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
Two Is Better Than One the top 40. It is also the group's biggest hit to date. By December 2011, "Two Is Better Than One" had sold 1,508,000 copies in the U.S. alone, outselling even other big Taylor Swift hits such as "Tim McGraw" and "Fifteen". As of November 2017, the song has sold 1.7 million copies in the United States. With both related artists receiving acclaim, the song became Boys Like Girls' second consecutive top 40 single on the "Billboard" Hot 100. Also, it gave Swift her twenty-first top 40 song on that chart. For the week of January 9, 2010, the song became