Images from Mercury 2nd Flyby
The spectacular image shown here was taken at an altitude of 27,000 km and shows a Wide Angle Camera image of Mercury taken about 90 minutes after the spacecraft’s closest approach to the planet. The surface we are seeing here is almost opposite to the side we see during the first flyby, so most of surfaces were previously unseen by spacecraft. Credit: NASA/JHUAPL/CIW
My first impression is “uh, watermelon??”… but wrong colour…
No, this is Mercury, taken by MESSENGER during its second flyby on Monday. The bright stripes that make it look like a watermelon is known as rays. When something slammed onto a surface it formed an impact crater, at the same time materials were thrown out in all direction from the crater forming radial streaks called rays. Look at any full moon pictures and you will see similar rays radiating out from some of the craters on our own Moon.
The crater responsible for these rays is located near the north pole of the planet and we can clearly see that the rays are stretching almost all the way around the globe to the south pole. These rays actually are not new to astronomers – we know they were there before MESSENGER by bouncing radar signals off Mercury from Earth.
The bright crater slightly below the middle of the image is called Kuiper, identified in the 1970s during the Mariner 10 mission. The rest of the terrain to the right of Kuiper is new.
Kuiper, and other bright craters with rays, are relatively young craters. Reason is we seldom see rays system on old craters because over time space weathering such as meteorite impacts will erase the rays. If we see rays system, then it must be a recent impact since there has been little time to erode it. Also, younger craters tend to be brighter for the same reason.
This close-up image of a portion of Mercury’s surface is imaged by spacecraft for the first time. Credit: NASA/JHUAPL/CIW
The largest impact feature at the top of the image is about 133 km in diameter and is named Polygnotus, after a Greek painter from the 5th century B.C. Another comparably large crater at the top left of the image is named Boethius, after the 6th century Roman philosopher. These two features appear to be filled with smooth plains, which is very different in texture form their surrounding terrain. Credit: NASA/JHUAPL/CIW
Source: MESSENGER Gallery
My Dark Sky 
