Recoil physics Comic-strip hero Superman meets an asteroid in outer space, and hurls it at 920 m/s, as fast as?

Comic-strip hero Superman meets an asteroid in outer space, and hurls it at 920 m/s, as fast as a bullet. The asteroid is two thousand times more mive than Superman. In the strip, Superman is seen at rest after the throw. Taking physics into account, what would be his recoil velocity?