( CNN ) As planets go , Mercury does n't get a lot of love . People spend more time on Google searching for Queen singer Freddy Mercury than planet Mercury ... and Freddie 's been gone for nearly a quarter-century . Not even NASA spends much time there , making it the least-explored inner planet in the solar system . But one question has long perplexed scientists : Why 's the darned thing so dark ? Compared with our own moon , which is about the same size , Mercury reflects much less light . Scientists at Lawrence Livermore National Laboratory , Brown University and the Planetary Sciences Institute say they may have found the answer : It 's been `` effectively painted black , '' in the words of Megan Bruck Syal , a postdoctoral researcher at Lawrence Livermore . Over the eons , the researchers argue in a paper published Monday in the journal Nature Geoscience , microscopic meteorites spawned from carbon-rich comets may have contributed enough dark-hued carbon to reduce the amount of reflected light . The pieces seem to fit together : There 's a lot more carbon dust thrown off from comets close to the sun , where Mercury orbits -- about 50 times as much for Mercury as for our moon , the researchers say . And tests using a big NASA gun made to simulate planetary impacts on a small scale seem to show the theory is plausible , the authors say . `` We show that carbon acts like a stealth darkening agent , '' said Peter Schultz , a professor emeritus of geological sciences at Brown University . `` From the standpoint of spectral analysis , it 's like an invisible paint . ''
Mercury was `` painted black '' by nearly a quarter-century of micrometeorites , researchers say . The research could solve the puzzle of why the planet appears so dark .