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OSIRIS-REx: Arrival

December 3 goes down as the day when OSIRIS-REx arrived at the asteroid called Bennu. The spacecraft, whose acronym untangles as Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer, has been performing braking maneuvers to slow for the approach since October. This has been a long and delicate operation, with arrival marked by a maneuver on Monday to set up the first flyover of the object’s north pole.

Even so, spacecraft and asteroid are flying together while not yet in an orbital relationship. That won’t happen until December 31, when the mission’s navigation team will use the preliminary survey they’re building now to initiate the orbit. Bear in mind that we are dealing with an object less than 500 meters across (about 1,600 feet), so one of Bennu’s distinctions will be that it is to become the smallest object ever orbited by a spacecraft. Now the learning period intensifies.

“During our approach toward Bennu, we have taken observations at much higher resolution than were available from Earth,” said Rich Burns, the project manager of OSIRIS-REx at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “These observations have revealed an asteroid that is both consistent with our expectations from ground-based measurements and an exceptionally interesting small world. Now we embark on gaining experience flying our spacecraft about such a small body.”

Image: Bennu in an image taken by the OSIRIS-REx spacecraft from a distance of around 80 kilometers (50 miles). Credit: NASA/Goddard/University of Arizona.

As of this morning, OSIRIS-REx is about 19 kilometers (11.8 miles) from Bennu’s surface, with flyovers of the asteroid taking it to within 7 kilometers (4 miles) as the preliminary survey operations intensify. As this is a sample return mission, an early goal is to help identify potential sites for sampling, while tightening up estimates of Bennu’s mass and spin rate. The sampling goal is to collect 60 grams or more of regolith and bring the sample back to Earth in 2023.

So far, another safe arrival, and a satisfying one following the InSight touchdown on Mars. OSIRIS-REx’s initiation of orbital operations at the end of this month coincides with the flyby of Ultima Thule by New Horizons, taking us deep into the Kuiper Belt. We’ll be unpacking and analyzing New Horizons data for months and years while OSIRIS-REx spends the next year mapping its own target (and let’s not forget Hayabusa2, now surveying asteroid 162173 Ryugu, with its own sample return plans). The early reconnaissance of the Solar System continues.


{ 49 comments… add one }
  • Charley December 4, 2018, 12:01

    So, the take away from this is that OSIRIS-REx will be pacing the asteroid Bennu ? And it will be flying in tandem with the asteroid until December 31, at which point you’ll initiate some type of maneuver to achieve an orbit ?
    Do you happen to know is this particular system OSIRIS-REx an ordinary chemical rocket, or is this a ion type of propulsion system? What is the purpose of this sample return? Is it simply curiosity or is this going to be going to be done with an eye on the idea that they want to ultimately bring an asteroid (that is move the asteroid) into an orbit about the moon, so that they can do some kind of study of asteroids in near earth orbit?

    • Paul Gilster December 4, 2018, 13:33

      OSIRIS-REx propulsion is covered in depth here:


      Here’s also a quote from mission PI Dante Lauretta:

      “The OSIRIS-REx propulsion system is based on the system developed for the Mars Reconnaissance Orbiter (MRO) and later customized for the Juno and MAVEN missions. Our system is called a “monopropellant” system, meaning that it uses a single fuel called hydrazine (N2H4). Monopropellants are chemicals that do not require an oxidizer to release their stored chemical energy. They are stable under certain storage conditions but they can decompose rapidly to produce a lot of high-temperature gas. The OSIRIS-REx system produces thrust when the hydrazine fuel is flowed over a heated catalyst bed and decomposes. The resulting gases expand through the sonic throat of a rocket engine and accelerate out the rocket engine nozzle.”

      Sample return is all about scientific investigation not only into the components that made up the early Solar System but knowledge that could help in any asteroid mitigation strategies, if we ever find one on a dangerous trajectory towards the Earth.

  • Gary Wilson December 4, 2018, 13:52

    There is a strange looking object in the southwest quadrant of the asteroid. Has anyone else commented on it? It looks like two parts of a divided cylinder with shadows at the upper ends. Overall the asteroid looks like a rocky debris field. Together with its overall shape it looks very interesting. I will be eagerly awaiting more details.

    • Ron S. December 4, 2018, 17:57

      Probably just rocks. Bennu is a rubble pile – made of small objects loosely held together by gravity.

