Mission to a Metal World: In August, NASA will Launch a Probe to Study a Strange Metallic Asteroid Called Psyche

When our solar system was very young, there were no planets—only a diffuse disk of gas and dust circled the sun. But within a few million years, that churning cloud of primordial material collapsed under its own gravity to form hundreds, or maybe thousands, of infant planets. Some of those planetesimals, as astronomers call them, grew to be hundreds of kilometers across as they swept up more dust and gas within the swirling solar nebula.