A blast from the past. This article and interview first appeared in Astronomy and Space magazine in June 2007.
The early Solar System was a violent place. One theory states that shortly after Earth’s formation four and a half billion years ago, a body the size of Mars thumped into Earth, blasting off massive amounts of debris. This debris eventually coalesced to form the Moon. After formation, the Moon underwent a period of intensive bombardment by meteorites that scared, fractured and left the Moon covered in craters of all sizes. This period was known as the late heavy bombardment and occurred between 4.1 and 3.8 billion years ago.
Eventually the bombardment slowed down and died out and the Moon’s surface became still and cool, but the core remained hot due to internal radioactivity. This heat caused the subsurface rocks to melt, and over the next 700,000 years, lava seeped out through the Moon’s fractured and battered crust forming the large dark “Lunar Seas” or “Mare” that we see today. Major cratering by meteorites is now almost non existent. Today, modem science proclaims the Moon as a silent, still and dead body where the occasional small impact is the only activity. There is however, an alternative view on the Moon, which has been around for hundreds of years. Many believe that the Moon is not as dead as we are led to believe. Reports of unexplained, short lived phenomenon on the Moon, which stretch back thousands of years continue to the present day. These phenomenon, known as Transient Lunar Phenomenon (TLP), consist of coloured glows, flashes, obscuration, and abnormal albedo (brightening) and shadow effects.
There have been reports of TLP on our Moon going back as far as 557 AD. In I540 observers at Worms in Germany noted a star like spot on the night side of the Moon. Since then, reports of TLP have been on the rise. In particular the intense study of the Moon during the period in the run up to and including the Apollo missions resulted in an increased amount of TLP reports. The crew of Apollo 11 even got in on the act when requested by NASA to see if they could confirm a TLP in the crater Aristarchus, which was seen from Earth. They did see some brightening, but this could have been a normal occurrence as Aristarchus is one of the most reflective areas and thus one of the brightest craters on the Moon. During this period, NASA was heavily involved in collecting and recording reports of TLP. Once the Apollo program ceased, NASA gradually lost interest in TLP.
That however was not the end of TLP. Reports of TLP have continued since then, and during the Clementine mission of 1994 NASA was once again involved in the search for TLP. Observers on Earth spotted a TLP in Aristarchus and mission control was alerted. Luckily Clementine was mapping the area around Aristarchus at the time and photos of the region were taken. The photos do seem to show a change in the albedo of the crater and at first glance seemed to provide conclusive proof for the existence of TLP. On further examination and when a before and after photo were processed to account for difference in lighting at the time of the photos, the brightening all but disappears.
Spectroscopic studies of the Moon have also provided their share of evidence. A Russian astronomer, Kozyrev, shocked the world when he announced that he had spectroscopic proof of a TLP which occurred in the crater Alphonsus during November 1958. The spectrographs do seem to show evidence of some sort of carbon out gassing, which was backed up by Kozyrev’s visual observations of Alphonsus at the time, in which he saw a blurring of the central peak as if it was covered by a reddish fog. Kozyrev also repeated this observation a few months later. Skeptics point out that perhaps Kozyrev was mistaken in his interpretation of the spectra. They also point out that it was not his only error, as he had also made a lot more controversial claims, such as a hydrogen atmosphere for Mercury and clouds causing the polar caps on Mars. Even though over fifty years have elapsed since Kozyrev’s observations, there is no consensus on what he saw.
Despite continuing reports of TLP, there is shortage of strong evidence. Recent years and months however, have seen a concerted effort by NASA to observe meteorite impacts on the Moon and they have recorded numerous impacts. In 107 hours observing, 20 impacts were recorded which show up on video as flashes. Apart from this evidence for impact TLP, the lack of evidence for other forms of TLP and the mysterious nature of TLP have led to TLP receiving a bit of a bad reputation in the past. Reports of faces on Mars and lost cities on the Moon have done little to help. In recent years TLP seem to have entered the mainstream again with The Association of Lunar and Planetary Observers (ALPO) leading the way in gathering and planning serious scientific observations of the Moon. TLP can be broadly classified into a number of categories. These classifications are based on a statistical piece of research by Winifred Cameron, one of the leading TLP researchers.
