Planet Nine

This article is about the hypothetical planet first suggested in 2014. For other uses, see Planet Nine (disambiguation).

Planet Nine[1]

Artist's impression of Planet Nine as an ice giant
Orbital characteristics
Aphelion 1200 AU (est.)[2]
Perihelion 200 AU (est.)[3]
700 AU (est.)[1]
Eccentricity 0.6 (est.)[3]
10,000 to 20,000 years[3]
Inclination 30° to ecliptic (est.)[3]
150°
Physical characteristics
Mean radius
 13,000–26,000 km
(8,100–16,000 mi)
2–4 R⊕ (est.)[3]
Mass 6×1025 kg (est.)[3]
≥10 Earth masses (est.)
>22 (est.)[2]

    Planet Nine is a hypothetical large planet in the far outer Solar System whose presence would explain the unusual orbital configuration of a group of trans-Neptunian objects (TNOs) that orbit mostly beyond the Kuiper belt.[1][4][5]

    On 20 January 2016, researchers Konstantin Batygin and Michael E. Brown at Caltech announced calculation-based evidence of a massive ninth planet in the Solar System.[1] The predicted planet would be a super-Earth with an estimated mass of about 10 times that of Earth (approximately 5,000 times the mass of Pluto), a diameter of two to four times that of Earth, and a highly elliptical orbit that is so far away that it could take it 15,000 years to orbit the Sun.[6][7]

    On the basis of models of planet formation that might include planetary migration from the inner Solar System, such as the fifth giant planet hypothesis, the authors suggest that it may be a primordial giant planet core that was ejected from its original orbit during the nebular epoch of the Solar System's evolution.[1]

    Naming

    In their original paper, Brown and Batygin simply referred to the object as "perturber",[1] and only in later press releases did they use the nickname "Planet Nine".[8] Because the planet is hypothetical, it will not be officially named until its existence has been confirmed with images.[9]

    Brown and Batygin have also used the names "Jehoshaphat" and "George" for Planet Nine. Brown has stated: "We actually call it "Fatty"[upper-alpha 1] when we're just talking to each other."[5] Previously proposed hypothetical planets located in the outer Solar System include Planet X and Tyche.

    Characteristics

    Orbit

    Planet Nine is hypothesized to follow a highly elliptical orbit around the Sun, with an orbital period of 10,000–20,000 years. The planet's orbit would have a semi-major axis of approximately 700 AU, or about 20 times the distance from Neptune to the Sun, though it might come as close as 200 AU (30 billion km, 19 billion mi), and its inclination estimated to be roughly 30 ± 10°.[2][3][11][upper-alpha 2] The high eccentricity of Planet Nine's orbit could take it as far away as 1200 AU at its aphelion.[12][13]

    The aphelion, or farthest point from the Sun, would be in the general direction of the constellations of Orion and Taurus,[14] whereas the perihelion, the nearest point to the Sun, would be in the general direction of the southerly areas of Serpens (Caput), Ophiuchus and Libra.[15][16]

    Size

    Planet Nine is hypothesized to be similar in size and composition to the blue ice giants Uranus and Neptune, pictured here to scale with the gas giants and terrestrial planets.[2][6]

    The planet is estimated to have 10 times the mass[11][10] and two to four times the diameter of Earth.[6][17] An object with the same diameter as Neptune has not been excluded by previous surveys. An infrared survey by the Wide-field Infrared Survey Explorer (WISE) in 2009 allowed for a Neptune-sized object beyond 700 AU.[18] A similar study in 2014 focused on possible higher-mass bodies in the outer Solar System and ruled out Jupiter-mass objects out to 26,000 AU.[19]

    Brown thinks that no matter where it is speculated to be, if Planet Nine exists, then its mass is higher than what is required to clear its feeding zone in 4.6 billion years, and thus that it dominates the outer edge of the Solar System, which is sufficient to make it a planet by current definitions.[20] Using a metric based on work by Jean-Luc Margot, Brown calculated that only at the smallest size and farthest distance was it on the border of being called a dwarf planet.[20] Margot himself says that Planet Nine satisfies the quantitative criterion for orbit-clearing developed by him in 2015 and that according to that criterion, Planet Nine will qualify as a planet, if and when it is detected.[21]

    Composition

    Brown speculates that the predicted planet is most likely an ejected ice giant, similar in composition to Uranus and Neptune: a mixture of rock and ice with a small envelope of gas.[2][6]

