Bennu tosses particles from its surface routinely
Tracked particles after August 28, 2019 ejection event.
During OSIRIS-REx’s more than twenty months flying close to the Bennu, scientists have found that the asteroid routinely kicks particles from its surface into space, with these events linked to the asteroid’s day-night cycle.
Since arrival the scientists have seen and tracked more than 300 ejection events, with the almost seven hundred objects detected ranging from about an eighth to a half inch in size. Most moved about eight inches per second, comparable to “a beetle scurrying across the ground.”
The image to the right, cropped, reduced, and brightened to post here, comes from the introductory paper of a suite of papers on the subject, published today.
The timing of the events however reveals the most.
As Bennu completes one rotation every 4.3 hours, boulders on its surface are exposed to a constant thermo-cycling as they heat during the day and cool during the night. Over time, the rocks crack and break down, and eventually particles may be thrown from the surface. The fact that particle ejections were observed with greater frequency during late afternoon, when the rocks heat up, suggests thermal cracking is a major driver. The timing of the events is also consistent with the timing of meteoroid impacts, indicating that these small impacts could be throwing material from the surface. Either, or both, of these processes could be driving the particle ejections, and because of the asteroid’s microgravity environment, it doesn’t take much energy to launch an object from Bennu’s surface.
The link includes a cool movie showing the ejections events and the tracked paths of the ejected particles.
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Tracked particles after August 28, 2019 ejection event.
During OSIRIS-REx’s more than twenty months flying close to the Bennu, scientists have found that the asteroid routinely kicks particles from its surface into space, with these events linked to the asteroid’s day-night cycle.
Since arrival the scientists have seen and tracked more than 300 ejection events, with the almost seven hundred objects detected ranging from about an eighth to a half inch in size. Most moved about eight inches per second, comparable to “a beetle scurrying across the ground.”
The image to the right, cropped, reduced, and brightened to post here, comes from the introductory paper of a suite of papers on the subject, published today.
The timing of the events however reveals the most.
As Bennu completes one rotation every 4.3 hours, boulders on its surface are exposed to a constant thermo-cycling as they heat during the day and cool during the night. Over time, the rocks crack and break down, and eventually particles may be thrown from the surface. The fact that particle ejections were observed with greater frequency during late afternoon, when the rocks heat up, suggests thermal cracking is a major driver. The timing of the events is also consistent with the timing of meteoroid impacts, indicating that these small impacts could be throwing material from the surface. Either, or both, of these processes could be driving the particle ejections, and because of the asteroid’s microgravity environment, it doesn’t take much energy to launch an object from Bennu’s surface.
The link includes a cool movie showing the ejections events and the tracked paths of the ejected particles.
Readers!
My annual February birthday fund-raising drive for Behind the Black is now over. Thank you to everyone who donated or subscribed. While not a record-setter, the donations were more than sufficient and slightly above average.
As I have said many times before, I can’t express what it means to me to get such support, especially as no one is required to pay anything to read my work. Thank you all again!
For those readers who like my work here at Behind the Black and haven't contributed so far, please consider donating or subscribing. My analysis of space, politics, and culture, taken from the perspective of an historian, is almost always on the money and ahead of the game. For example, in 2020 I correctly predicted that the COVID panic was unnecessary, that the virus was apparently simply a variation of the flu, that masks were not simply pointless but if worn incorrectly were a health threat, that the lockdowns were a disaster and did nothing to stop the spread of COVID. Every one of those 2020 conclusions has turned out right.
Your help allows me to do this kind of intelligent analysis. I take no advertising or sponsors, so my reporting isn't influenced by donations by established space or drug companies. Instead, I rely entirely on donations and subscriptions from my readers, which gives me the freedom to write what I think, unencumbered by outside influences.
You can support me either by giving a one-time contribution or a regular subscription. There are four ways of doing so:
1. Zelle: This is the only internet method that charges no fees. All you have to do is use the Zelle link at your internet bank and give my name and email address (zimmerman at nasw dot org). What you donate is what I get.
2. Patreon: Go to my website there and pick one of five monthly subscription amounts, or by making a one-time donation.
3. A Paypal Donation or subscription:
4. Donate by check, payable to Robert Zimmerman and mailed to
Behind The Black
c/o Robert Zimmerman
P.O.Box 1262
Cortaro, AZ 85652
You can also support me by buying one of my books, as noted in the boxes interspersed throughout the webpage or shown in the menu above.
First link says “Where rocks come alive”. Reminds me of the movie Apollo 18, where rocks do come alive. Completely silly, but nice Moonscape scenes.
and the particles are lost into space or they settle back to the surface of Bennu? If material is lost, then Bennu was larger in the past? How old is it?
How big is Bennu?
Both is diameter and mass.
pzatchok-
“73 billion kgs”
“Weird, wild gravity of asteroid Bennu”
March 2019
https://www.sciencedaily.com/releases/2019/03/190319142315.htm