differentiated parent body some 500 kilometers in diameter. Other versions of this include the idea that it was not the result of a single large collision but multiple (more than three) relatively slow sideswipe collisions with bodies of comparable or larger size. However, this idea has fallen out of recent favor as mass and density estimates are inconsistent with a remnant core. A second hypothesis is that Psyche was disrupted and gravitationally re-accreted into a mix of metal and silicate. In this case, it may be a candidate for the parent body of the mesosiderites, a class of stony–iron meteorites. A third hypothesis is that Psyche may be a differentiated object (like 1 Ceres and 4 Vesta) but has experienced a type of iron volcanism, also known as ferrovolcanism, while still cooling. If true, this model predicts that metal would be highly enriched only in those regions containing (relic) volcanic centers. This view has been bolstered by recent radar observations. Exploration No spacecraft has visited Psyche, but in 2014 a mission to Psyche was proposed to NASA. A team led by Lindy Elkins-Tanton, the director of the School for Earth and Space Exploration at Arizona State University, presented a concept for a robotic Psyche orbiter. This team argued that 16 Psyche would be a valuable object for study because it is the only metallic core-like body discovered so far. The spacecraft would orbit Psyche for 20 months, studying its topography, surface features, gravity, magnetism, and other characteristics and would be based on current technology, avoiding high cost and the necessity to develop new technologies. On 30 September 2015, the Psyche orbiter mission was one of five Discovery Program semifinalist proposals. The mission was approved by NASA on 4 January 2017 and was originally targeted to launch in October 2023, with an Earth gravity assist maneuver in 2024, a Mars flyby in 2025, and arriving at the asteroid in 2030. In May 2017, the launch date was moved up to target a more efficient trajectory, launching in 2022, with a Mars gravity assist in 2023 and arriving in 2026. On 28 February 2020, NASA awarded SpaceX a US$117 million contract to launch the Psyche spacecraft, and two smallsat secondary missions, on a Falcon Heavy rocket. As of October 2022, the mission is scheduled to launch no earlier than October 2023, reaching the asteroid in August 2029. See also List of minor