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takyon writes:

NASA's New Horizons spacecraft has imaged 2014 MU₆₉, nicknamed Ultima Thule, from about 172 million kilometers away:

Mission team members were thrilled – if not a little surprised – that New Horizons' telescopic Long Range Reconnaissance Imager (LORRI) was able to see the small, dim object while still more than 100 million miles away, and against a dense background of stars. Taken Aug. 16 and transmitted home through NASA's Deep Space Network over the following days, the set of 48 images marked the team's first attempt to find Ultima with the spacecraft's own cameras.

[...] This first detection is important because the observations New Horizons makes of Ultima over the next four months will help the mission team refine the spacecraft's course toward a closest approach to Ultima, at 12:33 a.m. EST on Jan. 1, 2019. That Ultima was where mission scientists expected it to be – in precisely the spot they predicted, using data gathered by the Hubble Space Telescope – indicates the team already has a good idea of Ultima's orbit.

Meanwhile, the OSIRIS-REx spacecraft is approaching 101955 Bennu, and has taken a series of images from a distance of about 2.2 million kilometers:

After arrival at Bennu, the spacecraft will spend the first month performing flybys of Bennu's north pole, equator and south pole, at distances ranging between 11.8 and 4.4 miles (19 and 7 km) from the asteroid. These maneuvers will allow for the first direct measurement of Bennu's mass as well as close-up observations of the surface. These trajectories will also provide the mission's navigation team with experience navigating near the asteroid.

"Bennu's low gravity provides a unique challenge for the mission," said Rich Burns, OSIRIS-REx project manager at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "At roughly 0.3 miles [500 meters] in diameter, Bennu will be the smallest object that any spacecraft has ever orbited."

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takyon writes:

Another Space Diamond! NASA Probe Snaps Great Photo of Asteroid Bennu

The asteroid Bennu is really coming into focus for NASA's approaching OSIRIS-REx spacecraft.

OSIRIS-REx snapped eight photos of the 1,650-foot-wide (500 meters) Bennu on Monday (Oct. 29), when the probe was about 205 miles (330 kilometers) away from the space rock. Mission team members combined these images into a single "super-resolution" shot, which reveals boulders and other features on the asteroid's surface.

The striking photo also highlights Bennu's diamond shape, which is similar to that of the 3,000-foot-wide (900 m) asteroid Ryugu. Japan's Hayabusa2 mission has been orbiting Ryugu since late June and has dropped three separate landing craft onto the space rock's surface over the past five weeks.

101955 Bennu has an average diameter of 492 meters, compared to about 1 kilometer for 162173 Ryugu. New Horizons will fly by (486958) 2014 MU₆₉, a 30-40 km object or objects, on January 1, capping the space rock trio for the year.

NASA/Goddard/University of Arizona photo.

Previously: New Horizons Spacecraft Approaches 2014 MU69; OSIRIS-REx Nears 101955 Bennu (images taken from 2.2 million km away)

Related: Hayabusa2 Reaches Asteroid 162173 Ryugu
Japan's Hopping Rovers Capture Amazing Views of Asteroid Ryugu
Short-Lived MASCOT Lander Reaches Asteroid Ryugu

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Anti-aristarchus writes:

NASA reports, via NASA, that OSIRIS-REx is leaving Bennu.

NASA's OSIRIS-REx completed its last flyover of Bennu around 6 a.m. EDT (4 a.m. MDT) April 7 and is now slowly drifting away from the asteroid; however, the mission team will have to wait a few more days to find out how the spacecraft changed the surface of Bennu when it grabbed a sample of the asteroid.

The OSIRIS-REx team added this flyby to document surface changes resulting from the Touch and Go (TAG) sample collection maneuver Oct. 20, 2020. "By surveying the distribution of the excavated material around the TAG site, we will learn more about the nature of the surface and subsurface materials along with the mechanical properties of the asteroid," said Dr. Dante Lauretta, principal investigator for OSIRIS-REx at the University of Arizona.

During the flyby, OSIRIS-REx imaged Bennu for 5.9 hours, covering more than a full rotation of the asteroid. It flew within 2.1 miles' (3.5 kilometers) distance to the surface of Bennu – the closest it's been since the TAG sample collection event.

Just to mention, the survey and selection of a sampling site was one of the recent "citizen science" projects.

takyon writes:

The OSIRIS-REx spacecraft, which "arrived" at the asteroid Bennu on December 3 but has been slowly approaching it for weeks, has found evidence of Bennu's interaction with liquid water in the past:

In a conference today, scientists announced that OSIRIS-REx has found evidence of hydrated minerals on the surface of Bennu using its on-board spectrometers - tools used to determine the exact chemical composition of a specific spot.

That means "evidence of liquid water" in Bennu's past, according to Amy Simon, the scientist overseeing OSIRIS-REx's spectral analysis.

"To get hydrated minerals in the first place, to get clays, you have to have water interacting with regular minerals," says Simon. "This is a great surprise."

And they're abundant, too. There's "strong convincing, evidence that the surface is dominated by these hydrated minerals," according to Dante Lauretta, leader of OSIRIS-REx's sample return mission, leading the team to believe Bennu is "water rich".

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takyon writes:

OSIRIS-REx completes New Year's Eve orbit insertion burn at asteroid

After four weeks of navigating in the vicinity of asteroid Bennu, NASA's OSIRIS-REx spacecraft fired its thrusters for eight seconds Monday to slip into orbit around the carbon-rich object, making Bennu the smallest planetary body ever orbited by a spacecraft.

OSIRIS-REx arrived at Bennu on Dec. 3, ending a journey from Earth that lasted more than two years and spanned 1.2 billion miles (2 billion kilometers). Since then, the robotic spacecraft has surveyed the 1,600-foot-wide (492-meter) asteroid through a series of flybys as close as 4.4 miles (7 kilometers) over Bennu's north pole, south pole and equator to measure the asteroid's gravitational tug on OSIRIS-REx, which helped scientists determine the object's mass.

The mass estimate helped navigators refine the parameters of OSIRIS-REx's maneuver to enter orbit around Bennu. The craft's thrusters ignited for 8 seconds at 2:43:55 p.m. EST (1943:55 GMT) Monday to slightly adjust OSIRIS-REx's velocity, nudging it just enough for Bennu's tenuous gravity to capture the probe into orbit.

[...] During the mission's first orbital phase, OSIRIS-REx is orbiting the asteroid at a range of 0.9 miles (1.4 km) to 1.24 miles (2.0 km) from the center of Bennu, setting another record for the closest distance any spacecraft has orbited to a planetary body.

Also at The Guardian.

Previously: NASA's OSIRIS-REx "Arrives" at Asteroid Bennu
NASA Finds Evidence of Water on Asteroid Bennu

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