    • Alex Tolley December 4, 2018, 17:59

      vulnerable exhaust ports. ;)

      • Michael December 4, 2018, 22:55

        Looks like a whole wheat bun to me. On a more serious note plenty of material to build space stations.

    • DCM December 5, 2018, 5:38

      We don’t know enough about off-earth items to make more than superficial descriptions till we get more information. Everybody is eager to see artifacts. And what will they do or say if such is found? I bet rely on it as proof religious beliefs or fall back on some favorite sci-fi story, denying the results of any subsequent studies….

      • ljk December 5, 2018, 12:11

        Or on the positive side, the space agency will get a heck of a budget boost and the human race will have something positive to focus on collectively. They may think they are aware of alien life, but the real deal will put things in a whole new perspective. Are the talking primates of Sol 3 ready for this collective cosmic consciousness expansion?

        • DCM December 5, 2018, 17:50

          Another self-hating or at least self-diminishing attitude. (“Are the talking primates of..”) That isn’t objectivity.
          It’s best not to see possible artifacts everywhere because we just don’t know anything about possible aliens. If they’re proven demonstrably to be artifacts, that’s a different matter.
          Since I was a little kid people have “seen” and “contacted” aliens or their craft and these evolve along with culture and knowledge from flattened bell shaped saucers inhabited by duplicates of humans who bring profound wisdom (that has never resulted in a better world) to sophisticated models inhabited by semihuman tadpoles.
          I just want us to separate mental projections from what’s really there.

          • AlexT December 6, 2018, 5:21

            Another self-hating or at least self-diminishing attitude. (“Are the talking primates of..”) That isn’t objectivity.

            Very, good point… It seams to be the common point of superior ETI fans, underestimate reality (the real existing Earth’s intelegent life) and overestimate virtuality (not found in reality virtual ETI).

            • ljk December 6, 2018, 10:54

              Generalizations to the point of stereotyping, as usual.

          • ljk December 6, 2018, 10:23

            Humans are primates that talk. If you feel the need to put a positive spin on this, we can add that they are capable of doing things like sending space probes to planetoids to study them and return samples to Earth.

            And I stand by my question of whether humans are really ready to face the realities of the much wider Universe. Most seem to think it will be some version of Star Trek, but I have my doubts.

            • DCM December 6, 2018, 12:47

              No, it wouldn’t be like a Star Trek show. I can’t venture much as to what it might be like because much depends on the prevailing culture here and the nature of alien life.

              One thing that strikes me is the persistent belief aliens will bring healing wisdom and benevolent teachings. As of now they’re equally likely to be friendly or hostile.
              Bearing in mind that we know nothing of life elsewhere, it’s better to remember that when Cortez and his army landed in Mexico it was one of the years the return of the god Quetzalcoatl, supposed inventor of much of Indian civilization, was predicted. Naturally the Aztecs were wary of fighting him, which they could effectively have done despite Cortez’ superior armaments by overwhelming him with sheer numbers. Inviting him into the palace was a deadly mistake, not least because it gave smallpox time to incubate.
              Better to err on the side of caution where you don’t know what aliens are really like.

              • ljk December 6, 2018, 14:58

                Allow me to clarify my statement about humans being ready (or not) for whoever or whatever may be out there in the Milky Way galaxy:

                I do not necessarily assume that ETI, even advanced ones, will automatically be benevolent. Even if they are not outright hostile, they could also be indifferent or unaware being so different from us. They might even think they could do us good without having the full picture, therefore making things worse.

                This is why I advocate more astronomical research and education, including multifaceted SETI, so we can be at the least be less caught off guard when we do venture out there – or someone comes to us. At this point this is what we can hope for; at least we have control over how much we intend to do to enlighten our species.

  • Robin Datta December 4, 2018, 15:23

    With such a small asteroid, escape velocity and orbital velocity would be small. Manoeuvring it to desired effect would take a lot of skill. The mishap with Rosetta and Philae comes to mind. Wishing this mission good fortune.

  • Ivar December 4, 2018, 17:15

    Hmm, no craters? I mean I get it that comets have none, being ice and all.. but asteroids are usually full of them as far as I have seen… it can’t really be a geological process?

    • ljk December 5, 2018, 12:26

      Maybe Bennu is just a really small target for other space rocks to run into based on the law of averages. Or maybe there is some kind of surface and/or interior shifting going on, especially if it is basically a rubble pile.

