NASA's Mars rover curiosity doesn't always keep its cameras focused on the Martian surface around it; it occasionally looks up, and recently captured the first-ever images of asteroids seen from the Red Planet.

Two asteroids in the belt of cosmic rubble between the orbits of Mars and Jupiter, Ceres and Vesta, appear as faint streaks in a 12-second exposure taken by the rover's Mast Camera, or Mastcam, on April 20, NASA's Jet Propulsion Laboratory in Pasadena, Calif., reported.

The camera was taking photos of the Mars moons Phobos and Deimos, but the camera was triggered at a specific time when Deimos would be closely aligned in the sky with the two asteroids, scientists said.

"This imaging was part of an experiment checking the opacity of the atmosphere at night in Curiosity's location on Mars, where water-ice clouds and hazes develop during this season," said camera team scientist Mark Lemmon of Texas A&M University. "The two Martian moons were the main targets that night, but we chose a time when one of the moons was near Ceres and Vesta in the sky."

NASA has a spacecraft, Dawn, on a mission to study both asteroids. The spacecraft spent much of 2011 and 2012 in orbit around Vesta, and is currently on its way to Ceres, expected to go into orbit around it next year.

Ceres is large enough -- 590 miles in diameter -- that in addition to being an asteroid it is also classified as a dwarf planet.

Of the five dwarf planets known so far -- Pluto, Ceres, Eris, Haumea and Makemake -- Ceres it the only one orbiting in the inner solar system.

Vesta is about 326 miles across, and both asteroids are considerable larger than either of the Martian moons. Phobos is about 14 miles across, while Deimos is less than 8 miles in diameter.

Both moons are thought to be possibly former asteroids themselves, captured by the gravitation pull of Mars.

An astronaut on the surface of Mars would be able to pick out Ceres and Vesta by sight, since both are close enough to the Red Planet to be seen from there with the naked eye. From the surface of the earth, Ceres, even at its brightest, it too dim to be picked out by eye except in the darkest of night skies.