[MacBookPro] Use Ubuntu on an external HD without any system modification ?

Hello,


I have a mid-2010 MBP with Mountain Lion installed.
I would like to use Ubuntu from time to time, without dual boot, as I would like to keep my MBP as clean as possible.


Is it possible to boot/use Ubuntu from an external HD without modifying at all the Mac system ? Is there some limitations ?

Is there any recent tutorial around ?


Regards,
redvivi