Rogue planet explained

A rogue planet, also termed a free-floating planet (FFP) or an isolated planetary-mass object (iPMO), is an interstellar object of planetary mass which is not gravitationally bound to any star or brown dwarf.^{[1] [2] [3] [4]}

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]

Terminology

The two first discovery papers use the names isolated planetary-mass objects (iPMO) and free-floating planets (FFP). Most astronomical papers use one 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,^[9] wandering planet and free-floating planet^[10] 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.^[11] 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 1999 the Japanese team Oasa et al. discovered objects in Chamaeleon I^[12] that were spectroscopically confirmed years later in 2004 by the US team Luhman et al.^[13]

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).^[14]

Observation

There are two techniques to discover free-floating planets: direct imaging and microlensing.

Microlensing

Astrophysicist Takahiro Sumi of Osaka University in Japan and colleagues, who form the Microlensing Observations in Astrophysics and the Optical Gravitational Lensing Experiment collaborations, published their study of microlensing in 2011. They observed 50 million stars in the Milky Way by using the 1.8m (05.9feet) MOA-II telescope at New Zealand's Mount John Observatory and the 1.3m (04.3feet) University of Warsaw telescope at Chile's Las Campanas Observatory. They found 474 incidents of microlensing, ten of which were brief enough to be planets of around Jupiter's size with no associated star in the immediate vicinity. The researchers estimated from their observations that there are nearly two Jupiter-mass rogue planets for every star in the Milky Way.^{[15] [16] [17]} One study suggested a much larger number, up to 100,000 times more rogue planets than stars in the Milky Way, though this study encompassed hypothetical objects much smaller than Jupiter.^[18] A 2017 study by Przemek Mróz of Warsaw University Observatory and colleagues, with six times larger statistics than the 2011 study, indicates an upper limit on Jupiter-mass free-floating or wide-orbit planets of 0.25 planets per main-sequence star in the Milky Way.^[19]

In September 2020, astronomers using microlensing techniques reported the detection, for the first time, of an Earth-mass rogue planet (named OGLE-2016-BLG-1928) unbound to any star and free floating in the Milky Way galaxy.^{[20] [21] [22]}

In December 2013, a candidate exomoon of a rogue planet (MOA-2011-BLG-262) was announced.^[23]

Direct imaging

Microlensing planets can only be studied by the microlensing event, which makes the characterization of the planet difficult. Astronomers therefore turn to isolated planetary-mass objects (iPMO) that were found via the direct imaging method. To determine a mass of a brown dwarf or iPMO one needs for example the luminosity and the age of an object.^[24] Determining the age of a low-mass object has proven to be difficult. It is no surprise that the vast majority of iPMOs are found inside young nearby star-forming regions of which astronomers know their age. These objects are younger than 200 Myrs, are massive (>5) and belong to the L- and T-dwarfs. There is however a small growing sample of cold and old Y-dwarfs that have estimated masses of 8-20 .^[25] Nearby rogue planet candidates of spectral type Y include WISE 0855−0714 at a distance of .^[26] If this sample of Y-dwarfs can be characterized with more accurate measurements or if a way to better characterize their ages can be found, the number of old and cold iPMOs will likely increase significantly.

The first iPMOs were discovered in the early 2000s via direct imaging inside young star-forming regions. These iPMOs found via direct imaging formed probably like stars (sometimes called sub-brown dwarf). There might be iPMOs that form like a planet, which are then ejected. These objects will however be kinematically different from their natal star-forming region, should not be surrounded by a circumstellar disk and have high metallicity.^[27] None of the iPMOs found inside young star-forming regions show a high velocity compared to their star-forming region. For old iPMOs the cold WISE J0830+2837 shows a V_tan of about 100 km/s, which is high, but still consistent with formation in our galaxy. For WISE 1534–1043^[28] one alternative scenario explains this object as an ejected exoplanet due to its high V_tan of about 200 km/s, but its color suggests it is an old metal-poor brown dwarf. Most astronomers studying massive iPMOs believe that they represent the low-mass end of the star-formation process.

Astronomers have used the Herschel Space Observatory and the Very Large Telescope to observe a very young free-floating planetary-mass object, OTS 44, and demonstrate that the processes characterizing the canonical star-like mode of formation apply to isolated objects down to a few Jupiter masses. Herschel far-infrared observations have shown that OTS 44 is surrounded by a disk of at least 10 Earth masses and thus could eventually form a mini planetary system.^[29] Spectroscopic observations of OTS 44 with the SINFONI spectrograph at the Very Large Telescope have revealed that the disk is actively accreting matter, similar to the disks of young stars.

