THE solid metal centre of Earth is shrouded in mystery. Or, more accurately, in thousands of kilometres of molten metal and swirling magma. It is impossible to examine up close, so everything we know about it must be inferred.
What would we give to study a naked core directly? NASA’s answer is $850 million – the cost of a mission led by planetary scientist Lindy Elkins-Tanton, the director of Arizona State University’s School of Earth and Space Exploration. She is only the second woman to lead a NASA deep-space mission.
Due to , the mission will venture to an extraordinary asteroid between Mars and Jupiter. Some 210 kilometres across, asteroid 16 Psyche is unique in that it seems to be composed of solid metal.
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It may represent the exposed core of a tiny planet that has had its outer layers smashed away, so Elkins-Tanton believes it could tell us a lot about the core and formation of our own planet. And its likely composition represents the ultimate fantasy for wannabe asteroid miners.
Why go to Psyche?
We want to learn about how Earth formed, but we can’t get to the core to test our ideas, so we are going to a metal world. It is the only place in the solar system where we can directly observe a planetary core.
Were you surprised last year, when NASA selected your project for funding as one of its Discovery-class missions?
We’re all still pinching ourselves. We started out competing against 27 other missions. We knew we had a really strong science case – it’s so exciting to go to the first metal world. But usually you don’t get through step one of NASA’s selection process the first time you try, so it’s crazy that we went all the way. We bucked all the trends, and now we’re trying to prove that we’re worthy.
How do you know Psyche is metal?
We’re pretty darn sure from its radar albedo: a very high percentage of radar is reflected back by Psyche compared with other asteroids. We also know from how quickly it heats and cools: its thermal inertia is four times higher than any other asteroid. So it really seems to be largely metal, if not completely metal. We think it’s the result of a planetesimal being hit over and over again as the solar system formed, leaving only its core.
When the , how will you tell whether the asteroid is a core or something else?
We’ve got a lot of predictions for what it will look like if it’s a core. To investigate, the Psyche spacecraft now being built will have an imager and a magnetometer, and we’ll do an experiment to measure exactly how its gravity varies around the asteroid’s surface, which will reveal composition and structure. But the key instrument is the gamma ray and neutron spectrometer, which will tell us the elemental composition of the surface. Based on the metal meteorites that fall to Earth, we think it’s mainly iron and nickel, and that’s what we think Earth’s core is too. But it has lots of goodies mixed in, which is what makes the asteroid miners excited.
The asteroid miners?!
At this point I have to say: “NASA reminds me this mission is about fundamental science and nothing to do with asteroid resources.” That said, Psyche is mainly iron and nickel, but we also expect silver, gold, palladium, iridium and copper.
So the asteroid would be worth a lot?
I calculated it for fun, and in the metals market of January 2017 it would have been worth 10 quintillion dollars. That’s a 1 followed by 19 zeros – a large multiple of Earth’s gross domestic product, which is in the region of $100 trillion. But of course it’s an irrelevant number because (a) if you brought it to Earth it wouldn’t be worth that any more and (b) there’s no way to bring it to Earth. It’s complete fantasy.
Nevertheless, people want to exploit the resources in asteroids, right?
We don’t have an Elon Musk for asteroid mining, and there is no significant technology for it yet, but there’s a huge amount of interest and a number of companies working on it, so I’m sure it will happen.
I’m on the for space resources at the University of Leiden in the Netherlands. And right now, Luxembourg is positioning itself in a bid to own the European processes of governance, industry and law concerning asteroid mining.
In terms of technology development, water on the moon is going to be the first target. Asteroids are going to be much more difficult.
You mean extracting water from the moon?
Yes, from ice or water absorbed in lunar minerals. That will be critical to future lunar settlements. The number of private consortia that are getting together to go to the moon, which seems attainable compared with Mars, means people will attempt this. There are going to be problems, but people are going to succeed.
How did you get into all this?
I actually wanted to be a veterinarian until I realised that animals hate veterinarians. Even at college I wasn’t sure if I wanted to study biology or Earth science. And I didn’t have the confidence to go for a PhD, so I went into business. Then I got married, had my son, then separated from my husband and became a math teacher. At 31 I decided to go back to get my PhD. I was a single mother and my son started kindergarten at the same time.
“On Earth, the metals in this asteroid would be worth 10 quintillion dollars”
You’re basically the J.K. Rowling of planetary science.
I guess! So in grad school I studied half Earth and half the moon. I studied return samples from the Apollo missions, which I just adored. I made a model of how a magma ocean could freeze and that launched me into planetary science.
And, ultimately, planetary politics. Tell me about the Interplanetary Initiative that you started with ASU president Michael Crow.
It’s an effort to shape our future in space. I believe we’re going to do a lot more space exploration, because it’s human nature to explore and space is the place to go. The sheer fact that we can do it is miraculous. And the thing about space exploration is that it’s almost uniquely inspiring to people – an illustration of an integrated society trying to do better. That was the great pull of Star Trek.
What happens when on Mars there’s an Elon Musk settlement right next to a settlement from China? Do they become the best allies to help each other survive, or does their allegiance remain to entities back on Earth, at least 7 radio-minutes away? Can we figure out a better set of legal and social norms to go into the future with? I think we can.
This article appeared in print under the headline “Seeking Earth’s core… in space”
