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OSIRIS-REx has completed its high resolution reconnaissance of the four candidate sites on the asteroid Bennu, chosen for possible sample capture during touch-and-go operations planned for the summer of 2020.

In the next few days the science team will decide which of these four sites, shown above, will be the primary and back-up landing locations. The decision however appears challenging, based on the information gathered.

Bennu has also made it a challenge for the mission to identify a site that won’t trigger the spacecraft’s safety mechanisms. During Recon A, the team began cataloguing Bennu’s surface features to create maps for the Natural Feature Tracking (NFT) autonomous navigation system. During the sample collection event, the spacecraft will use NFT to navigate to the asteroid’s surface by comparing the onboard image catalog to the navigation images it will take during descent. In response to Bennu’s extremely rocky surface, the NFT system has been augmented with a new safety feature, which instructs it to wave-off the sampling attempt and back away if it determines the point of contact is near a potentially hazardous surface feature. With Bennu’s building-sized boulders and small target sites, the team realizes that there is a possibility that the spacecraft will wave-off the first time it descends to collect a sample.

Based on the information at the link, plus the presentation by Dante Lauretta, OSIRIS-REx’s principal investigator, given at the asteroid conference I attended in November, I suspect that Nightingale will be primary landing site.

Regardless, it appears the science team has recognized that the landing will difficult, and will likely require multiple attempts before the spacecraft’s navigation system lets it happen.

The OSIRIS-REx engineering team has released a short video that flies over in close-up, showing the spacecraft’s four candidate sites on the asteroid Bennu, one of which will be where they will do a touch-and-go sample grab.

They continue to accumulate data on the four sites, all of which pose issues and risks because of nearby boulders and the looseness of Bennu’s rubble pile make-up.

Though all the sites are being considered, my sources in the industry suggest that the two dubbed Sandpiper and Nightingale are being favored. I like Osprey, because it is inside a crater and looks clear, but then, what do I know?

After months of photographing and analyzing the very rocky-shrewn surface of the rubble-pile asteroid Bennu, the OSIRIS-REx team has chosen four finalist sites, one of which they will do a touch-and-go sample grab.

This fall, OSIRIS-REx will begin detailed analyses of the four candidate sites during the mission’s reconnaissance phase. During the first stage of this phase, the spacecraft will execute high passes over each of the four sites from a distance of 0.8 miles (1.29 km) to confirm they are safe and contain sampleable material. Closeup imaging also will map the features and landmarks required for the spacecraft’s autonomous navigation to the asteroid’s surface. The team will use the data from these passes to select the final primary and backup sample collection sites in December.

The second and third stages of reconnaissance will begin in early 2020 when the spacecraft will perform passes over the final two sites at lower altitudes and take even higher resolution observations of the surface to identify features, such as groupings of rocks that will be used to navigate to the surface for sample collection. OSIRIS-REx sample collection is scheduled for the latter half of 2020, and the spacecraft will return the asteroid samples to Earth on Sept. 24, 2023.

They given the four sites the names Nightingale, Kingfisher, Osprey and Sandpiper.

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The OSIRIS-REx science team today released one of the first images taken of Bennu after the spacecraft lowered itself into its closest orbit in early June. I have reduced and cropped slightly that image slightly to post here on the right. As they note,

From the spacecraft’s vantage point in orbit, half of Bennu is sunlit and half is in shadow. Bennu’s largest boulder can also be seen protruding from the southern hemisphere. The image was taken from a distance of 0.4 miles (690 m) above the asteroid’s surface by NavCam 1, one of three navigation cameras that comprise the spacecraft’s TAGCAMS (the Touch-and-Go Camera System) suite. At this distance, details as small as 1.6 ft (0.5 m) across can be resolved in the center of the image.

In other words, if a person was moving across the asteroid’s surface you could see them.

OSIRIS-REx has moved into its next phase of research by lowering its orbit around the asteroid Bennu to only 2,231 feet above the surface.

