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For doomsday speculation concerning Planet Nine, se Nibiru cataclysm#Planet Nine.

Skabelon:Use dmy dates Skabelon:Good article Skabelon:Infobox planet

Planet Nine is a hypothetical planet in the outer region of the Solar System. Its gravitational influence could explain a statistical anomaly in the distribution of orbits of a group of distant trans-Neptunian objects (TNOs) found mostly beyond the Kuiper belt in the scattered disc region.[1][2][3] This undiscovered super-Earth-sized planet would have an estimated mass of ten Earths, a diameter two to four times that of Earth, and an elongated orbit lasting approximately 15,000 years.[4][5] To date, efforts to detect Planet Nine have failed.[6][7] Speculation that the clustering of the orbits of the most distant objects was due to a ninth planet began in 2014 when astronomers Chad Trujillo and Scott S. Sheppard noted the similarities in the orbits of Sedna and Skabelon:Mpl and several other objects.[2] In early 2016, Konstantin Batygin and Michael E. Brown described how the similar orbits of six TNOs could be explained by Planet Nine and proposed a possible orbit for the planet.[1] This hypothesis could also explain TNOs with orbits perpendicular to the inner planets[1] and others with extreme inclinations,[8] as well as the tilt of the Sun's axis.[9]

Batygin and Brown suggest that Planet Nine is the core of a primordial giant planet that was ejected from its original orbit by Jupiter during the genesis of the Solar System.[10][11] Others have proposed that the planet was captured from another star,[12] is a captured rogue planet,[13] or that it formed on a distant orbit and was scattered onto an eccentric orbit by a passing star.[1][14][15]

The extreme trans-Neptunian object orbits
6 original and 8 TNO object orbits with current positions near their perihelion in purple, with hypothetical Planet Nine orbit in green
Closer up view of 13 TNO current positions

Extreme trans-Neptunian objects with perihelion greater than 30 AU and a semi-major axis greater than 250 AU[16][ikke i angivne kilde]
Object Orbit Orbital plane Body
Barycentric[A]
Orbital
period
(years) 		Barycentric
Semimajor
axis
(AU) 		Perihelion
(AU) 		Barycentric
Aphelion
(AU) 		Current
distance
from
Sun
(AU) 		Eccent. Argum.
peri
ω (°) 		inclin.
i (°) 		Longitude of Hv Current
mag. 		Diameter
(km)
Ascending
node
☊ or Ω (°) 		Perihelion
ϖ=ω+Ω (°)
Sedna 11,400 507 76.04 936 85.5 0.85 311.5 11.9 144.5 96.0 1.5 20.9 1,000
Skabelon:Mpl- 5,900 327 47.32 607 47.7 0.85 327.1 25.6 66.0 33.1 6.5 23.3 200
Skabelon:Mpl- 11,300 503 35.57 970 37.3 0.93 285.7 18.6 112.9 38.6 6.2 22.0 200
Skabelon:Mpl 6,600 351 48.76 654 71.2 0.87 347.8 21.5 130.6 118.4 6.5 25.1 200
Skabelon:Mpl 4,300 266 80.27 441 83.5 0.69 292.8 24.1 90.8 23.6 4.0 23.3 600
Skabelon:Mpl 6,900 364 36.10 690 36.8 0.90 311.8 29.6 67.6 19.4 8.7 24.4 70
Skabelon:Mpl 5,050 295 43.60 546 57.0 0.86 40.2 17.3 217.8 258.0 (*) 6.7 24.4 200
Skabelon:Mpl 66,000 1,600 36.31 3,200 61.5 0.98 134.4 20.6 336.8 111.2 6.1 24.0 200
Skabelon:Mpl 5,160 299 47.57 549 56.3 0.84 341.4 18.0 34.8 16.2 6.6 24.2 200
Skabelon:Mpl 19,700 730 49.91 1,410 60.3 0.93 32.4 4.2 29.5 61.9 6.7 24.5 250
Skabelon:Mpl 5,510 310 38.45 580 41.7 0.89 129.2 8.8 46.1 175.3 (*) 8.5 24.9 80
Skabelon:Mpl 17,730 680 40.51 1,320 40.8 0.95 32.0 14.0 219.1 251.1 (*) 8.1 24.3 100
Skabelon:Mpl 8,920 430 45.48 815 61.4 0.89 65.4 12.2 8.6 74.0 6.2 24.2 250
uo5m93[19] 4,760 283 39.48 526 41.7 0.86 43.3 6.8 165.9 209.3 (*) 8.9 25.0 ?
Skabelon:Mpl "Caju"[20] 9,500 449 35.25 863 52.7 0.92 348.1 54.1 135.2 123.3 4.3 21.5 550[21]
Skabelon:Mpl 40,000 1,200 64.94 2,300 77.7 0.94 118.2 11.7 300.8 59.0 5.3 24.3 300
Ideal elements
under hypothesis		 — >250 >30 — — >0.5 — 10~30 — 2~120 — — —
Hypothesized
Planet Nine		 ~15,000 ~700 ~200 ~1,200 ~1,000? ~0.6 ~150 ~30 91±15 241±15 >22 ~40,000
  • (*) longitude of perihelion, ϖ, outside expected range;
  •        are the objects included in the original study by Trujillo and Sheppard (2014).[2]
  •        has been added in the 2016 study by Brown and Batygin.[1][22]
  • All other objects have been announced later.