      • Ivar December 5, 2018, 18:23

        @Ijk – Guess that’s probably it, thnx! Impact on rubble and then there’s no solid surface to make an impact on…

        Does that make this a different class compared to objects like phobos/deimos? (if they weren’t moons)
        (Similar to the difference between dwarf planets (rounded) and asteroids (free-form-shape) would this be a difference between large asteroids (solid) Bennu like small objects (rubble))

        • ljk December 6, 2018, 10:49

          According to their Wikipedia entry:


          The origin of the Martian moons is still controversial.[27] Phobos and Deimos both have much in common with carbonaceous C-type asteroids, with spectra, albedo, and density very similar to those of C- or D-type asteroids.[28] Based on their similarity, one hypothesis is that both moons may be captured main-belt asteroids.[5][29] Both moons have very circular orbits which lie almost exactly in Mars’s equatorial plane, and hence a capture origin requires a mechanism for circularizing the initially highly eccentric orbit, and adjusting its inclination into the equatorial plane, most probably by a combination of atmospheric drag and tidal forces,[30] although it is not clear that sufficient time is available for this to occur for Deimos.[27] Capture also requires dissipation of energy. The current atmosphere of Mars is too thin to capture a Phobos-sized object by atmospheric braking.[27] Geoffrey Landis has pointed out that the capture could have occurred if the original body was a binary asteroid that separated under tidal forces.[29]

          Phobos could be a second-generation Solar System object that coalesced in orbit after Mars formed, rather than forming concurrently out of the same birth cloud as Mars.[31]

          Bennu is also a carbonaceous planetoid of the Apollo group.

    • Bruce D. Mayfield December 5, 2018, 14:42

      Maybe one large core asteroid with just enough mass to attract and barely hold smaller rocks that are on very close trajectories so it piles up with rubble over time. This is a very interesting phase of the planet building process – getting over the gap where collisions can be constructive rather than disruptive. This body looks like it could easily be knocked to smitherines by not much of an impact. That could be why there are no craters; if it had ever been hit hard enough to form a crater it would have been totally disrupted.

    • AlexT December 6, 2018, 5:25

      This asteroid can be a huge diamond crystall (core) that is covered by some dust…

      • ljk December 6, 2018, 10:43

        What is your scientific evidence for this?

  • Michael Fidler December 4, 2018, 20:50

    Aliens Might Have Filled Space With Junk Like We Fill Our Oceans and Orbit.

    “If there are technological aliens in our galaxy, then it is possible that their space junk could be part of the Interstellar material that makes it to our solar system. How much depends upon how many technological alien civilizations there are and how much junk is made from what they are doing.

    It will be decades to centuries before we can go to another solar system or even very far beyond Pluto. We are able to take improving looks at what is in our solar system and what happens to drift into our solar system for evidence of Aliens.

    A Lot of Interstellar Space Junk Seems Inevitable If Aliens are Making Spaceships or Probes
    Space is huge so we and aliens will probably have to move at very high speeds like 20 to 99% of the speed of light if they want travel times to be as economically short as possible.”

    Could Benny be like a vacuum cleaner that may pickup anything floating around in our solar system, including alien tech garbage???
    Could we be being bombarded with alien spacecraft parts in small size nuts and bolts? How would we know? 13.5 billion years of a ET garbage should be relatively easy to find when you go down to the microscopic level of spheroids that pelt earth daily. But we need to look at the dust moons that orbit earth or asteroids like Benny to make sure it not our own garbage. So anyone that might have a good idea where to look for the most valuable garbage in our history please feel welcome to speak up – you may go down as the founder of a whole new industry worth quadrillion of dollars…

    • ljk December 5, 2018, 12:17

      I can see that as a future (maybe not so far) occupation of some spacefaring people, to explore planetoids and comets for any alien artifacts on them. It could be done as part of the larger survey programs designed to see how valuable such objects may be in terms of resources for space colonies and industry.

      • ljk December 5, 2018, 12:20

        This would be similar to construction workers who have to stop a work project if they find ancient human artifacts and remains and report them to await archaeologists and historians to study the area first.

        Are there alien artifacts on the planetoids and comets? Of course we have no idea yet. But if we are going to be there exploring them – and these bodies are going to be the key for permanent space settlements and infrastructure – we might as well check for all plausible scenarios in the process.

