Meteorite reveals that Mars volcanoes erupted recently
Canadian-led analysis reveals the meteorite's history in detail
A meteorite from Mars at Toronto's Royal Ontario Museum has changed the way scientists view the seemingly cold, dormant Red Planet, revealing that it was still hot and bubbly in places when the first mammals scampered on Earth.
"This paints a picture of a more geologically active planet — lots of volcanoes, lots of lava," said Brendt Hyde, a mineralogy research technician at the museum who helped analyze the meteorite, in an interview with The National's Ron Charles.
"It just paints a picture of a nice, vibrant planet, not a cold dead planet like we often envision other planets in the solar system."
The results of the meteorite analysis and a discussion of their implications were published in the journal Nature on Thursday.
The space rock analyzed in the study, which was led by Desmond Moser, a planetary scientist at Western University in London, Ont., is one of about 60 meteorites around the world known to have come from Mars.
Scientists in the past had tried to figure out how old the meteorite was in order to learn more about the geological history of Mars. In order to do that, they made chemical measurements of the ratio of uranium to lead — over time, uranium decays into lead at a constant rate, and the amount of lead increases relative to the uranium.
However, using this technique, age estimates for the meteorite had varied wildly from four billion years old (nearly as old as the solar system) to 200 million years old (young enough for it to have formed when the first mammals and dinosaurs roamed the Earth).
Moser and his team suspected that was because scientists were analyzing different parts of the rock and that the "age" they determined could refer to when the rock formed, when it was ejected from the volcano or when it was hit by the asteroid that launched it toward Earth.
In order to separate the different events, Moser and his team carefully examined the entire meteorite for minerals that provided evidence of specific incidents in the rock's history. In particular, they looked for a mineral called baddeleyite that grows after rock has been melted into lava and then cools after a volcanic eruption.
When baddeleyite forms, it contains no lead at all, said Moser in a phone interview Thursday.
"The clock starts at zero when you look at those minerals," he told CBCNews.ca from Iceland, where he was looking for Earthly rocks similar to the Mars meteorite.
By measuring the amount of lead that formed only since the volcanic eruption, the researchers learned that the eruption took place just 180 million years ago.
In contrast, the rock outside the baddeleyite appeared to be 4 billion years old.
Moser said that's because the lava that formed the meteorite melted from some other rock.
"If you melt a 4 billion-year-old piece of planet … it will carry kind of a signature or a memory of what it's melted from," he said. In fact, it seems the lava that came out of the volcano was melted from "very ancient material" within Mars that was only recently tapped by volcanoes, Moser added.
That's surprising because similarly old material isn't known to exist within the Earth — the magma beneath the Earth's crust is constantly circulating and the only rocks that are a few billion years old are found in parts of the Earth's crust that have been on the surface and out of circulation for most of its history.
In addition to pinpointing when the eruption took place, the researchers also figured out when an asteroid smashed into Mars, launching the meteorite into space and en route to Earth. To do that, they examined the rock for pockets of glass that form when the energy from an asteroid impact melts part of the rock — including minerals such as baddeleyite — before launching it off the surface of the planet.
"Then of course, it reaches outer space, where it's minus 200 C, so it freezes," Moser said.
In the process, a chemical reaction causes little rims of a mineral called zircon to form around the pockets of glass – pointing to areas of the rock that were most impacted by the asteroid. Conveniently, when baddeleyite melts, it tends to kick out any lead that was trapped in the crystal, resetting the uranium-lead clock.
So by measuring the amount of lead in pockets of baddeleyite glass rimmed by zircon, the researchers determined that the asteroid impact took place about 22 million years ago.
Moser said the researchers now hope to apply their analysis technique to other Mars meteorites, pieces of the moon, and chunks of asteroids from beyond Jupiter.
"Being able to tease out what happened when is something we can now apply to all meteorites," he said. "That should allow us to investigate in greater detail all these stories from these other pieces from space."
With files from Ron Charles