EART160 Homework #2 Due Friday 23rd Jan 2009
Show all your working for full credit
1. Here we’re going to investigate the effect of a thick atmosphere on impactors.
a) Venus has an atmospheric pressure of 9 MPa and a surface gravity of 9 ms-2. What is
the column density of the atmosphere, that is, the total mass of the atmosphere per unit
area, in kg m-2? [1]
b) If a spherical impactor of radius R and traveling vertically downwards enters an
atmosphere of column density
, write down an expression for the total mass of
atmosphere the projectile encounters assuming that it reaches the surface [1]
c) Theoretical calculations show that an impactor will break up if the mass of atmosphere
it encounters equals the mass of the impactor itself. Assuming an impactor density
,
write down an expression for the radius R at which an impactor will break up for a given
column density
. [3]
d) For the case of Venus, what is the impactor radius at which break-up occurs if the
impactor density is 2500 kg m-3? [1]
e) Using the expression from your notes, calculate the smallest size of impact crater you
would expect to see on the surface of Venus. Assume an impact velocity of 15 km/s. How
does your answer compare to the actual observations? [4]
f) If the impactor came it at an oblique angle, rather than vertically, what would happen
to the break-up radius and why? [1]
g) If the impactor was made of ice rather than rock, would the minimum crater size be
bigger or smaller? [2] [13 total]
