Image copyright Reuters Image caption Michael Brown specializes in finding distant objects
Caltech scientists Michael Brown and Konstantin Batygin have provided evidence for the existence of a giant planet in the solar system, located even further from the Sun than Pluto.
The researchers reported that they have not yet been able to see it through a telescope. According to them, the planet was discovered when studying the movement of small celestial bodies in deep space.
The mass of the celestial body is about 10 times the mass of the Earth, but scientists have yet to verify its existence.
Institute astronomers have only a rough idea of where the planet might be in the starry sky, and no doubt their suggestion will launch a campaign to find it.
"There are many telescopes on Earth theoretically capable of finding it. I really hope that now, after our announcement, people around the world will start looking for the ninth planet," said Michael Brown.
Elliptical orbit
According to scientists, the space object is about 20 times farther from the Sun than Neptune, which is 4.5 billion km away.
Unlike the almost circular orbits of other planets in the Solar System, this object is supposed to move in an elliptical orbit, and a complete revolution around the Sun takes from 10 thousand to 20 thousand years.
Scientists have studied the movement of objects consisting mainly of ice in the Kuiper Belt. Pluto is in this belt.
The researchers noticed a certain location of some bodies in the Belt, in particular such large objects as Sedna and 2012 VP113. In their opinion, this can only be explained by the presence of an unknown large space object.
Image copyright AFP Image caption The idea of the existence of the so-called Planet X, located on the periphery of the solar system, has been discussed in scientific circles for more than 100 years."All the most distant objects move in the same direction on an inexplicable trajectory, and we realized that the only explanation for this is the existence of a large, distant planet that holds them together as they orbit the Sun," Brown said.
Planet X
The idea of the existence of the so-called Planet X, located on the periphery of the solar system, has been discussed in scientific circles for more than 100 years. She is remembered and then forgotten.
The current speculation is of particular interest because of the study's lead author.
Brown specializes in finding distant objects, and it was his discovery of the dwarf planet Eris in the Kuiper Belt in 2005 that caused Pluto to lose planetary status a year later.
Then it was assumed that Eris is slightly larger than Pluto, but now it has become clear that it is slightly smaller than it.
Researchers studying distant objects in the solar system have been speculating for some time on the possibility of a planet the size of Mars or Earth due to the size and shape of the planets in the Kuiper Belt. But until you can see the planet through a telescope, the idea of its existence will be perceived with skepticism.
The study by Michael Brown and Konstantin Batygin was published in the Astronomical Journal.
The structure of the solar system is quite simple. At its center is the Sun - a star ideal for the development of life: not too hot, but not too cold, not too bright, but not too dim, with a long lifetime and very moderate activity. Closer to the Sun are the planets of the terrestrial group, which, in addition to the Earth, includes Mercury, Venus and Mars. These planets are relatively low-mass, but are composed of rocky rocks which allows them to have a hard surface. IN last years the concept of the habitable zone is gaining popularity: the so-called interval of distances from the central star, within which liquid water can exist on the surface of a terrestrial planet. In the solar system, the habitable zone stretches roughly from the orbit of Venus to the orbit of Mars, but only Earth can boast of liquid water (at least in significant quantities).
Further from the Sun are the giant planets (Jupiter and Saturn) and the ice giants (Uranus and Neptune). The giants are significantly more massive than the terrestrial planets, but this mass is gained by them due to volatile compounds, which is why the giants are significantly less dense and lack a solid surface. Between the last planet of the terrestrial group - Mars - and the first giant planet - Jupiter - is the main asteroid belt; behind the last ice giant - Neptune - the periphery of the solar system begins. Previously, there was another planet, Pluto, but in 2006 the world astronomical community decided that Pluto did not live up to a real planet in terms of its parameters, and now the most distant planet in the solar system (known!) Is Neptune, orbiting 30 AU . from the Sun (more precisely, from 29.8 AU at perihelion to 30.4 AU at aphelion).