The categories for TLP are:
These categories simply relate to areas of the Moon that are showing temporary unexplained brightness, darkness, or areas with reddish or blue tinges or blurring. Each of these categories can be broken down further if needed. The interesting thing about TLP is that a handful of features can account for a lot of the reports of TLP. According to Cameron in a paper entitled “Analyses of Lunar Transient Phenomenon Observations from 557-1994″, 12 sites on the Moon are responsible for over 60% of the reports of TLP. These sites are Proclus, Theophilus, Piton, Alphonsus, Plato, Tycho, Copernicus, Gassendi, Aristarchus, Herodotus, Schroeter’s Valley and Grimaldi. If we take Aristarchus, Herodotus and Schroeter’s Valley as one feature, it has been responsible for fully one third of TLP. Most of the sites mentioned above have features consistent with active volcanism in the past, such as domes, or riles.
TLP by their very nature are elusive and so actual evidence, photographic, videographic or simultaneous observations by numerous observers is hard to come by. Evidence does exist, but it is nowhere near as convincing enough to ensure that all astronomers, planetary scientists and lunar geologists believe in the phenomenon of TLP.
The causes of the majority of TLP are also unknown but there are a few clear leaders, the first of which is meteorite impact. lt has been speculated that the bright flash from meteorite impacts may be the cause of many TLP and that the inevitable temporary cloud of dust created from these impacts may also lead to reports of TLP of the gaseous kind. Recent NASA research and the impact of the Smart 1 probe on the Moon show that it is now relatively straightforward to record impact flashes. Another proposed cause of TLP is the condition of Earth’s atmosphere. Many of us are familiar with the frequent nights of bad seeing when stars will not come to a point in our scopes and the Moon and planets are dancing in the eyepiece. Skeptics believe that observing the Moon at high powers with bad atmospheric conditions, or observing the Moon at a low altitude can lead to false reports of colour on its features.
Theories also suggest that eruptions of gases from below the lunar surface may be a cause of TLP. These out gassing events may be caused by Moonquakes , triggered by impact events or tidal interactions with Earth. Another suggestion for causes of TLP is that radiation in the form of cosmic rays and charged particles from the Sun cause the Moon’s surface to glow. Here on the Earth we have an atmosphere and magnetic field to help protect us from these rays, but there is neither on the Moon. The study of TLP is an area where a dedicated amateur can make a difference. The Association of Lunar and Planetary Observers issue monthly observing lists of features and times of observations when conditions of illumination and librations of the Moon are the exact same as when observations of TLP have been made previously. If a repeat observation of the TLP can be made with the same illumination and under the same conditions, then it can be assumed that the TLP is an artifact of the play of light on the Moon’s surface or a regularly repeating process.
Dr Anthony Cook, the coordinator of the transient section of ALPO was kind enough to take the time to answer a few questions on TLP. First I asked him how often the ALPO get reports of TLP and how often these reports are independently corroborated.
“It varies, at a rough guess, 5 TLP per year at the present time and if you include impact flashes as well as TLP, then maybe 20 per year. During the Apollo era many more people were observing and somewhere in the region of 120 reports were received in 1969. However a lot more observing time was spent searching for TLP and to be honest many of those observers then were not so experienced at interpreting the lunar surface. If you look through the NASA catalogue by Cameron you see that 650 highest quality reports exist out of 2300 total TLP reports. These highest quality reports are either corroborated by independent observers or captured in a permanently recorded form.”
Next, I asked about the scientific evidence for TLP that has been gathered to date.
