Rogue planet

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.^[5][6]


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.^[7] A possible example is Cha 110913−773444, which may either have been ejected and become a rogue planet or formed on its own to become a sub-brown dwarf.^[8]

Name[edit]

The two first discovery papers use the names isolated planetary-mass objects (iPMO)^[9] and free-floating planets (FFP).^[10] Most astronomical papers use one of these terms.^[11][12][13] The term rogue planet is more often used for microlensing studies, which also often uses the term FFP.^[14][15] 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,^[16] starless planet,^[17] wandering planet^[18] and free-floating planet^[19] in different press releases.

Discovery[edit]

Isolated planetary-mass objects (iPMO) were first discovered in 2000 by the UK team Lucas & Roche with UKIRT in the Orion Nebula.^[10] In the same year the Spanish team Zapatero Osorio et al. discovered iPMOs with Keck spectroscopy in the σ Orionis cluster.^[9] The spectroscopy of the objects in the Orion Nebula was published in 2001.^[20] Both European teams are now recognized for their quasi-simultaneous discoveries.^[21] In the year 1999 the Japanese team Oasa et al. discovered objects in Chamaeleon I^[22] that were spectroscopically confirmed years later in 2004 by the US team Luhman et al.^[23]


In October 2023, based on observations of the Orion Nebula with the James Webb Space Telescope, astronomers reported the discovery of pairs of rogue planets, similar in mass to the planet Jupiter, called Jupiter Mass Binary Objects (JuMBOs).^[24][25]

Fate[edit]

Most isolated planetary-mass objects will float in interstellar space forever.


Some iPMOs will have a close encounter with a planetary system. This rare encounter can have three outcomes: The iPMO will remain unbound, it could be weakly bound to the star, or it could "kick out" the exoplanet, replacing it. Simulations have shown that the vast majority of these encounters result in a capture event with the iPMO being weakly bound with a low gravitational binding energy and an elongated highly eccentric orbit. These orbits are not stable and 90% of these objects gain energy due to planet-planet encounters and are ejected back into interstellar space. Only 1% of all stars will experience this temporary capture.^[63]