Here are eight things to know about the missions.

Studying the Trojan asteroids could provide information about how they moved before embedding in Jupiter's orbit. "They may be captured asteroids, comets, or even Kuiper Belt objects".

The spacecraft launches in 2021.

The Psyche spacecraft will arrive at the asteroid in 2030 after flying by Mars in 2025.

Lucy's target in the main asteroid belt has been named Donaldjohanson, as a nod to the paleontologist who discovered the famous 3.2 million-year-old fossil in 1974.

It is believed that Trojans are fossilized primordial material that made outer planets.

Psyche is the third short-listed mission, looking at the origin of planetary cores by studying the metallic asteroid Psyche. The mission was approved by NASA in January 2017. The probe is expected to be at its first destination - a main asteroid belt by 2025.

Because Jupiter's Trojan asteroids orbit far from the sun, they all have very cold surfaces.

"Psyche is thought to be the exposed core of a planetary embryo - perhaps like Vesta - that initially melted and later cooled to form a central metallic core, silicate mantle, and basaltic crust".

"Human kind has visited rocky worlds and icy worlds, but we've never seen a metal world", Lindy Elkins-Tanton, principal investigator for the Psyche Mission, which NASA just green-lit as part of its ongoing Discovery program, told reporters in a press call this afternoon.

The robotic missions will be launched in 2021 and 2023 respectively, a statement from the space agency said. Unlike Lucy, it will slow down and enter orbit.

- The Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy mission (VERITAS).

NEOCam, named after unsafe near-Earth objects (NEOs), would have helped discover 10 times the objects of any space rock-hunting mission to date.

The Discovery Missions are a relatively-low cost way of teaching scientists about the universe.

Lockheed Martin is already the base of six other mission operations, spokesman Gary Napier said. The latter, now on its way to visit asteroid Bennu, has a price tag of about $800 million, including the cost of its Atlas V carrier rocket. Numerous space agency's flagship missions cost more than $1 billion. The Curiosity and Mars 2020 rovers are flagships, as is the proposed Europa mission.

The mission is one of two selected from five proposals.

When you add the potential planetary science discoveries to the possible gains for space exploration and asteroid mining, scientists start to get pretty psyched about Psyche. Its newest members have been titled Psyche and Lucy.

The Near Earth Object Camera or NEOCam was also awarded an extended grant by the agency for an additional year. The Kepler space telescope that hunts for potentially habitable planets outside our solar system is also one of Discovery's missions.

A group from Arizona State is working on an out-of-this-world mission.

NASA's Jet Propulsion Laboratory managed by Caltech is the managing organization and will build the spacecraft with industry partner Space Systems Loral (SSL).

When practical, NASA likes to use flight-proven hardware-often referred to as heritage technology.

"These small bodies are really the fossils of planet formation and that's why we named Lucy after the human ancestor known as Lucy", lead scientist Hal Levinson, with the Southwest Research Institute in Boulder, Colorado, told reporters.