Bumpy Street Forward For NASA’s Osiris-REX

March 21, 2019 - Comment

Asteroid Bennu is popping out to be a hazardous place for the NASA spacecraft to pattern: It has uneven, rugged terrain and sometimes even hurls rocks into house. NASA’s Osiris-REX has revealed a number of surprises in regards to the floor of asteroid 101955 Bennu, the place the spacecraft is meant to retrieve a pattern

Asteroid Bennu is popping out to be a hazardous place for the NASA spacecraft to pattern: It has uneven, rugged terrain and sometimes even hurls rocks into house.

NASA’s Osiris-REX has revealed a number of surprises in regards to the floor of asteroid 101955 Bennu, the place the spacecraft is meant to retrieve a pattern in July 2020. Whereas preliminary research and en-route imaging had predicted a clean floor lined by fine-grained supplies, close-up analyses performed for the reason that craft reached the asteroid on December three, 2018, have revealed a bumpier actuality. The analyses seem in a slew of papers within the journals Nature, Nature Astronomy, and Nature Geoscience.

Asteroid Bennu

Asteroid 101955 Bennu. Click on to see the film of its rotation
NASA / Goddard / Univ. of Arizona

Challenges to Pattern Retrieval

Large boulders cowl Bennu’s floor, lots of them as much as 10 meters (30 toes) in diameter, leaving few secure spots for the spacecraft to land safely. The slopes are irregular, too. As well as, the regolith – the free gravel and rocks that cowl the floor – contains extra different sizes than predicted, which is problematic for pattern assortment techniques designed to retrieve particles lower than 2 centimeters (zero.eight inch) in diameter.

One other potential problem for the touchdown is that the reflectivity of floor supplies has a wider vary than anticipated. Bennu is without doubt one of the darkest identified objects within the photo voltaic system, reflecting on common solely four% of incoming daylight. Nonetheless, some components of the rocky floor replicate as much as 20% of the sunshine. This variability poses a problem for the spacecraft’s laser-based navigation techniques.

Osiris-REX principal investigator Dante Lauretta (College of Arizona) and his colleagues conclude in Nature that the asteroid’s different reflectivity, vary in particle dimension, and total roughness of terrain “are past the spacecraft design specs.” That’s the technical approach of claiming that they’ve bought their work minimize out for them. However, the workforce is assured that they’ll work with what they’ve and preserve inside their present schedule, even when meaning adjusting their unique plans for the way they’ll descend to the asteroid’s floor.

Candidate sample site on asteroid Bennu

As OSIRIS-REx surveys asteroid Bennu intimately, the mission workforce is starting to determine potential places for the spacecraft to gather a pattern, equivalent to this candidate website within the asteroid’s northern hemisphere. The candidate touchdown websites are smaller in radius than initially deliberate, requiring extra exact spacecraft operations.
NASA / Goddard / Univ. of Arizona

Meet Bennu: An Historic however Lively Rubble Pile

Even earlier than the spacecraft lands, it has already realized a terrific deal in regards to the asteroid’s traits and historical past.

Bennu is barely wider than the Empire State Constructing is tall, and researchers describe its form as that of a spinning high; although, as Dave Dickinson places it, it additionally bears an uncanny resemblance to a 10-sided die typical of desk video games. The asteroid’s form can be strikingly much like that of 162173 Ryugu, the goal of Japanese Aerospace Exploration Company’s Hayabusa 2.

Based mostly on Osiris-REX’s photos of the asteroid’s floor, Barnouin (Johns Hopkins College Utilized Physics Laboratory) and colleagues have decided that Bennu is a so-called rubble pile, with a porous, sponge-like inside. Nonetheless, its form — particularly the presence of a sequence of ridges that run from pole to pole — additionally signifies an inner stiffness that helps maintain the asteroid collectively, a minimum of for now.

At present, Bennu rotates with a interval of four.three hours, however its interval is shortening by a couple of second each 100 years. That is as a result of one thing known as the YORP impact (Yarkovsky-O’Keefe-Radzievskii-Paddack), the place the asteroid regularly spins up as daylight heats its floor erratically. Mission scientists assume that this YORP impact is driving modifications in Bennu’s floor. Regardless of its estimated 100 million to 1 billion years previous floor, Bennu doesn’t at all times present its age — it has giant, ancient-looking craters however few small ones, hinting that its floor is slowly evolving.

Researchers had labeled Bennu as a primitive carbonaceous chondrite, lots of which have water and carbon-based compounds on their surfaces. Osiris-REX has now taken spectra of the asteroid’s floor, revealing hydrated minerals in addition to proof of hydroxyls, molecules that comprise hydrogen and oxygen atoms bonded collectively. Researchers assume that these molecules are a part of water-bearing clay supplies, which level to a previous interplay with water, almost certainly earlier than Bennu broke off from a a lot bigger guardian asteroid.

Rocky Plumes

Osiris-REX has additionally witnessed the asteroid spew rocks and mud into house at irregular intervals. “I’d say [these events are] one of many greatest surprises of my science profession,” mentioned Lauretta on March 19th on the Lunar and Planetary Science Convention. The workforce nonetheless isn’t certain what’s inflicting these ejections. One thought is that, now that the asteroid is at perihelion — the closest it will get to the Solar in its orbit — the elevated heating of its floor may play a task.

Particle plumes from Bennu

This view exhibits asteroid Bennu ejecting particles from its floor on January 19th. The picture is a composite of two photos taken by the NavCam 1 imager onboard NASA’s Osiris-REX spacecraft: a short-exposure picture (1.four ms), which exhibits the asteroid clearly, and a long-exposure picture (5 sec) that exhibits the particles clearly.
NASA / Goddard / College of Arizona / Lockheed Martin

The primary plume occasion was detected on January sixth; since then, the workforce has detected a complete of 11 episodes. Throughout an occasion, the asteroid could eject dozens and even a whole lot of particles into the house round it. The particles vary in dimension from centimeters to tens of centimeters in diameter.

Most of those particles transfer slowly relative to the asteroid’s escape velocity. Whereas a few of them assume short-lived orbits which are anticipated to final a number of weeks or perhaps months, they ultimately make their approach again to the asteroid’s floor, Lauretta mentioned. However some particles attain velocities of a number of meters per second, quick sufficient to flee to interplanetary house.

The likelihood of any of those rocks hitting the spacecraft may be very low.

On the press convention, Lauretta speculated in regards to the risk that the particles these occasions depart behind may end in meteor showers seen from Earth, when our planet crosses Bennu’s orbit sooner or later. “That will occur in late September yearly,” he says. “We’re working with our colleagues on the SETI Institute in California to arrange some monitoring cameras and see if there really is a Bennu meteor bathe.”

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