# 9th planet location?

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I've seen a number of news reports indicating there is likely a 9th planet in our Solar System, something with an orbital period of between 10k-20k years, that is 10 times Earth's mass. I haven't seen any real indication of where this object might be. If I had access to a sufficient telescope, would I be able to find this planet, and what way would I point a telescope to find it? How far is it likely to be, or is that not well known?

It's too dim to be seen during a normal survey during the majority of its orbit.

Update: Scientists at the University of Bern have modeled a hypothetical 10 Earth mass planet in the proposed orbit to estimate its detectability with more precision than my attempt below.

The takeaway is that NASAs WISE mission would have probably spotted a planet of at least 50 Earth masses in the proposed orbit and that none of our current surveys would have had a chance to find one below 20 earth masses in most of its orbit. They put the planets temperature at 47K due to residual heat from formation; which would make is 1000x brighter in infrared than it is in visible light reflected from the sun.

It should however be within reach of the LSST once it is completed (first light 2019, normal operations beginning 2022); so the question should be resolved within a few more years even if its far enough from Batygin and Brown's proposed orbit that their search with the Subaru telescope comes out empty.

My original attempt to handwave an estimate of detectability is below. The paper gives potential orbital parameters of $400-1500~ extrm{AU}$ for the semi major axis, and $200-300~ extrm{AU}$ for perihelion. Since the paper doesn't give a most-likely case for orbital parameters, I'm going to go with the extreme case that makes it most difficult to find. Taking the most eccentric possible values from that gives an orbit with a $1500~ extrm{AU}$ semi-major axis and a $200~ extrm{AU}$ perihelion has a $2800~ extrm{AU}$ aphelion.

To calculate the brightness of an object shining with reflected light, the proper scaling factor is not a $1/r^2$ falloff as could be naively assumed. That is correct for an object radiating its own light; but not for one shining by reflected light; for that case the same $1/r^4$ scaling as in a radar return is appropriate. That this is the correct scaling factor to use can be sanity checked based on the fact that despite being similar in size, Neptune is $sim 6x$ dimmer than Uranus despite being only $50\%$ farther away: $1/r^4$ scaling gives a $5x$ dimmer factor vs $2.25$ for $1/r^2$.

Using that gives a dimming of 2400x at $210~ extrm{AU};.$ That puts us down $8.5$ magnitudes down from Neptune at perihelion or $16.5$ magnitude. $500~ extrm{AU}$ gets us to $20$th magnitude, while a $2800~ extrm{AU}$ aphelion dims reflected light down by nearly $20$ magnitudes to $28$ magnitude. That's equivalent to the faintest stars visible from an 8 meter telescope; making its non-discovery much less surprising.

This is something of a fuzzy boundary in both directions. Residual energy from formation/radioactive material in its core will be giving it some innate luminosity; at extreme distances this might be brighter than reflected light. I don't know how to estimate this. It's also possible that the extreme cold of the Oort Cloud may have frozen its atmosphere out. If that happened, its diameter would be much smaller and the reduction in reflecting surface could dim it another order of magnitude or two.

Not knowing what sort of adjustment to make here, I'm going to assume the two factors cancel out completely and leave the original assumptions that it reflects as much light as Neptune and reflective light is the dominant source of illumination for the remainder of my calculations.

For reference, data from NASA's WISE experiment has ruled out a Saturn-sized body within $10,000~ extrm{AU}$ of the sun.

It's also likely too faint to have been detected via proper motion; although if we can pin its orbit down tightly Hubble could confirm its motion.

Orbital eccentricity can be calculated as:

$$e = frac{r_ extrm{max} - r_ extrm{min}}{2a}$$

Plugging in the numbers gives:

$$e = frac{2800~ extrm{AU} - 200~ extrm{AU}}{2cdot 1500~ extrm{AU}} = 0.867$$

Plugging $200~ extrm{AU}$ and $e = 0.867$ into a cometary orbit calculator gives a $58,000$ year orbit.

While that gives an average proper motion of $22~ extrm{arc-seconds/year};,$ because the orbit is highly eccentric its actual proper motion varies greatly, but it spends a majority of its time far from the sun where its values are at a minimum.

Kepler's laws tell us that the velocity at aphelion is given by:

$$v_a^2 = frac{ 8.871 imes 10^8 }{ a } frac{ 1 - e }{ 1 + e }$$

where $v_a$ is the aphelion velocity in $mathrm{m/s};,$ $a$ is the semi-major axis in $mathrm{AU},$ and $e$ is orbital eccentricity.

$$v_a = sqrt{frac{ 8.871 imes 10^8 }{ 1500 } cdot frac{ 1 - 0.867 }{ 1 + 0.867 }} = 205~mathrm{m/s};.$$

To calculate the proper motion we first need to convert the velocity into units of $extrm{AU/year}:$

$$205 mathrm{frac{m}{s}}; mathrm{frac{3600 s}{1 h}} cdot mathrm{frac{24 h}{1 d}} cdot mathrm{frac{365 d}{1 y}} cdot mathrm{frac{1; AU}{1.5 imes 10^{11}m}} = 0.043~mathrm{frac{AU}{year}}$$

To get proper motion from this, create a triangle with a hypotenuse of $2800~ extrm{AU}$ and a short side of $0.043~ extrm{AU}$ and then use trigonometry to get the narrow angle.

$$sin heta = frac{0.044}{2800} implies heta = {8.799×10^{-4}}^circ = 3.17~ extrm{arc seconds};.$$

This is well within Hubble's angular resolution of $0.05~ extrm{arc seconds};$ so if we knew exactly where to look we could confirm its orbit even if its near its maximum distance from the sun. However its extreme faintness in most of its orbit means that its unlikely to have been found in any survey. If we're lucky and it's within $sim 500~ extrm{AU},$ it would be bright enough to be seen by the ESA's GAIA spacecraft in which case we'll located it within the next few years. Unfortunately, it's more likely that all the GAIA data will do is to constrain its minimum distance slightly.

Its parallax movement would be much larger; however the challenge of actually seeing it in the first place would remain.

Citing the original article:

We find that the observed orbital alignment can be maintained by a distant eccentric planet with mass $geq approx 10$ m⊕ whose orbit lies in approximately the same plane as those of the distant KBOs, but whose perihelion is 180° away from the perihelia of the minor bodies.

and

As already alluded to above, the precise range of perturber parameters required to satisfactorily reproduce the data is at present difficult to diagnose. Indeed, additional work is required to understand the tradeoffs between the assumed orbital elements and mass, as well as to identify regions of parameter space that are incompatible with the existing data.

So, finding out likely orbital parameters is work in progress.

The position of the hypothetical object is not known with any certainty, so it's hard to know where to point your telescope.

The paper proposes a wide range of orbital distances anywhere from 400 to 1500 AU semi-major axis, with a perihelion (closest approach to the sun) of 200-300AU. This is 8 times as far as Neptune. (I didn't read the article closely enough to determine whether the body would be near perihelion or not at present; it could be over 1000 AU away, 30 times Neptune's distance.)

With a mass of 10 Earths, we would expect the body to be something like 2-5 times Earth's radius -- somewhat smaller than Neptune.

The combination of distance and size suggests the body would be far fainter than Neptune, no brighter than magnitude 16.5 at perihelion, and likely much dimmer.

If you had access to a sufficient telescope, you could theoretically see it, if you looked in the right place (although no one knows where the right place might be). But if it's anywhere near aphelion there are only a handful of sufficient telescopes in the world (let's say an 8m mirror or larger), so I think it highly unlikely that you have access to one of them.