However, for quite a long time, many scientists have not left the idea that the number of planets in the solar system does not stop on Neptune. True, the farther the planet is from the Sun, the more difficult it is to detect it directly, but there are also indirect ways. One is to look for the gravitational influence of an invisible planet on the known bodies of the trans-Neptunian region. In particular, attempts have been repeatedly made, firstly, to find patterns in the orbits of long-period comets, and secondly, to explain these patterns by the attraction of a distant giant planet. In more extremist versions, the apparent periodicity in the extinction of living organisms on Earth or in the frequency of meteorite bombardment of our planet is considered a sign of the presence of a distant planet. However, until now, assumptions about unknown planets (Nemesis, Tyukhe, etc.), based on these regularities and periodicities, have not found wide recognition among the astronomical community. Not only the explanation, but the very existence of the regularities and periodicities to be explained seems rather unconvincing. In addition, as a rule, we are talking about fairly large bodies, perhaps many times more massive than Jupiter, which should be accessible to modern observational technology.
A new attempt to prove the existence of the ninth planet is also based on the search for signs of its gravitational influence, but not on long-period comets, but on Kuiper belt objects.
Kuiper Belt
The Kuiper belt is sometimes collectively referred to as all the objects inhabiting the periphery of the solar system. But in fact, they are several dynamically distinct groups: the classical Kuiper belt, the scattered disk, and resonant objects. The objects of the classical Kuiper belt revolve around the Sun in orbits with small inclinations and eccentricities, that is, in orbits of the "planetary" type. Scattered disk objects move in elongated orbits with perihelia in the region of Neptune's orbit, the orbits of resonant objects (Pluto among them) are in orbital resonance with Neptune.
The classical Kuiper belt ends rather abruptly at about 50 AU. Probably, it was there that the main boundary of the distribution of matter in the solar system passed. And although objects of the scattered disk and resonant objects at aphelion (the point of the orbit of a celestial body farthest from the Sun) move away from the Sun by hundreds of astronomical units, at perihelion (the point of the orbit closest to the Sun) they are close to Neptune, indicating that both are connected common origin with the classical Kuiper belt, and were “attached” to their modern orbits by the gravitational influence of Neptune.
Discovery of Sedna
The picture began to get more complicated in 2003, when the trans-Neptunian object (TNO) Sedna was discovered with a perihelion distance of 76 AU. Such a significant distance from the Sun means that Sedna could not get into its orbit as a result of interaction with Neptune, and therefore there was an assumption that it is a representative of a more distant population of the solar system - the hypothetical Oort cloud.
For some time, Sedna was the only known object with such an orbit. The discovery of the second "sednoid" in 2014 was reported by Chadwick Trujillo and Scott Sheppard. The object 2012 VP113 revolves around the Sun in an orbit with a perihelion distance of 80.5 AU, that is, even more than that of Sedna. Trujillo and Sheppard noticed that both Sedna and 2012 VP113 have similar values of the perihelion argument - the angle between the directions to the perihelion and to the ascending node of the orbit (the point of its intersection with the ecliptic). Interestingly, similar values of the perihelion argument (340° ± 55°) are typical for all objects with semi-major axes greater than 150 AU. and with perihelion distances greater than Neptune's perihelion distance. Trujillo and Sheppard suggested that such a grouping of objects near a particular value of the perihelion argument could be caused by the disturbing action of a distant massive (several Earth masses) planet.
Evidence for Planet X
A paper published in January 2016 by Konstantin Batygin and Michael Brown of the California Institute of Technology explores the possibility that the existence of a previously unknown planet can indeed explain the observed parameters of distant asteroids with similar values of the perihelion argument. The authors analytically and numerically studied the motion of test particles at the periphery of the Solar System over 4 billion years under the influence of a perturbing body with a mass of 10 Earth masses in an elongated orbit and showed that the presence of such a body actually leads to the observed configuration of TNO orbits with significant semi-major axes and perihelion distances. Moreover, the presence of an outer planet makes it possible to explain not only the existence of Sedna and other TNOs with similar values of the perihelion argument.
Unexpectedly for the authors in their simulations, the action of the perturbing body explained the existence of another TNO population, the origin of which has so far remained unclear, namely, the population of Kuiper belt objects in orbits with high inclinations. Finally, the work of Batygin and Brown predicts the existence of objects with large perihelion distances and other values of the perihelion argument, which provides an additional observational verification of their prediction.
