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NASA's planetary radar captures detailed view of oblong asteroid

103 points by wglb 4y ago

nicolashahn 4y ago
Here we go again!
CamperBob2 4y ago
Optimist: "It's a space potato" Pessimist: "It's a space grenade"
- moffkalast 4y ago
  It's a gigantic canteen, but it's only filled to 50%.
  - deleted 4y ago
    [deleted]
- TeMPOraL 4y ago
  Smartass: "If our distinguished colleague Optimist here is suggesting a living space potato, then I believe we would be better off if it was the other thing."
  - justinclift 4y ago
    Not sure I like the sound of a living space grenade????
- fl0ps 4y ago
  Idiot: "It's a space peanut!"
- notfunnyrando 4y ago
  1st grader (future class clown): it's a POOP
  - nerdponx 4y ago
    Me, an adult: it's a POOP.
grecy 4y ago
Now that we know exactly how big it is, do we have a good understanding of how bad things would be if it did impact earth? (I've watched too many sci-fi movies, I'm just really curious)
- Tuna-Fish 4y ago
  Making a lot of assumptions: https://impact.ese.ic.ac.uk/ImpactEarth/cgi-bin/crater.cgi?dist=5&diam=140&pdens=1500&pdens_select=0&vel=17&theta=45&tdens=2500&tdens_select=0 https://impact.ese.ic.ac.uk/ImpactEarth/cgi-bin/crater.cgi?d... So it would be equivalent to a pretty big nuke. More or less a city-killer. No effects more major than that, though.
  - tpmx 4y ago
    The vast majority of possible impact zones on Earth are mostly uninhabited. We'd be really unlucky to have one of these hit a city. https://www.visualcapitalist.com/wp-content/uploads/2020/08/global-population-density-spikes-3d-mapped-full.png https://www.visualcapitalist.com/wp-content/uploads/2020/08/...
  - jakzurr 4y ago
    Yeah, pretty big - en.wikipedia says maybe 100 MT. https://en.m.wikipedia.org/wiki/(367789)_2011_AG5 https://en.m.wikipedia.org/wiki/(367789)_2011_AG5
  - daveslash 4y ago
    I think it depends quite a bit on things like angle and speed. I'm sure that if it came in behind Earth, in a similar orbit, at an angle it'd be very different from a head on 90 degree angle collision with it headed in the opposite direction. Size alone is probably not a great factor to estimate damage. A starting point, but not final word.
- swader999 4y ago
  It would rain down french fries.
schwoll 4y ago
Why is it lit on one side? Wouldn't radar return a signal regardless of whether or not the part of the asteroid is lit by sunlight?
- hn8305823 4y ago
  The Sun emits microwaves that can be reflected by asteroids. Depending on the surface/composition it could be much more reflective to microwaves than visible light. A 70 meter dish can emit and focus a powerful signal but probably can't outshine the Sun at these distances. Radar emissions also consist of short pulses while the Sun emissions are continuous. Since the article mentions precise distance information being acquired, the radar system was able to detect it's own emissions (likely only from the unlit regions) This is related to the periodic outages of geostationary satellites when the Sun is directly behind them. Ground receivers are essentially "jammed" by the microwaves emitted by the Sun itself.
  - db48x 4y ago
    No, that’s not it. I believe that these are not true images. They are instead effectively graphs of the time of flight of the radar signals. The vertical axis is flipped, putting Earth (or rather the radio telescope) “above” the image and the bearing of the radar signal along the x axis. The shading happens because some fraction of the radar signal refracts instead of reflecting. You can think of this as reflecting off of the interior of the asteroid rather than the surface, or as reflecting off of internal features such as density or composition changes. Our eyes interpret it as a top–down view, or as a face–on view with lighting from one side, but it’s really more like a slice through the middle. Or rather, like a bunch of slices through the middle all stacked on top of each other, since the beam probably isn’t all _that_ narrow after traveling for a few million miles. I wish I could find the paper though; press releases so often don’t bother linking to them. Maybe it hasn’t even been published yet? The observations were just 19 days ago.
  - mturmon 4y ago
    Alas, the above comment is quite mistaken. The microwave reflection from sunlight is too faint to detect. All the information shown comes from the radar beam from Goldstone. The radar imaging process is complex, but suffice to say the shown "image" is not in physical coordinates. If it's a conventional radar image, the vertical coordinate of the shown image is "delay" (distance from observer). And also conventionally, the horizontal image coordinate is "doppler", which is the doppler shift given to the returned signal by the rotating asteroid. So, stuff on the left side of the image was moving away from the observer, and stuff on the right side was moving towards the observer. And of course the brightness is essentially the "amount of stuff" at that delay-doppler locus. The reason we can't plot an "image" in physical coordinates, and have to be content with the altered coordinates, is that all we get from the returned radar carrier signal is a delay, and a doppler shift. That's it - "delay-doppler" coordinates. So any set of sites on the asteroid surface with the same distance and the same relative velocity (w/r/t the observer) will be binned into the same place in the radar image. There is no guarantee that these sites are near each other, and for complex geometries (rough asteroids), they often will not be. If you want to get a real image in physical coordinates, you have a separate inversion problem to solve, and you'll probably need more images and some model constraints. For much more, see this paper (http://mel.ess.ucla.edu/jlm/publications/Ostro02.AsteroidsIII.pdf http://mel.ess.ucla.edu/jlm/publications/Ostro02.AsteroidsII...), and in particular, see around Fig. 1, Fig. 4 (especially), and Fig. 6.
thatcherc 4y ago
Any idea how this picture was made? Was the Goldstone dish scanning a really tightly focused beam across the region of space where this asteroid was, or are they relying on some kind of doppler or synthetic aperture radar effect with the relative movement of the dish (on a rotating Earth) and the asteroid let the image be recovered out of Doppler and timing info? I went looking for some details on how the picture was produced on the NASA page linked at the bottom of the article but I can't find much technical info on the process. However it was done I'm sure it's a cool technique!
- mturmon 4y ago
  > ... the image be recovered out of Doppler and timing info... Yes, that's right: they are using doppler shift of the rotating asteroid, and the delay of the propagating signal, to form the "image". See my other comment nearby.
- deleted 4y ago
  [deleted]
frankreyes 4y ago
Is it related to https://en.m.wikipedia.org/wiki/%CA%BBOumuamua https://en.m.wikipedia.org/wiki/%CA%BBOumuamua ? Or just the banana shape?
- ryanblakeley 4y ago
  This one had a 3:1 size ratio. Oumuamua was closer to 10:1, which was one (of several) reason it was so anomalous.
taskqa 4y ago
[dead]
lxchase 4y ago
3 times as long as its wide? They do everything in threes.

