rogue planet

A rogue planet (also termed a free-floating planet (FFP), isolated planetary-mass object (iPMO), interstellar, nomad, orphan, starless, unbound or wandering planet) is an interstellar object of planetary mass which is not gravitationally bound to any star or brown dwarf. Rogue planets may originate from planetary systems in which they are formed and later ejected, or they can also form on their own, outside a planetary system. The Milky Way alone may have billions to trillions of rogue planets, a range the upcoming Nancy Grace Roman Space Telescope will likely be able to narrow down. Some planetary-mass objects may have formed in a similar way to stars, and the International Astronomical Union has proposed that such objects be called sub-brown dwarfs. A possible example is Cha 110913−773444, which may have been ejected and become a rogue planet, or formed on its own to become a sub-brown dwarf. Name The two first discovery papers use the names isolated planetary-mass objects (iPMO) and Free-floating planets (FFP). Most astronomical papers use either of these terms. The term rogue planet is more often used for microlensing studies, which also often uses the term FFP. A press-release intended for the public might use an alternative name. The discovery of at least 70 FFPs in 2021 for example used the terms rogue planet, starless planet, wandering planet and free-floating planets in different press-releases. Discovery Isolated planetary-mass objects (iPMO) were first discovered in 2000 by the UK team Lucas & Roche with UKIRT in the Orion Nebula. In the same year the Spanish team Zapatero Osorio et al. discovered iPMOs with Keck spectroscopy in the σ Orionis cluster. The spectroscopy of the objects in the Orion Nebula was published in 2001. Both European teams are now recognized for their quasi-simultaneous discoveries. In the year 1999 the Japanese team Oasa et al. discovered objects in Chamaeleon I that were spectroscopically confirmed years later in 2004 by the US team Luhman et al.