Martian mystery

Study rewrites Mars' origin story, suggests planet took 15 million years to form

Past estimates suggested the planet formed in just 2 to 4 million years. But which figure is right is open to debate.

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A new study adds to the debate about how long it took for Mars to form, suggesting the Red Planet’s formation may have taken up to 15 million years — not 2 to 4 million years as previously thought.

By looking at the composition of Martian meteorites, and with the help of a simulation of how those parts of the planet were created in the first place, the researchers conclude that Mars may have been accruing mass anywhere up to 15 million years after its core was born.

In this case, the mass likely came in the form of three large planetoids slamming into the planet's surface, the researchers say.

“This gives us a new take in the way we look at the formation of planets,” Simone Marchi, research fellow at at Boulder University tells Inverse. “The timescale is crucial to understand the process by which the planet formed. Previously we were really focusing on a very fast planet formation, now maybe this could change.”

The findings contradicts past research about Mars’ formation, suggesting the planet developed far slower than previously thought. Better understanding of Mars’ developmental timeline helps shine a light on the planet's temperature, atmosphere, and habitability today. It also helps answer questions about how our Solar System — and our own planet — developed.

The results are detailed in a study published Wednesday in the journal Science Advances.

The making of Mars

Some 4.5 billion years ago, when the Solar System started forming, the planets slowly started to form from the dust and rocks left from the Sun's creation. This process is called accretion. Research had suggested that Mars’ accretion — gravity pulling together particles into its core to make the planet — took about 4 million years.

To get their new estimate, Marchi and colleagues analyzed Martian meteorites and their composition, as well as the elements in the mantle of Mars. The Martian mantle contains a lot of iron-loving elements, like tungsten. To understand how it formed, the researchers used a simulation to trace how elementary particles slammed together over time, slowly building up the planet.

They conclude that three large meteorites, each with a diameter of 1,000 to 2,000 kilometers, hit Mars at some point after its core formed. From there, they hypothesize that the planet gained both elements and mass for anywhere between 5 and 15 million years after it was born.

“All the data we have from the meteorites is compatible with it [Mars’ formation] starting earlier,” Marchi says. “We’re not saying that it started for sure, but there’s nothing in the meteorite that prevents this.”

But forensically recreating the planet-formation process is not an easy task.

“Formation is a loaded word. It means completely different things to different people,” Steven Desch, professor at Arizona State University, tells Inverse. “They're looking at a significant aspect: How long ago can you add mass to Mars? That is not the same thing as how long it takes to form.”

It is not that the simulation or the results are wrong, but the larger context has to be taken into account to make an accurate estimate, Desch says.

“They don't make a strong case for how late formation goes, just that a little bit of matter is coming in the end.”

Mars' origin story: A matter of debate

The idea that planets take a long time to form is based on old data collected from the Moon, Desch says. But future research will likely show they took far less time, he predicts.

“I don't think that it took that long [15 million years]. It was probably much closer to 5 million years,” Desch tells Inverse.

“I don't think [the study] changes the story that Mars pretty much formed in one to three million years,” Desch says.

The research is important, however, because it can help scientists better understand the process overall, he says.

"That it could have taken 15 million years is a good thing to know," he says.

To get to the bottom of it, scientists need more samples of the Martian mantle, Marchi says. Right now, scientists rely on meteorites that have landed on Earth, but these are scarce: There are just 200 or so.

To get better samples requires sending more powerful rovers to collect bigger bags of rocks — and return the samples to Earth. The samples should also be more varied to get a clear picture, Marchi says. For all scientists know, the meteorite samples at their current disposal may have come from very few places on Mars, meaning they aren't very representative of the whole planet.

“The planet could be radically different from what we expect. The future is in trying to remove this bias,” Marchi says.

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