Level 1 - Absolute Beginner
NASA has a spacecraft. Its name is Lucy. It left Earth in 2021.
Lucy is now in a new place near Jupiter. No other spacecraft has come here. Big rocks are here. We call them Trojan asteroids.
The place is very empty. The rocks are very far apart. Lucy looks at stars to know where it is.
Lucy flies to its first rock in 2027. The rock is called Eurybates.
- spacecraft
- a machine that flies in space
- asteroid
- a big rock that moves around the Sun
- rock
- a hard piece of stone
- empty
- with nothing in it
- star
- a very hot light far away in the sky
- Jupiter
- the biggest planet near us
- Earth
- the planet where we live
- far
- not near
Level 2 - Elementary
NASA's Lucy spacecraft has reached a part of space that no spacecraft has visited before. Lucy left Earth on October 16, 2021. It has now travelled more than 2.2 billion miles.
Lucy has entered the region of the Jupiter Trojan asteroids. These asteroids move around the Sun in two large groups. One group travels in front of Jupiter and the other group travels behind it. Lucy is approaching the group in front, and it will visit both groups in time.
The region is almost empty. The asteroids are on average more than 6 million miles apart. Because there is so little nearby, engineers find Lucy's position with radio signals from Earth and with pictures of background stars.
Lucy will fly past its first asteroid, Eurybates, on August 11, 2027. That close look will last only a few hours. NASA says the spacecraft and its instruments are working as expected.
- region
- a large area or part of space
- asteroid
- a rocky object that moves around the Sun
- approach
- to come closer to something
- engineer
- a person who designs or runs machines
- signal
- a message sent by radio or light
- position
- the place where something is
- average
- the usual amount when you count everything together
- instrument
- a tool used for measuring or studying
Level 3 - Intermediate
NASA's Lucy spacecraft has become the first ever to enter the region of the Jupiter Trojan asteroids, five years and more than 2.2 billion miles after it lifted off on October 16, 2021. Lucy is approaching the swarm that gathers at Lagrange point 4, a gravitationally stable location that leads Jupiter in its orbit around the Sun. A second swarm trails the planet at Lagrange point 5, and Lucy will eventually visit both.
Reaching the region is not the same as reaching an asteroid. Entering the region is NASA's own framing, and the first encounter, a flyby of the asteroid Eurybates, is still about nine months away, on August 11, 2027. It will give only a few hours of close observation. Polymele follows in September 2027, Leucus in April 2028 and Orus in November 2028. A third and final gravity assist from Earth in 2030 will sling the spacecraft toward the trailing swarm, where the binary pair Patroclus and Menoetius wait until March 2033.
The region is startlingly empty. The Trojans sit as far from Jupiter as Jupiter sits from the Sun, about 484 million miles, and individual Trojans are on average more than 6 million miles apart. With almost nothing nearby to steer by, engineers are fixing Lucy's position using radio signals from Earth together with images of background stars.
The scientific prize is age. Trojan asteroids are thought to be leftover planetesimals, the building blocks from which the planets were assembled about 4.5 billion years ago. Because these objects were never swept into a planet, their chemistry and structure should constrain how the planets formed and how they later migrated into the arrangement we see today. The spacecraft was designed to operate more than five times farther from the Sun than Earth is, and NASA says it and its instruments are working as expected.
- swarm
- a large group of objects moving together
- encounter
- a meeting with something, often brief
- flyby
- a pass close to an object without stopping
- gravity assist
- using a planet's pull to change a spacecraft's speed or direction
- planetesimal
- a small early body that planets were built from
- migrate
- to move gradually to a different place
- constrain
- to limit the possible explanations for something
- binary
- made of two objects orbiting each other
Level 4 - Advanced
Space missions are usually marked by arrivals, but Lucy's newest milestone is an entry into emptiness. Five years and more than 2.2 billion miles after its launch on October 16, 2021, NASA's Lucy spacecraft has crossed into the region of the Jupiter Trojan asteroids, the first craft ever to do so. It is closing on the swarm that clusters at Lagrange point 4, the gravitationally stable perch that leads Jupiter around the Sun; a mirror swarm trails the planet at Lagrange point 5, and Lucy is scheduled to call on both.
The word region deserves emphasis, because it is NASA's own careful framing. Nothing has been landed on, and nothing has yet been photographed from close range. The first encounter, a flyby of the asteroid Eurybates, lies roughly nine months ahead on August 11, 2027, and will yield only a few hours of close observation. Polymele follows that September, Leucus in April 2028 and Orus in November 2028, before a third and final gravitational slingshot past Earth in 2030 redirects the spacecraft toward the trailing swarm and, in March 2033, the binary pair Patroclus and Menoetius.
What makes the territory strange is how little of it is occupied. The Trojans orbit as far from Jupiter as Jupiter does from the Sun, some 484 million miles, and neighbouring members of each swarm are separated on average by more than 6 million miles. Crossing such a void offers no landmarks, so navigators are pinning Lucy down by combining radio signals from Earth with images of background stars, a method closer in spirit to celestial navigation at sea than to anything a driver would recognise. The spacecraft was built to operate more than five times farther from the Sun than Earth is, and NASA reports that it and its instruments are performing as expected.
The payoff for all this patience is chronological. Trojan asteroids are understood to be leftover planetesimals, the building blocks that accreted into planets roughly 4.5 billion years ago and were then stranded at gravitational way stations rather than folded into a world. Reading their composition at close range should therefore discipline the competing accounts of how the solar system assembled itself, and of how the giant planets later migrated into their present configuration. For now, though, Lucy has merely reached the neighbourhood. The knocking on doors begins in 2027.
- milestone
- an important stage or achievement
- framing
- the particular way something is described
- slingshot
- a manoeuvre that uses a planet's gravity to redirect a spacecraft
- void
- a large empty space
- celestial
- relating to the sky or outer space
- planetesimal
- a small early body from which planets were built
- accrete
- to grow by gradually gathering material
- configuration
- the arrangement of the parts of something
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