Astronomers have discovered a four-planet system with three super-Earths orbiting a bright, dwarf star, reports news24.

The planetary system is located in the M-shaped northern hemisphere constellation Cassiopeia 21 light years from Earth.

The system consists of four planets: one giant and three super-Earths orbiting a star called HD219134.

The planet with the shortest orbit, HD219134b, orbits its star once every three days and is the closest transiting planet known to scientists. Therefore, it allows the scientists a rare opportunity to study its composition and atmosphere. The mass of this planet is 4.5 times higher than Earth's, and it is 1.6 times larger than earth.

"Its mean density is close to the density of Earth, suggesting a possibly similar composition as well," said a press statement from the University of Geneva, whose astronomers took part in the research.

According to sci-news.com, the astronomers predict that HD219134b may be a terrestrial planet with a rocky, partly molten surface with geological activity, including volcanoes.

According to team member Prof Stéphane Udry from the University of Geneva in Switzerland, 

"Being able to characterize three transiting super-Earths in a single bright and close system would provide incomparable constraints for planet formation and composition models, in particular for super-Earths."