Lucy
What is Lucy?
Probes & telescopes· Launched 2021-10-16 – reaches Patroclus 2033-03 (under way). NASA's first mission to Jupiter's Trojan asteroids. Since its 2021 launch two Earth gravity assists have stretched its orbit past main-belt Dinkinesh and Donaldjohanson; from August 2027 it sweeps four L4 Trojans starting with Eurybates, then a third Earth flyby in 2030 sends it to the Patroclus binary in the L5 cloud in 2033. The bends in its orbit-view path are the Earth flybys.
The orbit of Lucy at this moment: https://nowsky.org/solar/orbit?fw=probe%3Alucy&sp=6 — replayed live, no login.
Mission timeline
- Lucy reaches Eurybates(planned)
Spacecraft specs
| Launch | 2021-10-16 |
|---|---|
| Earth flyby 1 | 2022-10-16 |
| Dinkinesh flyby | main belt) |
| Earth flyby 2 | 2024-12-13 |
| Donaldjohanson flyby | 2025-04-20 |
| Eurybates (+Queta) | 2027-08-12 · L4 |
| Polymele | 2027-09-15 · L4 |
| Leucus | 2028-04-18 · L4 |
| Orus | 2028-11-11 · L4 |
| Earth flyby 3 | 2030-12-26 |
| Patroclus–Menoetius | 2033-03-02 · L5 |
| Targets | 11 asteroids incl. satellites |
| Duration | 12 years, to 2033 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Frequently asked
- When did Lucy launch?
- 2021-10-16.
- What is the next milestone for Lucy?
- 12 Aug 2027 — Lucy reaches Eurybates.
- In one line, what is Lucy?
- Probes & telescopes — NASA's first mission to Jupiter's Trojan asteroids.
Why it is called Lucy
Lucy is the name of the 3.2-million-year-old Australopithecus fossil found in Ethiopia in 1974, so called because the Beatles' "Lucy in the Sky with Diamonds" was playing at the camp that evening; it became the fossil that illuminated human evolution. NASA chose the same name because the Trojan asteroids are fossils of the solar system's formation, and the spacecraft's first target was named for Donald Johanson, the fossil's discoverer.
The spacecraft really does carry diamond — the beam splitter of its thermal-emission spectrometer is synthetic diamond. And the asteroid Donaldjohanson, passed in April 2025, is dedicated to the fossil hunter; Lucy's images showed it to be a peanut-shaped contact binary 8 km long. A fossil, a song, an asteroid and a spacecraft, all joined by one name.
The mission in depth
Lucy is a NASA Discovery-class spacecraft bound for the Trojan asteroids that share Jupiter's orbit, clustered 60 degrees ahead of and behind the planet. Launched on 16 October 2021 on an Atlas V, it is named after the 3.2-million-year-old hominin fossil — fitting, because Trojans are frozen leftovers from the era of planet formation, so the name is the mission statement.
The itinerary, in order: (1) Earth gravity assist 1 on 16 Oct 2022 lifts aphelion into the main belt; (2) Dinkinesh flyby on 1 Nov 2023, which revealed the surprise contact-binary moon Selam; (3) Earth gravity assist 2 on 13 Dec 2024 stretches the orbit out to Jupiter's distance; (4) Donaldjohanson flyby on 20 Apr 2025; (5) first Trojan, 64-km Eurybates with its moon Queta, on 12 Aug 2027, followed by (6) Polymele (15 Sep 2027), (7) Leucus (18 Apr 2028) and (8) Orus (11 Nov 2028) in the L4 cloud; (9) Earth gravity assist 3 on 26 Dec 2030 redirects it to (10) the Patroclus–Menoetius binary in the L5 cloud on 2 Mar 2033, closing the mission.
Track Lucy in the orbit view and these ten milestones are marked as dots along its path. Every abrupt bend in the path is an Earth gravity assist — it looks like the spacecraft turns in empty space only because Earth was there at that moment; set the date to October 2022, December 2024 or December 2030 and the two coincide. One solar array never fully latched after launch, but the power margin is sufficient for the mission.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.