The most extreme case is that of 2015 BP519, nicknamed Caju, which has both the highest inclination[23] and the farthest nodal distance; these properties make it a probable outlier within this population.[24]

Simulations: Observed clustering reproduced, inference on Planet Nine orbit and mass

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The clustering of the orbits of extreme trans-Neptunian objects and raising of their perihelia is reproduced in simulations that include Planet Nine. In simulations conducted by Batygin and Brown swarms of large semi-major axis scattered disk objects[B] that began with random orientations were sculpted into roughly collinear groups of spatially confined orbits by a massive distant planet in a highly eccentric orbit. These surviving objects, about 10% of the population with initial semi-major axes of 250–550 AU,[25] were in orbits that were oriented with their long axes anti-aligned with respect to the massive planet and were roughly co-planar with it. The objects were also found to be in resonance with the massive planet. The resonances included high-order resonances, for example 27:17, and were interconnected, yielding an orbital evolution that was fundamentally chaotic, causing their semi-major axes to vary unpredictably on million-year timescales.[1] The perihelia of these objects were also raised temporarily, producing Sedna-like orbits, before being returned to orbits more typical of typical trans-Neptunian objects after several hundred million years.[26] Some of the eTNOs also evolved into orbits perpendicular to the plane of the Solar System, which Batygin and Brown later discovered had also been observed.[1] Similar results also occur if simulations began with the objects initially interacting with multiple planets, like in various versions of the Nice model. Lawler et al. and Nesvorny et al. both found that objects scattered outward by the giant planets would be captured in a cloud centered on Planet Nine's semi-major axis with most objects at greater semi-major axis. A significant fraction of these objects had inclinations of greater than 60°, and for an initial 20 Earth mass planetesimal disk roughly 0.3–0.4 Earth masses remained in the Planet Nine cloud at the end of a 4 billion year simulation.[27][28]

Batygin and Brown found that the distribution of the orbits of known extreme trans-Neptunian objects is best reproduced in simulations using a Skabelon:Earth mass[C] planet in the following orbit:

This orbit results in strong anti-alignment beyond 250 AU, weak alignment between 150 AU and 250 AU, and little effect inside 150 AU. Anti-alignment occurs with variable success using a semi-major axis between 400 AU and 1500 AU and an eccentricity between 0.5 and 0.8. Anti-alignment weakens as Planet Nine's inclination is increased.[30] Simulations conducted by Becker et al. found a similar range for the stability of eTNOs, semi-major axes ranging from 500 to 1200 AU and eccentricities ranging from 0.3 to 0.6 with lower eccentricities being favored at smaller semi-major axes. They noted that while stability was favored with smaller eccentricities, anti-alignment was more likely at higher eccentricities near the borders of stability.[31] Lawler et al. found that the population captured was smaller in simulations with a planet in a circular orbit which also produced few high inclination objects.[27] Investigations by Cáceres et al. showed that a planet with a lower perihelion led to a narrower confinement of orbits of the eTNOs, with a perihelion of 90 AU or higher being consistent with the distribution of the classical Kuiper belt objects.[32]

Dynamics: Effect on other objects in the Solar System

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Planet Nine modifies the orbits of extreme trans-Neptunian objects via a combination of effects. On very long timescales exchanges of angular momentum with Planet Nine causes the perihelia of anti-aligned objects to rise until their precession reverses direction, maintaining their anti-alignment, and later fall, returning them to their original orbits. On shorter timescales mean-motion resonances with Planet Nine provides phase protection, which stabilizes their orbits by slightly altering the objects' semi-major axes, keeping their orbits synchronized with Planet Nine's and preventing close approaches. The inclination of Planet Nine's orbit weakens this protection, resulting in a chaotic variation of semi-major axes as objects hop between resonances. The orbital poles of the objects circle that of the Solar System's Laplace plane, which at large semi-major axes is warped toward the plane of Planet Nine's orbit, causing their poles to be clustered toward one side.[25]