“Impact flashes are a defacto 100 % proven explanation now. There is a team at NASA Marshal! Space Flight centre who now video these on a regular basis. Of course amateur astronomers confirmed them originally. Scattering of, and polarization of light from the surface by dust has been proven by Dollfus. He speculates gas as a mechanism for getting the dust into clouds, but it is possible that electrostatic levitation of dust particles might be another cause. Electrostatically charged particles have been indirectly imaged from the Surveyor landers and detected by Clementine in orbit from their scattered light. For the majority of other types of TLP, we are still hunting around for theories that fit the observations. TLP might be caused by dust kicked up by land slides/Impacts, gaseous emission from heavy radiogenic gases from the interior of the Moon, like Argon, Radon etc., that hang around the release site, internal refraction of light from volcanic glass beads producing rainbow-like coloured areas, electrodynamic effects from the cracking of rocks due to thermal expansion/contraction etc. Then there are Earth side explanations related to our atmosphere. But these are all theories!”
Why does the scientific community have a hard time accepting TLP as an actual phenomenon?
“After the Apollo era, the Moon was considered to be geologically dead and interest turned elsewhere. They knew how tenuous the atmosphere was on the Moon and there was just no way that anybody could consider that a gas release, big enough to be seen from Earth, could not be detected by the remaining Apollo instruments on the surface. Although these instruments detected radon releases on the surface, it was not considered to be in sufficient quantities to make anything visible. We now have some different ideas and concepts that were not so obvious to scientists back in the early 1970’s.
There were a lot of rather doubtful TLP reports that made it into the official NASA catalogue and these discredited a lot of the good work that had also been going on. One very damming piece of evidence against TLP was that J. Alien Hynek and his team at the Corralitos Observatory, New Mexico had spent 6500 hours imaging the Moon with an image Orthocon camera and filters, but claimed to have found no convincing evidence! On the other hand in the few technical reports and very short papers that his group released, it seems that their equipment was perhaps not so sensitive to detecting colour on the Moon as modern equipment, or our eyes are.”
When asked about Kozyrev’s spectroscopic results, Dr Cook explained
“Scientific papers by other scientists who examined his results all agree that he detected something. What they were critical of though was his interpretation of these as being the Swan bands (evidence of the presence of molecular carbon).”
All this talk of spectroscopic evidence got me thinking of the possibility of continually monitoring some TLP hot spots for spectroscopic evidence. I asked if this continuous monitoring was feasible.
“Yes it would be if people had the time and the money to do this. One also has to be very careful of seeing conditions as this can jiggle the Moon’s surface across the slit and one can get spectra from all over the place!”
Taking this idea a step further I wondered if amateur astronomers could help in the spectroscopy of these regions.
“I would certainly encourage spot checks on known TLP hot spots and it would be really very useful if, when a TLP alert is received, spectroscopic equipment could be pointed at the site in question to see if there is any spectral emission or absorption.”
Finally I asked some questions about the practicalities of observing TLP’s and what equipment is needed.
“Observers make visual and CCD observations. The visual observers, although not as colour sensitive as CCD are our primary means of discovering TLP as they spend generally much longer watching the surface and do real-time analysis. In contrast CCD images are captured less frequently and are more often than not, not analysed. Visual observers will look for obvious signs of colour, obscuration of detail, or changes in brightness. For colour they can either use their eyes in white light or use a Moon Blink device. In a Moon Blink device you switch between red and blue filters and if there is say a faint red tinge then it will appear bright in red light and darker in blue light. To look for obscuration one just looks for fuzzy areas, you need a good memory and a photographic atlas to check whether this is a normal appearance or not. To check for brightness variations one needs to either use a light extinguishing device e.g. graduated cross-polaroid filters or utilize the Eiger scale: a set of features on the Moon of known brightness to compare against. For CCD observers one can detect much fainter surface colours using either a colour camera or a monochrome camera with filters. CCD’s are much better at measuring brightness too. In terms of scope size, obviously the bigger the better, but I’d say anything bigger than a 5” that gives a nice sharp image will do. TLP can be up to 100 km across or bigger, I am thinking here of examples when people have said for example that “the floor of Plato looks featureless tonight”. But TLP are usually a lot smaller e.g. <10 km or < 5″. I would expect TLPs to increase in number the smaller one goes”.
Obviously this is a fascinating area and will no doubt become more important as NASA aims to return to the Moon. In the meantime if you are interested in getting involved, or want to know more why not visit the transient section of the ALPO website.