NASA to Explore What Could Be The Iron Core of a Former Planet

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A spacecraft with purple wings flies above the ragged peaks of a gray asteroid.
Artist concept of NASA's Psyche spacecraft orbiting its destination asteroid. (NASA/JPL-Caltech/Arizona State University/Space Systems Loral/Peter Rubin)

NASA is preparing a journey to an unusual asteroid named Psyche,
a journey that no spacecraft has taken before.

Psyche is not your common asteroid. Scientists believe it's the metallic core of a planet that had its rocky layers stripped away by violent collisions with other space objects in the distant past.

NASA’s spacecraft will depart Earth on a SpaceX Falcon Heavy launch vehicle in August 2022, beginning a voyage to the solar system’s main asteroid belt, between the orbits of Mars and Jupiter. Along the way, in May 2023, it will fly near enough to Mars to gain a boost in speed from that planet's gravity.

A rough, cratered gray asteroid floats against the black backdrop of space.
An artist's concept of the asteroid Psyche, believed to be the remnant metallic core of an ancient planet. (NASA/JPL-Caltech/ASU)

Arizona State University will lead the Psyche mission, conducted by NASA’s Jet Propulsion Laboratory.

The asteroid

Psyche was discovered in 1852 by Italian astronomer Annibale de Gasparis, who named the slowly moving, star-like spot of light in the sky after the Greek goddess of the soul.

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Psyche circles the sun within the solar system’s main asteroid belt, between the orbits of Mars and Jupiter. At 140-miles wide, the asteroid is one of the most scientifically intriguing objects in the belt.

A fuzzy, white distorted circle sits against a jet black background.
Image of asteroid 16 Psyche captured by the Very Large Telescope using adaptive optics technology. (ESO/LAM/Very Large Telescope)

Psyche’s density, calculated from a mass estimated by its gravitational influence on other asteroids and a size measurement made by the IRAS infrared survey, tells scientists the asteroid is largely composed of metal — unlike typical asteroids, which are rocky.

That's why scientists believe it may be the dense metallic core of a former planet, whose outer rocky layers may have been  blasted away by collisions with other objects.

If the asteroid Psyche is the iron core of a former planet or planetoid, then it may serve as a rare chance to examine a planetary core directly — an opportunity that fully formed planets do not offer, hiding their precious cores in secrecy beneath hundreds or thousands of miles of rock and magma.

A planet that might have been?

The early solar system is thought to have been a tumultuous place, filled with whizzing asteroids, comets, and “planetesimals” — primordial, kilometer-plus-sized objects that merged with each other to form planets. All these objects flying about frequently shattered against other large objects. The collisions reshaped them, and they gradually rebuilt over time from a continual bombardment of smaller bits.

As these space objects became larger, their gravity’s strength also grew, which in turn pulled in even more stuff, and they snowballed. Some quickly dominated their regions of the solar system, and would eventually become the planets we know today.

A picture of blue, white and green Earth with a cutaway that shows its dark red crust; lighter red upper mantle and mantle; yellow-red outer core; and bright yellow inner core.
Cutaway of Earth showing the internal layered structure as we understand it through indirect measurements and observations. (NASA)

These planets — largely molten from the incredible heat generated by the impacts and bombardment of their formation — underwent a process called differentiation, in which heavier material, like metals, sank to form their cores, while lighter stuff — such as silicates — floated toward the surface. This layering effect led to the structures of planets and moons we understand today, with dense, metal-rich cores surrounded by mantles of lighter material.

Direct exploration of a one-time planetary core would provide insights into the formation and development of planets, like Earth, that can otherwise only be gleaned indirectly through measurements of gravity and the motion of seismic waves traveling through a planet’s interior.

Solar electric propulsion

The Psyche spacecraft will be specially equipped with a high-tech engine to propel it on its voyage and eventual rendezvous with the huge iron asteroid.

Picture of NASA's Psyche spacecraft during construction at the Jet Propulsion Laboratory. (NASA/JPL-Caltech)

The engine sounds like something from a science fiction novel.

Most robotic probes sent to distant reaches of the solar system rely on the momentum of their launch from Earth and changes in speed and trajectory provided by the gravity of planets they steer past.

The Psyche-bound craft will use solar-electric propulsion to change course and speed and eventually settle into an orbit around the destination asteroid. NASA has tested similar propulsion systems  before, such as on the Deep Space 1 and Dawn spacecraft.

Here’s how it works:Using electricity generated with solar panels, heavy atoms (in this case xenon) are ionized and accelerated by electric fields, then shot into space in a high-speed beam to produce thrust.

A black, round engine thruster with interior rings of bright blue.
A solar-electric propulsion engine being tested on Earth. The engine uses a beam of accelerated ions as thrust. (NASA)

Though this engine does not have the raw umph of a conventional chemical combustion rocket, it has distinct advantages.

For one, solar-electric propulsion is much more efficient, making the best use of its propellant with far less waste. And since the source of energy that drives it comes from sunlight, the spacecraft does not need to carry along the weight of chemical or nuclear fuel.

And though the power of this engine thrust is modest, it can run continually, the gentle acceleration building up over a long period of time.

The Psyche spacecraft will arrive at its destination in 2026, only four years after launch. Then, we may glimpse secrets of the birth and development of a planet. The kind of information that our own Earth keeps buried under thousands of miles of rock.