https://www.nasa.gov/press-release/nasa-mission-reveals-asteroid-has-big-surprises

A NASA spacecraft that will return a sample of a near-Earth asteroid named Bennu to Earth in 2023 made the first-ever close-up observations of particle plumes erupting from an asteroid’s surface. Bennu also revealed itself to be more rugged than expected, challenging the mission team to alter its flight and sample collection plans, due to the rough terrain. 

Bennu is the target of NASA’s Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) mission, which began orbiting the asteroid on Dec. 31. Bennu, which is only slightly wider than the height of the Empire State Building, may contain unaltered material from the very beginning of our solar system.

“The discovery of plumes is one of the biggest surprises of my scientific career,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson. “And the rugged terrain went against all of our predictions. Bennu is already surprising us, and our exciting journey there is just getting started.”

So what’s the likely cause?

Bubblecar said:

So what’s the likely cause?

I don’t know what cause is.

1) being a very primitive type of asteroid, it contains a lot of water ice. This could be caused by water ice subliming in the sunlight resuling in loosening of grains of dust that float free.

Or

2) disturbed by the driving jets of the spacecraft.

mollwollfumble said:

Bubblecar said:

So what’s the likely cause?

I don’t know what cause is.

1) being a very primitive type of asteroid, it contains a lot of water ice. This could be caused by water ice subliming in the sunlight resuling in loosening of grains of dust that float free.

Or

2) disturbed by the driving jets of the spacecraft.

I’d go for number one. Water or CO2

Michael V said:

mollwollfumble said:

Bubblecar said:

So what’s the likely cause?

I don’t know what cause is.

1) being a very primitive type of asteroid, it contains a lot of water ice. This could be caused by water ice subliming in the sunlight resuling in loosening of grains of dust that float free.

Or

2) disturbed by the driving jets of the spacecraft.

I’d go for number one. Water or CO2

That was my thought as well.

The surface gravitation is literally a few millionths of Earth gravity, so it wouldn’t take much gas pressure to dislodge these rocks.

Certainly weird and also cool though.

Makes me wonder whether it is gradually losing mass or are incoming rocks enough to cover it.

dv said:

The surface gravitation is literally a few millionths of Earth gravity, so it wouldn’t take much gas pressure to dislodge these rocks.

Certainly weird and also cool though.

Makes me wonder whether it is gradually losing mass or are incoming rocks enough to cover it.

Gradually losing mass. It has to be. As asteroids age, they lose more and more water, and presumably whatever dust goes with it.

Is Bennu cold enough for CO2 ice? Not sure, i’ll have to check the phase diagram for CO2 in vacuum. CO2 evaporates much more easily in a vacuum than H2O. Eg. At a pressure of 1 millibar, water evaporates at -20 degrees C, and CO2 evaporates at -140 degrees C. Pressures around Bennu would be much less than 1 millibar. I suspect that Bennu is too hot for solid CO2. Yes, Bennu’s surface temperature varies from -37 to 6 degrees C.

mollwollfumble said:

dv said:

The surface gravitation is literally a few millionths of Earth gravity, so it wouldn’t take much gas pressure to dislodge these rocks.

Certainly weird and also cool though.

Makes me wonder whether it is gradually losing mass or are incoming rocks enough to cover it.

Gradually losing mass. It has to be. As asteroids age, they lose more and more water, and presumably whatever dust goes with it.

Is Bennu cold enough for CO2 ice? Not sure, i’ll have to check the phase diagram for CO2 in vacuum. CO2 evaporates much more easily in a vacuum than H2O. Eg. At a pressure of 1 millibar, water evaporates at -20 degrees C, and CO2 evaporates at -140 degrees C. Pressures around Bennu would be much less than 1 millibar. I suspect that Bennu is too hot for solid CO2. Yes, Bennu’s surface temperature varies from -37 to 6 degrees C.

over time yes. It is all to be expected really. Awesome that it was actually photographed though.

A wide shot and two close-ups of a region in Bennu’s northern hemisphere.

https://science.anu.edu.au/research/research-stories/asteroids-rugged-surface-complicates-osiris-rex-mission

roughbarked said:

mollwollfumble said:

dv said:

The surface gravitation is literally a few millionths of Earth gravity, so it wouldn’t take much gas pressure to dislodge these rocks.

Certainly weird and also cool though.

Makes me wonder whether it is gradually losing mass or are incoming rocks enough to cover it.

Gradually losing mass. It has to be. As asteroids age, they lose more and more water, and presumably whatever dust goes with it.

Is Bennu cold enough for CO2 ice? Not sure, i’ll have to check the phase diagram for CO2 in vacuum. CO2 evaporates much more easily in a vacuum than H2O. Eg. At a pressure of 1 millibar, water evaporates at -20 degrees C, and CO2 evaporates at -140 degrees C. Pressures around Bennu would be much less than 1 millibar. I suspect that Bennu is too hot for solid CO2. Yes, Bennu’s surface temperature varies from -37 to 6 degrees C.

over time yes. It is all to be expected really. Awesome that it was actually photographed though.

Yes. Most near-surface water would have been lost more than a billion years ago.