Apsidal anti-alignment

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Secular evolution of eTNOs induced by Planet Nine for objects with semi-major axis of 250 AU.[33][25] Blue:anti-aligned, Red:aligned, Green:metastable, Orange:circulating. Crossing orbits above black line.[F]

The anti-alignment and the raising of the perihelia of extreme trans-Neptunian objects with semi-major axes greater than 250 AU is produced by the secular effects of Planet Nine. Secular effects act on timescales much longer than orbital periods so the perturbations two objects exert on each other are the average between all possible configurations. Effectively the interactions become like those between two wires of varying thickness, thicker where the objects spend more time, that are exerting torques on each other, causing exchanges of angular momentum but not energy. Thus secular effects can alter the eccentricities, inclinations and orientations of orbits but not the semi-major axes.[34][35]

Proposed resonances of distant trans-Neptunian objects[36]
Body Orbital period
Heliocentric
(years)		 Orbital period
Barycentric
(years)		 Semimaj.
(AU)		 Ratio
Skabelon:Mpl 1,830 151.8 9:1
Skabelon:Mpl 3,304 221.59±0.16 5:1
Skabelon:Mpl Lua-fejl i Modul:Gapnum på linje 16: Unable to convert "4,268" to a number.±179 4,300 265.8±3.3 4:1
Skabelon:Mpl Lua-fejl i Modul:Gapnum på linje 16: Unable to convert "5,845" to a number.±30 5,900 319.6±6.0 3:1
Skabelon:Mpl Lua-fejl i Modul:Gapnum på linje 16: Unable to convert "7,150" to a number.±827 6,600 350.7±4.7 5:2
90377 Sedna ≈ 11,400 506.84±0.51 3:2
Hypothetical planet ≈ 17,000 ≈ 665 1:1

Alignment due to the Kozai mechanism

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Trujillo and Sheppard (2014)

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Astronomers Chad Trujillo and Scott S. Sheppard argued in 2014 that a massive planet in a distant, circular orbit was responsible for the clustering of the arguments of perihelion of twelve extreme trans-Neptunian objects. Trujillo and Sheppard identified a clustering near zero degrees of the arguments of perihelion of the orbits of twelve trans-Neptunian objects (TNOs) with perihelia greater than 30 AU and semi-major axes greater than 150 AU.[1][2] After numerical simulations showed that after billions of years the varied rates of precession should leave their perihelia randomized they suggested that a massive planet in a circular orbit at a few hundred astronomical units was responsible for this clustering.[37] This massive planet would cause the arguments of perihelion of the eTNOs to librate about 0° or 180° via the Kozai mechanism so that their orbits crossed the plane of the planet's orbit near perihelion and aphelion, the closest and farthest points from the planet.[38][2] In numerical simulations including a 2–15 Earth mass body in a circular low-inclination orbit between 200 AU and 300 AU the arguments of perihelia of Sedna and Skabelon:Mpl librated around 0° for billions of years (although the lower perihelion objects did not) and underwent periods of libration with a Neptune mass object in a high inclination orbit at 1,500 AU.[2] An additional process such as a passing star would be required to account for the absence of objects with arguments of perihelion near 180°.[1][G]

These simulations showed the basic idea of how a single large planet can shepherd the smaller extreme trans-Neptunian objects into similar types of orbits. It was a basic proof of concept simulation that did not obtain a unique orbit for the planet as they state there are many possible orbital configurations the planet could have.[37] Thus they did not fully formulate a model that successfully incorporated all the clustering of the extreme objects with an orbit for the planet.[1] But they were the first to notice there was a clustering in the orbits of extremely distant objects and that the most likely reason was from an unknown massive distant planet. Their work is very similar to how Alexis Bouvard noticed Uranus' motion was peculiar and suggested that it was likely gravitational forces from an unknown 8th planet, which led to the discovery of Neptune.[41]

de la Fuente Marcos et al. (2014)

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Raúl and Carlos de la Fuente Marcos proposed a similar model but with two distant planets in resonance.[38][42] An analysis by Carlos and Raúl de la Fuente Marcos with Sverre J. Aarseth confirmed that the observed alignment of the arguments of perihelion could not be due to observational bias. They speculated that instead it was caused by an object with a mass between that of Mars and Saturn that orbited at some 200 AU from the Sun. Like Trujillo and Sheppard they theorized that the eTNOs are kept bunched together by a Kozai mechanism and compared their behavior to that of Comet 96P/Machholz under the influence of Jupiter.[43][44] However, they also struggled to explain the orbital alignment using a model with only one unknown planet. They therefore suggested that this planet is itself in resonance with a more-massive world about 250 AU from the Sun.[37][45] In their article, Brown and Batygin noted that alignment of arguments of perihelion near 0° or 180° via the Kozai mechanism requires a ratio of the semi-major axes nearly equal to one, indicating that multiple planets with orbits tuned to the data set would be required, making this explanation too unwieldy.[1]

Previous models with additional planets

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Se også Se også: Planets beyond Neptune#Orbits of distant objects og Detached object#Orbits.

