Cabeus A, not Cabeus
Published on Sep 12, 2009 at 8:05 pm.
5 Comments.
Filed under astronomy, moon.
For the last couple of months, I’ve been so busy that I have not had time to do much blogging. Then, I kept wondering what to start writing about. Recently, the LCROSS program announced their target crater on the Moon: Cabeus A. That gave me an idea for what to post about.
First of all, I know that when it comes time for the impact in a few weeks, the news reporters will likely get the name of the crater wrong. They’ll be calling it crater Cabeus. However, Cabeus is actually a nearby crater. The target crater is Cabeus A, another crater just north of Cabeus. So, I thought that it might be instructive to talk about lunar crater names. The following Lunar Orbiter image shows craters Cabeus and Cabeus A.
Lunar craters, by convention, are named for people who have made contributions to the sciences. The rule is that the craters are to be named for deceased scientists, scholars, artists, and explorers who have made significant or fundamental contributions to their fields. Astronauts or cosmonauts killed in the line of duty also have craters named for them. Craters near the Sea of Moscow, on the far side of the Moon, are named for cosmonauts, and small craters near the crater Apollo are named for American astronauts. The United States Geological Survey maintains a gazetteer of planetary feature names, and the rules of the naming conventions can be found there. These craters are also marked on the following USGS map (click on it to make it bigger).
Crater Cabeus is named for Niccolo Cabeo, an Italian Jesuit priest who was a natural philosopher who lived from 1586 to 1650, during the age of Galileo and Kepler. He taught theology and mathematics at a Jesuit college in Parma. He studied meteorology and physics, making contributions in the study of hydrology and electromagnetism. Cabeo also studied falling objects, showing much like Galileo that different bodies fall alike due to the influence of gravity. Cabeo was aware of Galileo’s studies, but he disputed some of Galileo’s findings. In the realm of electromagnetism, Cabeo studied the effects of static electricity. He also studied magnetism, though his explanation for magnetic phenomena turned out to be quite wrong.
The crater named for Cabeo is near the Moon’s south pole, located at 84.9° S and 35.5° W (-35.5°). The name for this crater was approved in 1935. Crater Cabeus is 98 kilometers across. But, Cabeus was not selected as the LCROSS target crater. The target crater is nearby 48 km diameter Cabeus A, located at 82.2° S and 39.1° W (-39.1°). So, why does this other crater share the name of Cabeus? Answering that is really what inspired me to write this posting.
As it turns out, Cabeus A has lots of company. There are thousands of lettered craters. Technically, these are called satellite craters. The term “lettered crater” is a depreciated term, though it is still in wide use. By early in the Twentieth Century, astronomers had high enough resolution images of the Moon to show far more craters than names available. So, the major or prominent craters got names. The less prominent craters, though, were still of some interest to cartographers and researchers, so they needed some sort of naming system. So, the solution was to name the less prominent features as satellites of the more prominent named features. My first introduction to the lettered naming system was the famous pair of craters Messier and Messier A. These are a famous pair of craters in Mare Fecunditatis. The original use of the lettered feature notation was for any otherwise unnamed depressed feature (crater, rille, etc) near a named feature. The designation of the lettered feature, thus, would be the name of the named feature followed by a letter. Originally, a single letter designation was sufficient for most of the otherwise unnamed features, but high enough resolution images showed far too many things that needed designation than letters of the alphabet, so many of the smaller and less prominent features got two letter designations (such as the crater Copernicus JD). Though the lettered craters are often smaller than the named features, that is not always the case. There are several lettered craters that are shallow or otherwise less prominent than some smaller craters that have names. Cabeus A, itself, is actually a pretty good sized crater. Were it located somewhere more easily seen, it would likely have gotten a full blown name rather than a letter designation.
Cabeus A was recently selected as the target crater for the Lunar Crater Observation and Sensing Satellite (LCROSS). The LCROSS will target Cabeus A with a spent Centaur rocket stage, which will plunge into the crater. When the rocket slams into the crater floor, is should blast stuff out that can be examined from orbit and with telescopes here on Earth. The LCROSS spacecraft will fly through the expanding debris plume, analyzing the content of the debris. Then, the LCROSS craft itself will plunge into a different part of the crater, creating a second debris plume that can be monitored by other spacecraft as well as Earth-based telescopes. It is possible that large amateur astronomer sized telescopes (ten to twelve inch diameter or larger) may be able to see something, too.
So, why Cabeus A? Well, there are several reasons that this is a good target crater. For one thing, there is speculation that there may be ice in the floors of craters at the lunar poles. The ice, if it exists, is believed to come from vapors settling in the polar craters after impacts on the Moon by comets and icy asteroids. The impact of these bodies vaporizes them and clouds of thin water vapor should encircle the Moon for a while. Most of that water is eventually lost to space, but in the far polar regions, the Sun shines at such a shallow angle that portions of the floors of some of the craters may never see direct sunlight. The non-sunlit portions of the Moon are very cold. So, any water vapor getting into the craters might stick to the rocks and soil in these permanently dark zones. The Navy’s Clementine spacecraft was the first to show some indications that ice may be present in these craters, but the data from Clementine is far from conclusive. Successive missions have either failed to show water or have had inconclusive results. LCROSS is the latest attempt to find this frozen water in the lunar polar craters. Cabeus A is close to the lunar South Pole, so it may fit the bill. There are some craters that are farther south and may have more permanently shadowed floors. Unfortunately, the closer a crater is to the pole, the harder it is to see from Earth. Cabeus A is far enough from the pole that it can be seen from Earth, facilitating Earth-based observations of the debris plumes from the impacts, but close enough to the poles that the northern parts of the crater may be permanently shadowed by the crater rim. The image below shows about the perspective that should be visible on the impact date, October 9, 2009.
The impact is scheduled to occur at about 11:30 UT (that will be about 6:30 am Central Daylight Time here in Texas). That is before dawn here in the US on October 9. If the weather is good, I will try to observe the impact, and perhaps even get some pictures.
-Astroprof
Images courtesy NASA, USGS
Andrej on September 14, 2009 at 6:47 am: 1
A pet peeve on the use of depreciate vs. deprecate:
http://www.dailywritingtips.com/deprecate-depreciate/
See also comments concerning the use in SW Development.
statscounter on September 16, 2009 at 4:25 am: 2
cabeaus a is north to cabeas ….
Astroprof on September 16, 2009 at 8:30 am: 3
Yes, Cabeus A is north of Cabeus. That puts it in a better position to be seen from Earth, which is probably why it was selected rather than the crates farther south. Still, the southern floor and walls of the crater should be permanently shadowed (hopefully).
Laura Crow on September 17, 2009 at 11:06 am: 4
I am attempting to create an online presence for myself in order to encourage enthusiasm and participation in astronomy and astronomical research in the general public. I am trying to get support from outstanding astronomers who seem to have a standing, well respected online presence, such as yourself. Would you be willing to help me by sharing information with me multiple times a week, following me on twitter, or simply offering input? Thank you!
Schuey on September 29, 2009 at 10:18 am: 5
Now it’s “Cabeus, not Cabeus A”