We recently got the chance to talk to Dr. Thomas Watters from the National Air and Space Museum, Smithsonian Institution. Dr. Watters is a Co-Investigator on the Lunar Reconnaissance Orbiter Camera, and discussing lunar tectonics with him was highly insightful:
ZME: Your background is in geology and tectonics, how was the transition to planetary sciences? How is studying geology on extraterrestrial bodies different?
Thomas Watters: Although my education was in traditional terrestrial geology and tectonics, I was always interested in the Moon and the terrestrial planets. With terrestrial geology, you have the great advantage of field work. With planetary studies, you’re of course limited to remote sensing data. However, field study of analog landforms is very important.
ZME: It just seems like astro-geology (I'm not really sure if that's the proper name) has developed so much in recent years. What were the most exciting findings in the field, in your opinion?
TW: We are really privileged to live in this era of exploration of the solar system! I’ve also had the good fortune to be on the science teams of planetary missions to the Moon, Mercury, and Mars. What has surprised me is that in spite of the similarities, we’ve discovered that every object in the solar system is unique in its own way.
ZME: About your recent research about the Lunar Reconnaissance Orbiter, the Moon has no proper tectonic activity [edit: I'm wrong], but there are still some tectonic features. Do you suspect that Earth's gravity actually caused the fault scarps during the Moon's formation, or did it simply activate them? What other features could Earth's gravity cause on the Moon?
TW: One of the exciting outcomes of the Lunar Reconnaissance Orbiter mission has been the discovery that the Moon is still a dynamic world. We’ve found evidence of young volcanic features and well as the very young faults. The faults are so young that they are very likely still active today. So our view of the Moon as a body that has not been geologically active for billions of years has completely changed. Our modeling suggests that Earth’s tidal forces have contributed to the formation of the faults. Tidal stresses alone would not be expected to form the faults (tidal stresses are too small), but when combined with stresses from global contraction due to cooling of the Moon’s still hot interior tidal stresses have influenced the orientations of the faults.
ZME: I know that the discovery of moonquakes was quite a surprise, because the Moon has no tectonics. Do we know what causes them? Could it be the same gravitational pull?
TW: Actually the Apollo seismic network while it was operating recorded thousands of moonquakes. Only about 30 quakes were determined to be shallow (near surface). These shallow moonquakes could be due to slip events on the young faults. Tidal forces from Earth’s gravitational pull may not have been large enough to cause the shallow moonquakes, but the combination of tidal stress and stresses from global contraction particularly at apogee (when the Earth-Moon distance is greatest) could be responsible for many of these quakes.
ZME: What is the current progress for the LRO mission? Have you gone through most of the data, or is there still more to analyze? Do you expect more exciting findings in the future?
TW: The LRO mission is in its second extended mission and we will be proposing to NASA for a third extended mission. We have only imaged about three-quarters of the lunar surface with the high resolution Narrow Angle Camera, so we have yet to map the entire population of young faults. During the next extended mission, we will be looking for visual evidence of current activity on the young faults.
ZME: Some plans were recently announced by Russia and the EU for establishing a permanent settlement on the Moon. What do you think about this perspective?
TW: A permanent base on the Moon is a logical first step to reaching the goal of human exploration of Mars. It would be good to avoid locating a lunar base close to one of the young faults.
ZME: In the end, what do you think is the future for astrogeology/geophysics? How well can we know the geology of other celestial body?
TW: Continued planetary exploration and investigation is not only critically important to understanding our solar system, it is critical to understanding the emerging population of extrasolar planets.
Thank you so much for taking the time, and good luck in your future endeavors!