Is NASA hiding something about Asteroid 2005 YU55?

Did it not occur to you that the close approach (11/8/2011 at 23:28UTC) occurred between these two videos?

In the first video, you are looking at the asteroid prior to its close encounter with Earth. It is approaching.

The second video, a few days after the approach, you are looking at its other hemisphere, it is departing.

The same thing would happen if you were to look at Earth's rotation from above the North Pole (counter clockwise) and compare it to the same motion, when viewed from above its south pole (clockwise).

Unfortunately, the person who posted that video on Youtube hasn't understood how these images were made, or what they mean. These are not like photographs taken with your digital camera, where the target is in focus so that light from a different part of the object falls onto a different part of the film. Instead, the Goldstone Array in California sends a pulse of radio waves at the asteroid (or Mars, or Mercury, etc.). Some of that energy bounces back and is detected again on Earth. The receiver measures very small differences in time delay of the received signal, and also very small shifts in frequency. With some number crunching, the time delays are turned into distances from Earth, and the frequency shifts are turned into velocities. The distances come from the shape of the asteroid: the signal from the closest face comes back a little bit sooner than the rest. The Doppler shift in frequency comes from the rotation of the asteroid. These are the two dimensions of the image you see: distance on the vertical axis, and frequency shift on the horizontal axis. The brightness shows the intensity of light reflected by the asteroid (and not time delay, as one poster said).

So it's a pretty different kind of image than you may be used to. The bright part at the top of the frame is actually the part nearest to Earth. It's bright because it's facing us, and reflects more of the radar pulse back at us. It's at the top of the frame because it's closest to us.

This technique gives you excellent ability to image distant objects, but it has one limitation: the northern and southern hemisphere of the asteroid come out in the same place. It's like a film image of a double exposure, where two different subjects are on top of each other. When you look at the movies, it's as if you're looking down on both the north and south poles of the asteroid, and those two images are combined.

Once you understand how the image is made, you can see it makes no difference at all which way the asteroid appears to be rotating. It's completely arbitrary. It doesn't tell you anything at all about the asteroid, it just tells you how they've chosen to plot the velocity data.

One more note, if you look at the original releases from Nasa, you'll see that both movies were made from observations taken on the same day. All the data was taken on Nov. 7. The coarser movie was released on Nov. 8, and the cleaner movie with more frames was released on Nov. 11 after some more number crunching had been done. It's probably a large data set and takes a while to fully process. So you're not looking at a change in 2005 YU55, you're just looking at a change in the presentation of exactly the same data. So the guesses of some responders about the two movies showing different sides of the asteroid at different times are reasonable, but incorrect.

This same technique has been used to learn about volcanic landscapes on Mars, and even to find ice in deep craters near the north pole and south pole of Mercury.

It's funny how someone sees something they don't understand, and sees it as a sign there's something wrong instead of an opportunity. (I mean the person who posted the video on Youtube, not you!) As a scientist, I'm happy when I see something new and unexpected. It means there's a chance to learn something interesting. Thanks for posting the question, and I hope you see it that way too.

It's funny how the video's author uses NASA's own radar images to say that NASA is hiding something... Well, it's there for you to see! How's that hiding something?!

Just to add to DLM's answer: remember this is radar images, brightness-coded for arrival time, bright=early, dark=late. That's why the backdrop is black anyway: the radar echo from it doesn't come back. So the lighting isn't from the Sun, but rather from the radar "pings" sent by the radar antenna used to collect the information that made the frames. You can measure the radar echo and paint an image anyway you want it -- e.g. red for early, blue for late, and so the backdrop would appear blue, or any other way.

But I suppose that is what has caused confusion in the video author's head: he/she assumed that it was observed with a telescope and that the image was illuminated by sunlight.

Let this be a lesson to you. *ANYONE* can post anything on the Internet, regardless of their level of information and understanding.

If the asteroid changed its rotation, then why would NASA need to hide that? It's not like that would be dangerous, just odd.

The first video was shot during its approach, when we saw one side, the other was shot when it was leaving the Earth, so we saw it from the other side.

You can try this for yourself! Just pick up any object, and make it rotate counter-clockwise with your hands. Then, slowly turn it around (while still making it rotate), so that you can see its other side. Now it will appear to rotate clockwise.

I would say that in the first images we are looking at one rotational pole of the asteroid as it is coming towards us, and in the second we are looking at the other rotational pole as it is going away from us.

Astronomy is mostly done by amateurs, with professional coordination. Asteroids, comets, and meteors are typically discovered by amateurs, often by more than one. Whoever discovers one, all the amateurs swing their telescopes that way to see what they can learn. There is no way to keep anything secret in that business.

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Yes

No. DLM gave an excellent explanation,

No, what would be the point given they are not the only ones observing it.