Lucy’s Super-Close Flyby on Earth

Oct. 15, 2022: Most spacecraft try to avoid hitting the atmosphere. Lucy is about to do it on purpose. On Oct. 16th, NASA’s Lucy spacecraft will skim Earth’s atmosphere, passing only 220 miles (350 kilometers) above our planet’s surface. Near closest approach over Australia it will be visible to the naked eye glowing almost as brightly as a 1st magnitude star.

This is a gravity assist maneuver–the first of three required for Lucy’s complicated mission to visit 8 different asteroids. The slingshot will give Lucy the energy it needs to fly towards the asteroid belt and, its ultimate destination, the orbit of Jupiter.

Named for a hominid fossil found in 1974 in Africa, Lucy is on a mission to study a completely different kind of relic: the Trojan asteroids. These are primitive leftovers from the formation of our solar system, collected into swarms around two of Jupiter’s Lagrange points. Sensors onboard the spacecraft will examine their appearance and composition, putting competing theories of planetary genesis to the test.

To reach the Trojans, Lucy must first return to Earth. Launched on Oct. 16, 2021, the spacecraft is coming home after exactly one year in space. Lucy’s trajectory will bring it deep into near Earth orbit, passing through a region full of Earth-orbiting satellites and debris. NASA will be ready to make last-minute adjustments to avoid collisions. The altitude is so low, the mission team had to include the effect of atmospheric drag when designing the flyby. Passing so close allows Lucy to extract maximum energy from Earth’s gravitational field.

On the left, the location in the sky where Lucy will first appear when it emerges from the Earth’s shadow for the Western United States. Red stars correspond to cities on the right.

Observers in western Australia will be the first to see Lucy. At around 10:55 UTC (6:55 p.m. local time) on Oct. 16th, the spacecraft will race overhead shining like a 1st or 2nd magnitude star. At the apex of its brightness, it will suddenly disappear into Earth’s shadow, vanishing at 11:02 UTC (7:02 p.m. local time).

Lucy will continue over the Pacific Ocean in darkness and emerge from the Earth’s shadow at 4:26 a.m. PDT (11:26 UTC). By that time it will have dimmed to 6th or 7th magnitude. Amateur astronomers in the western United States should be able to see Lucy using binoculars or a small telescope.

After the gravity assist, Lucy will recede from Earth, passing by the Moon and taking a few pictures before continuing out into interplanetary space. It might remain bright enough to see using backyard telescopes for more than 24 hours.

Want to see Lucy? You can spot the spacecraft using observing tips from the Southwest Research Institute. Ephemerides from JPL are recommended, too.

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