Lucy
What is Lucy?
Probes & telescopes· Launched 2021-10-16 – reaches Patroclus 2033-03 (under way). NASA's first mission to the Trojan asteroids, which share Jupiter's orbit ahead of and behind the planet. Launched in 2021, it reaches its first Trojan in 2027 and its last target in 2033.
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.
The fossil and the song behind Lucy's name
Lucy is the name of a fossil of a human ancestor, about 3.2 million years old, found in Ethiopia in 1974. It got its name because the Beatles song Lucy in the Sky with Diamonds was playing at the camp on the night of the find. The fossil became a key to understanding human evolution. NASA chose the same name because the Trojan asteroids are fossils of the solar system.
The links go further. Dinkinesh, the first asteroid Lucy passed, is the Ethiopian name for the Lucy fossil. Donaldjohanson, passed in April 2025, is named after Donald Johanson, the anthropologist who found the fossil, and it turned out to be peanut-shaped and about 8 km long. One of the spacecraft's instruments even contains a part made of synthetic diamond, so, like the song, Lucy really is in the sky with diamonds.
The mission in depth
Trojan asteroids share Jupiter's orbit, gathered in two swarms 60 degrees ahead of and 60 degrees behind the planet. At those spots the pulls of the Sun and Jupiter balance, so the asteroids have been able to stay there for billions of years. Scientists therefore treat the Trojans as fossils: leftovers of the material the solar system was built from, barely changed.
Lucy was launched on 16 October 2021. It first passed Earth twice, in October 2022 and December 2024, to stretch its orbit out toward Jupiter. Along the way, in November 2023, it flew past the main-belt asteroid Dinkinesh and made a surprise discovery: a small moon, Selam, made of two lumps stuck together. In April 2025 it passed the asteroid Donaldjohanson.
The main tour begins in August 2027. In the swarm ahead of Jupiter (L4) it visits 64-km Eurybates, which has a moon named Queta, and then Polymele, Leucus and Orus, finishing in November 2028. A final Earth flyby in December 2030 turns it around, and in March 2033 it reaches the paired asteroids Patroclus and Menoetius in the swarm behind Jupiter (L5).
In the orbit view Lucy's path bends sharply in a few places. It looks as if the spacecraft turned in empty space, but Earth was right there at that moment. Set the date to October 2022, December 2024 or December 2030 and you will see Earth sitting at each bend.
Frequently asked
- When did Lucy launch?
- Lucy was launched on 2021-10-16.
- What is the next milestone for Lucy?
- Next for Lucy, on 12 Aug 2027: Lucy reaches Eurybates.
- In one line, what is Lucy?
- Probes & telescopes — NASA's first mission to the Trojan asteroids, which share Jupiter's orbit ahead of and behind the planet.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.