    Indirect detection

    Early speculation

    Case for a new planet

    Trujillo and Sheppard

    The initial argument for the existence of a planet beyond Neptune was published in 2014 by astronomers Scott Sheppard and Chad Trujillo, who suggested that the similar orbits of certain objects such as sednoids might be influenced by a massive unknown planet at the edge of the Solar System via the Kozai mechanism to explain the alignments.[4] In this arrangement the arguments of perihelion of the objects would librate about 0° or 180°[upper-alpha 4] so that their orbits cross the plane of the planet's orbit near perihelion and aphelion, at the farthest points from the planet.[36]

    They proposed a "single body of 2–15 Earth masses in a circular low-inclination orbit between 200 AU and 300 AU" to explain the pattern. It was not the only way to create the clustering of the orbital orientations, and they admitted the possibility that a Mars-mass object that is closer or a Neptune-mass planet that is farther away could also cause the bunching of the perihelia.[33] However, they could not formulate a model that successfully incorporated the planet.[1]

    Carlos de la Fuente Marcos

    In a further analysis, Carlos de la Fuente Marcos and coworkers confirmed that the noted orbital alignment can only be explained by an undetected planet. They also theorized that a set of extreme trans-Neptunian objects (ETNOs) are kept bunched together by a Kozai mechanism similar to the one between Comet 96P/Machholz and Jupiter.[38] They speculated that it would have a mass between that of Mars and Saturn and would orbit at some 200 AU from the Sun. However, they also struggled to explain the orbital alignment using a model with only one unknown planet.[upper-alpha 5] They therefore suggested that this planet is itself in resonance with a more-massive world about 250 AU from the Sun, just like the one predicted in the work by Trujillo and Sheppard.[39][33] They also did not rule out the possibility that the planet could have to be much farther away but much more massive in order to have the same effect and admitted the hypothesis needed more work.[40] They also did not rule out alternate explanations and expected more clarity as researchers study orbits of more such distant objects.[41][42][43][44]

    Brown and Batygin

    Caltech's Michael E. Brown and Konstantin Batygin looked into refuting the mechanism proposed by Trujillo and Sheppard.[1] They showed that Sheppard and Trujillo's original formulation, which had identified a clustering of arguments of perihelion at 0°, was mostly under the effect of Neptune mean-motion resonances for many objects in their analysis set, and that, once filtered, the argument of perihelion for the remaining objects not affected by Neptune was at 318 ± 8°. This was grossly out of alignment with how the Kozai mechanism would align these orbits, at ~0°.[1][upper-alpha 6] However, Brown and Batygin did find that the four remaining detached objects not affected by Neptune were approximately co-planar with the sednoids Sedna and 2012 VP113, as well as clustered around an argument of perihelion with them, and found that there was only a 0.007% likelihood that this was due to chance. They then pursued a numerical simulation, and soon found they were able to explain both results with mean-motion resonances caused by a hypothesized 10 M⊕ massive object on a highly eccentric and moderately inclined orbit. Furthermore, the model generated a pattern of high-inclination objects that they speculated as resulting from a combination of mean-motion effect with the Kozai effect relative to the hypothetical planet,[1] and that they subsequently found in databases of minor objects in the Solar System. Their origin could previously not be explained well.

    Their theoretical model explained three elusive aspects of the trans-Neptunian region in a single, unifying picture: The physical alignment of the distant orbits, the generation of detached objects well separated from the Kuiper belt such as Sedna, and the existence of a population of objects with high-inclination orbits.[8]

    Planet Nine hypothesis

    Orbital correlations among six distant trans-Neptunian objects led to the hypothesis

    Brown and Batygin analyzed six extreme trans-Neptunian objects in a stable configuration of orbits mostly outside the Kuiper belt (namely Sedna, 2012 VP113, 2007 TG422, 2004 VN112, 2013 RF98, 2010 GB174).[1] A closer look at the data showed that these six objects have orbits that are not just clustered in their arguments of perihelion, but are aligned in approximately the same direction in physical space and lie in approximately the same plane.[8][46] They found that this would only occur with 0.007% probability by chance alone.[47]

    These six objects had been discovered by six different surveys on six different telescopes. That made it less likely that the clumping might be due to an observation bias such as pointing a telescope at a particular part of the sky. And again, being the six most distant objects meant they were least likely to be disturbed by Neptune, which orbits 30 AU from the Sun.[10][48] Generally, TNOs with perihelia smaller than 36 AU experience strong encounters with Neptune.[1]

    These six are the only minor planets known to have perihelia greater than 30 AU and a semi-major axis greater than 250 AU as of January 2016.[49] All six objects are relatively small, but currently relatively bright because they are near their closest distance to the Sun in their elliptical orbits.

