‘Exocomet’ numbers nearly tripled in new study

The first such "exocomet" was discovered in 1987 but since then only three more had been found. At the 221st American Astronomical Society meeting in the US, astronomer Barry Welsh gave details of seven more.
Proving that comets are common in the Universe has implications for their role in delivering water or even the building blocks of life to planets. Comets such as Halley’s Comet, which makes a long, elliptical path passing near the Sun every 75 years, make themselves known through their long "tails" of gas and debris that come off as they approach their host stars.
It is this that Dr Welsh and his collaborator Sharon Montgomery of Clarion University have measured, using the McDonald Observatory in Texas. The exocomets’ tails absorb a tiny amount of their host stars’ light – and the absorption changes with time as the comets speed and slow.
With patient observation, the pair came up with seven new exocomet sightings. In our Solar System, many comets come from the Kuiper belt, a disc of debris beyond the orbit of Neptune, and from the Oort cloud, an even larger and more distant debris disc.
Dr Welsh explained that these discs were characteristic "leftovers" of planet formation as we now understand it.