, triggering a heavy early bombardment that systematically declined from there. The idea is now further confirmed by the new study, says Desmond Moser, a Western University geochronologist who was not involved in the work. The work, he says, paints “a compelling picture” of Martian history.

The first recorded impacts from the team’s zircons, which hit two distinct peaks just 30 million years apart, are just circumstantial evidence that the gas giants moved at that time. Even when Jupiter and Saturn weren’t migrating, there was a lot of protoplanetary debris flying into the early Solar System, says Nicolle Zellner, a lunar geochemist at Albion College who wasn’t involved in the work.

Indeed, the new simulations suggest that a large amount of mass was flying around the Solar System during this time, even potentially providing complex molecules that can seed the chemistry of life on Earth and other planets. How much material? “A lunar mass, but spread over a billion years,” says Zellner.

While Bizzarro’s team can’t say why the first impacts took place, Black Beauty gave a taste of what they helped form: a water-rich planet. In a study published in Advances in science Late last month, his team inferred a drastic increase in oxygen 4.4 billion years ago, a jump that could only plausibly be explained by the presence of water, possibly supplied by water-rich asteroids. “Either the water was already there,” says Bizzarro, “or it came with the impactor.”