Daniel Ferrer
309-A Park Library
Central Michigan University
Mount Pleasant, MI
48859
989-774-2338
E-mail: Daniel.Ferrer@cmich.edu
Although most of the time we worry about a large asteroid hitting the earth, but the point to this short note is how important it is that moon not get hit. Near earth objects (NEOs) or the Potentially Hazardous Asteroids (PHAs) need to be re-thought to include objects that might hit the moon. Smaller objects would have greater potential impact on the moon than those hitting the earth. (August 7, 2027 is coming).
The moon does not enough atmosphere to slow down most asteroids. Although in October 1990 a sodium increase was noted near the south ecliptic pole, which may have been caused by the moon getting hit by a group of small particle masses. On earth an object hit the earth February 1, 1994, which had a diameter of 6 to17 meters. This object was observed by the Department of Defense and as it entered the atmosphere it broke up into fragments. The Sikhote-Alin meteorite was perhaps as much as 100 tons and traveling at 12 km per second - eyewitnesses reported hearing roars as it broke up. So, with very little atmosphere to slow down any asteroid from hitting the moon a smaller asteroid will have a bigger impact. The moon is smaller than the earth, so it will take a smaller asteroid to have a greater impacted on the moon.
The moon is lighter than the earth, the average density is 5.5 g/cm3 for the earth and the 3.3 g/cm3 for the moon. Therefore, if the density of the moon is lighter, it will take less force to have a great impact on it when hit by an asteroid. In addition, some asteroid that could hit the moon could be going at the amazing speed of 50 miles per second.
The moon would have a lower gravitational acceleration on asteroids that would hit the moon. The good news is that means the asteroid would not be moving as fast. However, the bad news is that larger pieces of the moon would be pushed out in space where they could hit the earth. That is, they would be less likely to fall back to the moon.
The Apollo seismic network detected a number of meteor hits on the moon and
various papers have been written on the subject. What direction did they come
from? What size were they? Has earth gravitational pull influenced the number
of meteors hitting the moon? These are important questions which need to be
answered. The June 1975 meteoroid storm detected on the moon also produced pronounced
disturbances on the earth as detected by VLF radar. This shows the moon and
earth can get hit together and in recent times.
There have been close approaches, for example, 1995 FF came within 0.0013 AU of the moon on 1995 March 27.0 TT. This object has an estimated absolute magnitude of H=26.5 (13-30 meters in diameter). The object 1999 AN10 will come within 0.0026 AU of the earth on August of 2027. This object has an estimated absolute magnitude of H=18 (670-1500 meters in diameter). How close will this object come to the moon and what would happen if it hit the moon? At what speed is 1999 AN10 traveling at when it is in the moon-earth space?
August 7, 2023 a Near Earth Object (NEO) called 1999 AN10 will come within
0 .002652 AU of the earth. It is 0.0026 AU from the earth to the moon. Therefore,
the question is how close with 1999 AN10 come to the moon itself? The size of
1999 AN10 is rated at about (more or less) 1 Km. (H of 17.9).
1) A very large hit would break up the moon and some large pieces would mostly likely hit the earth. Beside the really bad news of getting hit by large pieces, the next really bad news is that the earth axis without the moon could vary more 23.5' degrees. How much more than its current 23.5'? How much wobble would there be? Some studies say historically without the moon the Aearth=s axis would vary chaotically between 0' and 85' @ (Williams and Kasting). What would happen now, if the moon was gone?
2) The moon could be hit and pushed out far into space. We might get hit by some large pieces of the moon. What effect would having the moon farther out in space have on the earth=s axis?
3) The moon could be hit and pushed closer to earth. We might get hit by large pieces of the moon. But what about the Roche limit that says if its too close then the moon would be broken up into pieces? How close would the moon need to be? After getting hit would the moon be that much smaller that it would less harmful to us? Could we move the moon farther out in to space if it gets too close?
What would a meteorite hit like the 200 Km crater in Yucatan or the 100 Km
crater in Popigai, Russia have on the moon? What size asteroid would it take
to have a large impact on the moon? The Pallas Asteroid has been measured at
4.2 g/cm3. How big? How dense? Traveling how fast? What size object would effect
the moon? The Yucatan asteroid is said to have been 6-8 miles wide. Asteroid
1989 PB was estimated to be a mile wide, when it came within 2 2 million miles
of earth. In March 1989, the asteroid 1989 FC although only 2 mile in diameter
came within 500,000 miles of earth, however, it was not discovered until April
1989. How close were these to the moon?
The current for rate for the discovery of Potentially Hazardous Asteroid for
the earth is about one per month. Total PHA as of March 2000 is 231 PHAs. Should
we include finding PHAs that could hit the moon as part of our agenda? After
recent calculations show that the 1997 XF11 asteroid was not going to hit the
earth in 2028, it was determined that Aearth was safe after all.@ But what about
the moon?
How can we calculate how many times the earth has been hit by meteors? We know early on in history of the solar system that Mercury was hit by a very large meteorite that created the Caloris Basin. Did that move Mercury=s orbit or axis? How did Uranus axis get tipped over?
If the earth got hit in one of the oceans, which is likely and we had waves of >biblical proportions,= then perhaps only 20 percent of humanity would survive. However, even a smaller asteroid moving faster and hitting the moon could cause us to be wiped out.
I think we need to realize the importance of the moon for us on earth, if we want to survive in our turbulent solar system.
REFERENCES
Clark R. Chapman Institute Scientist
Southwest Research Institute, Dept. of Space Studies, Boulder CO
http://www.boulder.swri.edu/clark/clark.html
See a Near Earth Asteroid up close and personal
http://near.jhuapl.edu/
AUSTRALIAN SPACEGUARD SURVEY
Tsunami from Asteroid/Comet Impacts
http://www4.tpgi.com.au/users/tps-seti/spacegd7.html
CTH 3D Comet Impact Simulations
http://sherpa.sandia.gov/planet-impact/comet/