Attempts to detect planets beyond Neptune by indirect means such as orbital perturbation date back beyond the discovery of Pluto. A few observations were directly related to the Planet Nine hypothesis:

  • George Forbes was the first to postulate the existence of trans-Neptunian planets in 1880, and his work is considered similar to more recent Planet Nine theories. In Forbes's model the planet had a semi-major axis of ∼300 AU (roughly three hundred times the distance from Earth to the Sun); locations were based on clustering of the aphelion distances of periodic comets.[46]
  • The discovery of Sedna with its peculiar orbit in 2004 led to the conclusion that something beyond the known eight planets had perturbed Sedna away from the Kuiper belt. That object could have been an unknown planet on a distant orbit, a random star that passed near the Solar System, or a member of the Sun's birth cluster.[47][48][49] The announcement in March 2014 of the discovery of a second sednoid, Skabelon:Mpl, which shared some orbital characteristics with Sedna and other extreme trans-Neptunian objects, further raised the possibility of an unseen super-Earth in a large orbit.[50][51]
  • In 2008 Tadashi Mukai and Patryk Sofia Lykawka suggested that a distant Mars- or Earth-sized minor planet currently in a highly eccentric orbit between 100 and 200 AU and orbital period of 1000 years with an inclination of 20° to 40° was responsible for the structure of the Kuiper belt. They proposed that the perturbations of this planet excited the eccentricities and inclinations of the trans-Neptunian objects, truncated the planetesimal disk at 48 AU, and detached the orbits of objects like Sedna from Neptune. During Neptune's migration this planet is posited to have been captured in an outer resonance of Neptune and to have evolved into a higher perihelion orbit due to the Kozai mechanism leaving the remaining trans-Neptunian objects on stable orbits.[52][53][54][55]
  • In 2012, after analysing the orbits of a group of trans-Neptunian objects with highly elongated orbits, Rodney Gomes of the National Observatory of Brazil proposed that their orbits were due to the existence of an as yet undetected planet. This Neptune-massed planet would be on a distant orbit that would be too far away to influence the motions of the inner planets, yet close enough to cause the perihelia of scattered disc objects with semi-major axes greater than 300 AU to oscillate, delivering them into planet-crossing orbits similar to those of Skabelon:Mpl and Skabelon:Mpl or detached orbits like that of Sedna. Alternatively the unusual orbits of these objects could be the result of a Mars-massed planet on an eccentric orbit that occasionally approached within 33 AU.[56][57] Gomes argued that a new planet was the more probable of the possible explanations but others felt that he could not show real evidence that suggested a new planet.[58] Later in 2015, Rodney Gomes, Jean Soares, and Ramon Brasser proposed that a distant planet was responsible for an excess of centaurs with large semi-major axes.[59][60]

Searches for Planet Nine

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Visibility and location

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Due to its extreme distance from the Sun, Planet Nine would reflect little sunlight, potentially evading telescope sightings.[4] It is expected to have an apparent magnitude fainter than 22, making it at least 600 times fainter than Pluto.[22][H] If Planet Nine exists and is close to its perihelion, astronomers could identify it based on existing images. For its aphelion, the largest telescopes would be required. However, if the planet is currently located in between, many observatories could spot Planet Nine.[65] Statistically, the planet is more likely to be closer to its aphelion at a distance greater than 500 AU.[22] This is because objects move more slowly when near their aphelion, in accordance with Kepler's second law.

Searches of existing data

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The search in databases of stellar objects performed by Batygin and Brown has already excluded much of the sky the predicted planet could be in, save the direction of its aphelion, or in the difficult to spot backgrounds where the orbit crosses the plane of the Milky Way, where most stars lie.[66] This search included the archival data from the Catalina Sky Survey to magnitude c. 19, Pan-STARRS to magnitude 21.5, and infrared data from WISE.[22][22][66]

David Gerdes who helped develop the camera used in the Dark Energy Survey claims that it is quite possible that one of the images taken for his galaxy map may actually contain a picture of Planet Nine, and if so, purpose-built software, which was used to identify objects such as Skabelon:Mpl, can help to find it.[67]

Michael Medford and Danny Goldstein, graduate students at the University of California, Berkeley, are also examining archived data using a technique that combines multiple images, taken at different times. Using a supercomputer they will offset the images to account for the calculated motion of Planet Nine, allowing many faint images of a faint moving object to be combined to produce a brighter image.[68]