Jupiter-mass binary objects

In the Orion Nebula a population of 40 wide binaries and 2 triple systems were discovered. This was surprising for two reasons: The trend of binaries of brown dwarfs predicted a decrease of distance between low mass objects with decreasing mass. It was also predicted that the binary fraction decreases with mass. These binaries were named Jupiter-mass binary objects (JuMBOs). They make up at least 9% of the iPMOs and have a separation smaller than 340 AU. It is unclear how these JuMBOs formed, but an extensive study argued that they formed in situ, like stars.^[30] If they formed like stars, then there must be an unknown "extra ingredient" to allow them to form. If they formed like planets and were later ejected, then it has to be explained why these binaries did not break apart during the ejection process.^[31] Future proper motion measurements with JWST might resolve if these objects formed as ejected planets or as stars. Ejected planets should show a high proper motion, while a formation like stars should show proper motions similar to the Trapezium Cluster stars.

Other suspected JuMBOs are known outside the Orion Nebula, such as 2MASS J11193254–1137466 AB, 2MASS J1553022+153236AB,^{[32] [33]} WISE 1828+2650, WISE J0336−0143 (could also be a brown dwarf and a planetary-mass object (BD+PMO) binary) and 2MASS J0013−1143.

Total number of known iPMOs

There are likely hundreds of known candidate iPMOs, over a hundred^[34] objects with spectra and a small but growing number of candidates discovered via microlensing. Some large surveys include:

As of December 2021, the largest-ever group of rogue planets was discovered, numbering at least 70 and up to 170 depending on the assumed age. They are found in the OB association between Upper Scorpius and Ophiuchus with masses between 4 and 13 and age around 3 to 10 million years, and were most likely formed by either gravitational collapse of gas clouds, or formation in a protoplanetary disk followed by ejection due to dynamical instabilities.^{[35] [36] [37] [38]} Follow-up observations with spectroscopy from the Subaru Telescope and Gran Telescopio Canarias showed that the contamination of this sample is quite low (≤6%). The 16 young objects had a mass between 3 and 14, confirming that they are indeed planetary-mass objects.

In October 2023 an even larger group of 540 planetary-mass object candidates was discovered in the Trapezium Cluster and inner Orion Nebula with JWST. The objects have a mass between 13 and 0.6 . A surprising number of these objects formed wide binaries, which was not predicted.

Formation

There are in general two scenarios that can lead to the formation of an isolated planetary-mass object (iPMO). It can form like a planet around a star and is then ejected, or it forms like a low-mass star or brown dwarf in isolation. This can influence its composition and motion.

Formation like a star

See main article: Sub-brown dwarf. Objects with a mass of at least one Jupiter mass were thought to be able to form via collapse and fragmentation of molecular clouds from models in 2001.^[39] Pre-JWST observations have shown that objects below 3-5 are unlikely to form on their own. Observations in 2023 in the Trapezium Cluster with JWST have shown that objects as massive as 0.6 might form on their own, not requiring a steep cut-off mass. A particular type of globule, called globulettes, are thought to be birthplaces for brown dwarfs and planetary-mass objects. Globulettes are found in the Rosette Nebula and IC 1805.^[40] Sometimes young iPMOs are still surrounded by a disk that could form exomoons. Due to the tight orbit of this type of exomoon around their host planet, they have a high chance of 10-15% to be transiting.^[41]

Disks

Some very young star-forming regions, typically younger than 5 million years, sometimes contain isolated planetary-mass objects with infrared excess and signs of accretion. Most well known is the iPMO OTS 44 discovered to have a disk and being located in Chamaeleon I. Charmaeleon I and II have other candidate iPMOs with disks.^{[42] [43]} Other star-forming regions with iPMOs with disks or accretion are Lupus I, Rho Ophiuchi Cloud Complex,^[44] Sigma Orionis cluster,^[45] Orion Nebula, Taurus,^[46] NGC 1333^[47] and IC 348.^[48] A large survey of disks around brown dwarfs and iPMOs with ALMA found that these disks are not massive enough to form earth-mass planets. There is still the possibility that the disks already have formed planets. Studies of red dwarfs have shown that some have gas-rich disks at an relative old age. These disks were dubbed Peter Pan Disks and this trend could continue into the planetary-mass regime. One Peter Pan disk is the 45 Myr old brown dwarf 2MASS J02265658-5327032 with a mass of about 13.7, which is close to the planetary-mass regime.^[49]

