Everyone loves a compelling origin story and the lone satellite circling the Earth is no exception. A new research paper by NASA scientists is further solidifying the hypothesis that a massive Mars-sized object slammed into the Earth billions of years ago to create our one and only Moon.
The "giant impact theory," suggested decades ago, proposes that the Moon was formed when a gigantic world called Theia collided with a proto-Earth 4.4 billion years ago, causing an explosion of gas, magma, debris, and chemical elements that later came together and solidified as a moon orbiting our transforming planet.
Now researchers are bolstering those official claims by investigating lunar rocks returned to Earth by Apollo-era astronauts and employing digital age technology to determine the level and type of chlorine contained in the samples. Headed up by Anthony Gargano, graduate fellow at NASA's astromaterials research and exploration science division at the Johnson Space Center, this revealing new study was published this month in the Proceedings of the National Academy of Sciences.
“The chlorine loss from the Moon likely happened during a high-energy and heat event, which points to the Giant Impact theory,” noted Gargano in an official statement.
During that cataclysmic impactor's invasion of Baby Earth's personal space, it's believed the intrusive rock was traveling at the speed of 12 miles per second. Precisely how much of Earth's juvenile atmosphere was affected in the high-speed hit-and-run crash can only be guessed at, but by ducking a direct strike, astrophysicists estimate that only 10-50% of its atmosphere was ripped away.
Scientists participating in the investigation uncovered the interesting fact that the moon has a much greater concentration of "heavy" chlorine compared to Earth, which is home to more "light" chlorine. In distinguishing between the two types of chlorine, "heavy" and "light" versions of the element are known as isotopes, made up of differing numbers of neutrons in their molecule's nuclei.
"There’s a huge difference between the modern elemental makeup of the Earth and moon, and we wanted to know why," explained study co-author and NASA planetary scientist Justin Simon. "Now, we know that the moon was very different from the start, and it's probably because of the 'giant impact' theory. Many previous lunar studies have looked at chlorine inside a specific mineral, called apatite, but we developed a way to measure chlorine throughout the rock, which gives us a more complete story.”
The popular story goes, not long after the cosmic collision took place, Earth was barely able to hold itself together as chunks of both planets were ejected out into space which provided the matter to coalesce into the Moon.
Both infantile bodies contained a blend of light and heavy chlorine isotopes early on, but that percentage at first, but that balance began to shift as Earth's gravity took command and yanked on the proto Moon. During these growing pains, Earth pulled away most of the lighter, easily-vaporized chlorine for its own while the more difficult-to-lure heavy chlorine stayed behind on the Moon.
Yet another piece of evidence arrived in the form of scientists targeting elements known as halogens, which belong to the same chemical family as chlorine. "Light" halogens are also less prevalent on the moon, and researchers were unable to discover a better theory that would indicate another event down the timeline caused the depletion.
This new data bolsters the evolving chemical evidence to add credence to the "giant impact hypothesis," delivering a dramatic time capsule into our young solar system and its violent past that provided the turbulent arena that gave us our beloved Moon.