listen to part of a lecture in an astronomy class, the professor has been discussing the planet Mercury. I just want to clarify one thing before we go on. There\'s a common misconception that mercury doesn\'t have an atmosphere. All the planets in our solar system have gaseous atmospheres. Mercury, because of its size, can\'t exert enough gravitational force to hold on to anything but a minimal atmosphere. So Mercury is almost airless, but not quite. The same is true for Earth\'s moon. It does have a rudimentary atmosphere. despite what most people think. What else do Mercury and the moon have in common? Based on what you\'ve read so far. Nancy. impact craters, right? So is there a connection between impact craters and atmospheres? Yeah, meteorites usually burn up in the atmosphere before they reach the ground, but there\'s no atmosphere on Mercury. no atmosphere. Oh, there\'s not much of an atmosphere on Mercury. So it gets pounded with space rocks, and of course, that goes for the moon as well. Okay, but let\'s talk about a difference between Mercury and the moon. And there\'s a connection here to meteorite bombardment. When you look at the moon, it seems to shine, right because its surface reflects light from the sun. yes, but Mercury\'s surface appears darker because it reflects less sunlight. good, and why is that? Remember, last week, we were discussing the moon\'s regolith. A regolith is that layer of loose material, the top layer on the surface of rocky planets like Earth and Mars and Mercury and on the moon and asteroids too. We think the reason Mercury reflects less sunlight involves its regolith. Originally, we thought that iron particles in Mercury\'s regolith might be the reason behind its lower reflectivity. Iron is one of the primary known darkening agents on other basically airless bodies. But in fact, Mercury\'s regolith contains very little iron. We know this from analyzing the dim light that Mercury does reflect. A more plausible candidate is carbon, the element that makes coal black. Carbon\'s the fourth most common element in the universe, but unlike iron, it\'s very hard to detect remotely. So while we\'re pretty sure there\'s very little iron on Mercury surface, it\'s hard to prove the presence of carbon one way or the other. Nevertheless, some astronomers do think that carbon is the reason, and that mercury is acquiring carbon from comets orbiting the sun. Comets, as we know, are big chunks of ice and dust, and one of the main components of cometary dust is carbon. How does it get to Mercury? Micro meteorites, you see, comets have this particular type of orbit which brings them periodically quite close to the sun and therefore to Mercury, the sun\'s nearest neighbor. And as comets swing by the sun, they become unstable and send micrometeorites full of carbon crashing into mercury. According to researcher’s calculations, mercury gets hit by 50 times more cometary debris than the moon does. So on paper, at least, there should be a substantial amount of carbon in Mercury\'s regolith. And in fact, laboratory research has strengthened the case for carbon. This research two laboratory experiments were done at a facility that specializes in simulating collisions between objects in space. The experiments involved sending a projectile at high speed into a target chamber filled with a powder. made of crushed rock. This powder had been developed previously to approximate the moon\'s regolith. which is low in carbon. In the first experiment, researchers mixed sugar into the powder in order to imitate the carbon content of comet dust. Why would they use sugar? Because sugar comes from plants, and plants contain carbon compounds, right? And the force of the impact produced heat, which melted the powder and vaporized the sugar, leaving tiny black. Carbon particles embedded in the melted material, enough particles to darken the powder significantly. It reflected less than 5% of the light that hit it. Now for the second experiment, the researchers did something different. Instead of adding sugar to the powder, they used quartz sand. There\'s no carbon in quartz sand and well, when the researchers fired a projectile into this new mixture. the material melted, but it did not get darker. But there are still unanswered questions. One is whether enough carbon has, in fact, accumulated in Mercury\'s regolith. over the course of billions of years to. so to speak, Paint It Black.