Formation like a planet

Ejected planets are predicted to be mostly low-mass (<30 Figure 1 Ma et al.)^[50] and their mean mass depends on the mass of their host star. Simulations by Ma et al. did show that 17.5% of 1 stars eject a total of 16.8 per star with a typical (median) mass of 0.8 for an individual free-floating planet (FFP). For lower mass red dwarfs with a mass of 0.3 12% of stars eject a total of 5.1 per star with a typical mass of 0.3 for an individual FFP.

Hong et al.^[51] predicted that exomoons can be scattered by planet-planet interactions and become ejected exomoons.

Higher mass (0.3-1) ejected FFP are predicted to be possible, but they are also predicted to be rare.

Fate

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.^[52]

Warmth

Interstellar planets generate little heat and are not heated by a star.^[53] However, in 1998, David J. Stevenson theorized that some planet-sized objects adrift in interstellar space might sustain a thick atmosphere that would not freeze out. He proposed that these atmospheres would be preserved by the pressure-induced far-infrared radiation opacity of a thick hydrogen-containing atmosphere.^[54]

During planetary-system formation, several small protoplanetary bodies may be ejected from the system.^[55] An ejected body would receive less of the stellar-generated ultraviolet light that can strip away the lighter elements of its atmosphere. Even an Earth-sized body would have enough gravity to prevent the escape of the hydrogen and helium in its atmosphere. In an Earth-sized object the geothermal energy from residual core radioisotope decay could maintain a surface temperature above the melting point of water, allowing liquid-water oceans to exist. These planets are likely to remain geologically active for long periods. If they have geodynamo-created protective magnetospheres and sea floor volcanism, hydrothermal vents could provide energy for life. These bodies would be difficult to detect because of their weak thermal microwave radiation emissions, although reflected solar radiation and far-infrared thermal emissions may be detectable from an object that is less than 1,000 astronomical units from Earth.^[56] Around five percent of Earth-sized ejected planets with Moon-sized natural satellites would retain their satellites after ejection. A large satellite would be a source of significant geological tidal heating.^[57]

List

The table below lists rogue planets, confirmed or suspected, that have been discovered. It is yet unknown whether these planets were ejected from orbiting a star or else formed on their own as sub-brown dwarfs. Whether exceptionally low-mass rogue planets (such as OGLE-2012-BLG-1323 and KMT-2019-BLG-2073) are even capable of being formed on their own is currently unknown.

Discovered via direct imaging

These objects were discovered with the direct imaging method. Many were discovered in young star-clusters or stellar associations and a few old are known (such as WISE 0855−0714). List is sorted after discovery year.

