Register to reply

Moon is getting away from earth

by Mahbod|Druid
Tags: earth, moon
Share this thread:
HeLiXe
#19
May24-10, 10:18 PM
P: 412
This might be for another thread, but what were the effects on the moon's "drift", if any, caused by the LCROSS and LRO missions? Was the libration of the moon affected at all? If you have an answer for any of these questions (whether it be yes or no or whatever) can you please give me a detailed answer, including any magnitude of force and important equations which may be involved. Thx!
cahill8
#20
Jun2-10, 05:17 AM
P: 31
I'll leave a better explanation to someone else, but by simply looking at the size of the craters on the moon and thinking about the size of the objects that caused them, do you think LCROSS would have a noticeable effect?
HeLiXe
#21
Jun2-10, 04:32 PM
P: 412
Quote Quote by cahill8 View Post
I'll leave a better explanation to someone else, but by simply looking at the size of the craters on the moon and thinking about the size of the objects that caused them, do you think LCROSS would have a noticeable effect?
I started another thread on this. http://www.physicsforums.com/showthread.php?t=406050 I'm actually looking for the "better explanation" that someone else can offer. Someone else answered me in the same manner you have which tells me nothing in essence. I am looking for a more scientific answer with equations and the like.

But I will answer the question you posed to me. Simply looking at the moon does not give me any data about past impacts and the effect those impacts had. I can look at the moon and imagine the size of the objects that hit them, I can even research that some craters filled with lava and left only a rim and imagine just how enormous the object was that hit the moon in that particular region, but to be honest, that gives me no information of how the moon was affected by those past impacts, if at all. So it is the same with the LCROSS ...I do not know the velocity at which the centaur rocket or the shepherding spacecraft was traveling at before impacting the moon, I do not know how much matter was displaced or how big the crater was that it left, I do not know the force of impact. I do not know how to calculate what effect objects x and y traveling at a velocity of z Km/h impacting an object such as the moon which is about two percent the volume of the earth would have on said object's orbital path or libration if any. I am not asking for a "noticable effect," If the libration or orbit was affected at all I would like to know by what percentage and if there was none I would like to know how the calculation was made, same as if there was an effect.

BUT I resolve to continue study on my own as only 1 person has answered me seriously thus far. I should be having some classes regarding this in the future so perhaps at that time it will be better explained to me. I know that there are people here who are specialised in these areas of physics who could explain it to me which is why I asked.

The LCROSS mission is a search for water on the moon. The LCROSS mission is going to do this by sending a rocket crashing into the moon causing a big impact and creating a crater, throwing tons of debris and potentially water ice and vapor above the lunar surface.
^^Here is this from the Nasa site. How can I reasonably deduce what effect the mission had on the moon by just thinking of all the other "big impacts" which created a creater?
Janus
#22
Jun2-10, 05:42 PM
Emeritus
Sci Advisor
PF Gold
Janus's Avatar
P: 2,361
Quote Quote by HeLiXe View Post
I started another thread on this. http://www.physicsforums.com/showthread.php?t=406050 I'm actually looking for the "better explanation" that someone else can offer. Someone else answered me in the same manner you have which tells me nothing in essence. I am looking for a more scientific answer with equations and the like.
LCROSS masses about 585 kg. It hit at about 9000 kph. This equates to a momentum of 1462500 kgm/s The Moon masses 7.35e22 kg. If we divide the Moon's mass into the momentum of LCROSS, we get a fair estimate of what type of velocity change the impact could have on the Moon. It works out to be 2e-17 m/s. This is the equivalent of 1 meter per 1,000,000 yrs. Pretty darn insignificant.

And that's not all. You can't even count all of that 9000 kph impact speed. The vast majority of it is due to The Moon's gravity pulling the craft in. Since gravity is a two way street, as the Probe falls toward the Moon, the Moon falls toward the probe. The upshot is that any part of the probe's momentum on impact that is due to the gravitational attraction between it and the Moon is canceled out by the moon's own momentum. That means that any momentum change to the Moon is due to the small amount of the probe's momentum that is in excess of that. This makes the change in velocity to the Moon is even smaller than the last figure I gave.
HeLiXe
#23
Jun2-10, 06:11 PM
P: 412
OMG Thank you so much for the calculations!!!! D H also provided me a link to NASA's site with the information on the other thread. Thanks so very very much. I love you guys!!!! You have no idea how happy this makes me!
-------------------------------------------
Edit:
Also pls forgive my many grammatical errors above...had a full day and just had my first cup of coffee!


Register to reply

Related Discussions
Asteroid hits moon → moon hits Earth...possible? Astronomy & Astrophysics 68
Gravitational Force Between; Sun and Earth, Moon and Earth Introductory Physics Homework 21
Earth moon separation increasing Introductory Physics Homework 0
Moon and tides (tide on the moon instead of earth) General Physics 7
Is moon useful to the earth ? Astronomy & Astrophysics 13