For centuries Earth-based astronomers have reported seeing transient changes on the Moon’s surface, known as Transient Lunar Phenomena, or TLP. These have taken the form of short term brightness changes, coloured and non-coloured glows, obscuration of detail, shadow anomalies and flashes of light. The duration of TLP can be from a fraction of a second up to several tens of minutes; then everything returns to normal as far as we can tell from Earth. Unfortunately many of these so called TLP are from inexperienced observers, or made under poor observing conditions, however some TLPs are more intriguing as they are confirmed by more than one observer.
Although the Moon is widely believed by planetary scientists to be effectively geologically dead, there are four currently accepted theories that could explain some of these mysterious TLP reports: (1) Flashes of light seen on the night side are simply due to energy released at optical wavelengths from meteorite impacts – these are being studied by project ALaMO at NASA’s Marshall Space Flight Center and also by amateur astronomers at the Association of Lunar and Planetary Observers (ALPO). (2) Eruptive out-gassing from residual radiogenic gases such as Radon and Argon that accumulate in deep seated cracks and are released during Moon Quakes – we would effectively see the dust kicked up from this out-gassing. A robotic telescope at Cerro Tololo, Chile, is being used to look for white light changes on the Moon every few tens of seconds, and amateur astronomers at ALPO and the British Astronomical Association (BAA) are searching for coloured events, and TLP in Earthshine or more shaded areas not easily accessible by the Cerro Tololo scope. (3) Electrostatic levitation of dust particles forming dust clouds in electric fields that build up around sunrise in the form of Moon dust fountains. (4) Internal reflectance off volcanic glass beads – analogous to rainbows. However the only attempt to prove a TLP was caused in this way, in Torricelli B crater, was unsuccessful at reproducing this effect.
Figure 1. (Left) part of an LROC image (M116282876RC) of the Ina formation with an enlarged inset (right) showing craters on the chaotic terrain
Here at Abewrystwyth University we have been analysing some of the statistics of past TLP reports. A preliminary report was given at the Lunar and Planetary Science Conference in Houston in 2009 and we will provide an update in September 2010 at the European Planetary Science Congress in Rome. However we are also very interested to hear from Moon Zoo users, via the on-line forum (e.g. Picture of the Week) of any interesting surface features that they think might have been freshly disturbed or perhaps a vent from which out-gassing has come from. You may find such features as you go through “Boulder Wars” or the “Crater Survey”. However for those really keen to find additional interesting objects, then they can dip into the Apollo Metric and Panoramic Camera or higher resolution LROC image archives, though the latter has a bit of a learning curve. Things to look out for include small craters which are completely shadow filled, whereas their neighbours are not – these could be ceiling vents into underground lava tubes. Also unusual disturbed surfaces that do not look like anything elsewhere in the vicinity such as Figures 1-4. We do not propose that any of these are examples of where out-gassing may have occurred, but they are the kinds of unique features that we would like to know about, just in case.
Figure 2 (Left) M104476560LE LROC image of a small part of the floor of Hyginus Crater containing some geologically young sunken areas. (Right) M111972680LE LROC image of bright ray crater (east of Reiner Gamma) with a remarkably featureless central floor patch.
Figure 3(Left) Unusual dark shaded depressions, or dark textured material, to the north west of Vallis Alpes from LROC image M122218486RE. (Right) deep seated fractures on the floor of Tycho from LROC image M114031031LE.
So as Jules says in an earlier Moon Zoo blog, please get out there, looking at the Moon close up and report your findings to the Forum. Just maybe you will be the first to identify a true TLP site, and if not then I am sure that your findings will interest the Moon Zoo geologists anyway!