Exoplanet	Mass	Age(Myr)	data-sort-type="number"	Distance(ly)	Spectral type	Status	Stellar assoc. membership	Discovery
		0.5–3	554	M9.5	Likely a low-mass brown dwarf^[58]	Chamaeleon I	1998
		1–5	data-sort-value="1150"	1,150		Age and mass uncertain; may be a foreground brown dwarf	σ Orionis cluster	2000^[59]
		1	1,344	L4–L5	Candidate, 15 candidates in total from this work	Orion nebula	2001^[60]
		3	1150	T6	interloper?	σ Orionis cluster	2002
		2~	529	data-sort-value="M9.5"	>M9.5	Candidate	Chamaeleon I	2004^[61]
		200~	20-22	T2.5	Candidate	Carina-Near moving group	2006^[62] ^[63]
		1000 – 5000	13	T9	Mass uncertain	none	2010
M10-4450		1	325	T	Candidate	rho Ophiuchi cloud	2010^[64]
WISE 1828+2650			47	data-sort-value="Y2"	>Y2	candidate, could be binary	none	2011
		110–130	117–143	T7	Candidate	AB Doradus moving group	2012^[65]
SONYC-NGC1333-36		1	978	L3	candidate, NGC 1333 has two other objects with masses below 15	NGC 1333	2012^[66]
SSTc2d J183037.2+011837		3	848–1354	T?	Candidate, also called ID 4	Serpens Core cluster^[67] (in the Serpens Cloud)	2012^[68]
	^[69] ^[70]	21–27	72.32	L7	Confirmed; also known as 2MASS J21140802-2251358	Beta Pictoris Moving group	2013^[71] ^[72]
2MASS J2208+2921		21–27	115	L3γ	Candidate; radial velocity needed	Beta Pictoris Moving group	2014^[73]
WISE J1741-4642		23–130		L7pec	Candidate	Beta Pictoris or AB Doradus moving group	2014^[74]
WISE 0855−0714		data-sort-value="1000"	>1,000	7.1	Y4	Age uncertain, but old due to solar vicinity object;^[75] candidate even for an old age of 12 Gyrs (age of the universe is 13.8 Gyrs)	none	2014^[76]
2MASS J12074836–3900043	^[77]	7–13	200	L1	Candidate; distance needed	TW Hydrae association^[78]	2014^[79]
SIMP J2154–1055		30–50	63	L4β	Age questioned^[80]	Argus association	2014^[81]
SDSS J111010.01+011613.1		110–130	63	T5.5	Confirmed	AB Doradus moving group	2015^[82]
2MASS J11193254–1137466 AB		7–13	data-sort-value="90"	~90	L7	Binary candidate, one of the components has a candidate exomoon or variable atmosphere	TW Hydrae Association	2016^[83]
WISEA 1147		7–13	data-sort-value="100"	~100	L7	Candidate	TW Hydrae Association	2016^[84]
USco J155150.2-213457		6.907-10	104	L6	Candidate, low gravity	Upper Scorpius association	2016^[85]
		0.5–1	1,344	M9.5	Candidate with a photoevaporating disk	Orion Nebula	2016^[86]
Cha J11110675-7636030		1–3	520–550	M9–L2	Candidate, but could be surrounded by a disk, which could make it a sub-brown dwarf; other candidates from this work	Chamaeleon I	2017^[87]
PSO J077.1+24		1–2	470	L2	Candidate, work also published another candidate in Taurus	Taurus Molecular Cloud	2017^[88]
Calar 25		120	435		Confirmed	Pleiades	2018^[89]
2MASS J1324+6358		data-sort-value="150"	~150	data-sort-value="33"	~33	T2	unusually red and unlikely binary; robust candidate	AB Doradus moving group	2007, 2018^[90]
J1407b			data-sort-value="451"	<451		Candidate ALMA detection; although the object's brightness and proximity is consistent with it being the same object that eclipsed the star V1400 Centauri in 2007, follow-up observations by ALMA are needed to confirm whether it is moving, let alone in the right direction.	none	2012, 2020^[91]
WISE J0830+2837		data-sort-value="1000"	>1,000	31.3-42.7	data-sort-value="Y1"	>Y1	Age uncertain, but old because of high velocity (high Vtan is indicative of an old stellar population), Candidate if younger than 10 Gyrs	none	2020^[92]
2MASS J0718-6415		16-28	30.5	T5	Candidate member of the BPMG. Extremely short rotation period of 1.08 hours, comparable to the brown dwarf 2MASS J0348-6022.^[93] ^[94]	Beta Pictoris moving group	2021
DANCe J16081299-2304316		3–10	104	L6	One of at least 70 candidates published in this work, spectrum similar to HR 8799c	Upper Scorpius association	2021^[95]
WISE J2255−3118		24	data-sort-value="45"	~45	T8	very red, candidate	Beta Pictoris moving group	2011,2021^[96]
WISE J024124.73-365328.0		45	data-sort-value="61"	~61	T7	candidate	Argus association	2012, 2021
2MASS J0013−1143		45	data-sort-value="82"	~82	T4	binary candidate or composite atmosphere, candidate	Argus association	2017, 2021
SDSS J020742.48+000056.2		45	data-sort-value="112"	~112	T4.5	candidate	Argus association	2002, 2021
2MASSI J0453264-175154		24	data-sort-value="99"	~99	L2.5β	low gravity, candidate	Beta Pictoris moving group	2003, 2023
CWISE J0506+0738		22	104	L8γ–T0γ	Candidate member of the BPMG. Extreme red near-infrared colors.^[97]	Beta Pictoris moving group	2023

Discovered via microlensing

These objects were discovered via microlensing. Rogue planets discovered via microlensing can only be studied by the lensing event and are often also consistent with exoplanets in a wide orbit around an unseen star.