Prospects for the discovery of a new planet
The main test of recent research, of course, should be the discovery of the "troublemaker" itself - the very planet whose attraction, according to the authors, determines the distribution of bodies with perihelions outside the classical Kuiper belt. The task of finding it is very difficult. Planet X should spend most of the time near aphelion, which can be over 1000 AU away. from the sun. Calculations indicate the possible location of the planet very approximately - its aphelion is located approximately in the direction opposite to the direction on the aphelions of the studied TNOs, but the orbital inclination cannot be determined from the data on the available TNOs with semi-major axes of the orbits. So the review of a very large area of the sky, where an unknown planet may be located, will last for many years. The search may become easier if other TNOs moving under the influence of Planet X are discovered, which will narrow the range of possible values for its orbital parameters.
WISE (Wide-Field Infrared Survey Explorer) - NASA's space telescope, launched in 2009 to study the sky in the infrared, could not see a hypothetical planet. An analogue of Saturn or Jupiter, WISE would detect at a distance of up to 30,000 AU, that is, more than necessary. But the estimates were carried out specifically for the giant planet with the corresponding own IR radiation. It is possible that these results do not scale to an ice giant like Neptune or even a less massive planet.
There is currently, in fact, one telescope suitable for searching for Planet X, and that is the Japanese Subaru Telescope in the Hawaiian Islands. Thanks to the 8.2-meter mirror, it collects a lot of light and therefore has a high sensitivity, while its equipment allows you to take pictures of fairly large areas of the sky (approximately the area of the full moon). But even under these conditions, it will take several years to survey the vast area of the sky where Planet X may be now. If it fails, one can only hope for a specialized survey telescope LSST, which is currently under construction in Chile. With a mirror with a diameter of 8.4 meters, it will have a field of view with a diameter of 3.5 ° (seven times larger than that of the Subaru). At the same time, survey observations will be its main task, unlike Subaru, which works on numerous observational programs. The commissioning of the LSST is expected in the early 2020s.
On February 29, March 2 and 4, the PostNauka Academy on the Old Arbat will host Vladimir Surdin’s intensive course “The Solar System: In Search of a Spare Planet” - 9 classes that will help you understand the diversity of planets and find out if, in addition to the Earth, there are planets suitable for life .
In 2006, Pluto was stripped of its status as the ninth planet in the solar system thanks to the efforts of one astronomer, Michael Brown. Together with his colleagues, he discovered, and then other dwarf planets far beyond the orbit of Neptune. Thus, he proved that Pluto is not remarkable and big enough to be called a full-fledged planet. However, now Brown and our compatriot Konstantin Batygin are claiming that the new Planet 9 is already almost open ... and that all that remains is to see it.
Yes, yes, no one has yet seen the “almost open” ninth planet of the solar system! In fact, its discovery is the fruit of long observations of the orbits of other planets. According to Kepler and Newton, the place of each planet in the solar system is determined by its characteristics, mainly by mass. And if the orbit does not correspond to the parameters of the planet or is generally anomalous, then it is influenced by some other, no less massive object. The first planet discovered by mathematical equations, and not live observations, was - in 1846 it was found at a place calculated by the French mathematician Urbain Le Verrier.
Moreover, the planets can influence each other very actively - in the past of the solar system they traveled hundreds of millions of kilometers, approaching and moving away from the Sun. The gas giants were especially distinguished here. In young planetary systems, they absorb all the embryos of the planets and hang close to the star - as close as Mercury. Because of this, they become very hot and become unstable. Scientists call such planets "hot Jupiters" or "hot Neptunes" - depending on their mass and size.
Troubled History of the Solar System
However, Jupiter, the largest and most influential planet, changed everything in the solar system. Initially appearing at a distance of 5 to 10 from the Sun, it provoked active collisions of scattered material in the protoplanetary disk around the star. This gave impetus to the creation of other gas giants, like Saturn or Neptune, at distances equally close to the Sun.
