APOD: The Snows of Churyumov-Gerasimenko (2018 Apr 26)

[Chris Peterson]

When John Glenn was orbiting the Earth in his Mercury capsule, he reported a similar phemomenon, a cloud of bright white snowflake-like, star-like objects around the capsule. Could that have been something like what we're seeing here? :?:

I think that a second imaging instrument (eyeball) to provide 'binocular vision' would have been helpful. Cosmic rays will only be able to strike one of the eyeballs, thereby providing the ability to either remove them from the real image, or give the ability to visualize the 'cosmic rays' without the background image. The cost of the second other eyeball would have been inconsequential with respect to the cost of the mission, and the science value would be great.

Well, as I noted earlier, this could easily have added tens of millions of dollars to the mission cost and compromised other instruments. I'm not sure how much science value would have been added- the two cameras would be too close for stereo vision, and cosmic rays don't really compromise the data. Had there been significant science value, a second camera would have been proposed and either accepted or rejected after a long science and engineering review process (I've been in such meetings).

[neufer]

When John Glenn was orbiting the Earth in his Mercury capsule, he reported a similar phemomenon, a cloud of bright white snowflake-like, star-like objects around the capsule. Could that have been something like what we're seeing here?

I think that a second imaging instrument (eyeball) to provide 'binocular vision' would have been helpful. Cosmic rays will only be able to strike one of the eyeballs, thereby providing the ability to either remove them from the real image, or give the ability to visualize the 'cosmic rays' without the background image. The cost of the second other eyeball would have been inconsequential with respect to the cost of the mission, and the science value would be great.

Well, as I noted earlier, this could easily have added tens of millions of dollars to the mission cost and compromised other instruments. I'm not sure how much science value would have been added- the two cameras would be too close for stereo vision, and cosmic rays don't really compromise the data. Had there been significant science value, a second camera would have been proposed and either accepted or rejected after a long science and engineering review process (I've been in such meetings).

My "comments" were in regard to John Glenn's actual eyeballs.

[Chris Peterson]

:shock: My "comments" were in regard to John Glenn's actual eyeballs.

Oh. Never mind.

(I recall seeing pictures of snowy stuff outside the window of some early space mission. Something like ice breaking free? Anyway, real stuff, not a visual artifact of some kind. People can and do see cosmic rays, both from retinal impacts and impacts in the visual cortex. But even in space they're just here and there. If they looked like snow, you'd be quickly dead.)

[perigalacticon]

Is there any size reference available for the images? IE how big is that boulder-looking feature or how high is that cliff-looking feature?

[JohnD]

I asked first! (Post 4)
John

[neufer]

Extraordinary! And taken from orbit 13kms away? Doubly so, one might be walking across the surface!

What's the scale? Those rocks bottom right could be pebble, football or house sized, I presume the latter given the distance.

The Narrow angle OSIRIS camera has a field of view of 2.4 by 2.4 degrees or 560m x 560m from this distance.

(The CN Tower in Toronto is a 553.3 m-high.)

[JohnD]

Hmmmmm! So those rocks are BIG house sized! Or rather apartment block sized!!!
Thanks, neufer, gives a whole new perception to that scene.
John

[rstevenson]

The image is 491 px wide, and the large squarish block bottom-right (indicated below) is about 40 px wide. Poking my calculator tells me that rock is therefore about 45.6 m or about 150 of King John's feet in width. As it appears more or less square, that makes it roughly 15 stories high. That's a hunk of rock!

rock.jpeg (18.6 KiB) Viewed 30798 times

Rob

[neufer]

As it appears more or less square, that makes it roughly 15 stories high.

That's a hunk of rock!

• Mean density of Churyumov–Gerasimenko ~ 533 kg/m³
  Surface gravity ~ 0.0001 Earth's gravity
  
  'Effective weight' of boulder ~ 2 or 3 tons.