A search combining multiple images collected by WISE and NEOWISE data has also been conducted without detecting Planet Nine. This search covered regions of the sky away from the galactic plane at the "W1" wavelength (the 3.4 μm wavelength used by WISE) and is estimated to be able to detect a 10 Earth mass object out to 800–900 AU.[69][6]

Ongoing searches

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Because the planet is predicted to be visible in the Northern Hemisphere, the primary search is expected to be carried out using the Subaru Telescope, which has both an aperture large enough to see faint objects and a wide field of view to shorten the search.[51] Two teams of astronomers—Batygin and Brown, as well as Trujillo and Sheppard—are undertaking this search together, and both teams cooperatively expect the search to take up to five years.[63][70] Brown and Batygin initially narrowed the search for Planet Nine down to roughly 2,000 square degrees of sky near Orion, a swath of space, that in Batygin's opinion, could be covered in about 20 nights by the Subaru Telescope.[71] Subsequent refinements by Batygin and Brown have reduced the search space to 600–800 square degrees of sky.[72]

A zone around the constellation Cetus, where Cassini data suggest Planet Nine may be located, is being searched Skabelon:As of by the Dark Energy Survey—a project in the Southern Hemisphere designed to probe the acceleration of the Universe.[73] DES observes about 105 nights per season, lasting from August to February.

Radiation

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Although a distant planet such as Planet Nine would reflect little light, it would still be radiating the heat from its formation as it cools due to its large mass. At its estimated temperature of 47 K (−226,2 °C), the peak of its emissions would be at infrared wavelengths.[74] This radiation signature could be detected by Earth-based submillimeter telescopes, such as ALMA,[75] and a search could be conducted by cosmic microwave background experiments operating at mm wavelengths.[76][77][78][I] Additionally, Jim Green of NASA is optimistic that it could be observed by the James Webb Space Telescope, the successor to the Hubble Space Telescope, that is expected to be launched in 2021.[80]

Citizen science

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Zooniverse Backyard Worlds: Planet 9 project

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The Zooniverse Backyard Worlds project, started in February 2017, is using archival data from the WISE spacecraft to search for Planet Nine. The project will additionally search for substellar objects like brown dwarfs in the neighborhood of the Solar System.[81][82] 32,000 animations of four images each, which constitute 3 per cent of the WISE data has been uploaded to the Backyard World's website. By looking for moving objects in the animations, citizen scientists could find Planet Nine.[83]

Zooniverse SkyMapper project

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In April 2017,[84] using data from the SkyMapper telescope at Siding Spring Observatory, citizen scientists on the Zooniverse platform reported four candidates for Planet Nine. These candidates will be followed up on by astronomers to determine their viability.[85] The project, which started on 28 March, completed their goals in less than three days with around five million classifications by more than 60,000 individuals.[85]

Searches for additional extreme trans-Neptunian objects

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Finding more objects would allow astronomers to make more accurate predictions about the orbit of the hypothesized planet.[86] The Large Synoptic Survey Telescope, when it is completed in 2023, will be able to map the entire sky in just a few nights, providing more data on distant Kuiper belt objects that could both bolster evidence for Planet Nine and help pinpoint its current location.[87]

Extreme trans-Neptunian objects discovered by Trujillo and Sheppard include:

  • Skabelon:Mpl, located on the opposite side of the sky (Longitude of perihelion aligned with Planet Nine) – but well within the proposed orbit of Planet Nine, where computer modeling suggests it would be safe from gravitational kicks.[88]
  • Skabelon:Mpl, falling right in line with the earlier six objects.[88]
  • Skabelon:Mpl, an object with an orbit so extreme that it reaches about 3,000 AU from the Sun in a massively-elongated ellipse – at this distance its orbit is influenced by the galactic tide and other stars.[89][90][91][92]

Other extreme trans-Neptunian objects discovered by the Outer Solar System Origins Survey include:[93]

  • Skabelon:Mpl, which has a lower inclination than many of the objects, and which was discussed by Michele Bannister at a March 2016 lecture hosted by the SETI Institute and later at an October 2016 AAS conference.[94][95]
  • Skabelon:Mpl, which has an orientation similar to 2013 FT28 but has a larger semi-major axis that may result in its orbit crossing Planet Nine's.
  • Skabelon:Mpl, which fits with the other anti-aligned objects.
  • Skabelon:Mpl, which is in neither the anti-aligned nor the aligned groups; instead, its orbit's orientation is at a right angle to that of the proposed Planet Nine. Its argument of perihelion is also outside the cluster of arguments of perihelion.

