[HN Gopher] NASA's planetary radar captures detailed view of obl...
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NASA's planetary radar captures detailed view of oblong asteroid
Author : wglb
Score : 65 points
Date : 2023-02-21 21:08 UTC (1 days ago)
(HTM) web link (phys.org)
(TXT) w3m dump (phys.org)
| thatcherc wrote:
| 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!
| grecy wrote:
| 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 wrote:
| Making a _lot_ of assumptions:
| 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.
| jakzurr wrote:
| Yeah, pretty big - en.wikipedia says maybe 100 MT.
|
| https://en.m.wikipedia.org/wiki/(367789)_2011_AG5
| daveslash wrote:
| 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.
| tpmx wrote:
| 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/...
| nicolashahn wrote:
| Here we go again!
| frankreyes wrote:
| Is it related to https://en.m.wikipedia.org/wiki/%CA%BBOumuamua ?
| Or just the banana shape?
| ryanblakeley wrote:
| This one had a 3:1 size ratio. Oumuamua was closer to 10:1,
| which was one (of several) reason it was so anomalous.
| CamperBob2 wrote:
| Optimist: "It's a space potato"
|
| Pessimist: "It's a space grenade"
| fl0ps wrote:
| Idiot: "It's a space peanut!"
| TeMPOraL wrote:
| 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. "
| notfunnyrando wrote:
| 1st grader (future class clown): it's a POOP
| nerdponx wrote:
| Me, an adult: it's a POOP.
| moffkalast wrote:
| It's a gigantic canteen, but it's only filled to 50%.
| [deleted]
| schwoll wrote:
| 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?
| giantrobot wrote:
| These images are confusing. The "lit" side is where the radar
| beam is coming from. The perspective is looking "down" on the
| asteroid with "up" on the image being the direction of Earth.
| The radar scans a beam across the object and records the
| reflections. The brightness of a pixel is a function of the
| strength, phase, and polarity of the returned signal. The
| position of a pixel is a function of its distance from the
| receiver.
|
| From the perspective of the radar receiver it's just receiving
| a series of reflections over a period of time. These are
| processed for the above measures and then perspective
| transformed to show an "overhead" image that we see here.
| hn8305823 wrote:
| 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 wrote:
| 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.
| [deleted]
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