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Early Returns from Bennu

The science return from OSIRIS-REx has been surprisingly swift as the spacecraft returns data on near-Earth asteroid 101955 Bennu. We’re aided here by the timing, as early results are being discussed at the ongoing conference of the American Geophysical Union (AGU) in Washington, DC. The imagery we’ve received of Bennu’s surface has scientists buzzing. Thus Humberto Campins (University of Central Florida) a member of the OSIRIS-REx Science Team, who notes the comparison between what we see now and the Arecibo radar imagery in the late 1990s:

“The images are spectacular and spot on, what we expected thanks to predictions made with the instrumentation at the Arecibo Observatory in the late 90s and early 2000s. We will spend a year and a half mapping Bennu and have to wait until mid 2020 [when] we collect the sample, but it is pretty amazing to actually see it now. Christmas came early.”

The Arecibo work began shortly after the asteroid’s discovery in 1999, when both the Puerto Rico observatory and the Goldstone planetary radar system were used to examine Bennu. A second Arecibo investigation led to a shape model and pole orientation study published in 2013 by the OSIRIS-REx science team chief, Michael Nolan (University of Arizona). Arecibo’s radar data also firmed up Bennu’s size and rotation period, while even detecting a boulder on the asteroid’s surface. The 2013 model predicted Bennu’s shape, rotation rate, inclination and diameter, all of which have been confirmed by the OSIRIS-REx OCAMS camera suite.

“Radar observations don’t give us any information about colors or brightness of the object, so it is really interesting to see the asteroid up close through the eyes of OSIRIS-REx,” Nolan said. “As we are getting more details, we are figuring out where the craters and boulders are, and we were very pleasantly surprised that virtually every little bump we saw in our radar image back then is actually really there.”

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

But science observations were, of course, occurring long before the arrival at Bennu. During the approach phase, which began in August, OSIRIS-REx turned its two spectrometers, the OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) and the OSIRIS-REx Thermal Emission Spectrometer (OTES), on the target. We learn that the resulting data show the presence of oxygen and hydrogen atoms bonded together as hydroxyls, which researchers believe exist across the entire asteroid in water-bearing clay minerals.

To be sure, Bennu is too small an object to have had water on its surface at any point in its evolution, but at some point, its rocky components must have interacted with water. The implication is that liquid water was present on Bennu’s parent body, a much larger asteroid. What a find for the OSIRIS-REx team, given that the mission was designed to study the volatiles and organics found in the early Solar System through the lens of this asteroid. Rolling the dice on a sample mission here is paying off, as by 2023 we’ll have surface materials in a lab right here on Earth..

“This finding may provide an important link between what we think happened in space with asteroids like Bennu and what we see in the meteorites that scientists study in the lab,” said Ellen Howell, senior research scientist at the UA’s Lunar and Planetary Laboratory, or LPL, and a member of the mission’s spectral analysis group. “It is very exciting to see these hydrated minerals distributed across Bennu’s surface, because it suggests they are an intrinsic part of Bennu’s composition, not just sprinkled on its surface by an impactor.”

The number and variety of boulders on the surface is said to be unexpected, as is the size of the large boulder near the asteroid’s south pole. Observations from the ground pegged its height at 10 meters, but OSIRIS-REx is showing us through OCAMS imagery that it is more like 50 meters tall, with a width of approximately 55 meters. Given the scarcity of smooth surfaces, the search for a suitable sample site may be a complicated one.

With orbital insertion planned for December 31, we have an interesting conjunction for deep space aficionados, as New Horizons will be making its flyby of Kuiper Belt object Ultima Thule later that evening. After the OSIRIS-REx orbit is established, the spacecraft will remain in orbit until February, when it will begin another series of survey flybys. The upcoming orbit, by the way, is interesting in its own right. It will take the spacecraft between 1.4 and 2 kilometers from Bennu’s center, making this the tightest orbit of a space object by any spacecraft.

But before the orbit can be established, mission controllers are working on Bennu’s mass, a vital issue given its effects on the gravitational field of the object. The current preliminary survey passes within 7 kilometers of the north pole, equator and south pole, retrieving data that will also be useful in understanding the internal structure and composition of the asteroid. This mission has plenty of work ahead, but the early results could not be more interesting.


{ 13 comments… add one }
  • Douglas Dwyer December 12, 2018, 19:28

    A great achievement ; validates the use of RADAR and signal processing. Much lower cost than spacecraft. With FRBs we have already measured possible to observe reflections from astronomical neighbors in our lifetime.

