Recent observations prove that volcanoes were still active on satellite images around 100 million years ago.
Since the 1970s and the American Apollo lunar missions, we know that satellites were still shaking regularly. Small formations were discovered in flyovers manned by Apollo 15. Such formations have been since interpreted as the trace of a small volcanic episode old only tens of millions of years. Though it may seem like quite a long time ago, it is relatively recent and extremely young compared to the age of the moon (about 4.5 billion years old). The lunar earthquakes have multiple origins (meteorite impacts, landslides, thermal expansion and contraction of the surface, tidal effects caused by the Earth), but they are not related to the movement of tectonic plates, because the lunar crust would be too cold and too thick to be certain. Satellites being witness to recent volcanic activity appeared to be an isolated case exceptional enough to challenge the thermal history globally accepted by most satellites today. According to scientists, the lunar volcanic activity would peak between 3.9 and 3.1 billion years in the past when setting up huge expanses of lava we call “seas” and “oceans” then would have gradually subsided due to the cooling of the celestial body which much smaller than the Earth, dating around 1 billion years ago.
NASA/GSFC/Arizona State University
In astronomy, it is often that new observations with new and more powerful instruments bring more clear imagery to our attention and challenges what we currently know. The high resolution images (up to 50 cm on the surface) of the American Lunar Reconnaissance Orbiter, that launched June 18, 2009 with a circular polar orbit approximately 50 km altitude, allowed the detection of about 70 volcanic sites, too small to be recognizable from Earth. Their appearances and the small number of meteorite impacts on these structures indicate that they would were left there a hundred million years ago, when dinosaurs roamed the planet, and even more recently in other cases. This is indicated in the work of Sarah Braden (Arizona State University, USA) and colleagues published that published in an article on the journal Nature Geoscience, though is also mentioned elsewhere.
The extreme dimensions of detected sites range from 100 m to almost 5 km, with an average close to 500 m. Sarah Braden et. al estimated an age based on several parameters including, in particular, the density of meteoritic craters that cover them. The smaller the craters are, the younger it is. With this technique, three sites have an age between 18 and 58 million years ago. These ages would confirm the precision of their indications. It hadn’t been severely degraded by the constant bombardment of micrometeorites that inevitably fragmented and rounded corners, and slopes that line most of the lava effusion were very steep, more than 35° with the surface, so they were still far from the equilibrium angle (30°) generated gradually by the meteoritic erosion. In this sense, the formations cataloged in this study are really different from what is usually seen on satellites and should become a preferred site for future exploration missions, either in orbit or on the ground. If traces of recent volcanic episodes are found, we’d have to rewrite the thermal history of the satellites to explain how such events have occurred and could probably still occur in the future. The lunar crust is perhaps not as cold and dormant as once believed.