Upon arrival at Bennu, the team observed particles ejecting into space from the asteroid’s surface. To better understand why this is occurring, the first two weeks of Orbital B will be devoted to observing these events by taking frequent images of the asteroid’s horizon. For the remaining five weeks, the spacecraft will map the entire asteroid using most of its onboard science instruments: the OSIRIS-REx Laser Altimeter (OLA) will produce a full terrain map; PolyCam will form a high-resolution, global image mosaic; and the OSIRIS-REx Thermal Emission Spectrometer (OTES) and the REgolith X-ray Imaging Spectrometer (REXIS) will produce global maps in the infrared and X-ray bands. All of these measurements are essential for selecting the best sample collection site on Bennu’s surface.

The goal is to narrow to four the possible touch-and-go landing sites for grabbing a surface sample. They will pick the final choice in a reconnaissance phase now scheduled for the fall.

The present research phase will last until the middle of August, when they will raise the orbit slightly to give them a different perspective of its surface and the particles being released from it.

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Cool image from OSIRIS-REx. The picture on the right, cropped to post here, was taken by OSIRIS-REx and shows a square boulder about the size of a 15-passenger van, precariously perched on the rim of a large crater on the asteroid Bennu. The picture was taken April 11 from about 2.9 miles distance.

This scale is human-sized. If that rock is a 15 passenger van, then the small rocks around it are about the size of a person and that cliff is about 20-30 feet high. I can imagine strolling down the slope to check out the cliff face, though I would make sure I gave a wide berth to the part of the cliff directly below that boulder.

The OSIRIS-REx science team has shifted the spacecraft’s operation into a new phase aimed at carefully mapping the surface of the asteroid Bennu in preparation for an eventual touch-and-go sample grab.

During Detailed Survey: Equatorial Stations phase, the spacecraft’s instruments will make the scientific observations needed to help the team home in on the best location on Bennu to collect a sample of regolith (loose surface material). To obtain these data, the spacecraft will execute a series of slews between Bennu’s north and south poles while taking observations from seven different stations above the equator. These data will be studied to understand the geology of Bennu. The spacecraft will also conduct searches for dust and gas plumes.

During this phase, planned to last through mid-June, they are asking for the public’s help in mapping the surface and its innumerable rocks.

For this effort, NASA is partnering with CosmoQuest, a project run out of the Planetary Science Institute that supports citizen science initiatives. Volunteers will perform the same tasks that planetary scientists do – measuring Bennu’s boulders and mapping its rocks and craters – through the use of a simple web interface. They will also mark other scientifically interesting features on the asteroid for further investigation.

The boulder mapping work involves a high degree of precision, but it is not difficult. The CosmoQuest mapping app requires a computer with a larger screen and a mouse or trackpad capable of making precise marks. To help volunteers get started, the CosmoQuest team provides an interactive tutorial, as well as additional user assistance through a Discord community and livestreaming sessions on Twitch.

Seems like fun!

The OSIRIS-REx science team have released a short movie, compiled from data obtained in November 2018 as the spacecraft was first approaching the asteroid Bennu, that shows the dayside surface temperature and how it changes as the asteroid rotates.

I have embedded the movie below the fold.

Within a distance of only about 850 feet the temperature rises more than 270 degrees, from -99.67 °F to 170.33 °F. This change also occurs at every spot as the asteroid rotates. At dawn it will be that cold, and by noon it will be that hot.
» Read more

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In late March OSIRIS-REx completed its fourth fly-by of the asteroid Bennu. The image on the right, cropped and reduced to post here, was taken when the spacecraft was only 2.1 miles above the surface. If you were standing among these large boulders, we could easily see you.

The image itself shows the asteroid’s southern limb, and thus the shadows are accentuated. This makes it easier to see surface details. Though it is clear once again that Bennu is a pile of boulders and rocks cemented together and floating in space, the photograph also shows that it also has areas where the material is either much larger or fused together more solidly, as shown by the more massive sections in the left center of this picture. We might be looking a very large boulders peeking up from below the surface, or possibly this is the hint of some real bedrock.

The OSIRIS-REx team is continuing the spacecraft’s survey phase, gathering high resolution images in order to compile a detailed map of the surface, prior to planning the touch-and-go sample grab.

