APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

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APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by APOD Robot » Wed Nov 09, 2011 5:06 am

Image Asteroid 2005 YU55 Passes the Earth

Explanation: Asteroid 2005 YU55 passed by the Earth yesterday, posing no danger. The space rock, estimated to be about 400 meters across, coasted by just inside the orbit of Earth's Moon. Although the passing of smaller rocks near the Earth is not very unusual -- in fact small rocks from space strike Earth daily -- a rock this large hasn't passed this close since 1976. Were YU55 to have struck land, it might have caused a magnitude seven earthquake and left a city-sized crater. A perhaps larger danger would have occurred were YU55 to have struck the ocean and raised a large tsunami. The above radar image was taken two days ago by the Deep Space Network radio telescope in Goldstone, California, USA. YU55 was discovered only in 2005, indicating that other potentially hazardous asteroids might lurk in our Solar System currently undetected. Objects like YU55 are hard to detect because they are so faint and move so fast. However, humanity's ability to scan the sky to detect, catalog, and analyze such objects has increased notably in recent years.

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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by Beyond » Wed Nov 09, 2011 5:15 am

How come there's a better picture from 2005 :?: The one we have now is toooo pixelated :!:
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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by Quinn.Eskimo » Wed Nov 09, 2011 5:25 am

What would have happened if the asteroid hit the moon?

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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by Ann » Wed Nov 09, 2011 6:07 am

Quinn.Eskimo wrote:What would have happened if the asteroid hit the moon?
Image
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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by dneville » Wed Nov 09, 2011 6:08 am

Nice catch, drunky.

Oh Moon, you're so irresponsible with your glassware. Or is it eye-wear now?

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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by Chris Peterson » Wed Nov 09, 2011 7:27 am

Quinn.Eskimo wrote:What would have happened if the asteroid hit the moon?
It would make a crater a couple of miles across... large enough to see (with a telescope) from the Earth.

FWIW, this asteroid did not pass inside the orbit of the Moon... it passed on a completely different plane. At its closest, it was closer to the Earth than the Moon, that's all.
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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by Ele6 » Wed Nov 09, 2011 11:10 am

As long as it doesn't crack open: https://www.youtube.com/watch?v=3HjwbnhVnDM ;).

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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by saturn2 » Wed Nov 09, 2011 11:25 am

I think that the asteriods near to Earth are a danger.
Because the orbits can to change in few years.
In the sky nearly to Earth is many small and big asteroids.

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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by nstahl » Wed Nov 09, 2011 1:47 pm

Ok, this is a "radar image". Presumably it's made from the waves sent from point R to asteroid A and which bounced back to point R. But it sure looks like the "light" source is to one side and the other side is in shadow. What's going on here?

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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by OverlordE » Wed Nov 09, 2011 2:01 pm

I think it is ridiculous that such a poor quality picture was posted. Maybe you should have let an amateur with a backyard telescope post a picture it would most likely be something worth looking at.

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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by Psnarf » Wed Nov 09, 2011 2:27 pm

http://photojournal.jpl.nasa.gov/catalog/PIA15019 is a thumbnail that is far less pixelated. It shows a lot more detail than the blur in larger versions. All of the larger images therein are the same size as APOD. There is a way to specify the image display size in HTML.

"295px × 256px" vs "958 x 830" pixels for the APOD edition.
(scaled to 115px × 100px for the RSS edition)

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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by rstevenson » Wed Nov 09, 2011 2:41 pm

Psnarf wrote:http://photojournal.jpl.nasa.gov/catalog/PIA15019 is a thumbnail that is far less pixelated. It shows a lot more detail than the blur in larger versions.
It's the same picture and therefore has the same detail. The pixels are just smaller when seen in a thumbnail version.

I do hope a far better picture was obtained by some telescope or other, but perhaps it was just too faint and moving too fast.

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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by zbvhs » Wed Nov 09, 2011 3:33 pm

I agree with nstahl; the purported radar image doesn't look right. If Goldstone was viewing its own radar return, we should be seeing a full-face image of the object. If one powerful source had beamed radio energy at the object and it was then viewed by an array of radio telescopes, could the resolution have been improved?
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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by Wolf Kotenberg » Wed Nov 09, 2011 3:52 pm

Did the ISS guys get a picture ?

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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by neufer » Wed Nov 09, 2011 4:06 pm

zbvhs wrote:
I agree with nstahl; the purported radar image doesn't look right. If Goldstone was viewing its own radar return, we should be seeing a full-face image of the object. If one powerful source had beamed radio energy at the object and it was then viewed by an array of radio telescopes, could the resolution have been improved?
The radar "image" is really only a pseudo-image.

One only "sees" the near side of asteroids with radar imaging in accordance with the reflection delay and the doppler shift.

