Why is NASA sending a spacecraft to a metal world? - Linda T. Elkins-Tanton
Somewhere between the orbits
of Mars and Jupiter,
about 500 million kilometers
away from Earth,
floats a metallic orb
the size of Massachusetts.
That’s no moon... it’s 16 Psyche,
one of the most massive
asteroids in the solar system.
And it is the asteroid
our droids are looking for.
We humans have managed
to send robotic spacecraft
to all sorts of environments in space –
the gas clouds of Saturn and Jupiter,
the icy wastes of Europa,
and the rocky dunes of Mars.
But Psyche’s surface
isn’t just hard rock—
it’s heavy metal.
The asteroid mostly consists
of nickel and iron,
by far the largest known body
with such a composition.
But we don’t yet know what it looks like;
our best current radar images
show a pixelated smudge.
That’ll change in 2026,
when an unmanned spacecraft sent as
part of NASA’s Discovery Program
is scheduled to arrive.
So why is NASA so interested in Psyche?
Are we going to mine all that metal,
or build a giant space magnet?
Actually, the real reason
is right under our feet.
The core of the Earth is thought
to consist of a solid nickel-iron center
with a molten outer layer.
But we’re prevented from studying it up
close by 2,800 kilometers of solid rock.
The deepest we’ve been able
to drill is 12 kilometers.
Even if we could go further,
the pressure at the core is three million
times higher than at the surface,
with a temperature
of 5,000 degrees Celsius.
Simply put, a journey to the center of
the Earth is out of the question for now.
So scientists have had to resort
to indirect ways of studying the core,
like measuring earthquake waves
that pass through it,
or studying minerals thought
to have formed there.
But what if the best way to study
Earth’s inner space
is by visiting outer space?
After all, we have a pretty
good idea of how our planets formed.
Dust and gas orbiting our young Sun
cooled and collided
to form a few thousand miniature bodies
we call planetesimals.
As these continued to orbit,
some combined to grow larger,
eventually forming our planets.
Others experienced impacts that broke them
apart into smaller chunks—
the asteroids we see today
in the belt between Mars and Jupiter.
What makes Psyche so special
is that it appears
to have been a planetesimal
well on its way to becoming a planet,
with a rocky exterior
surrounding a metal core.
But its progress was cut short
by a series of hit-and-run collisions
with other planetesimals
that knocked off the rocky crust
until only the core remained.
Experiencing that many
destructive collisions
with no additive ones in between
is statistically very unlikely,
making Psyche an amazingly
rare opportunity
to study an exposed metallic core.
To do that, NASA’s robotic orbiter
will be equipped
with an array of advanced instruments.
A spectrometer will analyze
the gamma rays and neutrons
produced when Psyche
is struck by cosmic rays.
Each element in the periodic table
releases gamma rays
of specific wavelengths,
so these measurements will tell us
what elements are found on the surface.
A magnetometer will measure
Psyche’s magnetic field,
allowing us to learn more
about how Earth’s magnetic field
is generated at its core.
And of course, an imager will give us
a closer look at the surface
than ever before.
Visiting a whole new kind of world
is exciting enough on its own.
But the mission to Psyche gives us
a unique chance
to discover our own planet’s innermost
secrets in an orbit far, far away.