Batygin and Brown also predict a yet-to-be-discovered population of distant objects. These objects would have semi-major axes greater than 250 AU, but they would have lower eccentricities and orbits that would be aligned with that of Planet Nine. The larger perihelia of these objects would make them fainter and more difficult to detect than the anti-aligned objects.[1]

Skabelon:TNO-distance

Efforts toward indirect detection

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Cassini measurements of perturbations of Saturn

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An analysis of Cassini data on Saturn's orbital residuals was inconsistent with Planet Nine being located with a true anomaly of −130° to −110° or −65° to 85°. The analysis, using Batygin and Brown's orbital parameters for Planet Nine, suggests that the lack of perturbations to Saturn's orbit is best explained if Planet Nine is located at a true anomaly of 117.8+11−10 . At this location, Planet Nine would be approximately 630 AU from the Sun,[96] with right ascension close to 2h and declination close to −20°, in Cetus.[97] In contrast, if the putative planet is near aphelion it could be moving projected towards the area of the sky with boundaries: right ascension 3.0h to 5.5h and declination −1° to 6°.[98]

An improved mathematical analysis of Cassini data by astrophysicists Matthew Holman and Matthew Payne tightened the constraints on possible locations of Planet Nine. Holman and Payne developed a more efficient model that allowed them to explore a broader range of parameters than the previous analysis. The parameters identified using this technique to analyze the Cassini data was then intersected with Batygin and Brown's dynamical constraints on Planet Nine's orbit. Holman and Payne concluded that Planet Nine is most likely to be located within 20° of RA = 40°, Dec = −15°, in an area of the sky near the constellation Cetus.[99][73]

The Jet Propulsion Laboratory has stated that according to their mission managers and orbit determination experts, the Cassini spacecraft is not experiencing unexplained deviations in its orbit around Saturn. William Folkner, a planetary scientist at JPL stated, "An undiscovered planet outside the orbit of Neptune, 10 times the mass of Earth, would affect the orbit of Saturn, not Cassini ... This could produce a signature in the measurements of Cassini while in orbit about Saturn if the planet was close enough to the Sun. But we do not see any unexplained signature above the level of the measurement noise in Cassini data taken from 2004 to 2016."[100] Observations of Saturn's orbit neither prove nor disprove that Planet Nine exists. Rather, they suggest that Planet Nine could not be in certain sections of its proposed orbit because its gravity would cause a noticeable effect on Saturn's position, inconsistent with actual observations.

Analysis of Pluto's orbit

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An analysis of Pluto's orbit by Matthew J. Holman and Matthew J. Payne found perturbations much larger than predicted by Batygin and Brown's proposed orbit for Planet Nine. Holman and Payne suggested three possible explanations: systematic errors in the measurements of Pluto's orbit; an unmodeled mass in the Solar System, such as a small planet in the range of 60–100 AU (potentially explaining the Kuiper cliff); or a planet more massive or closer to the Sun instead of the planet predicted by Batygin and Brown.[101][102]

Optimal orbit if objects are in strong resonances

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An analysis by Sarah Millholland and Gregory Laughlin indicates that the commensurabilities (period ratios consistent with pairs of objects in resonance with each other) of the extreme TNOs are most likely to occur if Planet Nine has a semi-major axis of 654 AU. They used 11 then-known extreme TNOs with their semi-major axis over 200, and perihelion over 30 AU [1], with five bodies close to four simple ratios (5:1, 4:1, 3:1, 3:2) with a 654 AU distance: Skabelon:Mpl, Skabelon:Mpl (5:1), Skabelon:Mpl (5:1), Skabelon:Mpl (4:1), Skabelon:Mpl, Skabelon:Mpl, Skabelon:Mpl (3:1), Skabelon:Mpl, Skabelon:Mpl, Skabelon:Mpl, and (90377) Sedna (3:2). Beginning with this semi-major axis they determine that Planet Nine best maintains the anti-alignment of their orbits and a strong clustering of arguments of perihelion if it is near aphelion and has an eccentricity e ≈ 0.5, inclination i ≈ 30°, argument of perihelion ω ≈ 150°, and longitude of ascending node Ω ≈ 50° (the last differs from Brown and Batygin's value of 90°).[J] The favored location of Planet Nine is a right ascension of 30° to 50° and a declination of −20° to 20°. They also note that in their simulations the clustering of arguments of perihelion is almost always smaller than has been observed.[46]

A previous analysis by Carlos and Raul de la Fuente Marcos of commensurabilities among the known eTNOs using Monte Carlo techniques revealed a pattern similar to that of the Kuiper belt, where accidental commensurabilities occur due to objects in resonances with Neptune. They find that this pattern would be best explained if the eTNOs were in resonance with an additional planetary-sized object beyond Pluto and note that a number of these objects may be in 5:3 and 3:1 resonances if that object had semi-major axis of ≈700 AU.[104]

