Some Thoughts on Transient Lunar Phenomena
As a few of you might know, I always had a strong interesting in astronomy and related areas. In fact, many years ago, I seriously considered a career in astrophysics or something along those lines. In the end, I chose an area of research which was more likely to result in a well paid job. The point is that I always had a strong interest in, and considerable knowledge of, areas of science that concern the study of astronomy and space- which also explains why I have a much better than average understanding of rocketry, among other things.
But what does this have to do with my thoughts on Transient Lunar Phenomena?
Well.. a lot. One of the reasons I became interested in astronomy, was my interest in the moon. While humans had visited the moon many years before I was born, it still remains the easiest astronomical object to view and study. This is especially so if you grew up in a semi-urban area with moderate light pollution. I grew up in an area that was dark enough to catch a glimpse of many objects in the Messier and Herschel 400 list from the backyard, and often I ended up watching the moon for hours at a time- while waiting for a specific deep sky object to reach a high elevation in sky.
This brings me the topic of what I was watching on the moon. While the moon has been well-studied and documented for decades, and even before manned exploration, there are still many reasons for amateur astronomers to study it. For one, there is a certain thrill to being able to see, with your own eyes, craters as small as a few kilometers across (2-3 km) on something about 0.4 million km away. FYI- the limit to what you see on the moon (in terms of size) depends on aperture of your instrument, location of moon in sky and a combination of atmospheric and lighting conditions.
There is, also, the tiny chance that you will witness an example of what is popularly known as Transient Lunar Phenomenon aka TLP. To be fair, TLPs are often seen as the lunar version of UFOs, because for a long time considered to be observational artifacts- otherwise known as people seeing things. And why not.. over the past century, scientists were almost unanimous that the moon had been geologically dead for a couple billion years- at least. Moreover, many moon rocks collected in late 1960s and early 1970s have been dated to be 3 to 4 billion years old.
But before we go further, let us talk about the two major types of TLPs. The first type, which last less than a few seconds and are no longer controversial involve meteorite impacts on the moon. It is not unheard of, especially if you have a decent telescope and spend a lot of time observing the moon to occasionally see very tiny flashes of light on the unlit parts of the moon. Over a period of many years and hundreds of hours of observation with a 8-inch aperture telescope, I have seen two or three definitive transient flashes, near the terminator of moon.
An early and fortuitous photo of what appears to be a meteorite impact on the moon was taken in 1953 by an amateur astronomer named Dr. Leon H. Stuart. Since then, others have taken many more photos and videos of similar (but much fainter) events on the moon. Basically, any meteorite with a mass between several tens to several hundreds of kilograms hitting the lunar surface can produce enough light to be picked up CCD devices attached to telescopes with an aperture larger than 12 inches (or 300 mm)- if they happen to be looking at the right area. The event photographed by Leon was however likely caused by a much larger meteorite- one weighing several tons.
The second type of TLPs, which are far more controversial and rarer, appear as highly localized and often colored mists frequently accompanied by temporary brightening or darkening of the surrounding area. These events usually last somewhere between a few minutes to a few hours. Also, they seem to occur far more frequently near certain craters and features on the lunar surface than would otherwise be the case. An example of this second type, photographed by Audouin Dollfus in 1992, can be seen below. Over the decades, more than a few astronomers have reordered such localized and transient changes on the lunar surface- both in photographs as well as with other light-based measurement techniques.
So what is going on? Is it evidence of volcanic activity? Or outgassing? or some weird electrostatic phenomenon? Could it be all due to unfavorable observation conditions? or something else? My personal favorite explanation for the second type of TLPs involves a version of the outgassing hypothesis. However, as you will in the later part of this post, it is somewhat different from the common version of that explanation, and I will go into some detail behind my reasoning for that choice.
So.. after denying the existence of TLP before the late 1950s, professional astronomers seem to have gradually come to accept them as real. Of course, there are still some credentialed idiots.. I mean “professional” astronomers.. who love to invent elaborate explanations about how they are all an artifact of observation. But enough about those worthless hucksters. As things stand today, we are still don’t know for sure about the process/es which causes them in the first place.
Usually, four explanations are advanced to explain TLPs. Two of them, namely 'Impact Events' and 'Unfavourable Observation Conditions' have already been discussed with the prior being true for one category of TLPs and the later being an excuse for elaborate hand-waving by sophists. And this leaves us with the other two explanations: 'Outgassing' and 'Electrostatic Phenomena'. While both are feasible and not as mutually exclusive as you might think, they still do not answer the central question- what are we observing in the first place?
