Alumni Newsletter 2011-2012
Alberto Saal’s Team Presents the First Evidence for Lunar Water.
During NASA’s Apollo missions in the late 1960s and early 1970s, significant amounts of lunar samples were collected and returned to Earth. Among those samples there were glasses produced during lunar volcanic eruptions approximately 3 billion years ago. The importance of these lunar volcanic glasses is that they are frozen melts coming from deep regions inside the Moon, and therefore they give clues about the composition of the Lunar interior.
Since the ‘70s, scientists have sought to determine the content and origin of water in the lunar volcanic glasses. But such evidence remained elusive, consistent with the general consensus that the Moon was formed by a cataclysmic event where a Mars-size object collided with Earth about 4.5 billion years ago. The collision threw molten material into space, where some of the fragments coalesced to form the Moon. Scientists think that the high temperatures involved in this process vaporized the most volatile element Hydrogen in the material that formed the Moon, resulting in a bone-dry satellite.
In 2008, a research team led by Associate Professor Alberto Saal had, for the first time, found evidence of water deep within the Moon in the lunar volcanic glasses. Although the group found small quantities of water (46 parts pre million) within the lunar glasses, Saal and his collaborators then used modeling to estimate how much water originally existed in the magma before eruption and degassing. The researchers calculated that about 95 percent of the water in the magma was lost to space during this eruptive “degassing”, and therefore the pre-erupted water content of the lunar magma may have been up to 750 parts per million.
In 2011, the same research group confirmed the results of the model by reporting the first-ever measurements of water in lunar melt inclusions found in the lunar volcanic glass deposits. Lunar melt inclusions are tiny globules of molten magma trapped within crystals, and therefore protected from degassing during eruption. The new measurement indicates that the lunar magmas had an initial water content of 1400 parts per million, similar to that measured in primitive magmas erupted on the Earth’s seafloor at mid-ocean ridges. This result suggests the very intriguing possibility that the Moon’s interior might have contained just as much water as the Earth’s depleted upper mantle.
This revelation strongly suggests that water has been a part of the Moon since its early existence – and perhaps since it was first created. That points to two possibilities: Water either was not completely vaporized in that collision event that formed the Moon or it was added a short time – less than 100 million years – afterward by volatiles introduced from the outside, such as with meteorites and comets.
Several Brown undergraduate and graduate students have been involved in the project: Mauro Lo Cascio, Diane Wetzel, Ben Friedman, Tom Weinreich, Andrea Weber and John Ryan-Henry.