A later analysis by Elizabeth Bailey, Michael Brown and Konstantin Batygin found that if Planet Nine is in an eccentric and inclined orbit the capture of many of the eTNOs in higher order resonances and their chaotic transfer between resonances prevent the identification of Planet Nine's semi-major axis using current observations. They also determined that the odds of the first six objects observed being in N/1 or N/2 period ratios with Planet Nine are less than 5% if it is in an eccentric orbit.[105][106]

Ascending nodes of large semi-major axis objects

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In an article by Carlos and Raul de la Fuente Marcos evidence is shown for a possible bimodal distribution of the distances to the ascending nodes of the extreme TNOs. This correlation is unlikely to be the result of observational bias since it also appears in the nodal distribution of large semi-major axis centaurs and comets. If it is due to the extreme TNOs experiencing close approaches to Planet Nine, it is consistent with a planet with a semi-major axis of 300–400 AU.[107][108]

Orbits of nearly parabolic comets

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An analysis of the orbits of comets with nearly parabolic orbits identifies five new comets with hyperbolic orbits that approach the nominal orbit of Planet Nine described in Batygin and Brown's initial article. If these orbits are hyperbolic due to close encounters with Planet Nine the analysis estimates that Planet Nine is currently near aphelion with a right ascension of 83°–90° and a declination of 8°–10°.[109] Scott Sheppard, who is skeptical of this analysis, notes that many different forces influence the orbits of comets.[102]

Possible disrupted binary

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Similarities between the orbits of Skabelon:Mpl and Skabelon:Mpl have led to the suggestion that they were a binary object disrupted near aphelion during an encounter with a distant object. The visible spectra of (474640) 2004 VN112 and 2013 RF98 are also similar but very different from that of 90377 Sedna. The value of their spectral slopes suggests that the surfaces of (474640) 2004 VN112 and 2013 RF98 can have pure methane ices (like in the case of Pluto) and highly processed carbons, including some amorphous silicates.[110][111] The disruption of a binary would require a relatively close encounter with Planet Nine,[112] however, which becomes less likely at large distances from the Sun.

Commentary

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Batygin was cautious in interpreting the results of the simulation developed for his and Brown's research article, saying, "Until Planet Nine is caught on camera it does not count as being real. All we have now is an echo."[113] Brown put the odds for the existence of Planet Nine at about 90%.[4] Greg Laughlin, one of the few researchers who knew in advance about this article, gives an estimate of 68.3%.[3] Other skeptical scientists demand more data in terms of additional KBOs to be analysed or final evidence through photographic confirmation.[114][87][115] Brown, though conceding the skeptics' point, still thinks that there is enough data to mount a search for a new planet.[116]

Brown is supported by Jim Green, director of NASA's Planetary Science Division, who said that "the evidence is stronger now than it's been before".[80] But Green also cautioned about the possibility of other explanations for the observed motion of distant TNOs and, quoting Carl Sagan, he said that "extraordinary claims require extraordinary evidence."[4]

Tom Levenson concluded that, for now, Planet Nine seems the only satisfactory explanation for everything now known about the outer regions of the Solar System.[113] Alessandro Morbidelli, who reviewed the research article for The Astronomical Journal, concurred, saying, "I don't see any alternative explanation to that offered by Batygin and Brown."[3][4]

Malhotra remains agnostic about Planet Nine, but noted that she and her colleagues have found that the orbits of extremely distant KBOs seem tilted in a way that is difficult to otherwise explain. "The amount of warp we see is just crazy," she said. "To me, it's the most intriguing evidence for Planet Nine I've run across so far."[102]