The most poorly answered question about TLPs lasting for more than a few seconds has always been- "what is the chemical composition of whatever is being observed?". The simple answer to that question is that we either don't know for sure or have mutually contradictory data. But why is that so? How come we have tons of data about composition of the atmosphere of Venus, Mars, moons like Titan and other planets but very little information about temporary changes in the chemical composition on the lunar surface that accompany TLPs.
It comes down to two factors:
(1) Almost all studies on the chemical composition of non-terrestrial bodies are performed using some forms of spectroscopy. In other words, measurements of chemical composition of non-terrestrial bodies are almost always indirect measurements of how photons of some wavelength interact with the atoms (or molecules) of whatever is being studies. A secondary effect of being reliant on spectroscopy is that the equipment to do so is far scarcer than for simple observation.
(2) A lot of the scientific interest and funding for studying the moon disappeared after the late 1960s.Today, there are very few financial and instrumental resources for studying phenomena on the moon, especially one as ephemeral as TLPs. I should also point out that TLPs, while vaguely accepted by the professional astronomical community, are still not seen as "respectable" research especially in a world where scientific research has become another extension of neoliberal ideology- with an emphasis on "productivity", "metrics" and being non-offensive to "authority".
But we still have not touched what I believe is the central question about TLPS, namely, what are they made of- chemically speaking? Or perhaps a better way to phrase that question is- what would be the likely chemical constituents of TLPs?
Before we tackle that question, let us reacquaint ourselves with some basic facts about conditions at the lunar surface and the moon in general. Firstly, the moon has basically no atmosphere worth mentioning and therefore any gaseous emissions from the interior of the moon will quickly dissipate into the near vacuum which prevails near its surface. Contrast that to earth where, for example, the gas and dust from a volcanic eruption will hang around for days or weeks. Secondly, the lunar surface has not witnessed extensive volcanism for at least a billion years. There is however some evidence for volcanic activity on the moon as recently as 50-100 million years ago.
Thirdly, the moon is substantially smaller than the earth and contains a far smaller metallic core. The point I am trying to make is the moon should be geologically far more deader than it is seems to be. Then again, that is what most people used to believe about Pluto and Ceres until space-probes visited them in the past few years. To put it another way, a lot of what astronomers claimed to know about factors driving geological activity on planetary bodies is, at best, incomplete. And this brings us to what we know about the composition of gaseous emissions from the moon.
One of the first spectrograms of such an event, in 1958, suggested the presence of something containing carbon in the emissions. Observations by manned and unmanned spacecraft have also shown that some regions of the moon give of far more Radon-222 than others. Curiously enough, these areas of the moon happen to be TLP hotspots. To make a long story short, the idea that some regions of the moon often release small amounts of gases is now largely accepted. So far so good. But here comes the real curveball.. all gases known to emanate from the lunar surface (nitrogen, argon, radon, helium, methane?) are colorless.
As you might recall, TLPs were first noticed because of changes in luminosity and color in regions with a size of least 3-4 square km. Which means that whatever is released during these events is either one (or more) colored gasses or some form of dust with a composition and particle size which gives it some color. On earth, most of the color in the smoke of volcanic emanations is caused by compounds of sulfur or nitrogen and basalt dust which absorb light of certain wavelengths.
Given that the laws of physics are constant throughout the universe and chemical composition of the moon is unlikely to be radically different from Earth- it stands to reason that the colors and luminosity changes seen during TLPs are due to the release of emanations with more than a passing similarity to those from some volcanoes on earth. Yet, there is no evidence for currently active volcanoes (as we would define them) on the moon- even though we know the location of more than a few extinct ones. The lunar surface also has known atypical and small volcanoes.
TLPs, in my opinion, are due to the release of gaseous compounds (containing sulfur and nitrogen) and basaltic dust by volcanic features similar to Fumaroles and Fissure Vents on Earth. Their distribution on the moon might be linked to the presence of especially thin and fractured lunar crust. Of course, accepting such an explanation would mean that a lot of what we currently believe about the internal structure of moon and other celestial bodies of similar sizes is incomplete. Specifically, the Moon is far more geologically active than the “mathematical models” would predict.
What do you think? Comments?