Lucy’s first encounter with an asteroid produced surprises

Dinkinesh, with Salam

At the 55th annual Lunar and Planetary Science Conference presently being held in Texas, the science team for the Lucy asteroid mission presented their first papers outlining what they learned during the spacecraft’s first asteroid encounter, flying past the main belt asteroid Dinkinesh on November 1, 2023.

To the right is the the best image taken at closest approach, at about 270 miles distance, annotated to include the analysis of Dinkinesh’s shape by scientists. As noted in the summary paper [pdf], the asteroid is about a half mile in diameter, and appears to have an equatorial ridge, similar to the ridges found on the near-Earth rubble-pile asteroids Bennu or Ryugu. Dinkinesh is not a rubble pile, however. Though boulder-strewn, it appears more solid, and even has what the scientists call a longitudinal trough, as indicated in the picture.

The ridge overlays the trough implying that it is the younger of the two structures. However, there is as yet no information to better constrain their relative ages, and thus they could potentially have formed in the same event. Indeed, Dinkinesh’s ridge and trough are likely the result of mass failure and the reaccretion of material, and may both be linked to the formation of Selam.

That flyby had produced one major surprise, the existence of a smaller satellite asteroid orbiting Dinkinesh, now dubbed Selam. It is shown in the lower left, as it appeared from behind the main asteroid as Lucy flew past. A later picture however revealed an even greater surprise.
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Lucy: Dinkinesh’s moon is actually a contact binary

Dinkinesh's contact binary moon
Click for original image.

As more images have arrived from Lucy’s fly-by of Dinkinesh scientists have discovered that its moon is actually a contact binary.

The Lucy picture to the right, cropped, reduced and sharpened to post here, shows that contact binary on the right.

This image shows the asteroid Dinkinesh and its satellite as seen by the Lucy Long-Range Reconnaissance Imager (L’LORRI) as NASA’s Lucy Spacecraft departed the system. This image was taken at 1 p.m. EDT Nov. 1, 2023, about 6 minutes after closest approach, from a range of approximately 1,010 miles. From this perspective, the satellite is revealed to be a contact binary, the first time a contact binary has been seen orbiting another asteroid.

Data from the fly-by is still being downloaded.

Lucy discovers second small asteroid orbiting Dinkinesh

Dinkinesh as seen by Lucy

During its November 1, 2023 fly-by of the asteroid Dinkinesh the asteroid probe Lucy surprisingly discovered that the asteroid was actually a binary, with a second smaller asteroid orbiting it.

The picture to the right, cropped, reduced, and sharpened to post here, was taken by Lucy’s camera within a minute of the probe’s closest approach of 270 miles. The second asteroid is partly blocked by Dinkinesh.

In the weeks prior to the spacecraft’s encounter with Dinkinesh, the Lucy team had wondered if Dinkinesh might be a binary system, given how Lucy’s instruments were seeing the asteroid’s brightness changing with time. The first images from the encounter removed all doubt. Dinkinesh is a close binary. From a preliminary analysis of the first available images, the team estimates that the larger body is approximately 0.5 miles (790 m) at its widest, while the smaller is about 0.15 miles (220 m) in size.

The nature of both asteroids appears to lie between a rubble pile (like Bennu) or a solid smooth rock (like Eros), suggesting we are now beginning to see aspects of the overall evolution of asteroids over time.

So far only a few images from this fly-by have been released. It will take a week for the rest of the data from the fly-by to beamed back to Earth. However, these images prove that the prime purpose of this fly-by was successful, proving that Lucy is operating as planned, able to point, manuever, and obtain its data during such a fly-by. When it arrives in the Trojan asteroids in 2027 it will be able to do its prime mission.

Lucy completes fly-by of main belt asteroid Dinkinesh

Lucy's route through the solar system
Lucy’s route through the solar system

The Lucy science team has confirmed that the spacecraft has successfully completed its fly-by of the asteroid Dinkinesh (the white dot in the lower left of the main asteroid belt in the graphic to the right) and is in good health.

Based on the information received, the team has determined that the spacecraft is in good health and the team has commanded the spacecraft to start downlinking the data collected during the encounter. It will take up to a week for all the data collected during the encounter to be downlinked to Earth.

