beautiful view of moon at night
The moon is trailed by a comet-like tail of sodium atoms. Various theories for how that sodium got there have been offered by scientists throughout the years. Two recent studies point to a credible source for the majority of it: swarms of tiny meteorites that pound the moon regularly.
The Tail of the Moon
The tail was spotted nearly 23 years ago and was finally proved to be a torrent of atoms flowing off the moon. But what was causing them to be released remained a mystery.
Some scientists hypothesized that sunlight striking lunar rocks might provide sodium atoms with enough energy to escape. Others hypothesized that the solar wind, or charged particles pouring from the sun, knocked sodium atoms out of the rocks. This might be done by charged particles released by the sun during severe solar flares. Then there were those pesky micrometeorites. They may have released sodium as they collided with lunar rocks. That sodium might be derived from the meteorites themselves to make the tail.
In Massachusetts, Jeffrey Baumgardner works as a space scientist. He was a member of a Boston University team that chose to investigate the mystery.
The researchers examined pictures of a brighter-than-normal section of the tail obtained between 2006 and 2019 from an observatory in Argentina. That period is longer than an entire 11-year cycle of sunspot activity. As a result, the pictures should have been able to identify any relationship between the brightness of the tail and variations in the solar wind or solar flares. They didn’t find that.
There was a correlation between the brightness of the sodium tail and meteor activity. According to Baumgardner, the Earth and its natural satellite should suffer the same meteor activity. However, unlike Earth, which has a thick atmosphere that keeps most micrometeorites from reaching the surface, the moon has a thin atmosphere that prevents most micrometeorites from reaching the surface.
The Boston team published their findings in the March issue of the Journal of Geophysical Research: Planets. Scientists originally discovered the tail while “looking for something else,” according to Baumgardner.
It occurred immediately following the Leonid meteor shower in 1998. This shower occurs every year in mid-November. On November 17, scientists were waiting to see whether small meteorites made the tail. They didn’t. However, the team’s equipment did detect a dim patch of light in the sky during the next three nights. The golden color of sodium atoms shone through the blobby patch. It encompassed an area almost six times the size of the moon. This light had faded by the fourth night.
However, the yellow spot reappeared regularly in the months that followed. It appeared each time within a day or so of a new moon. That is when the moon is nearly precisely between the Earth and the sun. Furthermore, the luminous area always appeared practically squarely on the other side of the Earth from where the sun and moon were. Its brightness shifted somewhat. According to Baumgardner, these were significant clues to its origin.
Researchers deduced that sodium atoms ejected into space from the moon. The sun’s light and solar wind then drove the sodium tail away from the sun, just like a comet’s tail does. Earth passes through this tail regularly. As this occurs, Earth’s gravity pulls the tail behind our planet. Then, the tail is close and brilliant enough to see using telescopes. Astronomers nicknamed this concentrated area of the tail the “sodium moon spot.”