However, the newly formed planets behaved "ungratefully", following the laws of gravity - they pushed their "parent" closer to the Sun, into the modern orbit of Mars. Thus, Jupiter invaded the inner part of the solar system. In other planetary systems, this part is the most saturated with matter and space objects. But the heavy tread of the mass of Jupiter scattered the embryos of planets and asteroids there, throwing them into the nuclear furnace of the Sun or throwing them to the outskirts of the system in the zone of modern and.
If not for Saturn, which bound Jupiter with an orbital resonance and did not bring it into a modern orbit, the gas giant could completely ruin the solar system, throwing out 99% of the planetary matter from it. However, his travels did not go unnoticed - so Neptune and Uranus changed their orbits, forming most of the long-period comets.
Ultimately, an unusual balance reigned in the solar planetary system - gas giants that form near the star ended up on the outskirts, and "solid planets" like the Earth migrated closer to the Sun. However, some astronomers believed that another planet was needed to achieve such a balance - and one massive enough to influence the large Neptune and Uranus. It, Planet X, was searched for by many astronomers for a century and a half - and it seems that Brown and Batygin finally got close to it.
History of the search for planet X
After Le Verrier calculated Neptune from perturbations in Uranus's orbit, astronomers found that even its presence did not explain the features of the ice giant's orbit. For some time they tried to find another planet that could influence the last large objects of the solar system - however, they managed to find only Pluto, which, by mass and direction of the orbit, could not disturb larger bodies in any way. The issue of Uranus-Neptune anomalies was finally resolved by "", who measured the mass of Neptune in 1989 and thereby found that there are no contradictions in the orbits.
By that time, the power of telescopes had grown significantly, which allowed astronomers to look into the depths of the solar system. Many trans-Neptunian objects have been discovered - dwarf planets and large asteroids, whose closest orbital point is further from the Sun than Neptune. So, in 2005, the already mentioned Eris was discovered, the second largest dwarf planet after Pluto. And in 2003 they found an object with diameters over 2 thousand kilometers, which moves away from the Sun at a distance of 1.4 × 10 11 km - further than any large trans-Neptunian object! It soon acquired a whole family of "sednoids", isolated trans-Neptunian objects with similar characteristics.
The ninth planet - where and why?
Observing the newly discovered planetoids, astronomers C. Trujillo and S. Sheppard, colleagues, discovered an interesting pattern. Most of them have elongated, comet-like orbits that briefly come "close" to the Sun, at a distance of 40 to 70 astronomical units, and then move away for hundreds or even thousands of years. And the larger the object, the stronger its removal. In addition, the sednoids deviated from the Sun in the same direction.
Such a coincidence could be an accident, if we are talking about simple comets - over the billions of years of the history of the solar system, they were scattered by all the major planets, especially the already mentioned "travelers" Jupiter, Uranus and Neptune. However, for such a coincidence in the deviations of large objects, a very big planet, whose orbit would reach the Oort cloud.
Here Brown and Batygin distinguished themselves - by comparing the orbital characteristics of sednoids, they found mathematically that the probability of their random coincidence is only 0.007%. Scientists went further and compiled a computer model aimed at finding the characteristics of the planet, capable of changing the orbits of bodies located beyond Neptune. The data they received in January 2016 became the basis for the announcement of the pre-discovery of a new planet in the solar system.
Characteristics of Planet X
In his interviews, Brown claims that the probability of finding a new planet is 90%. However, until it is actually discovered, with the help of a telescope, it is too early to talk about the final discovery. Nevertheless, the calculated characteristics of Planet 9 have been published - they will be used in future searches.
- The orbital parameters of Planet X will be mirrored to those of the sednoids - the orbit of the planet will still be elongated and inclined relative to the plane of the main planets of the solar system, but directed in the opposite direction. Accordingly, the perihelion of the planet - the point of maximum approach to the Sun - will be 200 astronomical units at the nearest point, and the aphelion - the maximum distance - will reach 1200 astronomical units. This is even more than Sedna! A year on Planet 9 will last up to 20,000 Earth years, which is how long it may take to complete the entire orbit.
