Four new giant alien planets discovered

Astronomers have discovered four new giant exoplanets, with masses from 2.4 to 5.5 times that of Jupiter, orbiting stars much bigger than our Sun.

The newly detected worlds are enormous and have very long orbital periods ranging from nearly two to slightly more than four Earth years.

The researchers, led by Matias Jones of the Pontifical Catholic University of Chile, used the 1.5 m telescope at the Cerro Tololo Inter-American Observatory and the 2.2 m telescope at La Silla observatory in Chile, and the 3.9 m Anglo-Australian telescope in Australia.

Using spectrographs mounted on these telescopes, the researchers monitored a sample of 166 bright giant stars observable from the southern hemisphere.

They computed a series of precision radial velocities of four giant stars -- HIP8541, HIP74890, HIP84056 and HIP95124.

According to them, these velocities show periodic signal variations, that could be explained by the presence of planetary companions, 'Phys.org' reported.

HIP8541b is the most massive of the newly found planets. With a mass of about 5.5 Jupiter masses, this exoplanet also has a much longer orbital period than the other three worlds, equal to 1,560 days.

Its parent star is slightly more massive than the Sun and has a radius of nearly eight solar radii.

HIP74890b and HIP84056b are very similar in terms of mass and orbital period. The mass of HIP74890b is estimated to be 2.4 Jupiter masses.

HIP84056b has an orbital period lasting nearly 819 days -- about three fewer days than the other planet.

Their host stars are also of similar mass and size, about 1.7 the mass of the Sun, with a radius of 5.03 (HIP84056) and 5.77 (HIP74890) solar radii.

Among the exoplanets, HIP95124b has the shortest orbital period of 562 days. It has a mass of 2.9 Jupiter masses and orbits a star nearly two times more massive than the Sun, with a radius of 5.12 solar radii.

The discovery of these planets also yielded interesting results about correlations between the stellar properties and the occurrence rate of planets.

The study was published in the journal arXiv.org.

Image: Artist's concept of a giant extrasolar planet. Photograph: NASA/JPL-Caltech