Psyche arrives at the metal asteroid
NASA's Psyche spacecraft is due to reach the metal-rich asteroid (16) Psyche in August 2029. Its goal is to find out whether the asteroid is the metal core of an early planet or a different kind of mixed metal-and-rock world.
Available views: Orbit ✓ · Sky — (not visible in the sky)
The story
The Psyche spacecraft launched on a Falcon Heavy rocket on 13 October 2023. Its target is (16) Psyche, an asteroid in the main belt between Mars and Jupiter. In May 2026 the spacecraft swung past Mars, using the planet's gravity to change its speed and direction, and it is due to enter orbit around Psyche in August 2029.
Psyche is about 220 km across on average, which makes it one of the larger asteroids. That is a little less than the straight-line distance from Paris to Brussels, about 260 km. What makes it special is that its surface appears to contain a lot of metal. When radar waves are bounced off it, they come back much more strongly than they do from ordinary rock, which scientists read as a sign of metals such as iron and nickel.
The mission drew attention because of one idea. Perhaps, when the solar system was very young, a small planet lost its rocky outer layers in collisions, leaving only its metal core behind, and that core is Psyche. Earth's own core lies about 3,000 km beneath our feet and can never be seen directly. If Psyche really is an exposed core, it would give us our first close look at the inside of a planet.
Recent studies, however, urge caution. Density estimates and other observations suggest that Psyche may be a mixture of metal and rock rather than a solid lump of metal. In that case it would be neither a broken core nor an ordinary stony asteroid, but a new kind of object. Only close-up measurements from the spacecraft can settle which it is.
Mission goals
One key idea in explaining how planets form is called differentiation. When a young planet gets hot enough, heavy metal sinks to the middle and lighter rock floats to the top. Earth is thought to have separated this way into a metal core and a rocky shell. So far, though, this has been checked only indirectly, through earthquake waves and meteorites. Nobody has ever looked at a metal core directly.
That is why the search for traces of magnetism is so important. When a molten metal core cools and hardens, it can lock in the magnetic field of that time, like a fossil. If the spacecraft's magnetometer finds such a record, it would be strong evidence that Psyche once had a molten metal core. If it finds nothing, the core idea becomes weaker.
Gravity is another clue. As the spacecraft circles Psyche, tiny wobbles in its orbit reveal whether the inside is evenly packed or whether heavy material is bunched up in places. A gamma-ray and neutron spectrometer will also measure the chemical elements on the surface, showing how much iron and nickel are really there.
Mission chronology and background
(16) Psyche was discovered in 1852 by the Italian astronomer Annibale de Gasparis. It is named after Psyche, a figure in Greek mythology whose name means ‘soul’. The number 16 means it was the sixteenth asteroid to be numbered. For a long time it was just a line in a catalogue, until radar observations showed that it reflects radio waves strongly, as metal would.
Clues that metal asteroids exist had appeared earlier. Some meteorites that fall to Earth are iron meteorites, made almost entirely of iron and nickel. Scientists think these are pieces of bodies that once had metal cores and were later smashed apart. If so, there must have been metal-rich bodies somewhere in the solar system that these pieces came from, and Psyche is a leading candidate for such a body.
Besides its science instruments, the spacecraft carries a technology test. It is a deep-space optical communications system that sends information using laser light. In tests it sent data much faster than ordinary radio links from tens of millions of kilometres away. The mission is managed by NASA's Jet Propulsion Laboratory, and the science is led by Arizona State University.
Other milestones of this mission
Where to see it — sky and simulator
The Psyche spacecraft cannot be seen from the ground with any instrument. The asteroid itself can appear as a faint point in an amateur telescope when conditions are good, but no shape can be made out. Instead, move the time in NowSky's orbit view to August 2029 and you can replay the moment the spacecraft's path meets the orbit of Psyche.
During the replay, watch how the path curves. The Psyche spacecraft uses electric propulsion: electricity from its solar panels pushes out a stream of xenon ions. The push is very gentle, but it goes on for years, so the orbit widens slowly in long, smooth curves. The point in May 2026 where the spacecraft passed Mars and changed direction also shows up along its track.
After arrival, news will keep coming for years. The spacecraft is planned to begin in a distant orbit about 700 km up and work its way down through lower orbits, reaching about 75 km at its closest. Each step down brings sharper pictures and better measurements, and operations are planned to continue into 2031. The schedule may change as the flight goes on.
See this for yourself — replay the moment in the orbit view
FAQ
Is Psyche really a planetary core?
That is not settled yet. The evidence that it is rich in metal is solid, but its density and other observations also allow a mixture of metal and rock. The answer depends on the spacecraft measuring its gravity and searching for magnetic traces up close.
Can I see Psyche through a telescope?
Under good conditions it can show up as a very faint point in an amateur telescope, but no shape is visible. The spacecraft cannot be seen from the ground, so following its path in the replay in NowSky's orbit view is the practical choice.
Why does the trip take so long?
Electric thrusters push very gently, so they cannot change an orbit quickly. Instead they push a little at a time for years and slowly build up speed. Using a gravity assist from Mars saves even more fuel, but it makes the journey longer.
Will detailed pictures appear right after arrival?
They come in stages. The first images are taken from a distant orbit and show the whole asteroid, and the detail improves each time the spacecraft moves lower. Precise measurements of gravity and chemical elements are made in the lowest orbits, so the main results will come some time after arrival.
Related
- Psyche launch
- Lucy at the Trojan asteroids
- Hayabusa2 reaches 1998 KY26
- Psyche — object index
- Ceres — object index
- Mars — object index
Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.