A planet distant from the Sun is difficult to detect - this requires telescopes operating in the infrared spectrum, or powerful optical devices that can capture even the smallest sun glare on the surface. On infrared telescopes, work will move faster, but errors are possible - and on optical telescopes, the result will be reliable, albeit at the cost of time. The WISE Infrared Orbiting Telescope, which conducted broadband surveys in 2009, has yet to detect Planet X, although it has provided fairly detailed images.
Therefore, Brown, Batygin and other astronomers are planning to find it using the Subaru telescop in the Hawaiian Islands, which is considered one of the largest and highest quality in the world - the diameter of its main mirror exceeds 8 meters! In addition, it is capable of operating both in the optical and in the infrared ranges of light. But even with such a tool, it will take scientists at least 5 years to put an end to the issue of Planet X.
"She's huge"
The discoverer of the ninth planet of the solar system about a new cosmic body
Photo: R. Hurt / Infrared Processing and Analysis Center / Courtesy of California Institute of Technology / AP
The discovery of the ninth planet in the solar system by two astronomers from the California Institute of Technology in Pasadena became known on January 20. One of them - a native of Russia Konstantin Batygin - told Lente.ru about the search for Planet X, the difficulties with the name of a new celestial body and the unsolved mysteries of the solar system.
"Lenta.ru": What is the planet you discovered?
: It does not fall into the category of dwarf planets. This celestial body is quite massive. Our model gives a mass of about ten Earth's, this planet is simply gigantic. It is now defined as a celestial object whose gravitational field dominates that part of the solar system.
In general, there is not even a question: is it a planet or not. We know about it because its gravity affects the orbits of distant objects in the Kuiper Belt. The very mathematical modeling relies on this planet having enough mass to dominate the solar system gravitationally.
What about its physical properties?
Calculations, unfortunately, give us only the mass and General characteristics. We can only assume that it is similar in chemical composition to Uranus or Neptune. More precisely, we will say something when a device like New Horizons is sent to the planet. Although the flight is far, and it will take a very long time to wait.
Where did Planet X come from?
We believe that it formed in the first three million years of the solar system, that is, about 4.5 billion years ago, from about the same material as Uranus and Neptune. While the solar system was still shrouded in a gas cloud, this planet was gravitationally scattered into a longer orbit.
Were you guided by Chadwick Trujillo and Scott Sheppard's observations of trans-Neptunian object 2012 VP113 in 2004?
We relied on their work. What they found is called the perihelion argument of many orbits in the Kuiper belt. It turns out that this is only part of the story. The reality is an order of magnitude simpler and more fundamental: further orbits in the Kuiper belt look in approximately the same direction. Their physical orbits are almost the same. And it is this fundamental moment led to the fact that we were able to calculate the orbit of "Planet 9".
Image: NASA / JPL-CALTECH
How fast do you hope to find a planet with the Subaru telescope? Your colleagues, such as Professor Hal Levison, are looking forward to direct observations.
In principle, we get results from one night of observations fairly quickly. The problem is that you need a lot of nights: you need to examine enough most sky. So I think if we integrate, we have to spend two or three years to find the planet that we predicted.
Does this planet have moons?
We think so. My colleagues and I agree that there are no reasons that would prevent this. Can they be seen with a telescope? Maybe. But it's difficult...
Have you thought about what to name the new planet?
Mike Brown and I (Mike Brown, co-author of Konstantin Batygin - approx. "Tapes.ru") we believe that it is better to entrust the world community. It's not for the two of us to decide. Again, we have not thought about this yet: we have a theoretical model, but the planet has not been found astronomically.
Could there be other planets in the solar system?
I guess, yes. There is nothing that contradicts such a possibility. But at the moment we do not have any data indicating that, in addition to the ninth planet, there is something else.
When will observational astronomy put an end to this story?
Good question. By the middle of the 20th century, it seemed that observational astronomy had completed its work in the solar system. It turned out that this was not the case.
In principle, the solar system is huge, the gravitational field of the Sun dominates very far: the dominant ends somewhere after a hundred thousand astronomical units, and we see small objects in the Kuiper belt at a distance of a maximum of eighty astronomical units. There is still a huge area unknown.