Though the images and data of Dinkinesh obtained during this fly-by have science value, the real purpose of the fly-by was to test the operations of Lucy for when it reaches the Trojan asteroids in Jupiter’s orbit, as shown by the graphic. The spacecraft will now do a flyby of Earth in 2025 to slingshot it to the orbit of Jupiter, where it will do its main work exploring the Trojan asteroids there. On the way it will fly past a second main belt asteroid, dubbed Donaldjohanson.

Lucy’s first asteroid fly-by coming on November 1st

Lucy's route through the solar system
Lucy’s route through the solar system

The asteroid probe Lucy is about to do its first asteroid fly-by on November 1, 2023, the first of a planned ten asteroids it will see close-up during its twelve year mission.

The half-mile-wide asteroid, Dinkinesh, is indicated on the graphic to the right by the white dot in the lower left of the main asteroid belt. It was a late addition to the spacecraft’s plan in order to provide a perfect testbed for doing a dress rehearsal of the many later fly-bys.

As this encounter is intended as a test of Lucy’s systems, scientific observations will be simpler than for the mission’s main targets. The spacecraft and the platform that holds the instruments will move into position two hours before the closest approach to Dinkinesh. Once in place, the spacecraft will begin collecting data with its high-resolution camera (L’LORRI) and its thermal-infrared camera (L’TES). One hour before closest approach, the spacecraft will begin tracking the asteroid with the terminal-tracking system. Only in the last eight minutes will Lucy be able to collect data with MVIC and LEISA, the color imager and infrared spectrometer that comprise the L’Ralph instrument. Lucy’s closest approach is expected to occur at 12:54 p.m. EDT, when the spacecraft will be within 270 miles (430 kilometers) of the asteroid. Lucy will perform continuous imaging and tracking of Dinkinesh for almost another hour. After that time, the spacecraft will reorient itself to resume communications with Earth but will continue to periodically image Dinkinesh with L’LORRI for the next four days.

After this close encounter the spacecraft will return to do a flyby of Earth in 2025 to slingshot it to the orbit of Jupiter, where it will do its main work exploring the Trojan asteroids there. On the way it will fly past a second main belt asteroid, dubbed Donaldjohanson.

Lucy gets first images of its first target asteroid, Dinkinesh

The asteroid Dinkinesh as seen by Lucy

The asteroid probe Lucy has obtained its first images of Dinkinesh, the first of the ten asteroids the spacecraft is hoping to visit during its twelve year voyage to the Trojan asteroids.

The image to the left shows the motion of that asteroid over a two day period when Lucy was getting the pictures.

Lucy took these images while it was 14 million miles (23 million km) away from the asteroid, which is only about a half-mile wide (1 km). Over the next two months, Lucy will continue toward Dinkinesh until its closest approach of 265 miles (425 km) on Nov. 1, 2023. The Lucy team will use this encounter as an opportunity to test out spacecraft systems and procedures, focusing on the spacecraft’s terminal tracking system, designed to keep the asteroid within the instruments’ fields of view as the spacecraft flies by at 10,000 mph (4.5 km/s). Lucy will continue to image the asteroid over the next months as part of its optical navigation program, which uses the asteroid’s apparent position against the star background to determine the relative position of Lucy and Dinkinesh to ensure an accurate flyby. Dinkinesh will remain an unresolved point of light during the long approach and won’t start to show surface detail until the day of the encounter.

Lucy’s primary targets are asteroids in the two Trojan groups that orbit the Sun in the two Lagrange points in same orbit as Jupiter, fore and aft of the gas giant by 60 degrees. For a map of Lucy’s full mission profile, go here.

Lucy makes course correction in preparation for 1st asteroid fly-by

Lucy's route through the solar system
Lucy’s route through the solar system

The asteroid probe Lucy on May 9, 2023 fired its engines to successfully make a minor course correction in preparation for a fly by of the asteroid Dinkinesh, located in the main asteroid belt between Mars and Jupiter.

Even though the spacecraft is currently travelling at approximately 43,000 mph (19.4 km/s), this small nudge is enough to move the spacecraft nearly 40,000 miles (65,000 km) closer to the asteroid during the planned encounter on Nov. 1, 2023. The spacecraft will fly a mere 265 miles (425 km) from the small, half-mile- (sub-km)-sized asteroid, while travelling at a relative speed of 10,000 mph (4.5 km/s).

Dinkinesh, the white dot inside the main asteroid belt in the lower left of the map to the right, is the first of eight asteroids Lucy will fly past.