... The almost familiar scene depicted in this artist's vision of the surface of Saturn's largest moon looks across an eroding landscape into a stormy sky. MESSENGER at Mercury . ... On March 17, the MESSENGER spacecraft became the first to orbit Mercury, the solar system's innermost planet. ... NGC 5584: Expanding the Universe . ... Named Valles Marineris, the grand valley extends over 3,000 kilometers long, spans as much as 600 kilometers across, and delves as much as 8 kilometers deep. ...