Three major telescopes are being built on Earth at once: the Giant Magellan Telescope (GMT), the Thirty Meter Telescope (TMT) and the European Extremely Large Telescope (E-ELT). Will they be useful in such research?
The projects you mentioned are certainly important. However, to search for planets like ours, telescopes like Subaru, whose camera is designed to cover most of the sky, are more suitable. The same TMT will be good for characterization and bad for search.
What if the discovery of the ninth planet is not confirmed?
The most dramatic precedent is the discovery of Neptune in 1846 by Urban Le Verrier, who used mathematical models similar to those we have today. But our model is an order of magnitude more detailed and complex: it uses supercomputers.
And Le Verrier's calculations were confirmed in one night of observations.
Do you maintain contacts with Russian colleagues?
I lived in Russia until 1994, after which I moved with my family to Japan and then to the USA. I am mainly a theorist, sometimes I communicate by e-mail with colleagues from Russia and Russians working in the US and other countries.
I don't read Russian media because I don't have enough time. I try to do only science. I can say that Russia remains strong in theoretical science: there are many good scientists. The story of Mikhail Lidov comes to mind, who in the 1950s calculated the effect now called the Lidov-Kozai resonance. People did not understand for a long time how important this effect is. Lidov was decades ahead of mankind, and there are still such scientists in Russia.
Scientists at the California Institute of Technology announced the discovery. So far, no one has seen a new object through a telescope. According to Michael Brown and Konstantin Batygin, the planet was discovered by analyzing data on the gravitational perturbation it exerts on other celestial bodies. The name has not yet been given to her, but scientists have been able to determine various parameters. It weighs 10 times more than the Earth. The chemical composition of the new planet resembles two gas giants - Uranus and Neptune. By the way, it is similar to Neptune in its size, and is even further from the sun than Pluto, which, due to its modest size, has lost its status as a planet. Confirmation of the existence of a celestial body will take five years. Scientists have booked time at a Japanese observatory in Hawaii. The probability that their discovery is wrong is 0.007 percent. The new planet, if the discovery is recognized, will be the ninth in the solar system.
The solar system appears to have a new ninth planet. Today, two scientists announced evidence that a body nearly the size of Neptune-but as yet unseen-orbits the sun every 15,000 years. During the solar system's infancy 4.5 billion years ago, they say, the giant planet was knocked out of the planet-forming region near the sun. Slowed down by gas, the planet settled into a distant elliptical orbit, where it still lurks today.
The claim is the strongest yet in the centuries-long search for a "Planet X" beyond Neptune. The quest has been plagued by far-fetched claims and even outright quackery. But the new evidence comes from a pair of respected planetary scientists, Konstantin Batygin and Mike Brown of the California Institute of Technology (Caltech) in Pasadena, who prepared for the inevitable skepticism with detailed analyzes of the orbits of other distant objects and months of computer simulations. “If you say, ‘We have evidence for Planet X,’ almost any astronomer will say, ‘This again? These guys are clearly crazy.’ I would, too,” Brown says. Why is this different? This is different because this time we're right."
LANCE HAYASHIDA/CALTECH
Outside scientists say their calculations stack up and express a mixture of caution and excitement about the result. “I could not imagine a bigger deal if-and of course that’s a boldface ‘if’-if it turns out to be right,” says Gregory Laughlin, a planetary scientist at the University of California (UC), Santa Cruz. "What's thrilling about it is detectable."
Batygin and Brown inferred its presence from the peculiar clustering of six previously known objects that orbit beyond Neptune. They say there's only a 0.007% chance, or about one in 15,000, that the clustering could be a coincidence. Instead, they say, a planet with the mass of 10 Earths has shepherded the six objects into their strange elliptical orbits, tilted out of the plane of the solar system.
The orbit of the inferred planet is similarly tilted, as well as stretched to distances that will explode previous conceptions of the solar system. Its closest approach to the sun is seven times farther than Neptune, or 200 astronomical units (AUs). (An AU is the distance between Earth and the sun, about 150 million kilometers.) And Planet X could roam as far as 600 to 1200 AU, well beyond the Kuiper belt, the region of small icy worlds that begins at Neptune's edge about 30 AU.