Batygin and Brown made a website which describes the search for the 9th planet in clear terms. They specifically note the following:

perihelion (its closest approach to the sun) at around a Right Ascension in the sky of 16 hours, which means that the perihelion position is straight overhead in late May. Conversely, the orbit comes to aphelion (the furthest point from the sun) at about 4 hours, or straight overhead in late November.

So to look for it, one should look along the ecliptic, concentrating mostly on the area directly overhead in late November. Note that this is the part of the sky where the galactic center also appears. The inclination is estimated to be 30 degrees, plus or minus 20, so that distance from the ecliptic should be searched as well.

## New arguments in favor of a ninth planet in our solar system

Corresponding with the three-year anniversary of their announcement hypothesizing the existence of a ninth planet in the solar system, Caltech's Mike Brown and Konstantin Batygin are publishing a pair of papers analyzing the evidence for Planet Nine's existence.

The papers offer new details about the suspected nature and location of the planet, which has been the subject of an intense international search ever since Batygin and Brown's 2016 announcement.

The first, titled "Orbital Clustering in the Distant Solar System," was published in The Astronomical Journal on January 22. The Planet Nine hypothesis is founded on evidence suggesting that the clustering of objects in the Kuiper Belt, a field of icy bodies that lies beyond Neptune, is influenced by the gravitational tugs of an unseen planet. It has been an open question as to whether that clustering is indeed occurring, or whether it is an artifact resulting from bias in how and where Kuiper Belt objects are observed.

To assess whether observational bias is behind the apparent clustering, Brown and Batygin developed a method to quantify the amount of bias in each individual observation, then calculated the probability that the clustering is spurious. That probability, they found, is around one in 500.

"Though this analysis does not say anything directly about whether Planet Nine is there, it does indicate that the hypothesis rests upon a solid foundation," says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy.

The second paper is titled "The Planet Nine Hypothesis," and is an invited review that will be published in the next issue of Physics Reports. The paper provides thousands of new computer models of the dynamical evolution of the distant solar system and offers updated insight into the nature of Planet Nine, including an estimate that it is smaller and closer to the sun than previously suspected. Based on the new models, Batygin and Brown -- together with Fred Adams and Juliette Becker (BS '14) of the University of Michigan -- concluded that Planet Nine has a mass of about five times that of the earth and has an orbital semimajor axis in the neighborhood of 400 astronomical units (AU), making it smaller and closer to the sun than previously suspected -- and potentially brighter. Each astronomical unit is equivalent to the distance between the center of Earth and the center of the sun, or about 149.6 million kilometers.

"At five Earth masses, Planet Nine is likely to be very reminiscent of a typical extrasolar super-Earth," says Batygin, an assistant professor of planetary science and Van Nuys Page Scholar. Super-Earths are planets with a mass greater than Earth's, but substantially less than that of a gas giant. "It is the solar system's missing link of planet formation. Over the last decade, surveys of extrasolar planets have revealed that similar-sized planets are very common around other sun-like stars. Planet Nine is going to be the closest thing we will find to a window into the properties of a typical planet of our galaxy."

Batygin and Brown presented the first evidence that there might be a giant planet tracing a bizarre, highly elongated orbit through the outer solar system on January 20, 2016. That June, Brown and Batygin followed up with more details, including observational constraints on the planet's location along its orbit.

Over the next two years, they developed theoretical models of the planet that explained other known phenomena, such as why some Kuiper Belt objects have a perpendicular orbit with respect to the plane of the solar system. The resulting models increased their confidence in Planet Nine's existence.

After the initial announcement, astronomers around the world, including Brown and Batygin, began searching for observational evidence of the new planet. Although Brown and Batygin have always accepted the possibility that Planet Nine might not exist, they say that the more they examine the orbital dynamics of the solar system, the stronger the evidence supporting it seems.

"My favorite characteristic of the Planet Nine hypothesis is that it is observationally testable," Batygin says. "The prospect of one day seeing real images of Planet Nine is absolutely electrifying. Although finding Planet Nine astronomically is a great challenge, I'm very optimistic that we will image it within the next decade."

The work was supported by the David and Lucile Packard Foundation and the Alfred P. Sloan Foundation.

## Discoveries at the edge of our solar system

After Pluto, the second Kuiper Belt Object — 1992 QB1 — was discovered in 1992 by American astronomers David Jewitt and Jane Luu using the 2.2-m telescope at Mauna Kea in Hawaii. NASA

The Kuiper Belt is a collection of small, icy bodies that orbit the sun beyond Neptune, at distances larger than 30 AU (one astronomical unit or AU is the distance between the Earth and the sun). These Kuiper Belt objects (KBOs) range in size from large boulders to 2,000 km across. KBOs are leftover small bits of planetary material that were never incorporated into planets, similar to the asteroid belt.

The discoveries from the most successful Kuiper Belt survey to date, the Outer Solar System Origins Survey (OSSOS), suggest a sneakier explanation for the orbits we see. Many of these KBOs have been discovered to have very elliptical and tilted orbits, like Pluto.

Mathematical calculations and detailed computer simulations have shown that the orbits we see in the Kuiper Belt can only have been created if Neptune originally formed a few AU closer to the sun, and migrated outward to its present orbit. Neptune’s migration explains the pervasiveness of highly elliptical orbits in the Kuiper Belt, and can explain all the KBO orbits we’ve observed, except for a handful of KBOs on extreme orbits that always stay at least 10 AU beyond Neptune.

## Lokasi planet ke-9?

Saya telah melihat sejumlah laporan berita yang mengindikasikan kemungkinan ada planet ke - 9 di Tata Surya kita , sesuatu dengan periode orbit antara 10k-20k tahun, yaitu 10 kali massa Bumi. Saya belum melihat indikasi nyata di mana objek ini mungkin. Jika saya memiliki akses ke teleskop yang cukup, dapatkah saya menemukan planet ini, dan bagaimana cara saya mengarahkan teleskop untuk menemukannya? Seberapa jauh kemungkinannya, atau apakah itu tidak dikenal?

Terlalu suram untuk dilihat selama survei normal selama sebagian besar orbitnya.

Pembaruan: Para ilmuwan di Universitas Bern telah memodelkan sebuah planet 10 massa Bumi hipotetis dalam orbit yang diusulkan untuk memperkirakan kemampuan deteksi dengan lebih presisi daripada upaya saya di bawah ini.

Kesimpulannya adalah bahwa misi NASISE WISE mungkin akan melihat sebuah planet dengan setidaknya 50 massa Bumi dalam orbit yang diusulkan dan bahwa tidak ada survei kami saat ini yang memiliki kesempatan untuk menemukan satu di bawah 20 massa bumi di sebagian besar orbitnya. Mereka menempatkan suhu planet pada 47K karena panas sisa dari formasi yang akan membuat 1000x lebih terang dalam inframerah daripada dalam cahaya tampak yang dipantulkan dari matahari.

Namun harus berada dalam jangkauan LSST setelah selesai (lampu pertama 2019, operasi normal mulai 2022) jadi pertanyaannya harus diselesaikan dalam beberapa tahun lagi bahkan jika cukup jauh dari orbit yang diusulkan Batygin dan Brown sehingga pencarian mereka dengan teleskop Subaru menjadi kosong.

