NASA’s Lucy, The First Mission To The Trojan Asteroids, Will Uncover Early Solar System History

A space mission to explore a record-breaking number of asteroids launches today (16 October).

The Lucy mission is set to begin its 12-year journey by being shot up from the Cape Canaveral Space Force Station, Florida, on a United Launch Alliance Atlas V 401 rocket.

By taking the Earth’s gravitational assistance over many years, or “flybys” of the Earth, it will encounter several “Jupiter Trojan asteroids” with the aim of expanding our knowledge about the solar system in the very early days.

The Trojan asteroids are thought to be the remains of the primordial material that formed the outer planets — Jupiter, Saturn, Uranus, and Neptune. By getting a closer look at the asteroids, scientists aspire to pick up clues about the formation of the solar system and, more generally, planetary origins.

These small bodies go around the Sun, just like any other dweller of our solar system, but are interestingly grouped in two hives naturally. One hive leads Jupiter in an orbit around the Sun while the other trails.

NASA describes the placement of the asteroids thus: “Clustered around the two Lagrange points equidistant from the Sun and Jupiter, the Trojans are stabilized by the Sun and its largest planet in a gravitational balancing act.”

Lagrange points, named after the mathematician and astronomer Joseph-Louis Lagrange, are special locations around a planet’s orbit where the gravitational pull of the planet, the Sun, and the motion of the orbit together create an equilibrium state.

These places are where it is comfortable for space objects to settle down without much effort. The Trojan asteroids are comfortably placed around Jupiter’s orbit in this way. And because they’ve remained here naturally since the beginning of the solar system, they can tell us a thing or two about that crucial and fascinating early phase.

This is also how the mission gets its name, “Lucy”. Just as the fossilised human ancestor named Lucy, which was discovered in Ethiopia in 1974 by paleoanthropologists, provided unique insights into human evolution, the Lucy mission “promises to revolutionize our knowledge of planetary origins and the formation of the Solar System, including the Earth,” NASA explains.

Over its mission duration of 12 years, the Lucy spacecraft will cover a large distance of 6.3 billion kilometres. In order to do this, it will take the help of three Earth gravity assists in the years 2022, 2024, and 2030 — that will make it the first spacecraft ever to return to the Earth’s vicinity from the outer Solar System — and two massive solar arrays (7.3 m diameter each) to power its journey.

Lucy will first encounter the main belt asteroid called “Donaldjohanson”, which is named after the discoverer of the fossilised human ancestor Lucy, on 20 April 2025.

Two years later, it will begin a series of encounters with Trojan asteroids starting with Eurybates and its satellite, Queta, (binary system) in the swarm leading Jupiter. Five more Trojan asteroid visits are planned in the six years hence, ending with a binary system in the trailing swarm.

Lucy will study the surface geology, surface colour and composition, the interiors and bulk properties, and rings and satellites of these Trojan asteroids. A set of remote sensing instruments on board Lucy will help in recording scientific data. Three scientific instruments will get down to the business of uncovering the mysteries of the early solar system.

By the time Lucy completes its mission time, the spacecraft would have visited a record number of destinations in independent orbits around the Sun.

Though the mission will end in 2023, Lucy will live on. It will remain in orbit around the Sun, returning repeatedly to the Trojan asteroids, according to NASA, “for many thousands, and possibly millions, of years”.

Given that it will live long, Lucy will carry a golden plaque with messages from inspirational figures that could one day be discovered by our descendants. It will serve as a sign of early solar system exploration for those beings in the far future.

(For more information and insights, visit the Lucy mission page.)