Planets Orbit 75 Percent of All Stars in the Universe, Astronomers Report

Astronomers suggest that all of the universe's red dwarf stars have at least one planet in orbit around them, and one-quarter of those planets are within the star's habitable zone, where liquid water and life as we know it could exist.

This revelation comes after astronomers observed eight new planets around red dwarfs, including three potentially life-sustaining super-Earths. Red dwarfs are small, relatively cool stars that make up at least three-quarters of the stars in the universe.

Combined data obtained by HARPS and UVES, two high-precision European Southern Observatory planet surveys, led the team of UK and Chilean astronomers to their conclusions, which will appear in the journal Monthly Notices of the Royal Astronomical Society.

Installed on the ESO's 3.6 meter telescope at the La Silla Observatory in Chile, HARPS, or High Accuracy Radial Velocity Planet Searcher, is one of the most precise instruments of its kind. Its powers have been used to find dozens of unique planets.

The ESO's Very Large Telescope, located in the Atacama Desert in northern Chile, hosts a variety of special instruments, including the UVES (Ultraviolet and Visual Echelle Spectrograph), which is a high-resolution optical spectrograph.

"We were looking at the data from UVES alone, and noticed some variability that could not be explained by random noise. By combining those with data from HARPS, we managed to spot this spectacular haul of planet candidates," said lead study author Mikko Tuomi, from the University of Hertfordshire's Centre for Astrophysics Research.

"We are clearly probing a highly abundant population of low-mass planets, and can readily expect to find many more in the near future -- even around the very closest stars to the Sun," Tuomi said.

Tuomi and his colleagues focused on the so-called "wobble" of stars. The force of an orbiting planet's gravity causes a host star's ligth to wobble. Looking for this wobble is a way for astronomers to locate unseen planets.

For their study, the astronomers used a host of new techniques to identify planetary signals within the data. They applied what's known as Bayes' rule of conditional probabilities, which enables astronomers to determine the probability of a star hosting orbiting planets. Combining this principle with other techniques for refining and filtering their view of the cosmic data allowed the team to surmise that every brown dwarf in space has at least one planet orbiting it.

"This result is somewhat expected in the sense that studies of distant red dwarfs with the Kepler mission indicate a significant population of small radius planets. So it is pleasing to be able to confirm this result with a sample of stars that are among the brightest in their class," said Hugh Jones, an astronomy professor also from the University of Hertfordshire.