Upaya awal saya untuk melakukan handwave estimasi kemampuan mendeteksi di bawah ini. The kertas memberikan parameter orbital potensi untuk sumbu utama semifinal, dan 200 - 300 AU untuk perihelion. Karena makalah tidak memberikan kasus yang paling mungkin untuk parameter orbital, saya akan membahas kasus ekstrim yang membuatnya paling sulit ditemukan. Mengambil nilai yang paling eksentrik dari yang memberikan orbit dengan sumbu semi-mayor 1500 AU dan perihelion 200 AU memiliki aphelion 2800 AU . 400 − 1500 AU 200 − 300 AU 1500 AU 200 AU 2800 AU

Untuk menghitung kecerahan objek yang bersinar dengan cahaya yang dipantulkan, faktor penskalaan yang tepat bukanlah penurunan seperti yang dapat diasumsikan secara naif. Itu benar untuk objek yang memancarkan cahayanya sendiri tetapi tidak untuk satu yang bersinar oleh cahaya yang dipantulkan untuk kasus itu, penskalaan 1 / r 4 yang sama seperti pada pengembalian radar sesuai. Bahwa ini adalah faktor penskalaan yang benar untuk digunakan dapat diperiksa kewarasannya berdasarkan fakta bahwa meskipun ukurannya serupa, Neptunus ∼ 6 x lebih redup daripada Uranus meskipun hanya 50 % lebih jauh: 1 / r 4 1 / r 2 1 / r 4 ∼ 6 x 50 % 1 / r 4 scaling gives a 5 x dimmer factor vs 2.25 for 1 / r 2 .

Using that gives a dimming of 2400x at 210 AU . 8.5 16.5 magnitude. 500 AU gets us to 20 th magnitude, while a 2800 AU aphelion dims reflected light down by nearly 20 magnitudes to 28 magnitude. That's equivalent to the faintest stars visible from an 8 meter telescope making its non-discovery much less surprising.

Ini adalah sesuatu dari batas fuzzy di kedua arah. Energi residu dari formasi / bahan radioaktif pada intinya akan memberinya luminositas bawaan pada jarak ekstrem ini mungkin lebih terang daripada cahaya yang dipantulkan. Saya tidak tahu bagaimana memperkirakan ini. Mungkin juga bahwa dingin yang ekstrim dari Oort Cloud mungkin telah membekukan atmosfernya. Jika itu terjadi, diameternya akan jauh lebih kecil dan pengurangan permukaan pantulan dapat meredupkannya satu atau dua urutan besarnya.

Tidak tahu penyesuaian seperti apa yang harus dilakukan di sini, saya akan mengasumsikan dua faktor tersebut membatalkan sepenuhnya dan meninggalkan asumsi asli bahwa itu memantulkan cahaya sebanyak Neptunus dan cahaya reflektif adalah sumber penerangan yang dominan untuk sisa perhitungan saya .

Mungkin juga terlalu samar untuk dideteksi melalui gerakan yang tepat meskipun jika kita bisa mengitari orbitnya dengan erat Hubble dapat mengkonfirmasi gerakannya.

Eksentrisitas orbital dapat dihitung sebagai:

Memasukkan angka-angka memberi:

Plugging 200 AU and e = 0.867 into a cometary orbit calculator gives a 58 , 000 year orbit.

While that gives an average proper motion of 22 arc-seconds/year , because the orbit is highly eccentric its actual proper motion varies greatly, but it spends a majority of its time far from the sun where its values are at a minimum.

Kepler's laws tell us that the velocity at aphelion is given by:

where v a is the aphelion velocity in m / s , a is the semi-major axis in A U , and e is orbital eccentricity.

To calculate the proper motion we first need to convert the velocity into units of AU/year :

To get proper motion from this, create a triangle with a hypotenuse of 2800 AU and a short side of 0.043 AU and then use trigonometry to get the narrow angle.

This is well within Hubble's angular resolution of 0.05 arc seconds so if we knew exactly where to look we could confirm its orbit even if its near its maximum distance from the sun. However its extreme faintness in most of its orbit means that its unlikely to have been found in any survey. If we're lucky and it's within ∼ 500 AU , it would be bright enough to be seen by the ESA's GAIA spacecraft in which case we'll located it within the next few years. Unfortunately, it's more likely that all the GAIA data will do is to constrain its minimum distance slightly.

Its parallax movement would be much larger however the challenge of actually seeing it in the first place would remain.

## Contents

In the 1840s, the French mathematician Urbain Le Verrier used Newtonian mechanics to analyse perturbations in the orbit of Uranus, and hypothesised that they were caused by the gravitational pull of a yet-undiscovered planet. Le Verrier predicted the position of this new planet and sent his calculations to German astronomer Johann Gottfried Galle. On 23 September 1846, the night following his receipt of the letter, Galle and his student Heinrich d'Arrest discovered Neptune, exactly where Le Verrier had predicted. [10] There remained some slight discrepancies in the giant planets' orbits. These were taken to indicate the existence of yet another planet orbiting beyond Neptune.

Even before Neptune's discovery, some speculated that one planet alone was not enough to explain the discrepancy. On 17 November 1834, the British amateur astronomer the Reverend Thomas John Hussey reported a conversation he had had with French astronomer Alexis Bouvard to George Biddell Airy, the British Astronomer Royal. Hussey reported that when he suggested to Bouvard that the unusual motion of Uranus might be due to the gravitational influence of an undiscovered planet, Bouvard replied that the idea had occurred to him, and that he had corresponded with Peter Andreas Hansen, director of the Seeberg Observatory in Gotha, about the subject. Hansen's opinion was that a single body could not adequately explain the motion of Uranus, and postulated that two planets lay beyond Uranus. [11]

In 1848, Jacques Babinet raised an objection to Le Verrier's calculations, claiming that Neptune's observed mass was smaller and its orbit larger than Le Verrier had initially predicted. He postulated, based largely on simple subtraction from Le Verrier's calculations, that another planet of roughly 12 Earth masses, which he named "Hyperion", must exist beyond Neptune. [11] Le Verrier denounced Babinet's hypothesis, saying, "[There is] absolutely nothing by which one could determine the position of another planet, barring hypotheses in which imagination played too large a part." [11]

In 1850 James Ferguson, Assistant Astronomer at the United States Naval Observatory, noted that he had "lost" a star he had observed, GR1719k, which Lt. Matthew Maury, the superintendent of the Observatory, claimed was evidence that it must be a new planet. Subsequent searches failed to recover the "planet" in a different position, and in 1878, CHF Peters, director of the Hamilton College Observatory in New York, showed that the star had not in fact vanished, and that the previous results had been due to human error. [11]

In 1879, Camille Flammarion noted that the comets 1862 III and 1889 III had aphelia of 47 and 49 AU, respectively, suggesting that they might mark the orbital radius of an unknown planet that had dragged them into an elliptical orbit. [11] Astronomer George Forbes concluded on the basis of this evidence that two planets must exist beyond Neptune. He calculated, based on the fact that four comets possessed aphelia at around 100 AU and a further six with aphelia clustered at around 300 AU, the orbital elements of a pair of hypothetical trans-Neptunian planets. These elements concorded suggestively with those made independently by another astronomer named David Peck Todd, suggesting to many that they might be valid. [11] However, sceptics argued that the orbits of the comets involved were still too uncertain to produce meaningful results. [11] Some have considered Forbes's hypothesis a precursor to Planet Nine. [12]

In 1900 and 1901, Harvard College Observatory director William Henry Pickering led two searches for trans-Neptunian planets. The first was begun by Danish astronomer Hans Emil Lau who, after studying the data on the orbit of Uranus from 1690 to 1895, concluded that one trans-Neptunian planet alone could not account for the discrepancies in its orbit, and postulated the position of two planets he believed were responsible. The second was launched when Gabriel Dallet suggested that a single trans-Neptunian planet lying at 47 AU could account for the motion of Uranus. Pickering agreed to examine plates for any suspected planets. In neither case were any found. [11]