        Finding solid evidence of alien life certainly would not hurt either the reputation or the budget of any science mission, either.

        • Michael C. Fidler December 6, 2018, 2:25

          When I was growing up the theory in the 60’s was that the asteroid belt was the ruble left over after a 5th planet exploded between Mars and Jupiter. Now the accretion model is in the vogue, but the beautiful crystal pattern on the iron/nickel meteorites have always intrigued me. Take a look at this:

          “Strength in all of the meteorite samples examined here was higher than predicted for ironnickel alloys prepared in the laboratory, and higher than can be accounted for by inclusion of carbon in these alloys. The unexpectedly high yield in these materials appears correlated with high localized strain in crystallites. In the case of the one nonoctahedrite iron meteorite examined, the strength was less than for the octahedrites, but
          was high relative to iron, which may be due to extensive twinning in the meteorite sample. Inclusion of these measured values may improve atmospheric breakup and impact calculations done using iron-nickel meteorite compositions.”

          This is from a study by the Los Alamos National Laboratory,
          “Mechanical Properties of Several Fe-Ni Meteorites”

          What may be the case is that an ET civilization was here in the early days of the solar system and built a Dyson Sphere or Ring World in that location. My reasoning is the characteristics of the iron/nickel, stony irons and stony meteorites would make a perfect union for the substructure of the sphere if built in a layered structure.The Iron/Nickel would also make for a good source to generate a magnetic field around the object.

          Just another crazy idea, but if nothing else maybe we could do the same thing!

    • ljk December 5, 2018, 12:28
      • Michael C. Fidler December 5, 2018, 14:30

        Thanks, completely forgot the link – put the comment in off my cell phone and did not check, been traveling to do some christmas shopping!

  • Triffin December 4, 2018, 21:33

    I believe the mission to Bennu is partly
    motivated by it’s status as a NEO that has
    a 1/2700 probability of a near earth encounter
    in about 150 years .. Detailed knowledge of
    it’s composition etc would facilitate development
    of appropriate strategies to deflect it’s orbit if need be ..

    Triff ..

    • ljk December 5, 2018, 12:15

      That is correct. Now if Bennu were suddenly heading towards a collision with Earth, how would we deal with it? If it were a rubble pile and the human response was to nuke it, would this turn Bennu into a harmless if spectacular meteor shower, or would it just spread the potential carnage over a wider area?

      Could we use that space tug method for literally towing an NEO in a different and safer direction? If it is a rubble pile, might it break apart instead and again only spread out the potential for damage?

      • coolstar December 5, 2018, 19:17

        For an object the size of Bennu, the answer is easy: if it’s broken into small enough chunks, say 20 meters or smaller, then those chunks will be relatively harmless as they enter the earth’s atmosphere. That’s approximately the size of the Chelyabinsk impactor, and aside from injuries due to flying glass, there was very little damage on the ground as no fragments arrived at velocities larger than that of free fall from around 40 miles or so. This is true in general for all but huge “chunks” as the earth’s atmosphere can absorb a huge amount of energy from lots of small impactors as opposed to Meteor Crater sized objects making it thru to the ground at several km/sec (and even then, that object lost perhaps half of its kinetic energy in the atmosphere.).

        • ljk December 6, 2018, 10:26

          The reports said that over 1,000 people were injured due to flying glass and structures falling. I do not consider that minor just because no one was outright killed.

          The other thing we should be grateful for is that the Chelyabinsk impact was not mistaken for a missile attack by the Russian military.

          • ljk December 7, 2018, 11:32

            Speaking of potentially deadly cosmic impacts, I have always been amazed that the Tunguska event of June 30, 1908 over Siberia reportedly did not kill any humans.

            Yes I know the Russian tundra is remote, but it was not uninhabited even a century ago. I read reports of one man being knocked off his porch chair some 45 miles away and even a report of deer being killed. Yet how did the authorities KNOW that no humans were killed by the impact – which flattened trees for many miles around like toothpicks.

            It took them 20 years to get a scientific expedition there after the event due to how remote the Tunguska region is. How did the Russians know who was out there at the time?

  • wdk December 5, 2018, 12:50

    Read or heard nothing to suggest that Bennu is not of great antiquity, but have to wonder how the surface features are explained.

