Bennu’s cobbled equatorial ridge

Week Four: Ninth Anniversary Fund-Raising Drive for Behind the Black

The fourth week of my annual anniversary fund-raising campaign for Behind the Black has begun.

I once again must thank the many readers and listeners who have generously donated this month. Right now there is a chance this will be the best fund-raiser ever, though only if a lot of people donate during the month's last ten days. If you want to help me continue my reporting, you can give a one-time contribution, from $5 to $100, or a regular subscription for as little as $2 per month.

For one time donations via Paypal, click here:

To pick a subscription option via Paypal, click here:


If Paypal doesn't work for you, you can still support Behind The Black by sending your donation by check, payable to Robert Zimmerman, to
Behind The Black
c/o Robert Zimmerman
P.O.Box 1262
Cortaro, AZ 85652

Bennu as seen by OSIRIS-REx
Click for full image.

The OSIRIS-REx science team has released a new close-up image of Bennu, this time showing the asteroid’s equatorial ridge. The image on the right is that photograph, reduced to post here.

When the image was taken, the spacecraft was positioned over Bennu’s northern hemisphere, looking southward over the asteroid’s equatorial bulge. The field of view shown is 168 ft (51.2 m) wide. For scale, the bright, rectangular rock above the dark region is 8 ft (2.4 m) wide, about the size of a long bed on a pickup truck

Like Ryugu, the scientists for OSIRIS-REx are going to be challenged in finding a location smooth enough for their touchdown sample grab. That surface reminds me of some avalanche scree slopes I’ve hike across, where you’ve got nothing but rough rocks to walk on.



  • Darwin Teague

    Stupid question. How do scientists determine north and south on objects like this?

  • Darwin Teague: That is not a stupid question, it is brilliant. I myself had never asked, which means I don’t really know.

    I think, based on past reading of both these asteroid missions as well as others, that they use the asteroid’s rotation to determine the locations of the poles and equator, and then pick north based on its relative location compared to the Earth. In other words, they match the asteroid’s rotation with the solar system, and have north point away in the same direction as the Earth.

    This is an educated guess however.

  • mpthompson

    Robert, if the asteroid had a retrograde rotation, would that place the north pole in the same direction as Earth’s south pole? Looking this up, I see Venus and Uranus have retrograde rotation but it’s unclear which side is designated north. This question is explored at the following URL, but with no clear answer:

    Or, even a more in-depth discussion here on the same topic:

    Seems Darwin’s question is indeed a very good one.

  • Andi

    Especially since Uranus has a 98-degree tilt to its axis. That would imply that “north” is in a southerly direction compared with Earth.

Leave a Reply

Your email address will not be published. Required fields are marked *