NASA’s Lucy spacecraft is closing in on its next asteroid target: a small main-belt asteroid named Donaldjohanson. The approach marks a new milestone in Lucy’s 12-year journey to explore the Trojan asteroids that orbit the Sun along with Jupiter.
On November 1, 2023, Lucy successfully completed its first flyby of the asteroid Dinkinesh and its satellite, Selam. That encounter allowed scientists to test critical systems ahead of future missions.
The spacecraft is now on track for a second flyby, set to occur on April 20 at 1:51 p.m. EDT. This pass will serve as a dress rehearsal for the spacecraft’s main science mission, which involves exploring multiple Trojan asteroids—primitive bodies that share Jupiter’s orbit around the Sun.
During the upcoming flyby, Lucy will make its closest approach to Donaldjohanson at a distance of 596 miles (960 kilometers). The spacecraft is tasked with executing a complex observation sequence using all three of its onboard science instruments. To maintain precise tracking of the asteroid, Lucy will temporarily suspend communication with Earth. However, unlike with Dinkinesh, the spacecraft will stop tracking Donaldjohanson 40 seconds before closest approach to shield its sensitive instruments from intense sunlight.
“If you were sitting on the asteroid watching the Lucy spacecraft approaching, you would have to shield your eyes from staring at the Sun while waiting for Lucy to emerge from the glare. After Lucy passes the asteroid, the positions will be reversed, so we have to shield the instruments similarly,” said encounter phase lead Michael Vincent of Southwest Research Institute (SwRI) in Boulder, Colorado.
“These instruments are designed to photograph objects illuminated by sunlight 25 times dimmer than at Earth, so looking toward the Sun could damage our cameras.”
During the Trojan encounters, like with Dinkinesh, the spacecraft will collect data the whole time. “One of the weird things to wrap your brain around with these deep space missions is how slow the speed of light is,” says Vincent.
After closest approach, the spacecraft will tilt back to face the Sun, realigning its solar arrays. About an hour later, it will reconnect with Earth.
“Lucy is 12.5 light minutes away from Earth, meaning it takes that long for any signal we send to reach the spacecraft. Then it takes another 12.5 minutes before we get Lucy’s response telling us we were heard,” Vincent said. “So, when we command the data playback after closest approach, it takes 25 minutes from when we ask to see the pictures before we get any of them to the ground.”
Once Lucy is confirmed healthy by the NASA team, engineers will take several days to download science. “Every asteroid has a different story to tell, and these stories weave together to paint the history of our solar system,” said Tom Statler, Lucy mission program scientist at NASA Headquarters in Washington. “
Donaldjohanson is a debris fragment from 150 million years ago, making it one of the youngest main belt asteroids studied by any spacecraft.
“The fact that each new asteroid we visit knocks our socks off means we’re only beginning to understand the depth and richness of that history. Telescopic observations are hinting that Donaldjohanson is going to have an interesting story, and I’m fully expecting to be surprised – again.”
Chrissy Newton is a PR professional and founder of VOCAB Communications. She currently appears on The Discovery Channel and Max and hosts the Rebelliously Curious podcast, which can be found on The Debrief’s YouTube Channel on all audio podcast streaming platforms. Follow her on X: @ChrissyNewton and at chrissynewton.com.