In 1902, after observing the orbits of comets with aphelia beyond Neptune, Theodor Grigull of Münster, Germany proclaimed the existence of a Uranus-sized planet at 50 AU with a 360-year period, which he named Hades, cross-checking with the deviations in the orbit of Uranus. In 1921, Grigull revised his orbital period to 310-330 years, to better fit the observed deviations. [13]

In 1909, Thomas Jefferson Jackson See, an astronomer with a reputation as an egocentric contrarian, opined "that there is certainly one, most likely two and possibly three planets beyond Neptune". [14] Tentatively naming the first planet "Oceanus", he placed their respective distances at 42, 56 and 72 AU from the Sun. He gave no indication as to how he determined their existence, and no known searches were mounted to locate them. [14]

In 1911, Indian astronomer Venkatesh P. Ketakar suggested the existence of two trans-Neptunian planets, which he named Brahma and Vishnu, by reworking the patterns observed by Pierre-Simon Laplace in the planetary satellites of Jupiter and applying them to the outer planets. [15] The three inner Galilean moons of Jupiter, Io, Europa and Ganymede, are locked in a complicated 1:2:4 resonance called a Laplace resonance. [16] Ketakar suggested that Uranus, Neptune and his hypothetical trans-Neptunian planets were locked in Laplace-like resonances. His calculations predicted a mean distance for Brahma of 38.95 AU and an orbital period of 242.28 Earth years (3:4 resonance with Neptune). When Pluto was discovered 19 years later, its mean distance of 39.48 AU and orbital period of 248 Earth years were close to Ketakar's prediction (Pluto in fact has a 2:3 resonance with Neptune). Ketakar made no predictions for the orbital elements other than mean distance and period. It is not clear how Ketakar arrived at these figures, and his second planet, Vishnu, was never located. [15]

In 1894, with the help of William Pickering, Percival Lowell (a wealthy Bostonian) founded the Lowell Observatory in Flagstaff, Arizona. In 1906, convinced he could resolve the conundrum of Uranus's orbit, he began an extensive project to search for a trans-Neptunian planet, [17] which he named Planet X, a name previously used by Gabriel Dallet. [11] The X in the name represents an unknown and is pronounced as the letter, as opposed to the Roman numeral for 10 (at the time, Planet X would have been the ninth planet). Lowell's hope in tracking down Planet X was to establish his scientific credibility, which had eluded him due to his widely derided belief that channel-like features visible on the surface of Mars were canals constructed by an intelligent civilization. [18]

Lowell's first search focused on the ecliptic, the plane encompassed by the zodiac where the other planets in the Solar System lie. Using a 5-inch photographic camera, he manually examined over 200 three-hour exposures with a magnifying glass, and found no planets. At that time Pluto was too far above the ecliptic to be imaged by the survey. [17] After revising his predicted possible locations, Lowell conducted a second search from 1914 to 1916. [17] In 1915, he published his Memoir of a Trans-Neptunian Planet, in which he concluded that Planet X had a mass roughly seven times that of Earth—about half that of Neptune [19] —and a mean distance from the Sun of 43 AU. He assumed Planet X would be a large, low-density object with a high albedo, like the giant planets. As a result, it would show a disc with diameter of about one arcsecond and an apparent magnitude between 12 and 13—bright enough to be spotted. [17] [20]

Separately, in 1908, Pickering announced that, by analysing irregularities in Uranus's orbit, he had found evidence for a ninth planet. His hypothetical planet, which he termed "Planet O" (because it came after "N", i.e. Neptune), [21] possessed a mean orbital radius of 51.9 AU and an orbital period of 373.5 years. [11] Plates taken at his observatory in Arequipa, Peru, showed no evidence for the predicted planet, and British astronomer P. H. Cowell showed that the irregularities observed in Uranus's orbit virtually disappeared once the planet's displacement of longitude was taken into account. [11] Lowell himself, despite his close association with Pickering, dismissed Planet O out of hand, saying, "This planet is very properly designated "O", [for it] is nothing at all." [22] Unbeknownst to Pickering, four of the photographic plates taken in the search for "Planet O" by astronomers at the Mount Wilson Observatory in 1919 captured images of Pluto, though this was only recognised years later. [23] Pickering went on to suggest many other possible trans-Neptunian planets up to the year 1932, which he named P, Q, R, S, T, and U none were ever detected. [15]

### Discovery of Pluto Edit

Lowell's sudden death in 1916 temporarily halted the search for Planet X. Failing to find the planet, according to one friend, "virtually killed him". [24] Lowell's widow, Constance, engaged in a legal battle with the observatory over Lowell's legacy which halted the search for Planet X for several years. [25] In 1925, the observatory obtained glass discs for a new 13 in (33 cm) wide-field telescope to continue the search, constructed with funds from Abbott Lawrence Lowell, [26] Percival's brother. [17] In 1929 the observatory's director, Vesto Melvin Slipher, summarily handed the job of locating the planet to Clyde Tombaugh, a 22-year-old Kansas farm boy who had only just arrived at the Lowell Observatory after Slipher had been impressed by a sample of his astronomical drawings. [25]

Tombaugh's task was to systematically capture sections of the night sky in pairs of images. Each image in a pair was taken two weeks apart. He then placed both images of each section in a machine called a blink comparator, which by exchanging images quickly created a time lapse illusion of the movement of any planetary body. To reduce the chances that a faster-moving (and thus closer) object be mistaken for the new planet, Tombaugh imaged each region near its opposition point, 180 degrees from the Sun, where the apparent retrograde motion for objects beyond Earth's orbit is at its strongest. He also took a third image as a control to eliminate any false results caused by defects in an individual plate. Tombaugh decided to image the entire zodiac, rather than focus on those regions suggested by Lowell. [17]

By the beginning of 1930, Tombaugh's search had reached the constellation of Gemini. On 18 February 1930, after searching for nearly a year and examining nearly 2 million stars, Tombaugh discovered a moving object on photographic plates taken on 23 January and 29 January of that year. [27] A lesser-quality photograph taken on January 21 confirmed the movement. [25] Upon confirmation, Tombaugh walked into Slipher's office and declared, "Doctor Slipher, I have found your Planet X." [25] The object lay just six degrees from one of two locations for Planet X Lowell had suggested thus it seemed he had at last been vindicated. [25] After the observatory obtained further confirmatory photographs, news of the discovery was telegraphed to the Harvard College Observatory on March 13, 1930. The new object was later precovered on photographs dating back to 19 March 1915. [23] The decision to name the object Pluto was intended in part to honour Percival Lowell, as his initials made up the word's first two letters. [28] After discovering Pluto, Tombaugh continued to search the ecliptic for other distant objects. He found hundreds of variable stars and asteroids, as well as two comets, but no further planets. [29]

### Pluto loses Planet X title Edit

To the observatory's disappointment and surprise, Pluto showed no visible disc it appeared as a point, no different from a star, and, at only 15th magnitude, was six times dimmer than Lowell had predicted, which meant it was either very small, or very dark. [17] Because Lowell astronomers thought Pluto was massive enough to perturb planets, they assumed that its albedo could be no less than 0.07 (meaning that it reflected only 7% of the light that hit it) about as dark as asphalt and similar to that of Mercury, the least reflective planet known. [1] This would give Pluto an estimated mass of no more than 70% that of Earth. [1] Observations also revealed that Pluto's orbit was very elliptical, far more than that of any other planet. [30]