    Extreme Trans-Neptunian objects with perihelion greater than 30 AU and a semi-major axis greater than 250 AU[49]
    ObjectOrbitorbital planeBody
    Orbital period
    (years)    		Semimaj.
    (AU)    		Peri.
    (AU)     		Aphel.
    (AU)     		Current
    distance
    from Sun
    (AU)    		Eccen.Arg. peri
    ω (°)    		inclination
    i (°)    		Long. asc
    ☊ or Ω (°)    		Long. peri
    ϖ=ω+Ω (°)    		Current
    mag.    		 Diam.
    (km)
    2012 VP113 4,300 263 80450 83 0.70 292.9 24.0 90.8 23.7 23.4 600
    2013 RF98 5,600 317 36600 36.5 0.88 316.5 29.6 67.6 24.1 24.4 80
    2004 VN112 5,850 327 47607 48 0.85 327.2 25.6 66.0 33.2 23.3 200
    2007 TG422 11,200 501 36967 37 0.93 285.8 18.6 113.0 38.8 21.9 200
    90377 Sedna 11,400 506 76936 86 0.86 311.5 11.9 144.5 96.0 21.0 1,000
    2010 GB174 6,600 351 48650 71 0.87 347.7 21.5 130.6 118.3 25.2 200
    Hypothesized Planet Nine ~15,000 ~700 ~200 ~1,200 ~1,000 ? ~0.6 ~150 ~30 ~102? ~252? >22 ~40,000
    High-inclination Trans-Neptunian objects with a semi-major axis greater than 250 AU[1]
    ObjectOrbitBody
    Perihelion
    (AU)
    Figure 9[1]    		Semimaj.
    (AU)
    Figure 9[1]    		Current
    distance
    from Sun
    (AU)    		inc
    (°)[50]     		Eccen.Arg. peri ω
    (°)    		Mag. Diam.
    (km)
    (336756) 2010 NV1 9.4 323 14 141 .97 133 22 20–45
    (418993) 2009 MS9 11.1 348 12 68 .97 129 21 30–60
    2010 BK118 6.3 484 11 144 .99 179 21 20–50
    2013 BL76 8.5 1,213 11 99 .99 166 21.6 15–40
    2012 DR30 14 1,404 17 78 .99 195 19.6 185[51]

    Simulation

    Best-fit parameters

    Brown and Batygin simulated the effect of a planet of mass M = 10 M⊕ [upper-alpha 7] with a semi-major axis ranging from 200 to 2000 AU and an eccentricity varying from 0.1 to 0.9 on these extreme TNOs and inner Oort cloud objects. The capture of KBOs into long-lived apsidally anti-aligned orbital configurations occurs, with variable success, across a significant range of companion parameters (semi-major axis a ~ 400–1500 AU, eccentricity e ~ 0.5–0.8).

    They found that orbital parameters centered around the following values produced the best fit, for the kind of distribution of orbits observed.

    Results

    Inference

    Batygin was cautious in interpreting the results, saying, "Until Planet Nine is caught on camera it does not count as being real. All we have now is an echo."[55]

    Brown put the odds for the existence of Planet Nine at about 90%.[6] Greg Laughlin, one of the few researchers who knew in advance about this paper, gives an estimate of 68.3%.[5] Other skeptical scientists demand more data in terms of additional KBOs to be analysed or final evidence through photographic confirmation.[48][56][57] Brown, though conceding the skeptics' point, still thinks that there is enough data to mount a serious search for a new planet, and assures everyone that it will not be a wild goose chase.[58]

    Brown is supported by Jim Green, director of NASA's Planetary Science Division, who said that "the evidence is stronger now than it's ever been before".[59]

    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.[55] Alessandro Morbidelli, who reviewed the paper for The Astronomical Journal, concurred, saying "I don't see any alternative explanation to that offered by Batygin and Brown."[6][5]

    Alternate hypothesis

    Ann-Marie Madigan & Michael McCourt postulate that a yet to be discovered belt of objects far more massive than the current-day Kuiper Belt, at larger distances, and preferentially lifted off the plane of the major planets could be shaping the orbits of these ETNOs based on self-organization. But Brown remains confident that his and Batygin’s supposition is correct and regards the prospect of Planet Nine as more probable, because surveys do not suggest/support the existence of a scattered-disk region of sufficient mass to support this idea of "inclination instability".[60][61][upper-alpha 9]

