Phobos (moon) energy due to wind blowing dust off of its solar panels, took several short-exposure photographs of the night sky from the surface of Mars. Phobos and Deimos are both clearly visible in the photograph. The Soviet Union undertook the Phobos program with two probes, both launched successfully in July 1988. "Phobos 1" was accidentally shut down by an erroneous command from ground control issued in September 1988 and lost while the craft was still en route. "Phobos 2" arrived at the Mars system in January 1989 and, after transmitting a small amount of data and imagery but shortly before beginning
Solar System moons. The centaurs and many short-period comets also orbit in this region. Due to their greater distance from the Sun, the solid objects in the outer Solar System contain a higher proportion of volatiles, such as water, ammonia, and methane than those of the inner Solar System because the lower temperatures allow these compounds to remain solid. The four outer planets, or giant planets (sometimes called Jovian planets), collectively make up 99% of the mass known to orbit the Sun. Jupiter and Saturn are together more than 400 times the mass of Earth and consist overwhelmingly of hydrogen and helium.