The Justices are fairly limited in their ability to earn outside money. Other than teaching a class, book royalties are one of the few lucrative extra-curricular activities for the Nine.
Justice Breyer’s 2011 book, Making our Democracy work, earned $60,000 in 2011 and $29,980 in 2013. In 2015, he earned $7,214 for his new book, The Court and the World. This he notched $122,000 from Random House in royalty income and “nonemployee compensation.”
Justice Sotomayor’s book, My Beloved World, earned her more than $3 million, including $1.9 million in advances. In 2015, she did not earn any royalties on the book, nor did the publisher spend any money promoting it. As I speculated a few years ago, I doubt she earned back her advance, which is why no additional royalties have been paid out.