Almost immediately, some astronomers questioned Pluto's status as a planet. Barely a month after its discovery was announced, on April 14, 1930, in an article in The New York Times, Armin O. Leuschner suggested that Pluto's dimness and high orbital eccentricity made it more similar to an asteroid or comet: "The Lowell result confirms the possible high eccentricity announced by us on April 5. Among the possibilities are a large asteroid greatly disturbed in its orbit by close approach to a major planet such as Jupiter, or it may be one of many long-period planetary objects yet to be discovered, or a bright cometary object." [30] [31] In that same article, Harvard Observatory director Harlow Shapley wrote that Pluto was a "member of the Solar System not comparable with known asteroids and comets, and perhaps of greater importance to cosmogony than would be another major planet beyond Neptune." [31] In 1931, using a mathematical formula, Ernest W. Brown asserted (in agreement with E. C. Bower) that the presumed irregularities in the orbit of Uranus could not be due to the gravitational effect of a more distant planet, and thus that Lowell's supposed prediction was "purely accidental". [32]

Throughout the mid-20th century, estimates of Pluto's mass were revised downward. In 1931, Nicholson and Mayall calculated its mass, based on its supposed effect on the giant planets, as roughly that of Earth [33] a value somewhat in accord with the 0.91 Earth mass calculated in 1942 by Lloyd R. Wylie at the US Naval Observatory, using the same assumptions. [34] In 1949, Gerard Kuiper's measurements of Pluto's diameter with the 200-inch telescope at Mount Palomar Observatory led him to the conclusion that it was midway in size between Mercury and Mars and that its mass was most probably about 0.1 Earth mass. [35]

In 1973, based on the similarities in the periodicity and amplitude of brightness variation with Triton, Dennis Rawlins conjectured Pluto's mass must be similar to Triton's. In retrospect, the conjecture turns out to have been correct it had been argued by astronomers Walter Baade and E.C. Bower as early as 1934. [36] However, because Triton's mass was then believed to be roughly 2.5% of the Earth–Moon system (more than ten times its actual value), Rawlins's determination for Pluto's mass was similarly incorrect. It was nonetheless a meagre enough value for him to conclude Pluto was not Planet X. [37] In 1976, Dale Cruikshank, Carl Pilcher, and David Morrison of the University of Hawaii analysed spectra from Pluto's surface and determined that it must contain methane ice, which is highly reflective. This meant that Pluto, far from being dark, was in fact exceptionally bright, and thus was probably no more than 1 ⁄ 100 Earth mass. [38] [39]

Mass estimates for Pluto:
Year Mass Notes
1931 1 Earth Nicholson & Mayall [33]
1942 0.91 Earth Wylie [34]
1948 0.1 (1/10 Earth) Kuiper [35]
1973 0.025 (1/40 Earth) Rawlins [37]
1976 0.01 (1/100 Earth) Cruikshank, Pilcher, & Morrison [39]
1978 0.002 (1/500 Earth) Christy & Harrington [40]
2006 0.00218 (1/459 Earth) Buie et al. [41]

Pluto's size was finally determined conclusively in 1978, when American astronomer James W. Christy discovered its moon Charon. This enabled him, together with Robert Sutton Harrington of the U.S. Naval Observatory, to measure the mass of the Pluto–Charon system directly by observing the moon's orbital motion around Pluto. [40] They determined Pluto's mass to be 1.31×10 22 kg roughly one five-hundredth that of Earth or one-sixth that of the Moon, and far too small to account for the observed discrepancies in the orbits of the outer planets. Lowell's "prediction" had been a coincidence: If there was a Planet X, it was not Pluto. [42]

### Further searches for Planet X Edit

After 1978, a number of astronomers kept up the search for Lowell's Planet X, convinced that, because Pluto was no longer a viable candidate, an unseen tenth planet must have been perturbing the outer planets. [43]

In the 1980s and 1990s, Robert Harrington led a search to determine the real cause of the apparent irregularities. [43] He calculated that any Planet X would be at roughly three times the distance of Neptune from the Sun its orbit would be highly eccentric, and strongly inclined to the ecliptic—the planet's orbit would be at roughly a 32-degree angle from the orbital plane of the other known planets. [44] This hypothesis was met with a mixed reception. Noted Planet X sceptic Brian G. Marsden of the Minor Planet Center pointed out that these discrepancies were a hundredth the size of those noticed by Le Verrier, and could easily be due to observational error. [45]

In 1972, Joseph Brady of the Lawrence Livermore National Laboratory studied irregularities in the motion of Halley's Comet. Brady claimed that they could have been caused by a Jupiter-sized planet beyond Neptune at 59 AU that is in a retrograde orbit around the Sun. [46] However, both Marsden and Planet X proponent P. Kenneth Seidelmann attacked the hypothesis, showing that Halley's Comet randomly and irregularly ejects jets of material, causing changes to its own orbital trajectory, and that such a massive object as Brady's Planet X would have severely affected the orbits of known outer planets. [47]

Although its mission did not involve a search for Planet X, the IRAS space observatory made headlines briefly in 1983 due to an "unknown object" that was at first described as "possibly as large as the giant planet Jupiter and possibly so close to Earth that it would be part of this Solar System". [48] Further analysis revealed that of several unidentified objects, nine were distant galaxies and the tenth was "interstellar cirrus" none were found to be Solar System bodies. [49]

In 1988, A. A. Jackson and R. M. Killen studied the stability of Pluto's resonance with Neptune by placing test "Planet X-es" with various masses and at various distances from Pluto. Pluto and Neptune's orbits are in a 3:2 resonance, which prevents their collision or even any close approaches, regardless of their separation in the z axis. It was found that the hypothetical object's mass had to exceed 5 Earth masses to break the resonance, and the parameter space is quite large and a large variety of objects could have existed beyond Pluto without disturbing the resonance. Four test orbits of a trans-Plutonian planet have been integrated forward for four million years in order to determine the effects of such a body on the stability of the Neptune–Pluto 3:2 resonance. Planets beyond Pluto with masses of 0.1 and 1.0 Earth masses in orbits at 48.3 and 75.5 AU, respectively, do not disturb the 3:2 resonance. Test planets of 5 Earth masses with semi-major axes of 52.5 and 62.5 AU disrupt the four-million-year libration of Pluto's argument of perihelion. [50]

### Planet X disproved Edit

Harrington died in January 1993, without having found Planet X. [51] Six months before, E. Myles Standish had used data from Voyager 2's 1989 flyby of Neptune, which had revised the planet's total mass downward by 0.5%—an amount comparable to the mass of Mars [51] —to recalculate its gravitational effect on Uranus. [52] When Neptune's newly determined mass was used in the Jet Propulsion Laboratory Developmental Ephemeris (JPL DE), the supposed discrepancies in the Uranian orbit, and with them the need for a Planet X, vanished. [3] There are no discrepancies in the trajectories of any space probes such as Pioneer 10, Pioneer 11, Voyager 1, and Voyager 2 that can be attributed to the gravitational pull of a large undiscovered object in the outer Solar System. [53] Today, most astronomers agree that Planet X, as Lowell defined it, does not exist. [54]

## Hunt for ninth planet reveals new extremely distant Solar System objects

Washington, DC&mdash In the race to discover a proposed ninth planet in our Solar System, Carnegie&rsquos Scott Sheppard and Chadwick Trujillo of Northern Arizona University have observed several never-before-seen objects at extreme distances from the Sun in our Solar System. Sheppard and Trujillo have now submitted their latest discoveries to the International Astronomical Union&rsquos Minor Planet Center for official designations. A paper about the discoveries has also been accepted to The Astronomical Journal.

