Some satellites have changed geologically since then. These moons have a variety of surface features, including active volcanoes. Some satellites have an atmosphere. Titan, which orbits Saturn, and Neptune's moon Triton have atmospheres that are dense enough to measure accurately. Triton's atmosphere is much thinner.
Scientists use telescopes and spacecraft to study satellites and their parent planets.
Spacecraft have flown close to all the planets except Pluto. 1 Formation of satellites Many scientists believe that satellites formed at about the same time, and in the same way, as planets did. According to this theory, almost 5 billion years ago, a huge, disk-shaped cloud of gas and dust particles spun slowly in space. Particles collided, forming small chunks of material. The chunks, in turn, collided and formed larger objects.