You have probably all heard of the discovery of a fifth planet around 55CancriA:
http://www.jpl.nasa.gov/news/news.cfm?release=2007-128

What confuses me:
How is it possible that 3 (three!!) planets of that size (similar in size to Jupiter, Saturn and Neptune, respectively)
all orbit that star much closer than Mercury does in our system?

Shouldn't they interfere with each others' orbits, making them highly unstable?