The more objects that are found at extreme distances, the better the chance of constraining the location of the ninth planet that Sheppard and Trujillo first predicted to exist far beyond Pluto (itself no longer classified as a planet) in 2014. The placement and orbits of small, so-called extreme trans-Neptunian objects, can help narrow down the size and distance from the Sun of the predicted ninth planet, because that planet&rsquos gravity influences the movements of the smaller objects that are far beyond Neptune. The objects are called trans-Neptunian because their orbits around the Sun are greater than Neptune&rsquos.

In 2014, Sheppard and Trujillo announced the discovery of 2012 VP113 (nicknamed &ldquoBiden&rdquo), which has the most-distant known orbit in our Solar System. At this time, Sheppard and Trujillo also noticed that the handful of known extreme trans-Neptunian objects all cluster with similar orbital angles. This lead them to predict that there is a planet at more than 200 times our distance from the Sun. Its mass, ranging in possibility from several Earths to a Neptune equivalent, is shepherding these smaller objects into similar types of orbits.

Some have called this Planet X or Planet 9. Further work since 2014 showed that this massive ninth planet likely exists by further constraining its possible properties. Analysis of &ldquoneighboring&rdquo small body orbits suggest that it is several times more massive than the Earth, possibly as much as 15 times more so, and at the closest point of its extremely stretched, oblong orbit it is at least 200 times farther away from the Sun than Earth. (This is over 5 times more distant than Pluto.)

&ldquoObjects found far beyond Neptune hold the key to unlocking our Solar System&rsquos origins and evolution,&rdquo Sheppard explained. &ldquoThough we believe there are thousands of these small objects, we haven&rsquot found very many of them yet, because they are so far away. The smaller objects can lead us to the much bigger planet we think exists out there. The more we discover, the better we will be able to understand what is going on in the outer Solar System.&rdquo

Sheppard and Trujillo, along with David Tholen of the University of Hawaii, are conducting the largest, deepest survey for objects beyond Neptune and the Kuiper Belt and have covered nearly 10 percent of the sky to date using some of the largest and most advanced telescopes and cameras in the world, such as the Dark Energy Camera on the NOAO 4-meter Blanco telescope in Chile and the Japanese Hyper Suprime Camera on the 8-meter Subaru telescope in Hawaii. As they find and confirm extremely distant objects, they analyze whether their discoveries fit into the larger theories about how interactions with a massive distant planet could have shaped the outer Solar System.

&ldquoRight now we are dealing with very low-number statistics, so we don&rsquot really understand what is happening in the outer Solar System,&rdquo Sheppard said. &ldquoGreater numbers of extreme trans-Neptunian objects must be found to fully determine the structure of our outer Solar System.&rdquo

According to Sheppard, &ldquowe are now in a similar situation as in the mid-19th century when Alexis Bouvard noticed Uranus&rsquo orbital motion was peculiar, which eventually led to the discovery of Neptune.&rdquo

The new objects they have submitted to the Minor Planet Center for designation include 2014 SR349, which adds to the class of the rare extreme trans-Neptunian objects. It exhibits similar orbital characteristics to the previously known extreme bodies whose positions and movements led Sheppard and Trujillo to initially propose the influence of Planet X.

Another new extreme object they found, 2013 FT28, has some characteristics similar to the other extreme objects but also some differences. The orbit of an object is defined by six parameters. The clustering of several of these parameters is the main argument for a ninth planet to exist in the outer solar system. 2013 FT28 shows similar clustering in some of these parameters (its semi-major axis, eccentricity, inclination, and argument of perihelion angle, for angle enthusiasts out there) but one of these parameters, an angle called the longitude of perihelion, is different from that of the other extreme objects, which makes that particular clustering trend less strong.

Another discovery, 2014 FE72, is the first distant Oort Cloud object found with an orbit entirely beyond Neptune. It has an orbit that takes the object so far away from the Sun (some 3000 times farther than Earth) that it is likely being influenced by forces of gravity from beyond our Solar System such as other stars and the galactic tide. It is the first object observed at such a large distance.

Caption: An illustration of the orbits of the new and previously known extremely distant Solar System objects. The clustering of most of their orbits indicates that they are likely be influenced by something massive and very distant, the proposed Planet X. Image is courtesy of Robin Dienel.

Caption: An artist&rsquos conception of Planet X, courtesy of Robin Dienel.

## 9th planet location? - Astronomy

On the Earth Magnetic page of this site, I explained and manifested a different magnetic configuration to what most Scientists are claiming for planet Earth. While there is an induced south polarity magnetic field around the axis of rotation in the North Pole and South Pole, there exists a permanent magnet the solid Inner Core, that is free to swivel, tilt or flip inside the molten Outer Core. The fact that the 2 permanent magnetic poles are shifting eastward tells of a strong magnetic pull by another magnet/ planet that is unknown to current planetary configuration. The unprecedented present speed of the magnetic pole shift from Canada towards Siberia at 4 times the speed in the last century foretells such an unknown planet into the solar system that was never confirmed to exist.

However, in February 2011, the scientific journal Icarus published a paper by astrophysicists John Matese and Daniel Whitmire, who proposed the existence of a binary companion to our sun, larger than Jupiter, in the long-hypothesized “Oort cloud” — a faraway repository of small icy bodies at the edge of our solar system. The researchers use the name “Tyche”, which means “luck” in Greek, for the hypothetical planet. Their paper argues that evidence for the planet would have been recorded by NASA Wide-field Infrared Survey Explorer (WISE). But it hasn’t!

A new research that was published in the journal Monthly Notices of the Royal Astronomical Society Letters, is based on analysis of an effect called the “Kozai mechanism”, by which a large body disturbs the orbit of a smaller and more distant object. The research is being carried out by scientists at the University of Madrid and the University of Cambridge. They have been tracking large asteroids known as “extreme trans-Neptunion objects” (Etnos), which orbit the sun at least six billion kilometers away. Spanish lead scientist Professor Carlos de la Fuente Marcos, from the Complutense University of Madrid (UCM), explained: “This excess of objects with unexpected orbital parameters makes us believe that some invisible forces are altering the distribution of the orbital elements of the Etnos, and we consider that the most probable explanation is that other unknown planets exist beyond”. The scientists have found the objects orbit the Sun in a manner consistent with them being subject to the gravitational pull of a planet at least as large as Earth .

In January 2016, Caltech researchers have found evidence of a giant planet tracing a bizarre, highly elongated orbit in the outer solar system.

## Photographic Proof

Benjamin Apthorp Gould had a perfect Boston pedigree: son of the headmaster of the Boston Latin School, grandson of a Revolutionary War veteran, he graduated from Harvard College— where else?—in 1844, all of 19 years old. Then, having paid his debt to ancestry, he kicked over the traces. Heading to Europe, he took work at the Greenwich, Paris, and Berlin observatories just as Neptune made its (perceived) solar system debut. He studied math at the University of Göttingen, and in 1848 became the first American to receive a Ph.D. in astronomy—still only 23! On returning to Boston in 1849, he was appalled by the primitive state of research in his home country, and took it on himself to transform American astronomy. Most important for the future of the discipline as a whole, in the 1860s he became one of the first investigators skilled in the new technique of astrophotography, the marriage of a camera to a telescope.

Gould brought his cameras with him when he traveled to observe the same 1869 eclipse at which the amateurs had spied a possible Vulcan. He set up in the town of Burlington, Iowa, working on the right bank of the Mississippi River. His goal: to study the solar corona—the sun’s atmosphere, visible only during totality—and to survey the region close to the sun as precisely as possible, looking for whatever might reveal itself within the orbit of Mercury. He and his assistants made 42 photographs during the eclipse. Gould also examined many of what he estimated were 400 images made by others along the path of totality. In all those pictures, he saw—nothing.

