OSIRIS-REx snapped photos of the Earth and moon during its “slingshot” around our planet and gave researchers another test run of what might happen when the spacecraft reaches the asteroid Bennu.
The fuel-saving Earth gravity-assist maneuver Sept. 22 was done to alter the spacecraft’s trajectory and set it on course to Bennu, where it will collect a sample from the asteroid and return it to Earth.
It was also a useful exercise for the team, led by the University of Arizona’s planetary scientist and mission leader Dante Lauretta, to calibrate the on-board instruments; snap photos and spectra of the Earth and moon; and analyze the data as a full team, mimicking the process they’ll follow as they approach Bennu.
“Everyone in Tucson on Friday is in this picture,” Lauretta said Tuesday, when the images were made public.
OSIRIS-REx shot within 11,000 miles of Earth in its flyby. Once 105,000 miles away, it captured images of the receding Earth, with the Pacific Ocean in view. Australia peeked out from the lower left of the globe. Also pictured are Japan, East Asia, Hawaii and a sliver of Western North America.
There are what Lauretta called “icicles” on the top of the image, which were a product of the short exposure times used for the Earth photographs. The cameras on OSIRIS-REx were designed to capture images of a very dark asteroid, Lauretta said. “It’s darker than coal.”
The camera had to take a very short exposure image of Earth since it’s much brighter than Bennu, which resulted in read-out issues — the so-called icicles — as it quickly scanned the sky.
“We won’t see (the icicles) in images of Bennu,” Lauretta said.
During the hunt for Earth’s trailing Trojan asteroids earlier this spring as another practice, OSIRIS-REx was pushed to the longest exposure times and also performed well.
“(The cameras were) pushed beyond what they were designed to do,” during these long and short exposures, Lauretta said.
Data started coming down on the afternoon of Sept. 22.
“Everyone was huddled around their monitors,” Lauretta said. “The bits were coming in so slowly. Everyone was anxious.
“The first team member who saw it shrieked. We dove across the room. We were trying to shove the HDMI cable into a USB port,” so everyone could see the images.
“We know what the Earth looks like,” he said. “It was more the moment that everything worked.”
And despite the “icicles,” Lauretta said he thought the distortion was important to include. “It gives a complete picture of the data.”
As OSIRIS-REx approaches Bennu next August, the same systems will be executed and the world will have its first glimpse of the asteroid.
“We all have this image in our mind (of Bennu),” Lauretta said, “and I keep reminding everyone that it’s not going to look like that. It’s going to surprise us.”
OSIRIS-REx will then retrieve a sample of the asteroid and return it to Earth by 2023.