The planets were discovered using the High Accuracy Radial Velocity Planet Searcher, the European Space Observatory’s planet-hunting telescope in Chile. All have surface temperatures ranging from 1,100C (2,012F) to 1,800C (3,272F).
Researchers including scientists from the Open University published their findings in three separate papers in Nature.
Professor Carole Haswell said: “The rocky planets we are discovering offer opportunities to precisely measure the mass, the radius and the composition, and this gives us the chance to see how the planets are built.
“We can begin to measure geology of planets outside our Solar System.
“This means we can place the Earth in context and learn more about planet formation and evolution generally.”
Prof Haskell added: “For example, we don’t yet know if it is a coincidence that in the Solar System, the Earth and Venus are the biggest rocky objects and have the largest fraction of their mass made of iron.”
The international team of researchers studied three stars known as DMPP–1, DMPP–2 and DMPP–3, which are located between 160 and 440 light years from Earth.
JUST IN: North Korea nuclear warning – Kim ready to stake claim, warns expert
DMPP-2b, meanwhile, is half the mass of Jupiter mass, taking just five days to orbit its host star, DMPP–2.
Finally DMPP-3 is a binary star system in which the dimmer DMPP-3B orbits the brighter DMPP-3A, with its planet, DMPP-3Ab, taking seven days to orbit DMPP-3A.
Dr John Barnes, a research fellow at The Open University, said: “DMPP-3 was a huge surprise.
“We were looking for a tiny signal indicating an orbiting, low mass planet.
“But the first thing we found was a huge signal due to a companion star we hadn’t expected!”
The team believes the new planets, particularly DMPP-1d, DMPP-1e and DMPP-3Ab, may dramatically improve understanding of rocky planets such as Earth, Mars, Venus and Mercury.