Gould sent his findings to Yvon Villarceau at the Paris Académie. He began with a baseline estimate: in the shadow of the eclipse, a planet or planets substantial enough to account for Mercury’s motion should shine about as brightly as Polaris, the North Star, a second magnitude object—easily seen by the naked eye. His photographic equipment, Gould wrote, was sensitive enough to detect any object down to the limit of unaided human perception, well below what he considered the plausible threshold for the discovery of Vulcan. Thus, he concluded, “I am convinced that this investigation dispenses with the hypothesis that the movement of the perihelion of Mercury results from the effects of one or many small interior planets.” I’ve looked, he said, and Vulcan ain’t there.

Not so fast, though: Villarceau added a note of his own to the published version of Gould’s letter. It wasn’t necessary to accept the American’s conclusion as absolute, he argued. There were configurations of asteroids, for example, that could both provide the necessary gravitational influence on Mercury and evade detection. In other words: the problem remained. Mercury still wobbled, and in Newton’s cosmos, its motion still demanded something like a Vulcan. Absence of evidence, to invoke what has become a cliché, could not be taken as evidence of absence.

Others agreed. William F. Denning was by general agreement Victorian Britain’s greatest amateur astronomer. He had made his reputation with the first comprehensive analysis of the motion of the Perseid meteor shower, still to be seen from late July to its peak in mid-August, and meteors remained his primary obsession. Vulcan, though, was a sufficiently pressing problem to draw his attention. He was an obligate organizer, and he used his influence to launch a systematic search for solar transits during the next likely window: March and April of 1869. He persuaded 15 other sky-watchers to put the sun “continually under observation, when visible…with a view of rediscovering the suspected intra-Mercurial planet Vulcan.”

Vulcan obstinately refused to appear.

Glimpse after glimpse of possible candidate planets offered tantalizing hints.

Denning tried again the next year, recruiting a team of 25 to chase the elusive planet during the spring transit season in 1870, and yet once more with a plea to collaborators in 1871. As he gathered his volunteers, he had declared that his aim was to settle the issue once and for all. “There is every reason,” he wrote, “to suppose that the search will end satisfactorily, if not successfully.” End it did. After three conscientious attempts at locating the missing planet, he seems to have concluded that there was nothing more to be done. He did not repeat his call for aid on the search, and those fellow amateurs of the sky who had responded to him were released to their prior ambitions.

After what was to that point the largest systematic search for the object since word of Lescarbault’s sighting first spread, Denning’s null result left Vulcan in a predicament. An explanation for Mercury’s errant motion remained necessary. On one side of the ledger, there was the blunt fact of Le Verrier and his genuine abilities. No one doubted his calculation, and no one should have—a restudy of Mercury’s perihelion advance in the 1880s confirmed and slightly enlarged the very real anomaly he identified. Glimpse after glimpse of possible candidate planets offered tantalizing hints—yet a decade into the search, the most rigorous observers kept coming up empty. What could be done?

A way out was obvious to the more mathematically sophisticated Vulcan hunters. People simply could have gotten their sums wrong. There were enough imprecise assumptions about the elements of a putative Vulcan’s orbit so that calculations for transits could just be wrong. Princeton’s Stephen Alexander told his fellow members of the National Academy of Sciences that he had reworked Vulcan’s elements to arrive at the conclusion that there should be “a planet or group of planets at a distance of about twenty-one million miles from the sun, and with a period of 34 days and 16 hours.” In other words: we may have been looking in the wrong places, or at the wrong times. Vulcan could be elusive, but not absent.

That claim seemed to be confirmed when Heinrich Weber— for once, an actual well-trained professional astronomer—sent word from northeast China that he had seen a dark circular shape transit the sun on April 4, 1876. Sunspot expert and Vulcan devotee Rupert Wolf passed word of his colleague’s sighting on to Paris, taking a bit of a victory lap as he did so. He told Le Verrier that “the interval between Lescarbault’s observation and Weber’s amounts to exactly one hundred and forty eight times the period” that Wolf had calculated so many years before.

The news enthralled Le Verrier—and energized yet another corps of planet seekers more eager than expert. As historian Robert Fontenrose put it, “everyone with a telescope was looking for Vulcan some found it.” For a time, Scientific American eagerly trumpeted each new “discovery”: from “B. B.” in New Jersey to a Samuel Wilde in Maryland, to W. G. Wright in San Bernardino, to witnesses from beyond the grave, in the form of a minister who remembered that Professor Joseph S. Hubbard “had repeatedly assured him he had seen Vulcan with the Yale College Telescope.” New Vulcans kept turning up that autumn in seemingly every mail delivery, until at last Scientific American cried “Uncle!” and, following its December 16, 1876, issue, declined to publish any more such happy memories. It was as if the question of Vulcan had ridden a seesaw since 1859. Occasional sightings and seemingly consistent calculations would propel it up to the top of the ride hard-nosed attempts to verify its existence sent it crashing back down. Now, for all that the editors of Scientific American had tired of the flood of anecdotes, the teeter-totter was pointing up: between the one seemingly authoritative report from China and the sheer number, if not the quality of sky-gazer accounts, the matter of Vulcan seemed just about settled.

The popular press certainly thought so. In late 1876, The Manufacturer and Builder said, “Our text books on astronomy will have to be revised again, as there is no longer any doubt about the existence of a planet between Mercury and the sun.” That autumn, The New York Times was even less bashful, interrupting its coverage of the Hayes-Tilden presidential election to assert that any residual doubts about the intra-Mercurian planet could be put down to simple professional jealousy: “ ‘Vulcan may possibly exist,’ said the conservative astronomers, ‘but Professor So and So never saw it…’ ”—pure us-against-them nastiness, according to the Times , adding “they would hint, with sneering astronomic smiles, that too much tea sometimes plays strange pranks with the imagination.”

Now, such too-smart fellows were about to receive their due, the newspaper proclaimed. Why? Because, in the wake of Weber’s report, the grand old man himself, Urbain-Jean-Joseph Le Verrier, had roused himself. “The man who untied Neptune with his nose—so to speak—cannot be accused of confounding accidental flies with actual planets. When he firmly asserts that he has not only discovered Vulcan, but has calculated its elements, and arranged a transit especially for its exhibition to routing astronomers…” the Times wrote, “there is an end of all discussion. Vulcan exists…”

The Times got at least one thing right. After shifting his attention to other problems for a few years, Le Verrier had indeed returned to the contemplation of Vulcan. Wolf’s news had fired his passion for the planet, and he began a comprehensive reexamination of everything that might bear upon its existence. Starting with yet another catalogue of claimed sightings dating back to 1820, he identified five observations spread from 1802 to 1862 that seemed to him most likely to represent repeat glimpses of a single planet. That allowed him to construct a new theory for the planet, complete with the prediction the Times had rated so high: a transit that could perhaps be observed, Le Verrier suggested, on October 2 nd or 3 rd .

The headline writers would be disappointed. Vulcan did not cross the face of the sun in early October. More confounding, Weber’s revelation from China was debunked: two photographs made at the Greenwich Observatory clearly revealed his “Vulcan” to be just another sunspot. Scientific American called this the “ coup de grace ” for this latest “discovery,” but, as usual in the annals of Vulcan, its real impact was more deflating than destructive. Le Verrier’s calculation turned on earlier observations, not Weber’s, and there was a way to explain away the missed transit, by positing an orbit for Vulcan that was much more steeply inclined than previously assumed. Thus Le Verrier hedged his bets: there might be a chance to see Vulcan against the face of the sun in the spring of 1877, but given the full range of possible orbits this insufferably errant planet might occupy, it might be five years or more before the next transit would occur.

