There has been lots of talk in the news lately surrounding a video released by NASA's STEREO spacecraft of a solar flare hitting mercury. Here's an image of the event.
In the image, you're seeing a solar flare released from the sun smack right into Mercury! It appears in the image that there is some bright object to the right of Mercury that is also being hit by the flare! UFO theorists think that this could be a spaceship, with a protective shield, that is being irradiated by the solar flare! This sure sounds and looks like a good theory, but it's not correct. What you're actually seeing in the video is a "ghost image" of Mercury, not a space ship. Now I'm not an expert on ghost imaging or STEREO data reduction, but here's the basic idea. You take an image of mercury on a "normal" day, and use a model of the planets brightness to subtract away the planet. Unfortunately, your model overestimates, slightly, the brightness of the planet. Now you have an image of a noisy background and an extra dark spot where mercury was. Today, the solar flare hits mercury and you take an image right when it hits. To clean up the image and make both the solar flare and the planet visible, you again subtract mercury (it fits accurately the model this time) and then subtract the "normal" image from today's image. This results in a new image where the planets position is extra bright. In other words, dark spots in the original image are now bright. But remember, you over-subtracted the brightness of mercury in your "normal" image, and the planet has moved a little bit in space between the time that the two images are taken. So what does this mean? Your resulting image will show Mercury's current position very brightly, and a ghost image of the old Mercury nearby. This is exactly what you are seeing in the video above, the ghost image of mercury. Long story short, data processing is very difficult, and these sorts of over-subtractions occur all the time in astronomy. Normally, astronomers further correct the final result and remove any ghost images, but they did not in the image above. Sorry to destroy the hopes of all you Star-Trek fans, but we didn't discover a spaceship.
