Physics question - no looking up online!

[ChrisGreaves]

Vesta this image of the giant asteroid Vesta set me thinking.
The image(s) look quite like the surface of our moon, although this asteroid is not moon-shaped, and that suggests that its mass is much less.

Still and all I found myself wondering about those impact craters, on Vesta and on our Moon.
Vesta has a mass of about 2 x 10^20 whereas the Moon is about 7 x 10^22, so Vesta is about one-hundredth the mass of the moon.
I now suppose a small rock one hundredth the mass of Vesta.

Question 1: When my rock hits Vesta, does the mass of Vesta increase?
Question 2: When my rock hits the Moon, does the mass of the Moon increase?

Try to answer these questions without looking up a reference source (books, web pages).

I have got as far as
(a) Mass is energy
(b) Energy is mass
(c) Conversion between mass and energy always increases entropy (loses usable energy)
(d) When two objects collide, material is ejected and possibly leaves the gravitational field of the joined object
(e) Material can escape the gravitational pull of a small object (Vesta) than it can a large object (the moon)
(f) I suspect that the larger an object is, the more likely it is to increase in mass as the result of a collision. Two dried peas colliding in space would most likely be converted into heat energy. Two particles of clay would probably collide like billiard balls. Two earth-sized objects would probably ... ?

Cheers, Chris

[BobH]

If Vesta and our moon (and, presumably, other objects in space) have all those impact craters made by other objects, why isn't the Earth's surface (above sea level) equally pock marked? I know that Eastern North and South Carolina have (had, as many have been plowed flat for farmland) impact craters (some called pocosins), but where are all the others? My speculation is that the other objects are much older than Earth and have, therefore, been exposed longer thereby accreting more craters.

Sorry for the ripple in the thread, Chris.

[ChrisGreaves]

... why isn't the Earth's surface (above sea level) equally pock marked? ...

Atmosphere!

Our weather brings forces of erosion.
We have tectonic activity too - moving plates - but I think that weather erosion is the second biggest force (see Hans's response below).

But please see also Lake Manicouagan and Wolfe Creek Crater

Cheers, Chris

[HansV]

Plus: smaller space debris burns up in the atmosphere before reaching the Earth's surface.

Mars has a very thin atmosphere compared to ours. Our Moon, and all asteroids/planetoids have none.

[ChrisGreaves]

Plus: smaller space debris burns up in the atmosphere before reaching the Earth's surface.

Good one! I wish that I had thought of that!
Yes, of course, stuff burns off before it makes impact, and smaller stuff burns up completely.
For the big stuff that makes it to Earth ( ... weather and tectonics ...)
Cheers, Chris

[Graeme]

Question 1: When my rock hits Vesta, does the mass of Vesta increase?
Question 2: When my rock hits the Moon, does the mass of the Moon increase?
(a) Mass is energy
(b) Energy is mass
(c) Conversion between mass and energy always increases entropy (loses usable energy)
(d) When two objects collide, material is ejected and possibly leaves the gravitational field of the joined object
(e) Material can escape the gravitational pull of a small object (Vesta) than it can a large object (the moon)
(f) I suspect that the larger an object is, the more likely it is to increase in mass as the result of a collision. Two dried peas colliding in space would most likely be converted into heat energy. Two particles of clay would probably collide like billiard balls. Two earth-sized objects would probably ... ?

Cheers, Chris

1. Yes
2. Yes
a. Equivalence Principle
b. Equivalence Principle
c. The losses would be mass (escaping matter) or energy (heat) or gravitational waves.
d. Meteorites have been found on the Earth made of Mars rock ejected following a larger Martian meteorite collision
e. Yes
f. It's thought that the Moon coalesced from the cloud of debris when a Mars sized body collided with the proto planetary Earth.

Graeme