So in reality the impact speeds of objects can be much higher on Mercury: 48 km/ sec + 4.3 km/sec = 52 km/sec, compared to 30 km/sec + 11 km/sec = 41 km/sec for Earth.

What if the object is going in the same direction as Mercury? It’s the difference in velocity between the two objects, not their absolute velocities.

[edit] Though, re-reading the above, I realize that you did say can be.

Interesting! I didn’t know the timing was that close.

Because Mercury is the closest in to the sun planet, it will probably consist of a much higher concentration of heavy metals such as Gold, Platinum etc. That would make mining such a planet a possible, well, goldmine opportunity!

If it is considered too dangerous or expensive for humans to survive and mine Mercury, why not robotic miners then?

A note from the Department of Mathematical Pedantry: 11.2 km/s for Earth and 4.3 km/s for Mercury are the minimum velocities of bodies colliding with the two planets, not an addition to the orbital velocity of the planets. So, say a rock is dropped from just at the radius of influence of a planet’s gravity, that’s what you see.

If, however, the rock has an initial relative velocity (= planet velocity + rock velocity) of its own, the new impact velocity is given by v(impact) = sqrt[v(original) + 2*G*M/r]. The addition to the original velocity is the infall acceleration, but it is not the same as simply adding the escape velocity to an existing orbital velocity.

Interestingly, if you apply the vis-viva equation to the same sort of bodies that strike Earth, their orbital velocities are more than double by the time they get to Mercury’s neighborhood around 0.4 AU, as compared to what they are crossing Earth’s orbit at 1 AU. For impactors with retrograde orbits, that can mean relative velocities in excess of 120 km/s!

“Although the crater floor is shielded from direct sunlight, it won’t be in total darkness because of reflected light from the crater walls.”

Yes, the Kaguya orbiter tried this angle at the Moon:

http://lunarscience.nasa.gov/articles/kaguya-satellite-has-shown-no-exposed-ice-in-lunar-crater

Of course, they may be covered with regolith and only the penetrating power of radar can reach to the ice.

The bit about perpetual shadow reminds me of an old sci-fi story I read about a mission to the “coldest place in the solar system”. The story sets it up to make you think of Pluto, but at the end of the story the location is revealed to be the “dark side” of Mercury. This was back before it was discovered that Mercury rotates in a 2:3 resonance to its orbit with the sun, as opposed to being tidally locked.

Edit: @#10 Trebuchet:

This post reminded me of an early Larry Niven story titled, if I recall correctly, “The Coldest Place”. Set on the dark side of Mercury — it was written when it was believed that Mercury was tidally locked and presented just one face to the sun.

D’oh!! That’ll teach me to read the thread before posting

NASA scientists, with managerial guns held to their paychecks, today announced the likelihood of Peltier life at planet Mercury’s south pole. “We observe a temperature gradient of 450 C between shadow and sunlight. Assuredly life evolved was created to derive energy from this abundant thermodynamic gradient.” NASA immediately demanded a Bernanke Buck ($1 trillion at -0.25% interest) for studies.

“We forsee an end to all Earth’s energy shortages from manned exploration of Mercury. Retrieval of Peltier life followed by a century of quarantine under vigorous Enviro-whiner litigation is the solution to all our energy needs.”

http://en.wikipedia.org/wiki/Goethe_Basin

As a general rule craters are circular. I understand this is because craters are mostly caused by the release of energy at impact – it’s effectively a bomb going off at that point – rather than the angle of impact. What many people miss is the effect of the speed at impact is so high that the meteor is vaporised, and that material then spreads out evenly in all directions.

Yes, there are some elliptical craters on the Moon, but I understand they’re very rare.

@ #2 and #7: I wonder if most craters are circular because the planet’s gravity tends to cause an approaching asteroid to curve into it and strike more perpendicularly? Phil??

You figured correctly! I’ve seen a few elliptical craters posted here on the BA Blog every so often. A Google image search yields some nice examples as well.