When most people think of a meteorite, they imagine a lump of iron-nickel metal. And while there are plenty of those, stony meteorites peppered with fine metal flakes are far more common. Psyche, a robotic spacecraft, scheduled to launch in October 2023, will target one of these sources of those ‘heavy metal’ meteorites, when it visits the giant metal asteroid and namesake, 16 Psyche (SY-kee).
This potato-shaped asteroid measures about 130 miles (210 km) in diameter and, unlike most other asteroids that are rocky or icy bodies, is thought to be comprised mostly of metallic iron and nickel, similar to Earth’s core. Astronomers arrived at that conclusion by examining how Psyche the return echoes of radio waves directed at the asteroid. It also shows signs of rock, too – about 10%.
Scientists wonder whether Psyche could be the remains of a one-time planet that lost its rocky outer layers in violent collisions with asteroids eons ago, leaving behind only a core of exposed metal. Imagine. Instead of the surface of the body, we’ll be able to peer directly at its interior. No drilling required. Even better, the mission will place the spacecraft in orbit about Psyche, so we’ll be able to map the entire asteroid in great detail unlike the recent Pluto flyby, where we saw one hemisphere crisply and the other less so.
“This is an opportunity to explore a new type of world — not one of rock or ice, but of metal,” said Psyche Principal Investigator Lindy Elkins-Tanton of Arizona State University. “16 Psyche is the only known object of its kind in the solar system, and this is the only way humans will ever visit a core. We learn about inner space by visiting outer space.”
The mission will help scientists understand how planets and other bodies separated into their layers – including cores, mantles and crusts – early in their histories. Our is such a world with an iron-nickel core, silicate mantle and granite crust. The probe will arrive at the asteroid in 2030 after getting a gravity assist from Earth in 2024 and Mars in 2025. Spacecraft pick up extra speed when they’re sent on paths that pass close to planets or moons. Essentially, they rob some of the body’s energy and use it to speed up towards their target. NASA’s been stealing planetary momentum ever since the Voyager’s Grand Tour of the outer solar system.
Psyche is one of two asteroid missions NASA has up its sleeve. Lucy, another robotic spacecraft, will launch earlier, in October 2021, and reach its first destination in the main asteroid belt in 2025. From 2027 to 2033, Lucy will explore six Jupiter Trojan asteroids. The Trojans number over 6,100 and are trapped by Jupiter’s gravity in two swarms that share the planet’s orbit, one leading and one trailing Jupiter in its 12-year circuit around the sun. They’re thought to be relics of a much earlier era in the history of the solar system, and may have formed far beyond Jupiter’s current orbit and later captured by the giant planet.
“This is a unique opportunity,” said Harold F. Levison, principal investigator of the Lucy mission from the Southwest Research Institute in Boulder, Colorado. “Because the Trojans are remnants of the primordial material that formed the outer planets, they hold vital clues to deciphering the history of the solar system. Lucy, like the human fossil for which it is named, will revolutionize the understanding of our origins.”
Both Psyche and Lucy are Discovery Program class missions — innovative, relatively low-cost missions to address key questions about the solar system as well as planets around other stars. The program began in 1992 and includes some familiar names: Mars Pathfinder, Dawn (to asteroids Vesta and Ceres), Kepler (extraterrestrial planets) and Stardust (comet sample-return).