Exoplanet	Mass	Mass	data-sort-type="number"	Distance (ly)	Status	Discovery
MOA-2011-BLG-262L	115 or 3.6	36,550 or 1,144	1,800 or 23,000	potentially a red dwarf	2013^[98]
OGLE-2012-BLG-1323	0.0072–0.072	2.3–23		candidate; distance needed	2017^[99] ^[100] ^[101] ^[102]
OGLE-2017-BLG-0560	1.9–20	604–3,256		candidate; distance needed	2017
MOA-2015-BLG-337L	9.85	3,130	23,156	may be a binary brown dwarf instead	2018^[103] ^[104]
KMT-2019-BLG-2073	0.19	59		candidate; distance needed	2020^[105]
OGLE-2016-BLG-1928	0.001-0.006	0.3–2	30,000–180,000	candidate	2020
OGLE-2019-BLG-0551	0.0242-0.3	7.69–95		Poorly characterized	2020
VVV-2012-BLG-0472L	data-sort-value="31"	10.5	3,337	3,200		2022^[106]
MOA-9y-770L	0.07		22,700		2023^[107]
MOA-9y-5919L	0.0012 or 0.0024	or	14,700 or 19,300		2023

See also

• • Interstellar object – an astronomical object in interstellar space that is not gravitationally bound to a star
• ʻOumuamua – an interstellar object that passed through the Solar System in 2017
• Rogue black hole – a gravitationally unbound black hole
• Rogue extragalactic planets – rogue planets outside the Milky Way galaxy
• Tidally detached exomoon – rogue planets that were originally moons

In fiction

• Remina (2004–2005) – horror manga by Junji Ito
• Melancholia (2011) – science fiction film by Lars von Trier
• Dark Eden (2012) – a social science fiction novel by Chris Beckett
• The Wandering Earth (2019) – a science fiction film directed by Frant Gwo
• Gemini Home Entertainment (2019–present) – horror anthology web series by Remy Abode
• Carol & the End of the World (2023) - an animated adult comedy miniseries by Dan Guterman

Bibliography

• "Possibility of Life Sustaining Planets in Interstellar Space" Article by Stevenson similar to the Nature article but with more information.

External links

• Definition of a "Planet" (Resolution B5 – IAU)
• Strange New Worlds Could Make Miniature Solar Systems Robert Roy Britt (SPACE.com) 5 June 2006 11:35 am ET
• The IAU draft definition of "planet" and "plutons" press release (International Astronomical Union) 2006