    Direct detection

    Location

    If the planet 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.[11] Statistically, the planet is more likely to be closer to its aphelion at a distance more than 500 AU.[2] This is because objects move more slowly when near their aphelion, in accordance with Kepler's second law. The search in databases of stellar objects performed by Brown and Batygin 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.[15]

    Radiation

    A distant planet such as this would reflect little light, but, because it is hypothesized to be a large body, its radiation signature is more likely to be detected by Earth-based infrared telescopes, such as ALMA. However, this still would need to be confirmed with visual corroboration, as ALMA cannot readily distinguish between a small, nearby body and a large, distant one.[62] However, Jim Green of NASA is optimistic that the James Webb Space Telescope, which will be the successor to the Hubble Space Telescope and is expected to launch in 2018, could find it.[59]

    Visibility

    Telescopes are searching for the object, which, due to its extreme distance from the Sun, would reflect little sunlight and potentially evade telescope sightings.[6] It is expected to have an apparent magnitude fainter than 22, making it at least 600 times fainter than Pluto.[2] [upper-alpha 10]

    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 enough objects and a wide field of view to shorten the search.[32] Two teams of astronomers—Brown and Batygin, as well as Sheppard and Trujillo—are undertaking this search together, and both teams cooperatively expect this search to take up to five years.[10][65]

    A preliminary search of the archival data from the Catalina Sky Survey to magnitude ~19, Pan-STARRS to magnitude 21.5, and WISE has not identified Planet Nine.[2] The remaining areas to search are near aphelion, which is located close to the galactic plane of the Milky Way.[2] This aphelion direction is where the predicted planet would be faintest and has a complicated star-rich field of view to spot it in.[15]

    More predicted objects

    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 Planet Nine. The larger perihelia of these objects would make them fainter and more difficult to detect than the anti-aligned objects.[1]

    Finding more such objects would allow astronomers to make more accurate predictions about the orbit of the hypothesized planet.[66] 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.[56]

    Origin

    According to Batygin and Brown, the solar nebula would have needed to be "exceptionally expansive to be compatible with in situ formation of a planet on such a distant and eccentric orbit", and so they speculate that Planet Nine, if it exists, likely formed nearer to the Sun but was eventually knocked farther away by Jupiter or Saturn during the nebular epoch,[1] flinging it into the outer extremes of the Solar System, via a mechanism reminiscent of the ejection of a hypothetical fifth giant planet in recent variations of the Nice model.[1] However, gravitational interactions with the Sun's birth cluster, and possibly gaseous remnants of the solar nebula, could have influenced Planet Nine as it was ejected, putting it in a very wide but stable orbit well outside the Kuiper belt, but also well within the inner Oort cloud.[67][54] Brown considered that Planet Nine could have developed into the core of a gas giant, had it not been flung into the Solar System's farthest reaches.[6]

    According to Batygin's current estimates, for the ejection theory to be a feasible explanation, the timeline for ejection would have been between three million and ten million years after the formation of the Solar System.[10] This timing suggests that Planet Nine is not the planet ejected in the Nice model instability, unless that occurred too early to be the cause of the Late Heavy Bombardment,[68] which would then require another explanation. Batygin also agrees that these ejections must have been two separate events.[69]

    Ethan Siegel, who is deeply skeptical of the existence of an undiscovered new planet in the Solar System, nevertheless speculates that at least one super-Earth, which have been commonly discovered in other planetary systems but have not been discovered in the Solar System, might have been ejected from the inner Solar System due to the inward migration of Jupiter in the early Solar System.[53][70] Hal Levinson thinks that the chance of an ejected object ending up in the inner Oort cloud is only about 2%, and speculates that many objects must have been thrown past the Oort cloud if one has entered a stable orbit.[71]

    Astronomers expect that the discovery of Planet Nine would aid in understanding the processes behind the formation of the Solar System and other planetary systems, as well as how unusual the Solar System is with a lack of planets with masses between that of Earth and that of Neptune, compared to other planetary systems.[72]

    Exploration

    Brown thinks that if Planet Nine is confirmed to exist, a probe could reach it in as few as 20 years, with a powered slingshot around the Sun.[73]

