A U.S. Supreme Court justice chooses to retire and move to Florida. What will happen to the justice's old position?

The president will nominate someone to fill the position, and the Senate will approve the choice.
The position will remain empty because there is no set number of justices for the Supreme Court.
The Congress will vote to select one person to fill the empty position.
The Supreme Court will meet and read the Constitution to determine what action to take.