SMART-1 (Part Two)
Published on Sep 1, 2006 at 1:42 pm.
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Filed under moon, space exploration.
Yesterday, I had a posting about the European Space Agency’s SMART-1 craft. For the last couple of years, SMART-1 has been circling the Moon. Well, it is at the end of its mission. So, rather than let it die and continue to orbit the Moon forever as a piece of space junk, ESA has decided to deliberately plunge the spacecraft into the Moon. This isn’t really a new concept. Lots of other spacecraft have plunged into the Moon. The first missions to the Moon were not equiped to land, so they just crashed into the Moon. They call that a “hard landing” in spacecraft jargon. Yeah, it is pretty hard. They make a little crater where they hit.
After completing their missions, NASA’s Lunar Orbiters crashed into the Moon, in part to make sure that they didn’t hit the Apollo craft that were coming later. The chances of impact were almost zero, but they figured it was better to be safe than sorry. After all, the Moon is far too far away to keep track of whatever is in orbit around it once those satellites cease to function. Likewise, following transfer of men and material from the lunar Ascent Module to the Command Module, the ascent stage of the lunar lander was also deliberately plunged into the lunar surface. This was done for two reasons. One was to get it out of the way. The other was to create an impact whose seismic waves would register on seismographs left on the lunar surface. The Moon is geologically quiet, so there were hardly any naturally occuring seismic waves to use to probe the lunar interior.
After completing its mission, NASA’s Lunar Prospector also was plunged into the Moon at the end of July, 1999. Again, this got the craft out of the way. But more importantly, NASA realized that useful science could be done even during the demise of the craft. The Lunar Prospector was deliberately crashed into a crater in far south of the Moon. It was believed that ice may have been in this crater. The spacecraft crashing into the crater should have created a small crater of its own, throwing debris outward, and vaporizing some of the ice. Telescopes across Earth carefully monitored the area of the impact to detect the signature of water vapor from the vaporized ice, thus proving that indeed ice were in the crater. Unfortunately, no water vapor was detected. Explanations for the lack of detection range from ice not being there, to not as much ice as expected being there, to the impact simply not being big enough to free enough water vapor to detect. NASA is planning on sending an impactor along with the Lunar Reconaissance Orbiter in two years. Hopefully, a spacecraft up near the Moon with specialized instruments will have a better opportunity to detect water, if it is there.
So, what does all this have to do with SMART-1? Well, SMART-1, in a little over a day from this posting, will crash into the Moon, as well. ESA has decided to use this crash to study cratering on the Moon. To make the study easier, the crash is to occur on the near side of the Moon. The Moon will be a waxing gibbous phase, and the impact will be in Lacus Excellentiae (the Lake of Excellence). 
The Lake of Excellence is located just a bit south of Mare Humorum. It is a volcanic plain in the midst of the southern highlands. This part of the Moon will be in darkness at the time of impact, permitting any flash or glow from the impact to be seen from Earth.Â
SMART-1 will impact the lunar surface at a speed of about 2 km/s. The impact should occur at about 05:41 UT on September 3. That will be at 12:41am here in Texas. Unfortunately, at that time, the Moon will be very low in the western sky, and so I might not get to see anything. But, there are some uncertainties about lunar topography. So, the craft might actually miss the Moon then and impact on its next pass, at 10:46 UT. At that time, the Moon will be well below the horizon, and I won’t be able to see anything. But, it is also possible that the craft might hit a hill or mountain peak on the pass just before nominal impact, in which case it might hit sometime near 00:36 UT. Unfortunately, I still wouldn’t be able to see anything from here, as the Sun would still be up for me at that time! So, I am in just the wrong spot. Observers farther east or west will have a better shot.
So, what might you see if you are in the right spot? Probably not much, unless you are using a large telescope and a CCD. Now, it is possible that the debris plume might extend high enough to catch sunlight a few minutes after impact. If that is the case, then observers farther west of me should be able to see a fuzzy white dot over the impact site. Observers with a larger telescope, and at a location where the Moon is high in the sky, will have a chance to see a glow at the impact site. Personally, I think that the glow will likely be pretty dim, and so you’d need a quite large telescope and a CCD. I rather doubt that most amateurs would see the actual impact, but you never know. We really don’t know much about impacts, so this might be far more spectacular than I think. It is unlikely that anyone will see anything at all with the naked eye, so most hope of catching anything would be with binoculars, or a telescope.
If you want to read more, there is even a blog about the whole impact.Â
-Astroprof
(Image credit:Â ESA)
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