Northern hemisphere & Southern hemispheres can have identical reflection delays and doppler shifts and therefore they get averaged together just as if one was observing a quasi transparent asteroid in orthographic polar projection.
http://www.planetary.org/blog/article/00003248/ wrote: The Planetary Society Blog By Emily Lakdawalla Nov. 8, 2011
How radio telescopes get "images" of asteroids
ImageImage
<<Every time I post a radio telescope image of a near-Earth asteroid, I get at least one reader question asking me to explain how radio telescopes take photos, so I'm hereby writing a post explaining the basics of how delay-Doppler imaging works.

To begin with, imaging of any kind done with radio telescopes (or radio antennae on spacecraft) is an active technique: the imaging requires that the antenna first broadcast a signal at the object of interest. The signal reflects from the object, and the antenna waits for the return signal.

The simplest sort of radio "imaging," then, is just radio ranging. Send out a ping, wait for the echo. Use a precise clock to time how long it takes the reflection to return to the antenna, and you know very precisely the range or distance to the target. That's RADAR, which is an acronym for Radio Detection and Ranging.

But we can do better than that. Here's a very simple cartoon that I drew, grossly simplifying what happens when you broadcast a signal at a lumpy object.The signal goes out as a nice waveform. It's reflected from the parts of the asteroid that are closest to the radio dish first, but while those first reflections are happening, the radio wave is still propagating toward more distant parts of the asteroid. So when the radio dish detects the return signal, the sharp signal has been spread out in time.

You can see how you could use these data to crudely estimate the size of the object you were looking at. The first reflection comes from the nearest parts of the object. The last reflections come from the most distant parts of the object that you can see. Take the amount of time that separates the first and last reflections, multiply it by the speed of light, and you get the distance between those two points. Then double that, assuming the body is quasi-spherical and has a hidden hemisphere behind the hemisphere we can see. This will not be a particularly accurate estimate, but it's a start.

One thing we can't do is figure out which reflections were coming from which parts of the asteroid. All we know is how strong the return signal was with respect to time.

Radio imaging gets better, though. It takes advantage of the fact that everything in the whole solar system is rotating. Some things rotate pretty fast. Imagine a set of waves propagating toward a rotating body. Actually you don't have to imagine it, I've drawn another horribly oversimplified cartoon.

As an asteroid rotates, some parts of it are moving toward us, while other parts are moving away. As the broadcast radio wavefronts hit the part of the asteroid that is moving toward us, the asteroid smacks into each wavefront faster than it would if it were not rotating. The speed of the wavefronts does not change, because the speed of light is constant, so the wavefronts end up being packed closer together. This is a Doppler shift. The asteroid has taken the broadcast wavelength and reflected it at a shorter wavelength from the parts of the asteroid that are rotating toward us. On the other side of the asteroid, which is rotating away, the opposite thing happens; each arriving wavefront smacks into the asteroid a little later than it would if the asteroid were not rotating, so the reflected waves are spread farther apart.

(One minor point here: the asteroid is not only rotating, it is also moving at some high speed with respect to Earth. So the whole return signal is already going to be Doppler shifted in one direction or the other depending on whether the asteroid is coming at us or going away from us; radio scientists account for this and "look" for the reflection around the expected return frequency given this Doppler shift due to the asteroid's motion. The Doppler shift due to the asteroid's rotation is a small increment of shift on top of the shift due to the asteroid's motion.)

Back at the radio dish, we have a detector that can split the incoming reflected waves into its different wavelengths. (Much like color cameras split incoming light into their different wavelengths.) The radio dish records the time and strength of the return signal at many different wavelengths. The result, as you can see in the crude graph at the bottom of the animation, is a "picture," actually a sort of colored-in graph with time on one axis and wavelength on the other axis. The faster the object is rotating, the more Doppler-shifted the return signals are; fast rotators spread out more across the wavelength axis. Things that aren't rotating at all, like in my first animation, collapse into a blip at the central wavelength.

Radio scientists refer to time as "delay," as in "the delay between our broadcast and when we heard the return signal," and the wavelength axis of my crude graph above as "Doppler." So turn that graph on its side and you get an explanation of how radio scientists can arrive at an image like this one, the significance of which I will explain in the next post. Arecibo would be two million kilometers above your head; delay increases from top to bottom, Doppler from left to right.>>
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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by Chris Peterson » Wed Nov 09, 2011 4:35 pm

zbvhs wrote:I agree with nstahl; the purported radar image doesn't look right. If Goldstone was viewing its own radar return, we should be seeing a full-face image of the object. If one powerful source had beamed radio energy at the object and it was then viewed by an array of radio telescopes, could the resolution have been improved?
As noted, the image is synthesized by an inverse transform from time resolved delay data and doppler data. The shadowing is part of the synthesis process.

Illuminating the object from one location and observing it from another would not improve resolution. Resolution could theoretically be improved by monitoring the reflection from two or more stations and combining the data- essentially, just increasing the radar aperture. I think this would also require modifying the illumination signal, and there are probably a load of practical issues that make such multiple station radar imaging impractical (or so I assume, since I don't recall ever seeing images produced that way).
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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by nstahl » Wed Nov 09, 2011 4:43 pm

So may we infer the brighter parts are moving toward us?

