NASA’s Lucy spacecraft has flown past its first asteroid, and found a second one at the same time. Lucy flew past the small asteroid Dinkinesh on 1 November, and the images it has sent back to Earth have revealed that Dinkinesh has an even smaller space rock orbiting it – the smallest main belt asteroid ever observed up close.
This finding wasn’t entirely a surprise. As Lucy approached Dinkinesh over the past few weeks, the asteroid’s brightness seemed to oscillate over time, which is often an indication of the presence of some sort of satellite. Dinkinesh is only about 790 metres across, though, so it was impossible to spot its satellite from Earth and even the spacecraft was still too far away until 1 November to tell for sure.
During the 1 November flyby, Lucy flew just 430 kilometres away from Dinkinesh at a speed of about 16,000 kilometres per hour, snapping pictures as it went by. The pictures revealed a second small asteroid in a binary with Dinkinesh, this one only about 220 metres across.
“We knew this was going to be the smallest main belt asteroid ever seen up close,” said Keith Noll at NASA’s Goddard Space Flight Center in Maryland in a statement. “The fact that it is two makes it even more exciting. In some ways these asteroids look similar to the near-Earth asteroid binary Didymos and Dimorphos that [NASA’s Double Asteroid Redirection Test mission] saw, but there are some really interesting differences that we will be investigating.”
The main goal of the flyby was to test Lucy’s scientific instruments, in particular the system that keeps it pointed at its target as it hurtles by, and the fact that these first images show anything at all demonstrates that the tracking system is working properly. The rest of the data from the encounter will be sent back to Earth over the next week or so for the mission’s scientists and engineers to dig into more thoroughly.
Now that Lucy is past Dinkinesh and its partner asteroid, its next target is the asteroid 52246 Donaldjohanson, which it will visit in 2025 before speeding onwards to Jupiter’s Trojan asteroids. The Trojans travel just ahead of and behind Jupiter as it orbits the sun, and they are probably crumbs left over from the formation of the solar system, so they could hold valuable insights as to how the planets formed and evolved over time. Lucy will reach the Trojans in 2027.