The metal ball that has caught Nasa's fancy rate hikes this year

Humankind has visited rocky worlds & icy worlds and worlds made of gas, but never seen a metal world

Nasa will be heading to a metal world.

The space agency announced on Wednesday that a spacecraft named Psyche would visit an asteroid named Psyche, one of two new missions it will be launching into the solar system in the 2020s.

“For the purpose of simplicity, and out of our initial excitement, we just named our mission directly after what we’re going to visit,” said Lindy Elkins-Tanton, director of the Arizona State University school of earth and space exploration, who will serve as the mission’s principal investigator.

From radar observations, Psyche the asteroid appears ellipsoid in shape, about as wide as Massachusetts. It is also quite dense, with estimates of 200 to 450 pounds per cubic foot, which is much denser than most asteroids. (By comparison, the average density of Earth is 344 pounds per cubic foot.)

Psyche is also very bright, adding to suspicions that it is made of metal. “Humankind has visited rocky worlds and icy worlds and worlds made of gas, but we have never seen a metal world,” Elkins-Tanton said. “It’s the only roundish, fairly spherical metal body in our solar system. Not only is it unique, it’s improbable.”

Planetary scientists like Elkins-Tanton think it is the nickel-iron core of a small planet that was bashed to pieces early in the history of the solar system. A trip to Psyche could reveal clues about what is at the centre of Earth, something scientists will never be able to observe directly.

Psyche, the spacecraft, is to launch in 2023 and arrive at Psyche, the asteroid, in 2030. The spacecraft is to orbit the asteroid for 20 months.

Lucy, the other mission Nasa selected on Wednesday, will also explore asteroids. Named after the fossil of a hominid ancestor of humans that lived more than three million years ago, Lucy is to launch in 2021 and then fly by six asteroids that are thought to be relics of the solar system, completing its mission in 2033. Its targets are the Trojans, asteroids that have been captured by Jupiter’s gravity and now share the same orbit around the sun as Jupiter.

The characteristics of Trojan asteroids vary widely, and planetary scientists think they formed in different parts of the solar system before being swept into Jupiter’s orbit.

“We believe that’s telling something about how the solar system formed and evolved,” said Harold F. Levison, a scientist at the Southwest Research Institute in Boulder, Colorado, who is the principal investigator of Lucy. “The small bodies are really the fossils of planet formation.”

Both Psyche and Lucy are part of Nasa’s Discovery program, a competition where scientists propose missions to the space agency to fit within a certain cost. The price tags for Psyche and Lucy are capped at $450 million each.

Nasa also announced that a third finalist, Neocam, a telescope to search for asteroids that could collide with Earth, would receive another year of funding to address issues that have been raised about that proposal. The other two finalists had proposed explorations of Venus, a planet neglected by Nasa in recent decades.