After posting that comment it occurred to me the Sun is probably the strongest broadcaster in the area on those wavelengths also, so maybe the bright area is pointed toward the Sun, and it really is a shadow situation.

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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by geckzilla » Wed Nov 09, 2011 5:07 pm

So to image the asteroid is it something similar to using sonar to map the ocean floor? That data is used to generate a height map in some kind of 3d program which can then light the surface and make it a lot easier for humans to interpret. Er, I mean that's what I always thought went on. I can't seem to think of a way to explain it more clearly.
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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by neufer » Wed Nov 09, 2011 5:09 pm

nstahl wrote:
So may we infer the brighter parts are moving toward us?
No.

The brighter parts represent relatively flat reflective perpendicular surfaces (or possibly corner reflectors).

The rotating regions with the greatest red/blue doppler shifts are place on the far right/left of the image respectively.
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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by neufer » Wed Nov 09, 2011 5:16 pm

geckzilla wrote:
So to image the asteroid is it something similar to using sonar to map the ocean floor? That data is used to generate a height map in some kind of 3d program which can then light the surface and make it a lot easier for humans to interpret. Er, I mean that's what I always thought went on. I can't seem to think of a way to explain it more clearly.
Sonar that maps the ocean floor (or fetuses) provides for its own horizontal resolution.

Asteroid images depend entirely upon the objects spinning motion to provide a pseudo-horizontal resolution.
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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by geckzilla » Wed Nov 09, 2011 5:19 pm

I don't know about anyone else, but this is pretty counter-intuitive to me.
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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by neufer » Wed Nov 09, 2011 5:32 pm

geckzilla wrote:
I don't know about anyone else, but this is pretty counter-intuitive to me.
That's probably because you are not a bat.
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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by orin stepanek » Wed Nov 09, 2011 5:41 pm

It the asteroid was to hit Earth; I don't think there would be much that could be done other than evacuating the area that it was likely to hit! :?
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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by Chris Peterson » Wed Nov 09, 2011 5:55 pm

orin stepanek wrote:It the asteroid was to hit Earth; I don't think there would be much that could be done other than evacuating the area that it was likely to hit! :?
It is doubtful the location could be predicted with enough accuracy. Most analyses I've seen of this scenario show that more people would be killed in the evacuation process (necessarily over a wide area) than in the impact itself. If modeling showed an ocean impact, it is possible that coastal evacuations could be carried out similar to the way things are now done when hurricane storm surges are predicted.

In reality, if a 400m asteroid struck the Earth, the odds are that casualties would be very low.
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Re: APOD: Asteroid 2005 YU55 Passes the Earth (2011 Nov 09)

Post by zloq » Wed Nov 09, 2011 6:53 pm

geckzilla wrote:I don't know about anyone else, but this is pretty counter-intuitive to me.
I think the image is really hard to interpret if it's viewed literally as an x/y image - but the figures and text linked to by neufer above are pretty good - especially the plot that gets drawn at the very lower right of the animated figure.

A key is that these are very raw and abstract "images" and they don't represent an x/y cross-section - they represent range vertically and frequency horizontally - with brightness corresponding to the intensity of the reflection. If you try to view it too literally as an image, then it just won't work.

I don't know why no one answers more clearly the most obvious question about these images - which is - if the object is viewed face on, why do we only see a crescent of information - corresponding to only 1/4 of the object? The reason is that you are seeing a full 1/2 of the object, but the 2 quarters cannot be distinguished, so their features are superimposed. This makes it even harder to interpret as an image of a 3d object - but if a distinct feature is on either of the two sides, it will remain distinct as the object rotates and you can track it.

If you image many "poses" of the object as it rotates and passes by - only then can you invert all the information to construct a 3D model of the true surface geometry - and then make synthetic renderings of it as a shaded object for more direct visual interpretation. Those 3D shaded renderings may look completely different from these range/freq. views - but localized structures may be identifiable in both.

So - the view direction is from the top, and the top of the image represents objects that are closest - i.e. the facing surface of the roughly ellipsoidal object, while to the right are features somewhere down along the surface that are moving toward you and to the left are features moving away. You are sort of looking along the axis of rotation - but really you are just in the plane formed by the rotation axis and the direction to earth since the rotation axis is tilted. Since the closest surface is also fairly perpendicular to us - it reflects strongly and is bright.

I think this asteroid is getting a lot of coverage by radar, in addition to detailed light curves from many observers. I expect that eventually the data will be put together for a pretty good model and 3d rendering - but I'm not sure how long that will take. In the meantime I expect there will be more animations of "images" like this - and they should not be interpreted too literally when they are actually animations of raw range/frequency plots of the data.

Recently there was a very close and fast asteroid, 2011MD, and I don't think there was any radar done for it, and amateur light curves showed interesting structure. The Goldstone radar tried to aim at it - but apparently failed to acquire the target - I guess because its orbit had been perturbed so much that the predictions weren't accurate enough. So I don't think there are any radar views of it, let alone 3d models - but there are some intriguing light curves. I hope there is better luck with this asteroid.

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