Supreme Court Justices are nominated by the President, and then subjected to confimation by the Senate. If confirmed, all bets are off. They are then a member of the Third Leg of the Government, and answer to no one, period. It's their job for life, do do as they please.
With one exception. If Congress does not like what a Justice is doing, they can impeach him or her, and if a guilty verdict is the product of the proceeding, then the Justice can be removed.
Aside from that, a Justice does not have to explain anything, especially the way he or she votes, to anybody. Period. Those that say bullshit stuff like "they should recuse themselves" are ignorant of the priveledges that the members of the Court enjoy.
http://www.huffingtonpost.com/2011/1..._lnk1%7C115730