Re: How did rocks from Mars end up here on earth (/columns/read/2615/)

I’d like to bring the question up again, but also ask: we should have empirical data on this subject now, so how do we know the rocks are from mars? Or more to the point, are they?

I asked myself that question a couple of decades ago. Trapped gas inclusions. Read more about it here:

As to how the rocks ended up here, they’re meteorites. They’re blasted into space from an impact to the Martian surface and eventually end up here. Equally neat is that if we could search enough, we should find rocks from Earth on Mars.

It looks like this is in response to one of Cecil’s columns. I’ll let the mods know so they can move it to the appropriate forum.

Thanks. I’ll move it.

The lead sentence about meteor/meteorite reminds me of the legendary answer a student wrote when asked the difference in a test:

A meteor is a streak of light
Made by a falling meteorite

I sure hope this answer’s right!

For years, no, for most of my life I couldn’t remember which was which when it came to meteoroid, meteor and meteorite. Not even Cecil’s description of “Meteors are space rocks that fry in the atmosphere; meteorites are the remnants that make it all the way down” helped me keep them straight.

I finally came up with this when I was writing “My Illustrated Astronomy Definitons” (which is definitely not for astronomers):

It’s not catchy. But it works for me. For the past two years, I’ve actually been able to keep them straight and use the correct terminology.

Mind you, it’s not instinctive. I have to do a quick mental run through that and then select the correct word to use. It’s like when I’m discussing a rock formation in caves, I have to go through the mnemonic I learned in junior high that a stalactite has to cling tight to the ceiling and a stalagmite might reach the ceiling one day before I say the term.

The rocks have similar composition to samples taken on Mars, and appear to have come from a planet that has been subject to weathering. So it’s a pretty good guess that the rocks came from Mars, not a certainty.