Strange planetary system with brown dwarf orbited by Jupiter-sized world puzzles astronomers

Astronomers have discovered a planetary system in the Milky Way that defies existing classification, featuring a brown dwarf orbited by a Jupiter-sized exosatellite Source: cna. The system consists of a red dwarf star about 40% of the Sun's mass, a brown dwarf (an object between a planet and a star), and a gaseous world with at least 90% of Jupiter's mass orbiting the brown dwarf every 170 days Source: cna. This hierarchical three-tiered structure mirrors our solar system's moon arrangement, but the object's size and host body challenge the definition of an exomoon.

Lead author Kevin Hoy notes the lack of a formal definition: "The lack of any definition to even argue on the criteria is why we say we are unsure if this counts as the first exomoon or not" Source: gizmodo. Co-author Alice Zurlo adds, "We deliberately chose not to call it a moon. That's because this object is unlike any moon in our solar system" Source: cna. The researchers used radio velocity analysis with the Very Large Telescope to discover the satellite, demonstrating a promising technique for finding exomoons Source: cna, gizmodo.

The discovery raises fundamental questions about planetary system formation and terminology. As Hoy emphasizes, "We're really hitting the limits of how far we can stretch the words we invented to describe the solar system" Source: cna. Future theoretical models will explore whether such systems are common or rare Source: cna.