103 points by wglb 4y ago

nicolashahn 4y ago

Here we go again!

CamperBob2 4y ago

Optimist: "It's a space potato" Pessimist: "It's a space grenade"

moffkalast 4y ago
It's a gigantic canteen, but it's only filled to 50%.
- deleted 4y ago
  [deleted]
TeMPOraL 4y ago
Smartass: "If our distinguished colleague Optimist here is suggesting a living space potato, then I believe we would be better off if it was the other thing."
- justinclift 4y ago
  Not sure I like the sound of a living space grenade????
fl0ps 4y ago
Idiot: "It's a space peanut!"
notfunnyrando 4y ago
1st grader (future class clown): it's a POOP
- nerdponx 4y ago
  Me, an adult: it's a POOP.

grecy 4y ago

Now that we know exactly how big it is, do we have a good understanding of how bad things would be if it did impact earth? (I've watched too many sci-fi movies, I'm just really curious)

Tuna-Fish 4y ago
Making a lot of assumptions: https://impact.ese.ic.ac.uk/ImpactEarth/cgi-bin/crater.cgi?dist=5&diam=140&pdens=1500&pdens_select=0&vel=17&theta=45&tdens=2500&tdens_select=0 https://impact.ese.ic.ac.uk/ImpactEarth/cgi-bin/crater.cgi?d... So it would be equivalent to a pretty big nuke. More or less a city-killer. No effects more major than that, though.
- tpmx 4y ago
  The vast majority of possible impact zones on Earth are mostly uninhabited. We'd be really unlucky to have one of these hit a city. https://www.visualcapitalist.com/wp-content/uploads/2020/08/global-population-density-spikes-3d-mapped-full.png https://www.visualcapitalist.com/wp-content/uploads/2020/08/...
- jakzurr 4y ago
  Yeah, pretty big - en.wikipedia says maybe 100 MT. https://en.m.wikipedia.org/wiki/(367789)_2011_AG5 https://en.m.wikipedia.org/wiki/(367789)_2011_AG5
- daveslash 4y ago
  I think it depends quite a bit on things like angle and speed. I'm sure that if it came in behind Earth, in a similar orbit, at an angle it'd be very different from a head on 90 degree angle collision with it headed in the opposite direction. Size alone is probably not a great factor to estimate damage. A starting point, but not final word.
swader999 4y ago
It would rain down french fries.

