# How did Martin Rocks get to Earth **URL:** \ **Category:** Factual Questions\ **Created:** [May 6, 2004, 6:35am UTC](https://boards.straightdope.com/t/how-did-martin-rocks-get-to-earth/243797 "2004-05-06T06:35:05Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Reepicheep](https://avatars.discourse-cdn.com/v4/letter/r/ed655f/32.png) [@Reepicheep](https://boards.straightdope.com/u/Reepicheep)\ **Post date:** [May 6, 2004, 6:35am UTC](https://boards.straightdope.com/t/how-did-martin-rocks-get-to-earth/243797/1 "2004-05-06T06:35:05Z")
In this [thread](http://boards.straightdope.com/sdmb/showthread.php?t=254753) everyone agrees we humans have never had an unpowered projectile reach escape velocity. Escape velocity meaning leaving the gravity well of the earth and never returning. Since it is demonstratively extremely hard to escape the gravity well of the earth could someone please fight my ignorance by explaining how rocks from Mars got on Earth. Since Mars is smaller than Earth, escape velocity will not be as fast, that much I get. However, if the only thing that would produce escape velocity for martian rocks is the impact of a body from space, that’s going to have to be one very large impact. The caveat question is how do we know that the rocks are from Mars, not from the moon or just unusual earth rock? Thanks. ---
**Author:** ![ITR\_champion](https://avatars.discourse-cdn.com/v4/letter/i/c67d28/32.png) [@ITR\_champion](https://boards.straightdope.com/u/ITR_champion)\ **Post date:** [May 6, 2004, 6:43am UTC](https://boards.straightdope.com/t/how-did-martin-rocks-get-to-earth/243797/2 "2004-05-06T06:43:22Z")
Well, yeah. It did have to be one very large impact. In the early solar system, there was more debris floating around then there is right now, so planet were more likely to get pelted with meteors. The general consensus behind the “Mars rocks” that we find on Earth is that they were flung into space relatively early in Martian geological history by a massive impact, swirled around the inner solar system for a while, and eventually got trapped by Earth’s gravity. This didn’t happen too often. I believe that when I read up on the topic in the late 1990s, only eleven such rocks had been found. As for how we know, chemical analysis. The Martian crust is sufficiently different from Earth’s crust in terms of chemical composition that we can be pretty sure that a rock comes from Mars, if it certain amounts of certain elements. ---
**Author:** ![Askance](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/askance/32/8281_2.png) [@Askance](https://boards.straightdope.com/u/Askance)\ **Post date:** [May 6, 2004, 6:48am UTC](https://boards.straightdope.com/t/how-did-martin-rocks-get-to-earth/243797/3 "2004-05-06T06:48:11Z")
Martin who? We know because they exactly match rocks on Mars, and do not match any rocks here on earth. Yes, it took a hell of an impact for them to escape Mars. But in the time of the formation of the solar system there were large numbers of huge rocks smashing into all planets all the time, and debris such as this was thrown up with great speed and energy. After all we believe the moon itself was ripped out of the earth by such an impact, a few little rocks are nothing compared to that! ---
**Author:** ![Tapioca\_Dextrin](https://avatars.discourse-cdn.com/v4/letter/t/3d9bf3/32.png) [@Tapioca\_Dextrin](https://boards.straightdope.com/u/Tapioca_Dextrin)\ **Post date:** [May 6, 2004, 6:48am UTC](https://boards.straightdope.com/t/how-did-martin-rocks-get-to-earth/243797/4 "2004-05-06T06:48:12Z")
The obvious place to start would be the [Mars Meteorite Home Page](http://www2.jpl.nasa.gov/snc/) at JPL. They are thought to come from Mars as there isotopic composition is totally out of whack with Terran rocks, but is closer to that from Mars. Escape velocity from Mars is 5.02 km/s, which is less than half that of Earth ---
**Author:** ![Tapioca\_Dextrin](https://avatars.discourse-cdn.com/v4/letter/t/3d9bf3/32.png) [@Tapioca\_Dextrin](https://boards.straightdope.com/u/Tapioca_Dextrin)\ **Post date:** [May 6, 2004, 7:42am UTC](https://boards.straightdope.com/t/how-did-martin-rocks-get-to-earth/243797/5 "2004-05-06T07:42:19Z")
And a quick follow up from [this page](http://scienceworld.wolfram.com/astronomy/SNCMeteorites.html) > [@](#): > > several possible mechanisms were proposed and their consequences discussed by Vickery and Melosh (1987). Of the several scenarios they considered, they found a single ejection by a very large impact event 200 million years ago to be the most likely candidate… They speculated that the size of a crater large enough to have been formed in the impact event which ejected the SNC meteorites to be ~175 km in diameter Possibly the best bang since the Big One 😃 It seems that the best evidence for Martian origin is the Isotopic analysis of Oxygen from small inclusions in the meteorites. We can measure the O[sub]2[/sub] isotopes in the Martian atmosphere and the gas from the meteors is a pretty good match.