    See also

    Notes

    1. ↑ most news outlets reported the name as Phattie[10] but The New Yorker seems like a nearly one of a kind variation.
    2. ↑ The New Yorker put the average orbital distance of Planet Nine into perspective with an apparent allusion to one of the magazine's most famous cartoons, View of the World from 9th Avenue: "If the Sun were on Fifth Avenue and Earth were one block west, Jupiter would be on the West Side Highway, Pluto would be in Montclair, New Jersey, and the new planet would be somewhere near Cleveland."[5]
    3. ↑ Assuming that the orbital elements of these objects have not changed, Jilkova & co 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.[34][35]
    4. ↑ In their paper Brown & Batygin note that "the lack of ω ~ 180 objects suggests that some additional process (such as encounter with a passing star) is required to account for the missing objects at 180°"
    5. ↑ In their paper Brown & Batygin note that, "this (ratio of the perturbed object to perturber semimajor axis to be nearly equal to one) means that trapping all of the distant objects within the known range of semimajor axes into Kozai resonances likely requires multiple planets, finely tuned to explain the particular data set". Hence, they do not favor this theory as too unwieldy.
    6. ↑ Two types of protection mechanisms are possible:[45]
      • 1. For bodies whose values of a and e are such that they could encounter the planets only near perihelion (or aphelion), such encounters may be prevented by the high inclination and the libration of ω about 90° or 270° (even when the encounters occur, they do not affect much the minor planet's orbit due to comparatively high relative velocities).
      • 2. Another mechanism is viable when at low inclinations when ω oscillates around 0° or 180° and the minor planet's semimajor axis is close to that of the perturbing planet: in this case the node crossing occurs always near perihelion and aphelion, far from the planet itself, provided the eccentricity is high enough and the orbit of the planet is almost circular.
    7. ↑ Brown & Batygin provide an order of magnitude estimate for the mass.
      • If M were equal to 0.1 M⊕, 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 1 M⊕, 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 10 M⊕ would imply a longer semi-major axis.
      Hence they estimate that the mass of the object is likely in the range of 5 M⊕ to 15 M⊕.
    8. ↑ Fixing of the orbital plane requires a combination of two parameters: inclination and longitude of the ascending node. The average of Long. asc. node for the 6 objects is ~102°. Brown & Batygin are expected to publish their estimates of the orbital parameters in another paper later.
    9. ↑ In their paper Brown & Batygin note that "the vast majority of this (primordial planetesimal disk) material was ejected from the system by close encounters with the giant planets during, and immediately following, the transient dynamical instability that shaped the Kuiper Belt in the first place. The characteristic timescale for depletion of the primordial disk is likely to be short compared with the timescale for the onset of the inclination instability (Nesvorný 2015), calling into question whether the inclination instability could have actually proceeded in the outer solar system."
    10. ↑ The 8-meter Subaru telescope has achieved a 27.7 magnitude photographic limit with a ten-hour exposure,[63] 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.[64] However, Hubble's field of view is very narrow, as is the Keck Observatory Large Binocular Telescope.[10]

