Colorized Mercury
Published on Jan 24, 2008 at 9:15 pm.
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Filed under Mercury, planets.
Per a request from a geology professor at my college, I am posting another image of Mercury taken by the MESSENGER spacecraft during its flyby of that planet earlier this month.
Mercury has no appreciable atmosphere, so its surface shows eons of impacts. Erosion does not cover up the craters as it does on Earth. In this respect, Mercury is much like our Moon. Unlike the Moon, though, the craters are a bit more sparse on Mercury. Photos of Mercury actually show spaces between the larger craters, while on the Moon craters lay on top of craters. The standard interpretation of this result has been that many impactors have come from the asteroid belt, so Mercury, being farther from the source of the asteroids, has been hit less. However, there are alternate theories held by a few people. It has been suggeted, for example, that Mercury’s surface may be a bit younger than the Moon’s surface (through more volcanism early in Mercury’s history) or that the violent nature of how our Moon is believed to have formed may have resulted in more things flying around Earth to run into the Moon. The MESSENGER data may shed light on whether the standard explanation is indeed correct, or if some other explanation is needed for why Mercury appears to have fewer craters than the Moon.
The earliest MESSENGER images of Mercury that have been released have been black and white images. The imaging system on MESSENGER just records light intensity, not color. However, the images can be taken through a number of colored filters. To construct a color image of the planet Mercury, all that you need to do is to combine the images taken with several colored filters. MESSENGER’s Dual Imaging System has 11 filters covering a range of wavelengths from 390nm to 1040nm. The human eye sees light from about 400nm to about 700nm, so this means that MESSENGER sees both visible and near infrared light. (Note: 1 nm = 10-9 meters)
The color image above was produced using three of these filters, centered at 430nm, 700nm, and 1000nm. But, I just said that the human eye sees only 400nm (deep purple) to 700nm (deep red). So, how do they use the 1000nm image to produce the color image above? Well, they use the 430nm to be the blue part of the image. That is about right. But, they use the 700nm, which is actually a deep red, to be the green part of the image. And, the 1000nm, which is infrared, is the red part of the image. Combining the red, blue, and green images yields a color picture. But, note that this is a false colored image. This is not really what Mercury would look like if you were to see it up close.
So, why did the imaging team for MESSENGER do this to the image? Well, it was done to show off features on the planet. MESSENGER sees a much wider range of colors of light than does the human eye. So, what they have done is essentially to compress the range of wavelengths that MESSENGER sees to cover the range of colors that the human eye can see. That way, one image visible to humans can see about what the MESSENGER spacecraft sees. If you look carefully at the image, you will notice that some areas are slightly different shades of color than other regions. This is due to differences in the rocks in those areas. Understanding these differences can help understand the geology of Mercury.
-Astroprof
(Image courtesy of NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)