  • ljk December 13, 2018, 10:14


    3D Bennu

    Image Credit: NASA, GSFC, U. Arizona – Stereo Image Copyright: Patrick Vantuyne

    Explanation: Put on your red/blue glasses and float next to asteroid 101955 Bennu. Shaped like a spinning top toy with boulders littering its rough surface, the tiny Solar System world is about 1 Empire State Building (less than 500 meters) across. Frames used to construct this 3D anaglyph were taken by PolyCam on board the OSIRIS_REx spacecraft on December 3 from a distance of about 80 kilometers.

    Now settling in to explore Bennu from orbit, the OSIRIS-REx mission is expected to deliver samples of the asteroid to planet Earth in 2023. Samples of dust from another asteroid will streak through Earth’s atmosphere much sooner though, when the Geminid meteor shower peaks in predawn skies on December 14. The parent body for the annual Geminids is asteroid 3200 Phaethon.

  • Michael C. Fidler December 13, 2018, 10:53

    With all these NEO asteroids and comets coming in from out of nowhere and people being turned to stone from bolide or fireballs, we need to look at a little history. This page has how much and how hard the Earth has been affected by impacts:
    But they even missed this one;
    Eltanin impact: 2.5 million years ago.
    The size of a possible tsunami has been calculated. An asteroid that was four km (two mi) in diameter falling onto the five km (three mi) deep ocean would have blasted the water off the ocean floor for at least 60 km (37 mi), and made a wave over 200 m (660 ft) high on the southern end of Chile and the Antarctic Peninsula. After ten hours, waves around 35 m (115 ft) would reach Tasmania, Fiji and Central America, and the New Zealand east coast would have been washed with 60 m (200 ft) high waves.

    So what can we do about it happening again?

    “A startup is developing a 100-gigawatt laser to propel a probe to another star system. That may be powerful enough to ‘ignite an entire city.”


    Yes, Breakthrough-Starshot is in the news again, but no one has mentioned that this 100 gigawatt laser/proton beamer could knock out those pesky rocks and iceballs out of the sky! Just think if some lurking megacomet comes storming in from the direction of the Sun and we only have some 15 minutes to kiss our a-s goodbye all we need to do is light up that 100 gigawatt monster and turn the comet into liquid sunshine!!!

    • ljk December 14, 2018, 13:16

      That may be their “front” for being built, along with the starship concept, but no one is going to put the money and resources into these mega lasers without it being for a weapon overall.

      Pioneers had nice ideas for rockets as launchers for satellites, but nothing really took off until WW2 and the V-2, which was then fed by the Cold War. Maybe history will not repeat itself here, but I am skeptical.

      So the Breakthrough Starshot sail laser may be built, but only for other less enlightened reasons first. Anyone who thinks it will be done out of pure altruism does not know history or human nature.

  • Gary Wilson December 13, 2018, 14:16

    The strange looking object in the southwest quadrant looks much less exciting now. It’s still apparent but no longer looking as interesting. The two relatively massive boulders, one in the southeast and one in the southwest are now absorbing my attention. Are there faint crater shapes present? As others have said any strike by a significant object probably significantly rearranges a lot of the surface. There is an area in the southeast that looks potentially flat enough to be a landing site. What is the resolution of the picture above?

  • Antonio December 14, 2018, 11:58
  • wdk December 16, 2018, 17:46

    Have to say that Bennu looks more substantial than the ball of lint that a small gravity field suggests, especially with all those objects seeming to adhere to its surface, such as the what resembled an engine nacelle a couple of weeks ago (more like a mushroom now). But I do see circular patterns on the surface in the higher resolution images as those I noted in the earlier report. If you move your head away from the initial screen image, you ( or maybe just me) circular patterns as though half buried in the surface. And they don’t seem to disappear completely when you move back to closer viewing. It is is as though some viscous fluid soaked up an impact and then left a trace. Subjective of course, but these are all first impressions ( sic) of a different type of solar system object.

    By the way, in terms of planetary origins theory, what should it be called? A planetesimal? Even if the original building blocks were similar…

    T’was several eons ago when a mean sequence sun
    had a planet building festival
    But absent from the fun
    amid disk accretion and planet completion
    And notions that primitive bodies being identical
    there remains Bennu the Dud Planetesimal.

    • Bruce D. Mayfield December 17, 2018, 18:22

      Nice points wdk, both in your prose and your poetry.

  • Ron S. December 16, 2018, 21:57

    “Bennu the Dud Planetesimal.”

    It hasn’t failed, yet. It’s still aiming at us and may one day achieve coalescence. Bennu remains a viable planetesimal despite being long delayed in comparison to the ones that came before.

  • ljk December 17, 2018, 18:32

    When the search for asteroids is under the weather

    Fickle weather can disrupt the search for potentially hazardous near Earth asteroids. Jeff Foust reports on how some planetary astronomers are pushing for a space-based telescope immune to the weather and able to make observations not possible from Earth.

    Monday, December 17, 2018


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