The Supreme Court is different from lower federal courts, and not just because its rulings can't be appealed. Another difference is that its justices are exempt from the ethical standards imposed on judges in less lofty positions. That's an unjustifiable anomaly that Congress should rectify.
The Code of Conduct for United States Judges was established by the U.S. Judicial Conference and covers all federal lower court judges. Among other things, the code says that "a judge should avoid impropriety and the appearance of impropriety in all activities." Supreme Court justices insist that they too are guided by the code, but when it comes to ensuring public confidence, voluntary compliance is no substitute for mandatory adherence.
One of the most important ethical decisions facing a judge is when to recuse himself or herself from sitting in a case. Supreme Court justices fairly regularly step aside in situations in which they have a personal or financial interest in the case. But, again, that is at their discretion, and generally the reasons for recusal are not made public. What's more, a decision by a Supreme Court justice not to step aside cannot be appealed.
These vague rules have created controversy on many occasions. Critics have suggested, for instance, that Justice Clarence Thomas should recuse himself from any case involving the federal healthcare reform law because of his wife's work with a group that opposes it. And some people thought Justice Antonin Scalia should have withdrawn from a case involving then-Vice President Dick Cheney, with whom he had recently gone duck hunting.