Which reminds me.....

Here's something I don't understand.... one 78 gajillion things I don't understand. How they know where certain object come from. The new object coming in from deep space I get.... it''s trajectory.... but I've heard (read) that they "KNOW" certain meteorites came from the moon, and mars... how do they know that? or am I reading articles from astronomers who have dipped a bit to far into their Jack Daniels when they penned the article? Trajectory doesn't work with all those ancient meteorites.