Not long after the recent discovery of two new "hot Jupiter" exoplanets using data from NASA's Kepler spacecraft during its K2 mission, new findings have revealed the existence of four new giant exoplanets that orbit stars bigger than our sun. With masses from 2.4 to 5.5 that of Jupiter and orbital periods ranging from almost two to more than four Earth years, the newly discovered planets are massive in size.

The team responsible for the discovery made the findings using observations gained from the Exoplanets Around Evolved Stars (EXPRESS) radial velocity program, which took advantage of two Chilean telescopes in the Atacama desert and one Anglo-Australian telescope in Australia.

During the observation of 166 bright giant stars using spectrographs, the team computed the velocities of four giant stars: HIP8541, HIP74890, HIP84056 and HIP95124. After observing the periodic signal variations in these velocities, the team came to the conclusion that the stars were in the presence of planetary objects.

"These velocities show periodic signals, with semi-amplitudes between approximately 50 to 100 ms^-1, which are likely caused by the doppler shift induced by orbiting companions," the authors wrote. "We performed standard tests (chromospheric emission, line bisector analysis and photometric variability) aimed at studying whether these radial velocity signals have an intrinsic stellar origin. We found no correlation between the stellar intrinsic indicator with the observed velocities."

In addition to revealing four new exoplanets, the new discoveries also contained interesting results regarding the correlations between stellar properties and the occurrence rate of planets, revealing that giant planets tend to be found near metal-rich stars.

"We also present a statistical analysis of the mass-metallicity correlations of the planet-hosting stars in our sample," the team wrote. "We show that the fraction of giant planets increases with the stellar mass in the range between 1 to 2.1 solar masses, despite the fact that planets are more easily detected around less massive stars."

This finding confirms the trend of metal-rich stars being more likely to host planets and could help in future studies that aim to discover new alien worlds.

The findings were released March 11 on the arXiv server.