Moons of Mars formed a large moon. Gravitational interactions between this moon and the outer ring formed Phobos and Deimos. Later, the large moon crashed into Mars, but the two small moons remained in orbit. This theory agrees with the fine-grained surface of the moons and their high porosity. The outer disk would create fine-grained material. While many Martian probes provided images and other data about Phobos and Deimos, only few were dedicated to these satellites and intended to perform a flyby or landing on the surface. Two probes under the Soviet Phobos program were successfully launched in 1988, but neither conducted the
Shepherd Moons and elements of Celtic and New age music, though Enya believes her music does not belong in the latter genre. "Shepherd Moons" received generally positive reviews from critics and became a greater commercial success than "Watermark". It went to number one on the UK Albums Chart and peaked at number seventeen on the "Billboard" 200 in the United States. The album was certified multi-platinum by the British Phonographic Industry and Recording Industry Association of America for shipments of 1.2 million and five million copies, respectively. Between 1991 and 1994, Enya released four singles from "Shepherd Moons": "Caribbean Blue", "How Can