schwoll 4y ago

Why is it lit on one side? Wouldn't radar return a signal regardless of whether or not the part of the asteroid is lit by sunlight?

hn8305823 4y ago
The Sun emits microwaves that can be reflected by asteroids. Depending on the surface/composition it could be much more reflective to microwaves than visible light. A 70 meter dish can emit and focus a powerful signal but probably can't outshine the Sun at these distances. Radar emissions also consist of short pulses while the Sun emissions are continuous. Since the article mentions precise distance information being acquired, the radar system was able to detect it's own emissions (likely only from the unlit regions) This is related to the periodic outages of geostationary satellites when the Sun is directly behind them. Ground receivers are essentially "jammed" by the microwaves emitted by the Sun itself.
- db48x 4y ago
  No, that’s not it. I believe that these are not true images. They are instead effectively graphs of the time of flight of the radar signals. The vertical axis is flipped, putting Earth (or rather the radio telescope) “above” the image and the bearing of the radar signal along the x axis. The shading happens because some fraction of the radar signal refracts instead of reflecting. You can think of this as reflecting off of the interior of the asteroid rather than the surface, or as reflecting off of internal features such as density or composition changes. Our eyes interpret it as a top–down view, or as a face–on view with lighting from one side, but it’s really more like a slice through the middle. Or rather, like a bunch of slices through the middle all stacked on top of each other, since the beam probably isn’t all _that_ narrow after traveling for a few million miles. I wish I could find the paper though; press releases so often don’t bother linking to them. Maybe it hasn’t even been published yet? The observations were just 19 days ago.
- mturmon 4y ago
  Alas, the above comment is quite mistaken. The microwave reflection from sunlight is too faint to detect. All the information shown comes from the radar beam from Goldstone. The radar imaging process is complex, but suffice to say the shown "image" is not in physical coordinates. If it's a conventional radar image, the vertical coordinate of the shown image is "delay" (distance from observer). And also conventionally, the horizontal image coordinate is "doppler", which is the doppler shift given to the returned signal by the rotating asteroid. So, stuff on the left side of the image was moving away from the observer, and stuff on the right side was moving towards the observer. And of course the brightness is essentially the "amount of stuff" at that delay-doppler locus. The reason we can't plot an "image" in physical coordinates, and have to be content with the altered coordinates, is that all we get from the returned radar carrier signal is a delay, and a doppler shift. That's it - "delay-doppler" coordinates. So any set of sites on the asteroid surface with the same distance and the same relative velocity (w/r/t the observer) will be binned into the same place in the radar image. There is no guarantee that these sites are near each other, and for complex geometries (rough asteroids), they often will not be. If you want to get a real image in physical coordinates, you have a separate inversion problem to solve, and you'll probably need more images and some model constraints. For much more, see this paper (http://mel.ess.ucla.edu/jlm/publications/Ostro02.AsteroidsIII.pdf http://mel.ess.ucla.edu/jlm/publications/Ostro02.AsteroidsII...), and in particular, see around Fig. 1, Fig. 4 (especially), and Fig. 6.

thatcherc 4y ago

Any idea how this picture was made? Was the Goldstone dish scanning a really tightly focused beam across the region of space where this asteroid was, or are they relying on some kind of doppler or synthetic aperture radar effect with the relative movement of the dish (on a rotating Earth) and the asteroid let the image be recovered out of Doppler and timing info? I went looking for some details on how the picture was produced on the NASA page linked at the bottom of the article but I can't find much technical info on the process. However it was done I'm sure it's a cool technique!

mturmon 4y ago
> ... the image be recovered out of Doppler and timing info... Yes, that's right: they are using doppler shift of the rotating asteroid, and the delay of the propagating signal, to form the "image". See my other comment nearby.
deleted 4y ago
[deleted]

frankreyes 4y ago

Is it related to https://en.m.wikipedia.org/wiki/%CA%BBOumuamua https://en.m.wikipedia.org/wiki/%CA%BBOumuamua ? Or just the banana shape?

ryanblakeley 4y ago
This one had a 3:1 size ratio. Oumuamua was closer to 10:1, which was one (of several) reason it was so anomalous.

taskqa 4y ago

[dead]

lxchase 4y ago

3 times as long as its wide? They do everything in threes.