See also

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Portal Portal:Solar System


Notes

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  1. ^ Given the orbital eccentricity of these objects, different epochs can generate quite different heliocentric unperturbed two-body best-fit solutions to the semi-major axis and orbital period. For objects at such high eccentricity, the Sun's barycenter is more stable than heliocentric values. Barycentric values better account for the changing position of Jupiter over Jupiter's 12 year orbit. As an example, Skabelon:Mpl has an epoch 2012 heliocentric period of ~13,500 years,[17] yet an epoch 2017 heliocentric period of ~10,400 years.[18] The barycentric solution is a much more stable ~11,300 years.
  2. ^ Objects began with perihelia of 30–50 AU and semi-major axes of 50–550 AU, confinement was observed in those with semi-major axis greater than 250 AU.
  3. ^ Batygin and Brown provide an order of magnitude estimate for the mass.
    • If M were equal to Skabelon:Earth mass, then the dynamical evolution would proceed at an exceptionally slow rate, and the lifetime of the Solar System would likely be insufficient for the required orbital sculpting to transpire.
    • If M were equal to Skabelon:Earth mass, then long-lived apsidally anti-aligned orbits would indeed occur, but removal of unstable orbits would happen on a much longer timescale than the current evolution of the Solar System. Hence, even though they would show preference for a particular apsidal direction, they would not exhibit true confinement like the data.
    • They also note that M greater than Skabelon:Earth mass would imply a longer semi-major axis.
    Hence they estimate that the mass of the object is likely in the range of Skabelon:Earth mass to Skabelon:Earth mass.
  4. ^ calculated values in parentheses.
  5. ^ The average of longitude of the ascending node for the 6 objects is about 102°. In a blog published later, Batygin and Brown constrained their estimate of the longitude of the ascending node to 94° .
  6. ^ Similar figures in articles by Beust[33] and Batygin and Morbidelli[25] are plots of the Hamiltonian, showing combinations of orbital eccentricities and orientations that have equal energy. If there are no close encounters with Planet Nine, which would change the energy of the orbit, the object's orbital elements remain on one of these curves as the orbits evolve.
  7. ^ Assuming that the orbital elements of these objects have not changed, Jílková et al. proposed an encounter with a passing star might have helped acquire these objects – dubbed sednitos (eTNOs with q > 30 and a > 150) by them. They also predicted that the sednitos region is populated by 930 planetesimals and the inner Oort Cloud acquired ∼440 planetesimals through the same encounter.[39][40]
  8. ^ The 8-meter Subaru Telescope has achieved a 27.7 magnitude photographic limit with a ten-hour exposure,[61] which is about 100 times dimmer than Planet Nine is expected to be. For comparison, the Hubble Space Telescope has detected objects as faint as 31st magnitude with an exposure of about 2 million seconds (555 hours) during Hubble Ultra Deep Field photography.[62] However, Hubble's field of view is very narrow, as is the Keck Observatory Large Binocular Telescope.[63] Brown hopes to make a request for use of the Hubble Space Telescope the day the planet is spotted.[64]
  9. ^ It is estimated that to find Planet Nine, telescopes that can resolve a 30 mJy point source are needed, and that can also resolve an annual parallax motion of ~5 arcminutes per year.[79]
  10. ^ A 3-D version of this orbit and those of several eTNOs is available.[103]

References

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  113. ^ a b Levenson, Thomas (25 januar 2016). "A New Planet or a Red Herring?". The Atlantic. Hentet 18 juli 2016. 'We plotted the real data on top of the model' Batyagin recalls, and they fell 'exactly where they were supposed to be.' That was, he said, the epiphany. 'It was a dramatic moment. This thing I thought could disprove it turned out to be the strongest evidence for Planet Nine.'
  114. ^ Grush, Loren (20 januar 2016). "Our solar system may have a ninth planet after all — but not all evidence is in (We still haven't seen it yet)". The Verge. Hentet 18 juli 2016. The statistics do sound promising, at first. The researchers say there's a 1 in 15,000 chance that the movements of these objects are coincidental and don't indicate a planetary presence at all. ... 'When we usually consider something as clinched and air tight, it usually has odds with a much lower probability of failure than what they have,' says Sara Seager, a planetary scientist at MIT. For a study to be a slam dunk, the odds of failure are usually 1 in 1,744,278. ... But researchers often publish before they get the slam-dunk odds, in order to avoid getting scooped by a competing team, Seager says. Most outside experts agree that the researchers' models are strong. And Neptune was originally detected in a similar fashion — by researching observed anomalies in the movement of Uranus. Additionally, the idea of a large planet at such a distance from the Sun isn't actually that unlikely, according to Bruce Macintosh, a planetary scientist at Stanford University.
  115. ^ Crocket, Christopher (31 januar 2016). "Computer simulations heat up hunt for Planet Nine". Science News. Hentet 7 februar 2016. 'It's exciting and very compelling work,' says Meg Schwamb, a planetary scientist at Academia Sinica in Taipei, Taiwan. But only six bodies lead the way to the putative planet. 'Whether that's enough is still a question.'
  116. ^ "We can't see this possible 9th planet, but we feel its presence". PBS NewsHour. 22 januar 2016. Hentet 18 juli 2016. 'Right now, any good scientist is going to be skeptical, because it's a pretty big claim. And without the final evidence that it's real, there is always that chance that it's not. So, everybody should be skeptical. But I think it's time to mount this search. I mean, we like to think of it as, we have provided the treasure map of where this ninth planet is, and we have done the starting gun, and now it's a race to actually point your telescope at the right spot in the sky and make that discovery of planet nine.' – Mike Brown

Further reading

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