Video of asteroid DA14 near Earth last week

Last week, asteroid 2012 DA14 flew relatively close to Earth. The asteroid is about 150 feet in diameter and passed about 17,000 miles above Earth's surface. NASA has just released a movie compiling 72 radar images of DA14 captured over 8 hours with the Deep Space Network antenna in Goldstone, California. I had no idea that DA14 was built in Minecraft. "NASA Releases Radar Movie of Asteroid 2012 DA14" (JPL)


  1. Does anyone know why it is the case that we have detailed images of distant planets and galaxies, but have no images of decent resolution of this object that passed through the moon’s orbit?

    1. 2012 DA14 was moving significantly faster, relative to us, than more distant objects.
      It’s also much smaller than a planet. This isn’t a problem of angular size, but of the amount of light being sent back to us. A larger object reflects more light for us to see, and DA14 wasn’t sending back much at all. That’s part of the reason that the video shows a RADAR-like scan instead of visible light.

    2. Because it’s both extremely dim and moving extremely fast. Those glorious images of distant objects require very long exposures and telescopes can only move fast enough to compensate for the earth’s orbit (or for being in orbit like the Hubble). There is no way they would be able to track an object moving that fast. The radar images were produced by using large antennae and blasting a huge amount of radio waves at it to “brighten” it up.

    3. In part because radar imaging works fundamentally different that other types of light-based imaging. Unlike cameras that use a 2-d sensor and lenses to create the image, with long exposure times as some others have mentioned, radar works in the range/doppler domain. The radar signal transmitted from earth is reflected by the asteroid and received by large radio telescopes. The reflected light from various parts of the asteroid are delayed in time, based on the slight differences in distance between the telescope and asteroid, and doppler shifted in frequency, based on whether the reflecting region of the asteroid is moving towards or away from the telescope. 

      Deconvolution of the range/doppler data converts it to a 2-d spatial image for viewing. The advantage to this system is that the spatial resolution of the radar imaging system is independent of the distance to the asteroid. Whether it’s as close as this one, or out near the orbit of Jupiter, we can image it at 4m/pixel. Of course, this isn’t strictly true because the amount of reflected signal from the asteroid falls off as the fourth power of the distance to the object, so it doesn’t have to be too far away for the signal levels to be too low to observe. But that’s why the displayed ‘size’ of this asteroid doesn’t change despite a change in distance of nearly a factor of 3. The number of reflected photons would have changed by a large amount, but the spatial resolution was fixed by the observation parameters set at the telescope. 

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