The OSIRIS-REx science team today released a global map of Bennu, compiled from images taken in December.

The map is above. It was released with no commentary. In comparing it with this global map of Ryugu, created by the Japanese probe Hayabusa-2, I am struck by how much both asteroids resemble each other.

This fact is in many ways a first. Since the first planetary probes left Earth in the 1960s the one reliable expectation that has consistently proven true is that no planetary object, be it planet, dwarf planet, moon, asteroid, or comet, was going to resemble any other planetary object. Each has been entirely unique, and unique in very startling and obvious ways.

Ryugu and Bennu represent the first planetary objects that actually look pretty much the same. Scientist will of course be able to note differences, but overall these objects clearly belong to a specific class of asteroids, which in this case is the rubble pile.

In a sense, this similarity marks a significant advancement in our knowledge. Up until now, we had observed so few objects that our knowledge base wasn’t large enough to start seeing patterns within our general classifications of planet, asteroid, or comets. That is now finally changing.

Click for full resolution.

The OSIRIS-REx science team has released new high resolution images of one particular area on Bennu’s northern hemisphere. The image on the right, cropped and reduced to post here, shows what they label a “pond of regolith,” seen as the relatively smooth area in the upper left.

This is not literally a pond, but instead is a low-lying spot where smaller particles have settled over time, producing a flattish area that looks, and in some ways, resembles a pond or puddle, only in this case the material isn’t water but fine-grained dust or pebbles.

On March 19 the science team will be presenting their initial results at a special session at the 50th Lunar and Planetary Science Conference in Texas. That same day they will hold a press conference summarizing the most interesting aspects of those results. Stay tuned.

The OSIRIS-REx science team has released two new images of Bennu’s southern hemisphere, taken from orbit. The image on the right is a cropped section of the highest resolution version of a montage of two images. Click on the image to see the entire two-image montage.

These two OpNav images of Bennu’s southern hemisphere, which each have an exposure time of about 1.4 milliseconds, were captured Jan. 17 from a distance of about one mile (1.6 km). They have been cropped and the contrast has been adjusted to better reveal surface features. The large boulder – fully visible in the middle of the left frame and in partial shadow in lower portion of right frame – is about 165 feet (50 meters) across.

The cropped section to the right shows that large boulder in the middle of the frame.

I’m sorry, but when I look at this rubble-pile asteroid I cannot help but think of the cat-litter clumps I remove from our cats’ litter box. The only fundamental difference is that the grains in cat litter are made to be a uniform size, while at Bennu the grains are much coarser and not uniform. Nonetheless, this asteroid is a clump of many grains, just like those cat litter clumps, and will likely crumple easily into a cloud of grains if smacked just hard enough.

This knowledge is actually very critical, as Bennu is a potentially dangerous asteroid with an orbit that might have it impact the Earth in about two hundred years.

OSIRIS-REx has successfully completed an eight second engine burn to place it into a close orbit with the asteroid Bennu.

Now, the spacecraft will circle Bennu about a mile (1.75 kilometers) from its center, closer than any other spacecraft has come to its celestial object of study. (Previously the closest orbit of a planetary body was in May 2016, when the Rosetta spacecraft orbited about four miles (seven kilometers) from the center of the comet 67P/Churyumov-Gerasimenko.) The comfortable distance is necessary to keep the spacecraft locked to Bennu, which has a gravity force only 5-millionths as strong as Earth’s. The spacecraft is scheduled to orbit Bennu through mid-February at a leisurely 62 hours per orbit.

There is a bit of hype here. Other spacecraft have gotten far closer (NEAR, Hayabusa-1, Hayabusa-2) but then retreated for a variety of reasons. What makes this different is the plan to stay this close while they compile detailed data about Bennu’s surface in preparation for touchdown to grab a sample.

Cool movie time! OSIRIS-REx has completed its first planned fly-over of Bennu, this time above its north pole, and the science team has released a short movie showing part of that fly-over. I have embedded the movie below the fold.