    References

    1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Batygin, Konstantin; Brown, Michael E. (20 January 2016). "Evidence for a distant giant planet in the Solar system". The Astronomical Journal 151 (2): 22. arXiv:1601.05438. Bibcode:2016AJ....151...22B. doi:10.3847/0004-6256/151/2/22.
    2. 1 2 3 4 5 6 7 8 9 "Where is Planet Nine?". FindPlanetNine.com. January 20, 2016. Archived from the original on Jan 30, 2016.
    3. 1 2 3 4 5 6 7 Witze, Alexandra (20 January 2016). "Evidence grows for giant planet on fringes of Solar System". Nature 529 (7586): 266–7. Bibcode:2016Natur.529..266W. doi:10.1038/529266a. PMID 26791699.
    4. 1 2 3 Trujillo, Chadwick A.; Sheppard, Scott S. (27 March 2014). "A Sedna-like body with a perihelion of 80 astronomical units" (PDF). Nature 507 (7493): 471. Bibcode:2014Natur.507..471T. doi:10.1038/nature13156. PMID 24670765.
    5. 1 2 3 4 5 Burdick, Alan (20 January 2016). "Discovering Planet Nine". The New Yorker. Retrieved 20 January 2016.
    6. 1 2 3 4 5 6 7 8 Achenbach, Joel; Feltman, Rachel (20 January 2016). "New evidence suggests a ninth planet lurking at the edge of the solar system". The Washington Post. ISSN 0190-8286. Retrieved 20 January 2016.
    7. ↑ Sahil Badani in 'Other Engineering Trades' (Jan 21, 2016). "Time To Welcome Planet Nine? Scientists Obtain Substantive Proof". CrazyEngineers.com.
    8. 1 2 3 4 5 Konstantin Batygin (19 January 2016). "Search for Planet 9 – Premonition". FindPLanetNine.com. Archived from the original on Jan 30, 2016.
    9. ↑ Sanden Totten (January 22, 2016). "Planet 9: What should its name be if it's found?". Southern Californa Public Radio on 89.3 KPCC. Retrieved Feb 7, 2016. 'We like to be consistent,' said Rosaly Lopes, a senior research scientist at NASA’s Jet Propulsion Laboratory and a member of the IAU’s Working Group for Planetary System Nomenclature. ... For a planet in our solar system, being consistent means sticking to the theme of giving them names from Greek and Roman mythology.
    10. 1 2 3 4 5 6 Hand, Eric (20 January 2016). "Astronomers say a Neptune-sized planet lurks beyond Pluto". Science. Retrieved 20 January 2016.
    11. 1 2 3 4 Fesenmaier, Kimm (20 January 2016). "Caltech Researchers Find Evidence of a Real Ninth Planet". California Institute of Technology. Retrieved 20 January 2016.
    12. ↑ Drake, Nadia (20 January 2016). "Scientists Find Evidence for Ninth Planet in Solar System". National Geographic.
    13. ↑ Plait, Phil (21 January 2016). "More (and Best Yet) Evidence That Another Planet Lurks in the Dark Depths of Our Solar System". Slate. Retrieved 22 January 2016. The best fit was for a planet that never got closer than 200 AU from the Sun (... Neptune is roughly 30 AU out from the Sun). The orbit of this planet would be highly elliptical, but it’s not clear how elliptical; that's less well constrained. At its most distant, it could be between 500 and 1,200 AU out ... The most likely mass of the planet is about 10 times Earth’s mass ..., though it could be somewhat less or more.
    14. ↑ Mike Brown (@plutokiller) visits Griffith Observatory to discuss Planet 9 – Griffith Observatory
    15. 1 2 3 See RA/Dec chart at Konstantin Batygin; Mike Brown (20 January 2016). "Where is Planet Nine?". The Search for Planet Nine (http://www.findplanetnine.com). Archived from the original on Jan 30, 2016. Retrieved 24 January 2016.
    16. ↑ See embedded video simulation at Michael D. Lemonick; (Worldwide Telescope, Caltech/R. Hurt (IPAC)) (20 January 2016). "Strong Evidence Suggests a Super Earth Lies beyond Pluto". Scientific American. Retrieved 22 January 2015.
    17. ↑ Watson, Traci (20 January 2016). "Researchers find evidence of ninth planet in solar system". USA Today.
    18. ↑ Lakdawalla, Emily (27 August 2009). "The Planetary Society Blog: "WISE Guys"". The Planetary Society. Retrieved 26 December 2009.
    19. ↑ Luhman, K. L. (20 January 2014). "A search for a distant companion to the Sun with the Wide-Field Infrared Survey Explorer". The Astrophysical Journal 781 (4): 4. Bibcode:2014ApJ...781....4L. doi:10.1088/0004-637X/781/1/4. Retrieved 21 January 2015.
    20. 1 2 Brown, Mike (19 January 2016). "Is Planet Nine a "planet"?". FindPlanetNine.com. Retrieved Feb 7, 2016.
    21. ↑ Margot, Jean-Luc (22 January 2016). "Would Planet Nine Pass the Planet Test?". Department of Earth, Planetary, and Space Sciences & Department of Physics and Astronomy, University of California at Los Angeles.
