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Jason Davis • May 15, 2019

Here's a Roundup of Recent OSIRIS-REx Postcards from Bennu

NASA's OSIRIS-REx spacecraft is continuing to chug along at asteroid Bennu. It’s currently sweeping arcs between the asteroid's north and south poles, gathering scientific data that will also be used to select 12 possible sites for sample collection. The OSIRIS-REx team has also been releasing stunning new images from the mission's prior phase.

The current phase of the OSIRIS-REx mission, which began began in April and will continue into June, is called Detailed Survey: Equatorial Stations. The spacecraft is scanning Bennu from top to bottom at different sun angles from a distance of 5 kilometers from the asteroid's center. Emily Lakdawalla summed this phase up well in our OSIRIS-REx at Bennu preview article:

These data will help the team build models for how the surface of Bennu reflects light differently at different angles. This is called photometry. With this data set, the team will be able to correct images for solar illumination, to help them produce seamless photo mosaics. Once they have the photometry data set in hand, they'll be able to make color ratio maps, which should make subtle color variations on the asteroid much easier to see. They'll also make a map of the asteroid's thermal properties. In the long term, these maps will be important for geology research, but in the short term, it will help identify regions of interest and regions that are hazardous for sampling.

At the end of the equatorial survey phase, the team should have 12 candidate sample collection sites. OSIRIS-REx will next move into its Orbital B phase, which is similar to Orbital A but with an even-closer orbital radius of roughly a kilometer. As the team gets closer looks at the candidate sample sites, they'll pick just 1 or 2 finalists, and perform a detailed reconnaissance of the top site from a distance of 225 meters no earlier than September. If that up-close look proves that the site is hazard-free and a good choice for sampling, they’ll proceed, but if the spacecraft discovers the site is unsuitable, it can recon others.

The mission has also been releasing a steady drip of images from its prior Detailed Survey: Baseball Diamond phase. This survey sent OSIRIS-REx flying past Bennu at a variety of different angles, resulting in images from lots of unique perspectives.

Here are a couple overhead shots: A panorama that includes a potential sample collection candidate site, and a picture of some boulders sorted neatly by size.

Bennu panorama from Baseball Diamond phase
Bennu panorama from Baseball Diamond phase This image combines two pictures captured on 29 March 2019 by the OSIRIS-REx OCAMS (PolyCam) during flyby 4B of the mission's Detailed Survey: Baseball Diamond phase. The image was taken from a height of about 3.6 kilometers near Bennu's equator. The boulder-free region on the left is a crater 21.6 meters wide, and a candidate sample site. The large boulder at the bottom is one of Bennu's darkest, with an albedo of about 3.3%.Image: NASA/Goddard/University of Arizona/Processed by Jason Davis
Graduated Boulder Sizes
Graduated Boulder Sizes This image shows a rocky patch in the northern hemisphere of asteroid Bennu where the rocks and boulders are situated by size. It was taken by the OSIRIS-REx PolyCam camera on 29 March 2019 from a distance of 3.4 kilometers. For scale, the little rock sitting on the boulder in the lower left corner is 2.5 meters wide. The image was obtained during Flyby 4B of the mission’s Detailed Survey: Baseball Diamond phase. When the image was taken, the spacecraft was over the northern hemisphere, pointing PolyCam slightly to the south.Image: NASA/Goddard/University of Arizona

There are also some pretty unique images where the camera is pointing off-nadir, near Bennu's horizon. My preferred way to view most of these is by orienting them with space up, to make me feel like I’m standing on the surface.

Bennu's "spine"
Bennu's "spine" Bennu has a region of large boulders that runs like a spine from the equator down toward the south pole. This image of the top of Bennu's spine was taken by PolyCam from the northern hemisphere during Flyby 5A of the mission’s Detailed Survey: Baseball Diamond phase on 4 April 2019 from a distance of 4.6 kilometers. The triangular boulder in the center is 9.2 meters high.Image: NASA/Goddard/University of Arizona/Processed by Jason Davis
Bennu’s Equatorial Ridge
Bennu’s Equatorial Ridge On 29 March 2019, the PolyCam camera on NASA’s OSIRIS-REx spacecraft took this image of a region of dark regolith on asteroid Bennu. When the image was taken, the spacecraft was positioned over Bennu’s northern hemisphere, looking southward over the asteroid’s equatorial bulge. The field of view shown is 51.2 meters wide. For scale, the bright, rectangular rock above the dark region is 2.4 meters wide, about the size of a long bed on a pickup truck. This image was taken during Flyby 4 of the mission’s Detailed Survey: Baseball Diamond phase. Instrument Used: OCAMS (PolyCam).Image: NASA/Goddard/University of Arizona
View of the North from Bennu’s Southern Hemisphere
View of the North from Bennu’s Southern Hemisphere This image provides a steeply angled view of a region of asteroid Bennu’s equator and northern hemisphere. It was taken by the OSIRIS-REx PolyCam on 28 March 2019 from a distance of 3.6 kilometers during Flyby 4A of the mission’s Detailed Survey: Baseball Diamond phase. The largest boulder in the upper left corner of the image is 14.5 meters wide. When the image was taken, the spacecraft was over the southern hemisphere, pointing PolyCam up toward the far north.Image: NASA/Goddard/University of Arizona

Finally, there’s this great shot of one of Bennu’s easiest-to-identify surface features: Boulder No. 1, also known as “BenBen.” This was the first boulder OSIRIS-REx identified during approach, and at 21.7 meters tall, it also happens to be the largest.

Bennu's Boulder No. 1
Bennu's Boulder No. 1 This image, taken by the PolyCam camera on NASA’s OSIRIS-REx spacecraft on 29 March 2019 from a distance of 3.6 kilometers, shows Bennu’s largest boulder. The height of the boulder is 21.7 meters. The image was obtained during Flyby 4B of the mission’s Detailed Survey: Baseball Diamond phase. When the image was taken, the spacecraft was over the northern hemisphere, pointing PolyCam down toward the south.Image: NASA/Goddard/University of Arizona/Processed by Jason Davis

Here’s a wide shot of Bennu from earlier in the mission. You can see Boulder No. 1 sticking out of the asteroid in the lower-right.

Bennu PolyCam mosaic
Bennu PolyCam mosaic This mosaic image of asteroid Bennu is composed of 12 PolyCam images collected on Dec. 2, 2018, by the OSIRIS-REx spacecraft from a range of 15 miles (24 km).Image: NASA / Goddard / University of Arizona

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