Scientists have successfully measured the mass of an ‘invisible’ rogue planet, known as PSO J318.5-22, which is not orbiting any star. The achievement is significant as it is the first time the mass of such an isolated planet has been measured directly. The research, carried out by astronomers at the European Southern Observatory (ESO) and other institutions, was published in the journal “Astronomy & Astrophysics”.
Rogue planets, also known as free-floating planets, are celestial bodies that don’t orbit a star, making them difficult to detect and study. They are typically identified by their faint infrared glow, which is significantly dimmer than that of a star. PSO J318.5-22, located about 80 light-years away from Earth, was first discovered in 2013. It’s an exoplanet, meaning it is outside our solar system, and is roughly eight times the mass of Jupiter, the largest planet in our solar system.
The scientists used a technique known as gravitational microlensing to measure the mass of PSO J318.5-22. This method relies on the gravitational field of a foreground object (in this case, the rogue planet) bending the light of a background object (a distant star), thus acting like a lens. When the two objects align perfectly, the background star brightens, allowing astronomers to measure the mass of the foreground object based on the amount of light bending.
To conduct this study, the team used the Very Large Telescope (VLT) and the Next-Generation Transit Survey (NGTS), both located at ESO’s Paranal Observatory in Chile. The VLT is one of the world’s most advanced optical instruments, while the NGTS is designed to search for exoplanets as they pass in front of their host stars.
The results of this study provide valuable insights into rogue planets, which are still largely mysterious due to their elusive nature. It also demonstrates the effectiveness of gravitational microlensing as a tool to study these objects.
However, the researchers also highlighted the challenges of this approach. A microlensing event is rare and unpredictable, requiring continuous monitoring of the sky and rapid response when an event is detected. Moreover, once the foreground and background objects move apart, the microlensing event cannot be repeated.
The next generation of telescopes, such as ESO’s Extremely Large Telescope (ELT), currently under construction, will provide even more detailed observations of these elusive objects. The ELT will be the world’s largest optical and infrared telescope, with a primary mirror that is 39 meters in diameter. This will allow astronomers to detect smaller rogue planets and further our understanding of these cosmic wanderers.
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