16 Psyche

Discovery and name

Psyche was discovered by the Italian astronomer Annibale de Gasparis on March 17, 1852. He named it after Psyche, the Greek goddess of the soul, who was born mortal and married Eros. Because it was the 16th asteroid found, it is often written as 16 Psyche.^[1]

Its old astronomical symbol was a butterfly's wing topped by a star — in Greek, psyche means both “butterfly” and “soul.”^[5]

Size and shape

Psyche is one of the larger objects in the main belt, averaging about 222 km across with dimensions of roughly 278 × 238 × 171 km.^[3] NASA describes it as irregular and potato-like, with a surface area of about 165,800 km² (64,000 square miles).^[1] Its mass, about 2.4 × 10¹⁹ kg according to Gaia data, makes it the largest known M-type (metal-type) asteroid.^[5]

Psyche spins once every 4.2 hours, and its axis is tilted by about 98°, so it rolls around the Sun nearly on its side.^[3][5]

Metal world — or metal-and-rock world?

For years scientists described Psyche as mostly metal. More recent data point to a mixture of metal and silicate rock, with metal making up an estimated 30% to 60% of its volume. That estimate comes from radar observations and from measurements of its thermal inertia — how quickly it gains or re-radiates heat.^[1]

Psyche's radar brightness varies across its surface and is two to four times higher than that of most main-belt asteroids, and a few patches look especially metal-rich.^[5] Its bulk density of about 4.2 g/cm³ is far below the 7.9 g/cm³ of solid iron-nickel, which is one reason researchers now picture a porous or mixed body rather than a solid ball of metal.^[3][5]

Where did Psyche come from?

One leading idea is that Psyche contains a large amount of metal from the core of a planetesimal — one of the building blocks of the planets — stripped bare by violent hit-and-run collisions in the early Solar System. If so, it offers a way to study a planetary core, something we can never visit on Earth.^[1]

Other proposals include a body that re-accreted from a mix of metal and rock, which could make it a candidate parent body for the mesosiderites, a rare class of stony-iron meteorites.^[5][9] Answering this question is a central goal of NASA's Psyche mission.^[1]

NASA's Psyche mission

NASA's Psyche spacecraft launched on October 13, 2023, on a SpaceX Falcon Heavy from Kennedy Space Center's Launch Complex 39A.^[2] It is the first interplanetary spacecraft to use Hall-effect thrusters, and it carries NASA's first test of laser (optical) communications beyond the Earth–Moon system.^[6]

After a Mars gravity assist on May 15, 2026, the spacecraft is cruising toward the asteroid belt.^[6] Its prime mission begins in August 2029, when it will spend about two years orbiting Psyche with a multispectral imager, a gamma-ray and neutron spectrometer, a magnetometer and a radio gravity experiment.^[1][2] The mission is led by Arizona State University and managed by NASA's Jet Propulsion Laboratory.^[4]

Can you hold a piece of something like Psyche?

Not of Psyche itself — but iron meteorites are thought to come mostly from the cores of planetesimals, the very kind of object Psyche may be.^[7] Many show a striking crisscross Widmanstätten pattern when cut, polished and etched, created by extremely slow cooling of molten metal in the early Solar System.^[8] That makes them a popular first specimen for collectors — see our meteorite buying guide.

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