Now, you have already a very accurate feedback up there! I'll add something more :)
is the number of opportunities available to each undergraduate student and what better way to spend a summer than participating in research?
It would be good to separate the two parts as Didgeridoo suggested, but I still find it a little confusing. Summer research is one of the opportunities students get, but not the only one, right? maybe you should say something like "among the others, the summer reserch interest me the most" ..
Also, why do you want to do summer research? If I understend correctly, you get to work in a real lab? If so I would place "experience" and "professional networking" as motivations.
Moreover, the opportunity to interact with like-minded people from different countries is one of the reasons I chose Engineering as a career and if admitted into the University of Michigan
Maybe it is better putting it the other way around " As I enjoy interacting with many different people and cultures, I hope Engineering will help me came in contact with like-minded people from different countries. If admitted etc etc..."
I know how difficult it is to stay in the 500 words limit, do your best! And good luck!