This series of MapCam images was taken over the course of about four hours and 19 minutes on Dec. 4, 2018, as OSIRIS-REx made its first pass over Bennu’s north pole. The images were captured as the spacecraft was inbound toward Bennu, shortly before its closest approach of the asteroid’s pole. As the asteroid rotates and grows larger in the field of view, the range to the center of Bennu shrinks from about 7.1 to 5.8 miles (11.4 to 9.3 km).

They have four more fly-overs of the asteroid’s poles and equator as they assemble a detailed map of its surface.
» Read more

One of OSIRIS-REx’s instruments has now found evidence of water on the rubble-pile asteroid Bennu.

Recently analyzed data from NASA’s Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) mission has revealed water locked inside the clays that make up its scientific target, the asteroid Bennu.

During the mission’s approach phase, between mid-August and early December, the spacecraft traveled 1.4 million miles (2.2 million km) on its journey from Earth to arrive at a location 12 miles (19 km) from Bennu on Dec. 3. During this time, the science team on Earth aimed three of the spacecraft’s instruments towards Bennu and began making the mission’s first scientific observations of the asteroid. OSIRIS-REx is NASA’s first asteroid sample return mission.

Data obtained from the spacecraft’s two spectrometers, the OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) and the OSIRIS-REx Thermal Emission Spectrometer (OTES), reveal the presence of molecules that contain oxygen and hydrogen atoms bonded together, known as “hydroxyls.” The team suspects that these hydroxyl groups exist globally across the asteroid in water-bearing clay minerals, meaning that at some point, Bennu’s rocky material interacted with water. While Bennu itself is too small to have ever hosted liquid water, the finding does indicate that liquid water was present at some time on Bennu’s parent body, a much larger asteroid.

The image on the right, reduced to show here, was created from 12 images taken on December 2, 2018 from about 15 miles. If you click on the image you can see the full resolution photograph, which is quite incredible. While the asteroid’s shape is approximately what was expected from ground-based observations and computer modeling, the giant boulder on the limb on the bottom right is about four times bigger than expected.

OSIRIS-REx has successfully completed its last maneuver engine burn to place it in proximity orbit around the asteroid Bennu.

The link takes you to the live NASA stream, which has been a bit hokey. This event is actually not that visually exciting, a bunch of engineers staring at computer screens awaiting data back from the spacecraft indicating that all has occurred as planned. In fact, some felt a bit staged, though the actual event was really happening.

The OSIRIS-REx team has released relatively little data so far, compared to most NASA missions. There will be a press conference in a week when they say they will release more information. I guess we will have to wait until then.

Update: the live stream has shifted to the docking of the manned Soyuz capsule at ISS, which is in itself a more riveting event than OSIRIS-REx’s last engine burn.

In preparation for its December 3 rendezvous with the asteroid Bennu OSIRIS-REx successfully unfolded its robot arm for the first time since launch this week.

The website has a nice short video showing how the arm will grab its samples. Very innovative, and not what you would expect. The technique had to be clever because Bennu is so small and has such a tiny gravity.

OSIRIS-REx yesterday successfully completed the fourth planned engine firing to refine its course towards the asteroid Bennu, planned for December 3.

They will do one more course correction on November 30th.

The image above of the two hemispheres of the asteroid Bennu, cropped and reduced very slightly to post here, was created from several images taken by OSIRIS-REx on two different days last week.

These two super-resolution views of asteroid Bennu were created using eight 2.5-millisecond exposure images captured by OSIRIS-REx on two separate days. The view on the left is composed of eight PolyCam images taken over the span of two minutes on Nov. 1, 2018, when the spacecraft was about 126 miles (203 km) from the asteroid. The one on the right – showing the opposite side of the asteroid – was generated using eight images taken during the same two-minute time slot on Nov. 2, from a distance of about 122 miles (196 km).

The rock on the southern limb is the same in both images, merely seen from opposite sides. Bennu appears very similar to Ryugu, except that there do appear to be dark areas on its surface, possibly crater sites, that might be smooth enough for landing.

The rendezvous at Bennu will occur on December 3.

UPDATE: The OSIRIS-REx science team has now released a short movie showing Bennu’s rotation as imaged during this same time period.