Why Is an Asteroid Worth $10,000,000,000,000,000,000?

The asteroid 16 Psyche, which a NASA space probe is scheduled to visit in 2026, is a massive object about 140 miles (226 kilometers) in diameter. It orbits about 235 million to 309 million miles (378 million to 497 million kilometers) from the sun. Unlike most asteroids, which are made of rock or ice, 16 Psyche is believed to be made mostly of iron and nickel, just like Earth's core.

The asteroid's composition also makes it, at least in theory, almost unfathomably valuable. Its estimated worth is $10,000 quadrillion, or $10,000,000,000,000,000,000. That's vastly more than the estimated $86 trillion gross domestic product (GDP) of all the nations on Earth combined (that number comes from the World Economic Forum).

But how do you actually value an asteroid? Linda Elkins-Tanton, the Psyche mission's principal investigator, says in an email that she developed the $10,000 quadrillion estimate back in 2017, using the price of the materials in the asteroid on the metals market. But that price is really a way of understanding the asteroid's unusual nature, rather than incentive for future space mining entrepreneurs.

"The critical thing, of course, is that the estimate is meaningless in every way," explains Elkins-Tanton, who is a foundation professor in the School of Earth and Space Exploration at Arizona State University, where she's managing director and co-chair of the ASU Interplanetary Initiative.

"First, we have absolutely no available technology for bringing Psyche back to Earth. And even if we did, the abundance of its metal would immediately render metals valueless on the markets. But, nonetheless, it was a fun exercise!"

Additionally, Elkins-Tanton says that the best current measurements of the asteroid's density indicate that it isn't pure metal, but instead has cracks and pore space, and more rock in the mix.

"We assume the metal in Psyche is iron and nickel, since that is the composition of all the metal meteorites that have fallen to Earth, and that is what we think the Earth's core is made of, " she says.

She provided a chart, showing that iron accounts for 94 percent of the mass of an average metal meteorite, which also typically contains about 5 percent nickel, plus smaller amounts of gallium, iridium, tungsten, cobalt, gold, copper, rhenium, platinum and other trace elements.

But she says it's important to stress that scientists don't yet know for sure what Psyche 16 is made of.

"We will find out what it really is when we get there," she says.