    22. ↑ Mike Wall (August 24, 2011). "A Conversation With Pluto's Killer: Q & A With Astronomer Mike Brown". Space.com. Retrieved Feb 7, 2016.
    23. ↑ "Discovery of a Candidate Inner Oort Cloud Planetoid". arXiv:astro-ph/0404456. Bibcode:2004ApJ...617..645B. doi:10.1086/422095.
    24. ↑ Brown, Michael E. (October 28, 2010). "There's something out there -- part 2". Mike Brown's Planets.
    25. ↑ Patryk S., Lykawka; Tadashi, Mukai (April 2008). "An Outer Planet Beyond Pluto and the Origin of the Trans-Neptunian Belt Architecture". The Astronomical Journal 135 (4): 1161–1200. arXiv:0712.2198. Bibcode:2008AJ....135.1161L. doi:10.1088/0004-6256/135/4/1161.
    26. ↑ "Earth-Size Planet to Be Found in Outer Solar System?".
    27. ↑ "Large 'Planet X' May Lurk Beyond Pluto".
    28. ↑ "Japanese scientists eye mysterious 'Planet X'".
    29. ↑ Natalie Wolchover (May 25, 2012). "Planet X? New Evidence of an Unseen Planet at Solar System's Edge". LiveScience.com. Retrieved Feb 7, 2016. More work is needed to determine whether Sedna and the other scattered disc objects were sent on their circuitous trips round the sun by a star that passed by long ago, or by an unseen planet that exists in the solar system right now. Finding and observing the orbits of other distant objects similar to Sedna will add more data points to astronomers' computer models.
    30. ↑ "New Planet Found in Our Solar System?".
    31. ↑ Ian Sample (26 March 2014). "Dwarf planet discovery hints at a hidden Super Earth in solar system". Guardian News.
    32. 1 2 Mortillaro, Nicole (February 9, 2016). "Meet Mike Brown: Pluto killer and the man who brought us Planet 9". Global News. 'It was that search for more objects like Sedna ... led to the realization ... that they're all being pulled off in one direction by something. And that's what finally led us down the hole that there must be a big planet out there.' – Mike Brown
    33. 1 2 3 Christopher Crocket (November 14, 2014). "A distant planet may lurk far beyond Neptune". ScienceNews. Archived from the original on April 15, 2015. Retrieved Feb 7, 2015.
    34. ↑ Lucie Jílková; Simon Portegies Zwart; Tjibaria Pijloo; Michael Hammer (September 3, 2015). "How Sedna and family were captured in a close encounter with a solar sibling". Monthly Notices of the Royal Astronomical Society. Volume 453 (3): 3157–3162. arXiv:1506.03105. Bibcode:2015MNRAS.453.3157J. doi:10.1093/mnras/stv1803. Retrieved Feb 7, 2016.
    35. ↑ David Dickinson (Aug 6, 2015). "Stealing Sedna". UniverseToday.com. Retrieved Feb 7, 2016.
    36. 1 2 de la Fuente Marcos, C.; de la Fuente Marcos, R. (2014). "Extreme trans-Neptunian objects and the Kozai mechanism: signalling the presence of trans-Plutonian planets". Monthly Notices of the Royal Astronomical Society: Letters 443 (1): L59–L63. arXiv:1406.0715. Bibcode:2014MNRAS.443L..59D. doi:10.1093/mnrasl/slu084.
    37. ↑ Xaq Rzetelny (Jan 21, 2015). "The Solar System may have two undiscovered planets". ArsTechnica.com. Retrieved Feb 7, 2016.
    38. ↑ Carlos de la Fuente Marcos; Raúl de la Fuente Marcos; Sverre J. Aarseth (November 21, 2014). "Flipping minor bodies: what comet 96P/Machholz 1 can tell us about the orbital evolution of extreme trans-Neptunian objects and the production of near-Earth objects on retrograde orbits". Monthly Notices of the Royal Astronomical Society 446 (2): 1867–187. arXiv:1410.6307. Bibcode:2015MNRAS.446.1867D. doi:10.1093/mnras/stu2230. Retrieved Feb 7, 2016.
    39. ↑ Nicola Jenner (June 11, 2014). "Two giant planets may cruise unseen beyond Pluto". The New Scientist. Retrieved Feb 7, 2016.
    40. ↑ Michael D. Lemonick (Jan 19, 2015). "There May Be ‘Super Earths’ at the Edge of Our Solar System". Time magazine. Retrieved Feb 7, 2016.
    41. ↑ Mike Wall (January 16, 2015). "Mysterious Planet X May Really Lurk Undiscovered in Our Solar System". Space.com. Retrieved Feb 7, 2016.
    42. ↑ Nancy Atkinson (Jan 15, 2015). "Astronomers are predicting at least two more large planets in the solar system". UniverseToday.com. Retrieved Feb 7, 2016.
    43. ↑ Lisa Winter (January 16, 2015). "New Evidence Suggests There Are More Dwarf Planets In Our Solar System". IFLScience.com. Retrieved Feb 7, 2016.
    44. ↑ Paul Gilster (January 16, 2015). "Planets to Be Discovered in the Outer System?". CentauriDreams.org. Retrieved Feb 7, 2016.
    45. ↑ "NEAR-EARTH ASTEROIDS AND THE KOZAI-MECHANISM" (PDF).
    46. ↑ Bob McDonald (January 24, 2016). "How did we miss Planet 9?". CBC News. It's like seeing a disturbance on the surface of water but not knowing what caused it. Perhaps it was a jumping fish, a whale or a seal. Even though you didn't actually see it, you could make an informed guess about the size of the object and its location by the nature of the ripples in the water.
