Following an 18-month observation period of a small, cool dwarf star located approximately 35 light years from Earth, along with earlier observations dating back to 2010, a team of astronomers utilized the Very Long Baseline Array radio telescope to identify the presence of a massive, invisible exoplanet similar in size to Saturn.
Characterizing the Saturn-Sized Exoplanet
The newly discovered exoplanet, designated TVLM 513, boasts a mass comparable to that of Saturn and orbits its host star at a distance similar to that of Mercury’s orbit around the Sun. The detection of planets with characteristics similar to TVLM 513 around small, cool stars presents a significant challenge due to their faintness. This limitation is also encountered when searching for planets similar to the elusive Planet Nine, which has been the subject of extensive research for over a century.
A thorough analysis of the data revealed that the ultracold dwarf star TVLM 513-46546 is orbited every 221 days by a planet with a mass similar to that of Saturn. The discovery of planets around faint objects such as ultracold dwarfs is particularly challenging, but the new technique employed in this study may facilitate the detection of numerous additional exoplanets in the future.
Gisela Ortiz-León, the lead author of the study from the Max Planck Institute for Radio Astronomy (MPIfR), emphasized that the discovery was made possible by extremely high-precision measurements of the star’s position, which can only be achieved with a network of radio telescopes.
The Power of Radio Telescopes in Exoplanet Detection
The discovery of TVLM 513 marks the first time an exoplanet has been detected using a radio telescope, which relies on a technique that requires extremely precise measurements of a star’s position in the sky. This method has been known for some time but has proven challenging to implement.
The technique involves tracking the actual motion of the star in space and detecting a tiny wobble in that movement caused by the gravitational effect of the planet. The star and planet orbit a common center of mass, and the planet is revealed indirectly if this point, called the barycenter, is far enough from the center of the star to cause a detectable wobble.
This astrometric technique is particularly useful for detecting Jupiter-like planets in orbits distant from the star. As a massive planet orbits a star, the wobble produced in the star increases with the separation between the planet and the star, making it easier to detect planets at greater distances.
A Planet in a Close Orbit
Notably, the newly discovered exoplanet is closer to its host star than Mercury is to the Sun. The astrometric technique can be used to infer the presence of an exoplanet by monitoring changes in the real position of a star. Alternatively, astronomers can also detect planets by measuring slight changes in the radial velocity of a star.
Other methods, such as those employed by NASA’s Kepler satellite and TESS mission, involve detecting planets by measuring the dimming of starlight as the exoplanets transit the star’s disk. The astrometric method has been successful in detecting binary star systems nearby and has been recognized as a potential means of discovering extrasolar planets since the 19th century.