NASA's Juno spacecraft has spotted the elusive fifth moon of Jupiter transiting the giant planet's Great Red Spot, giving astronomers a rare view of this small but intriguing natural satellite.

New images returned by NASA spacecraft Juno show Amalthea, a tiny moon with a radius of just 52 miles (84 kilometers). It's the reddest moon known.

Amalthea is within the orbit of Io, the closest of Jupiter's four large moons, along with three other oddly shaped mini moons: Metis, Adrastea, and Thebe. It's so close to Jupiter, in fact, it only takes Amalthea half of a day on Earth to circle its planet.

NASA's plan to build a train track on the moon is part of the agency's Innovative Advanced Concepts program, which aims to develop "science fiction-like" projects for future space exploration.

NASA is considering building a railway on the moon that uses levitating robots to move payloads around the lunar surface.

If it is eventually deployed, the lunar railway system will provide “reliable, autonomous, and efficient payload transport on the Moon,” NASA explained in a statement. NASA’s Artemis program is facing delays due in part to delays in the development of SpaceX’s modified lunar lander Starship.