Notes and References

1. Web site: Shostak . Seth . 24 February 2005 . Orphan Planets: It's a Hard Knock Life . 13 November 2020 . Space.com.
2. Web site: Lloyd . Robin . 18 April 2001 . Free-Floating Planets – British Team Restakes Dubious Claim . dead . https://web.archive.org/web/20081013054054/http://www.space.com/scienceastronomy/astronomy/free_floaters_010403-1.html . 13 October 2008 . Space.com.
3. Web site: 18 April 2001 . Orphan 'planet' findings challenged by new model . dead . https://web.archive.org/web/20090322091340/http://astrobiology.arc.nasa.gov/news/expandnews.cfm?id=783 . 22 March 2009 . NASA Astrobiology.
4. Kirkpatrick . J. Davy . Gelino . Christopher R. . Faherty . Jacqueline K. . Meisner . Aaron M. . Caselden . Dan . Schneider . Adam C. . Marocco . Federico . Cayago . Alfred J. . Smart . R. L. . Eisenhardt . Peter R. . Kuchner . Marc J. . Wright . Edward L. . Cushing . Michael C. . Allers . Katelyn N. . Bardalez Gagliuffi . Daniella C. . 2021-03-01 . The Field Substellar Mass Function Based on the Full-sky 20 pc Census of 525 L, T, and Y Dwarfs . The Astrophysical Journal Supplement Series . 253 . 1 . 7 . 10.3847/1538-4365/abd107 . 2011.11616 . 2021ApJS..253....7K . 0067-0049 . free .
5. [Neil deGrasse Tyson]
6. "The research team found that the mission will provide a rogue planet count that is at least 10 times more precise than current estimates, which range from tens of billions to trillions in our galaxy." https://scitechdaily.com/our-solar-system-may-be-unusual-rogue-planets-unveiled-with-nasas-roman-space-telescope/
7. http://www.dtm.ciw.edu/boss/definition.html Working Group on Extrasolar Planets – Definition of a "Planet"
8. http://edition.cnn.com/2000/TECH/space/10/06/space.planets.reut/index.html "Rogue planet find makes astronomers ponder theory"
9. Web site: 2021-12-23 . Billions of Starless Planets Haunt Dark Cloud Cradles . 2023-09-09 . NAOJ: National Astronomical Observatory of Japan . en.
10. Web site: Largest Collection of Free-Floating Planets Found in the Milky Way - KPNO . 2023-09-08 . kpno.noirlab.edu.
11. Lucas . P. W. . Roche . P. F. . 2000-06-01 . A population of very young brown dwarfs and free-floating planets in Orion . Monthly Notices of the Royal Astronomical Society . 314 . 4 . 858–864 . 10.1046/j.1365-8711.2000.03515.x . free . astro-ph/0003061 . 2000MNRAS.314..858L . 119002349 . 0035-8711.
12. Oasa . Yumiko . Tamura . Motohide . Sugitani . Koji . 1999-11-01 . A Deep Near-Infrared Survey of the Chamaeleon I Dark Cloud Core . The Astrophysical Journal . 526 . 1 . 336–343 . 10.1086/307964 . 1999ApJ...526..336O . 120597899 . 0004-637X. free .
13. Luhman . K. L. . Peterson . Dawn E. . Megeath . S. T. . 2004-12-01 . Spectroscopic Confirmation of the Least Massive Known Brown Dwarf in Chamaeleon . The Astrophysical Journal . 617 . 1 . 565–568 . 10.1086/425228 . astro-ph/0411445 . 2004ApJ...617..565L . 18157277 . 0004-637X.
14. News: O’Callaghan . Jonathan. The Orion Nebula Is Full of Impossible Enigmas That Come in Pairs - In new, high-resolution imagery of the star-forming region, scientists spotted worlds that defied explanation, naming them Jupiter Mass Binary Objects. . 2 October 2023 . . live . https://archive.today/20231002114507/https://www.nytimes.com/2023/10/02/science/orion-nebula-webb-planets.html . 2 October 2023 . 2 October 2023 .
15. http://news.sciencemag.org/sciencenow/2011/05/homeless-planets-may-be-common.html?ref=hp Homeless' Planets May Be Common in Our Galaxy
16. http://www.physorg.com/news/2011-05-class-planets.html Planets that have no stars: New class of planets discovered
17. T. . Sumi . 1105.3544 . Unbound or Distant Planetary Mass Population Detected by Gravitational Microlensing . 2011 . etal . 10.1038/nature10092 . 21593867 . 473 . 7347 . Nature . 349–352 . 2011Natur.473..349S . 4422627.
18. Web site: Researchers say galaxy may swarm with 'nomad planets' . 29 February 2012 . Stanford University. 2012-02-23.
19. P. Mroz . 1707.07634 . No large population of unbound or wide-orbit Jupiter-mass planets . 2017 . etal . 10.1038/nature23276 . 28738410 . 548 . 7666 . Nature . 183–186 . 2017Natur.548..183M. 4459776.
20. Mróz . Przemek . Poleski . Radosław . Gould . Andrew . Udalski . Andrzej . Sumi . Takahiro . Szymański . Michał K. . Soszyński . Igor . Pietrukowicz . Paweł . Kozłowski . Szymon . Skowron . Jan . Ulaczyk . Krzysztof . Albrow . Michael D. . Chung . Sun-Ju . Han . Cheongho . Hwang . Kyu-Ha . 1 . 2020 . A Terrestrial-mass Rogue Planet Candidate Detected in the Shortest-timescale Microlensing Event . The Astrophysical Journal Letters . 903 . 1 . L11 . 2009.12377 . 2020ApJ...903L..11M . 10.3847/2041-8213/abbfad . free . free . Jung . Youn Kil . Kim . Hyoun-Woo . Ryu . Yoon-Hyun . Shin . In-Gu . Shvartzvald . Yossi . Yee . Jennifer C. . Zang . Weicheng . Cha . Sang-Mok . Kim . Dong-Jin . Kim . Seung-Lee . Lee . Chung-Uk . Lee . Dong-Joo . Lee . Yongseok . Park . Byeong-Gon . Pogge . Richard W..
21. News: Gough . Evan . 1 October 2020 . A Rogue Earth-Mass Planet Has Been Discovered Freely Floating in the Milky Way Without a Star . . 2 October 2020.
22. News: Redd . Nola Taylor . Rogue Rocky Planet Found Adrift in the Milky Way – The diminutive world and others like it could help astronomers probe the mysteries of planet formation . 19 October 2020 . . 19 October 2020.
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