    Had remarked earlier that Bennu looks an awful lot like a charcoal briquette, at least the kind that we use around here for barbecues.
    Consequently looked up the processing for briquettes to see if there was any significance associated with their shape. Actually, no more than with cookies or bricks in clay molds. The shape probably originated in Japan. Many other charcoal briquettes around the world simply look like bricks.

    Yet still, as you look at that picture of Bennu, it looks like there is some sort of regular geometric process or folding. There is a remarkable absence of craters. Phobos and Deimos? They’ve got them. Other small asteroids, they’ve got them too.

    Additionally, when you look at unfamiliar territory, frequently you might reverse the topographic features: which are high and which are low.
    Looking at this image, I have to wonder why the dark spots appear to be the highest elevation. We are practically looking downward with the sun behind us, except that the terminator shows a little on the right. The dark spots elsewhere seem inconsistent. And then the “tubular” forms near the bottom, there is a little shadow there too.

    Perhaps there is an impact or some feature on the opposite side that explains the strange jumble; or perhaps the cohesiveness of the whole object is such that crater formation is not in the cards?

    • Bruce D. Mayfield December 5, 2018, 14:58

      More like the incoheseveness of the whole makes crater formation different than on solid bodies. When it gets hit, it gets greatly fragmented, but then the pieces slowly pile up again over time.

      • ljk December 6, 2018, 10:52

        Almost like a ball of quicksand.

        Now there would make an interesting science fiction story: Seemingly harmless planetoids roaming the Sol system, ready to swallow up any expeditions that attempt to land there.

  • Gary Wilson December 5, 2018, 16:48

    That strange object could be a discarded engine nacelle from the Enterprise. :)

    • ljk December 6, 2018, 10:29

      It’s too short. Plus there is no visible ship registration number.

  • wdk December 5, 2018, 17:09

    Wonder how many people I might be able to con into this?

    Seriously, when I back away from my monitor different patterns on Bennu become more prominent. It is as though something like “Mare” features start to come out underneath all the granularity, kind of ghostly. Large fractions of the exposed image, about the size of fingerprints on a baseball. Perhaps they are indicative of some sort of impact shocks radiating out?

    And when you do that, the tubular image does not seem so prominent any more. It seems like it reverts into a flatter feature.

    … At least you don’t have to observe the warning: Don’t try this at home.

  • Bruce D. Mayfield December 5, 2018, 21:34

    Since this object has been orbiting in the Earth’s vicinity for billions of years I would think that it is highly probable that some or maybe even a large fraction of that rubble is pieces of the giant impact that created the Earth/Moon system.

  • Nishu December 6, 2018, 2:54

    That is right. Presently if Bennu were all of a sudden heading towards an impact with Earth, how might we manage it? In the event that it were a rubble heap and the human reaction was to nuke it, would this transform Bennu into a safe if tremendous meteor shower, or would it simply spread the potential slaughter over a more extensive zone?
    Might we be able to utilize that space pull strategy for truly towing a NEO in an alternate and more secure bearing? On the off chance that it is a rubble heap, may it break separated rather and again just spread out the potential for harm?

    • Bruce D. Mayfield December 7, 2018, 13:59

      Fortunately Bennu’s orbit is completely known, so it will never “all of a sudden” threaten Earth. But in the future it could be a real threat of course. Having plenty of lead time before an impact is predicted means many options are on the table. Nuking it might lead to unpredictable results. Its rotation could be spun up so that centrifugal “force” causes dispersal, but that also might be less predictable than desirable.

      A cool idea I’ve heard of that probably has been discussed here before that can work when there’s plenty of advanced warning is to gravitationally tow it into a non-threatening orbit (no tether required!).

  • Gary Wilson December 6, 2018, 12:53

    If the “self-hating attitude” is in reference to my comment then that is disturbing. It suggests an attempt to censor someone for curiosity about the universe at large. I have no idea what the shape is. Human beings use pattern recognition to make sense of things, hence all the face on Mars controversy. I agree it is probably not an artifact of any kind but making a comment does not mean I have a self-hating attitude.

  • Patrick Underwood December 8, 2018, 16:46

    In this (gif?) you can see the apparently flat object is actually a sizable rock. https://www.nasa.gov/content/osiris-rex-images

    Or, a sizable artifact. ;)

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