    47. ↑ Lakdawalla, Emily (20 January 2016). "Theoretical evidence for an undiscovered super-Earth at the edge of our solar system". The Planetary Society.
    48. 1 2 Loren Grush (January 20, 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. 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.
    49. 1 2 "MPC list of q>30 and a>250". IAU Minor Planet Center.
    50. 1 2 "MPC list of a>250 i>40 q>6". IAU Minor Planet Center.
    51. ↑ "A portrait of the extreme Solar System object 2012 DR30". Astronomy and Astrophysics. arXiv:1304.7112. doi:10.1051/0004-6361/201321147.
    52. ↑ Hruska, Joel (20 January 2016). "Our solar system may contain a ninth planet, far beyond Pluto". Extreme Tech.
    53. 1 2 Seigel, Ethan. "Not So Fast: Why There Likely Isn't A Large Planet Beyond Pluto". Starts with a Bang. Forbes. Retrieved 22 January 2016.
    54. 1 2 Chang, Kenneth (20 January 2016). "Ninth Planet May Exist Beyond Pluto, Scientists Report". The New York Times.
    55. 1 2 Thomas Levenson (Jan 25, 2016). "A New Planet or a Red Herring?". The Atlantic. '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.'
    56. 1 2 Kate Allen (Jan 20, 2016). "Is a real ninth planet out there beyond Pluto?". The Toronto Star.
    57. ↑ Christopher Crockett (February 2, 2016) [January31, 2016]. "Computer simulations heat up hunt for Planet Nine". Science News. Retrieved Feb 7, 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.'
    58. ↑ "We can't see this possible 9th planet, but we feel its presence". PBS Newshour. January 22, 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
    59. 1 2 Sarah Fecht (Jan 22, 2016). "Can there really be a planet in our solar system that we don't know about?". Popular Science.
    60. ↑ "Why Planet Nine might not exist".
    61. ↑ "'Planet Nine'? Cosmic Objects' Strange Orbits May Have a Different Explanation". We need more mass in the outer solar system," she (Madigan) said. "So it can either come from having more minor planets, and their self-gravity will do this to themselves naturally, or it could be in the form of one single massive planet — a Planet Nine. So it's a really exciting time, and we're going to discover one or the other.
    62. ↑ Corey S. Powell (January 22, 2016). "A Little Perspective on the New "9th Planet" (and the 10th, and the 11th)". Discover Magazine (Blog).
    63. ↑ "What is the faintest object imaged by ground-based telescopes?". Sky Telescope. 24 July 2006.
    64. ↑ G. Illingworth; D. Magee; P. Oesch; R. Bouwens (September 25, 2012). "Hubble goes to the eXtreme to assemble the deepest ever view of the Universe". SpaceTelescope.org. Retrieved Feb 7, 2016.
    65. ↑ Wall, Mike (21 January 2016). "How Astronomers Could Actually See 'Planet Nine'". Space.com. Retrieved 24 January 2016.
    66. ↑ Nathaniel Scharping (January 20, 2016). "Planet Nine: A New Addition to the Solar System?". Discover Magazine (blog).
    67. ↑ Totten, Sanden (20 January 2016). "Caltech researchers answer skeptics' questions about Planet 9". Southern Californa Public Radio on 89.3 KPCC.
    68. ↑ Gomes, R.; Levison, H. F.; Tsiganis, K.; Morbidelli, A. (2005). "Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets". Nature 435 (7041): 466–469. Bibcode:2005Natur.435..466G. doi:10.1038/nature03676. PMID 15917802.
    69. ↑ Drake, Nadia (22 January 2016). "How Can We Find Planet Nine? (And Other Burning Questions)". National Geographic Phenomena. National Geographic. Retrieved 23 January 2016. 'These two events are both ejections, but they are well separated in epoch,' Batygin says. 'The planet that was ejected during the giant instability of the solar system—which, by the way, coincided with the formation of the Kuiper Belt—that planet, if it was there, it was just ejected. It doesn’t get to stick around.'
    70. ↑ Siegel, Ethan (3 November 2015). "Jupiter May Have Ejected A Planet From Our Solar System". Forbes. Retrieved 22 January 2016.
    71. ↑ Kelly Beatty (March 26, 2014). "New Object Offers Hint of "Planet X" By Kelly Beatty". Sky and Telescope.
    72. ↑ Paul Scott Anderson (January 22, 2016). "Has ‘Planet X’ finally been found? A cautionary tale". Planetaria.ca.
    73. ↑ Adam Becker, Lisa Grossman, Jacob Aron (2016). "How Planet Nine may have been exiled to solar system's edge". New Scientist. Retrieved 25 January 2016.

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