## More support for Planet Nine

This illustration depicts orbits of distant Kuiper Belt objects and Planet Nine. Orbits rendered in purple are primarily controlled by Planet Nine's gravity and exhibit tight orbital clustering. Green orbits, on the other hand, are strongly coupled to Neptune, and exhibit a broader orbital dispersion. Updated orbital calculations suggest that Planet Nine is an approximately 5 Earth mass planet that resides on a mildly eccentric orbit with a period of about ten thousand years. Credit: James Tuttle Keane/Caltech

Corresponding with the three-year anniversary of their announcement hypothesizing the existence of a ninth planet in the solar system, Caltech's Mike Brown and Konstantin Batygin are publishing a pair of papers analyzing the evidence for Planet Nine's existence.

The papers offer new details about the suspected nature and location of the planet, which has been the subject of an intense international search ever since Batygin and Brown's 2016 announcement.

The first, titled "Orbital Clustering in the Distant Solar System," was published in The Astronomical Journal on January 22. The Planet Nine hypothesis is founded on evidence suggesting that the clustering of objects in the Kuiper Belt, a field of icy bodies that lies beyond Neptune, is influenced by the gravitational tugs of an unseen planet. It has been an open question as to whether that clustering is indeed occurring, or whether it is an artifact resulting from bias in how and where Kuiper Belt objects are observed.

To assess whether observational bias is behind the apparent clustering, Brown and Batygin developed a method to quantify the amount of bias in each individual observation, then calculated the probability that the clustering is spurious. That probability, they found, is around one in 500.

"Though this analysis does not say anything directly about whether Planet Nine is there, it does indicate that the hypothesis rests upon a solid foundation," says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy.

The second paper is titled "The Planet Nine Hypothesis," and is an invited review that will be published in the next issue of Physics Reports. The paper provides thousands of new computer models of the dynamical evolution of the distant solar system and offers updated insight into the nature of Planet Nine, including an estimate that it is smaller and closer to the sun than previously suspected. Based on the new models, Batygin and Brown—together with Fred Adams and Juliette Becker (BS '14) of the University of Michigan—concluded that Planet Nine has a mass of about five times that of the earth and has an orbital semimajor axis in the neighborhood of 400 astronomical units (AU), making it smaller and closer to the sun than previously suspected—and potentially brighter. Each astronomical unit is equivalent to the distance between the center of Earth and the center of the sun, or about 149.6 million kilometers.

"At five Earth masses, Planet Nine is likely to be very reminiscent of a typical extrasolar super-Earth," says Batygin, an assistant professor of planetary science and Van Nuys Page Scholar. Super-Earths are planets with a mass greater than Earth's, but substantially less than that of a gas giant. "It is the solar system's missing link of planet formation. Over the last decade, surveys of extrasolar planets have revealed that similar-sized planets are very common around other sun-like stars. Planet Nine is going to be the closest thing we will find to a window into the properties of a typical planet of our galaxy."

Batygin and Brown presented the first evidence that there might be a giant planet tracing a bizarre, highly elongated orbit through the outer solar system on January 20, 2016. That June, Brown and Batygin followed up with more details, including observational constraints on the planet's location along its orbit.

Over the next two years, they developed theoretical models of the planet that explained other known phenomena, such as why some Kuiper Belt objects have a perpendicular orbit with respect to the plane of the solar system. The resulting models increased their confidence in Planet Nine's existence.

After the initial announcement, astronomers around the world, including Brown and Batygin, began searching for observational evidence of the new planet. Although Brown and Batygin have always accepted the possibility that Planet Nine might not exist, they say that the more they examine the orbital dynamics of the solar system, the stronger the evidence supporting it seems.

"My favorite characteristic of the Planet Nine hypothesis is that it is observationally testable," Batygin says. "The prospect of one day seeing real images of Planet Nine is absolutely electrifying. Although finding Planet Nine astronomically is a great challenge, I'm very optimistic that we will image it within the next decade."

Michael E. Brown et al. Orbital Clustering in the Distant Solar System, The Astronomical Journal (2019). DOI: 10.3847/1538-3881/aaf051

## More Support for Planet Nine

Corresponding with the three-year anniversary of their announcement hypothesizing the existence of a ninth planet in the solar system, Caltech's Mike Brown and Konstantin Batygin are publishing a pair of papers analyzing the evidence for Planet Nine's existence.

The papers offer new details about the suspected nature and location of the planet, which has been the subject of an intense international search ever since Batygin and Brown's 2016 announcement.

The first, titled "Orbital Clustering in the Distant Solar System," was published in The Astronomical Journal on January 22. The Planet Nine hypothesis is founded on evidence suggesting that the clustering of objects in the Kuiper Belt, a field of icy bodies that lies beyond Neptune, is influenced by the gravitational tugs of an unseen planet.It has been an open

question as to whether that clustering is indeed occurring, or whether it is an artifact resulting from bias in how and where Kuiper Belt objects are observed.

To assess whether observational bias is behind the apparent clustering, Brown and Batygin developed a method to quantify the amount of bias in each individual observation, then calculated the probability that the clustering is spurious. That probability, they found, is around one in 500.

"Though this analysis does not say anything directly about whether Planet Nine is there, it does indicate that the hypothesis rests upon a solid foundation," says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy.

The second paper is titled "The Planet Nine Hypothesis," and is an invited review that will be published in the next issue of Physics Reports. The paper provides thousands of new computer models of the dynamical evolution of the distant solar system and offers updated insight into the nature of Planet Nine, including an estimate that it is smaller and closer to the sun than previously suspected. Based on the new models, Batygin and Brown—together with Fred Adams and Juliette Becker (BS ✔) of the University of Michigan—concluded that Planet Nine has a mass of about five times that of the earth and has an orbital semimajor axis in the neighborhood of 400 astronomical units (AU), making it smaller and closer to the sun than previously suspected—and potentially brighter. Each astronomical unit is equivalent to the distance between the center of Earth and the center of the sun, or about 149.6 million kilometers.

"At five Earth masses, Planet Nine is likely to be very reminiscent of a typical extrasolar super-Earth," says Batygin, an assistant professor of planetary science and Van Nuys Page Scholar. Super-Earths are planets with a mass greater than Earth's, but substantially less than that of a gas giant. "It is the solar system's missing link of planet formation. Over the last decade, surveys of extrasolar planets have revealed that similar-sized planets are very common around other sun-like stars. Planet Nine is going to be the closest thing we will find to a window into the properties of a typical planet of our galaxy."

Batygin and Brown presented the first evidence that there might be a giant planet tracing a bizarre, highly elongated orbit through the outer solar system on January 20, 2016. That June, Brown and Batygin followed up with more details, including observational constraints on the planet's location along its orbit.

Over the next two years, they developed theoretical models of the planet that explained other known phenomena, such as why some Kuiper Belt objects have a perpendicular orbit with respect to the plane of the solar system. The resulting models increased their confidence in Planet Nine's existence.

After the initial announcement, astronomers around the world, including Brown and Batygin, began searching for observational evidence of the new planet. Although Brown and Batygin have always accepted the possibility that Planet Nine might not exist, they say that the more they examine the orbital dynamics of the solar system, the stronger the evidence supporting it seems.

"My favorite characteristic of the Planet Nine hypothesis is that it is observationally testable," Batygin says. "The prospect of one day seeing real images of Planet Nine is absolutely electrifying. Although finding Planet Nine astronomically is a great challenge, I'm very optimistic that we will image it within the next decade."

The work was supported by the David and Lucile Packard Foundation and the Alfred P. Sloan Foundation.