If Planet X is out there, Brown and Batygin say, astronomers ought to find more objects in telltale orbits, shaped by the pull of the hidden giant. But Brown knows that no one will really believe in the discovery until Planet X itself appears within a telescope viewfinder. "Until there's a direct detection, it's a hypothesis-even a potentially very good hypothesis," he says. The team has time on the one large telescope in Hawaii that is suited for the search, and they hope other astronomers will join in the hunt.
Batygin and Brown published the result today in The Astronomical Journal. Alessandro Morbidelli, a planetary dynamicist at the Nice Observatory in France, performed the peer review for the paper. In a statement, he says Batygin and Brown made a "very solid argument" and that he is "quite convinced by the existence of a distant planet."
Championing a new ninth planet is an ironic role for Brown; he is better known as a planet slayer. His 2005 discovery of Eris, a remote icy world nearly the same size as Pluto, revealed that what was seen as the outermost planet was just one of many worlds in the Kuiper belt. Astronomers promptly reclassified Pluto as a dwarf planet-a saga Brown recounted in his book How I Killed Pluto.
Now, he has joined the centuries-old search for new planets. His method-inferring the existence of Planet X from its ghostly gravitational effects-has a respectable track record. In 1846, for example, the French mathematician Urbain Le Verrier predicted the existence of a giant planet from irregularities in the orbit of Uranus. Astronomers at the Berlin Observatory found the new planet, Neptune, where it was supposed to be, sparking a media sensation.
Remaining hiccups in Uranus's orbit led scientists to think that there might yet be one more planet, and in 1906 Percival Lowell, a wealthy tycoon, began the search for what he called "Planet X" at his new observatory in Flagstaff, Arizona. In 1930, Pluto turned up-but it was far too small to tug meaningfully on Uranus. More than half a century later, new calculations based on measurements by the Voyager spacecraft revealed that the orbits of Uranus and Neptune were just fine on their own: No Planet X was needed.
Yet the allure of Planet X persisted. In the 1980s, for example, the researchers proposed that an unseen brown dwarf star could cause periodic extinctions on Earth by triggering fusillades of comets. In the 1990s, scientists invoked a Jupiter-sized planet at the solar system's edge to explain the origin of certain oddball comets. Just last month, researchers claimed to have detected the faint microwave glow of an outsized rocky planet some 300 AU away, using an array of telescope dishes in Chile called the Atacama Large Millimeter Array (ALMA). (Brown was one of many skeptics, noting that ALMA's narrow field of view made the chances of finding such an object vanishingly slim.)
Brown got his first inkling of his current quarry in 2003, when he led a team that found Sedna, an object a bit smaller than both Eris and Pluto. Sedna's odd, far-flung orbit made it the most distant known object in the solar system at the time. Its perihelion, or closest point to the sun, lay at 76 AU, beyond the Kuiper belt and far outside the influence of Neptune's gravity. The implication was clear: Something massive, well beyond Neptune, must have pulled Sedna into its distant orbit.
(DATA)JPL; BATYGIN AND BROWN/CALTECH; (DIAGRAM) A. CUADRA/ SCIENCE
That something didn't have to be a planet. Sedna’s gravitational nudge could have come from a passing star, or from one of the many other stellar nurseries that surrounded the nascent sun at the time of the solar system’s formation.
Since then, a handful of other icy objects have turned up in similar orbits. By combining Sedna with five other weirdos, Brown says he has ruled out stars as the unseen influence: Only a planet could explain such strange orbits. Of his three major discoveries-Eris, Sedna, and now, potentially, Planet X-Brown says the last is the most sensational. Killing Pluto was fun. Finding Sedna was scientifically interesting,” he says. "But this one, this is head and shoulders above everything else."
Brown and Batygin were nearly beaten to the punch. For years, Sedna was a lone clue to a perturbation from beyond Neptune. Then, in 2014, Scott Sheppard and Chad Trujillo (a former graduate student of Brown’s) published a paper describing the discovery of VP113, another object that never comes close to the sun. Sheppard, of the Carnegie Institution for Science in Washington, D.C., and Trujillo, of the Gemini Observatory in Hawaii, were well aware of the implications. They began to examine the orbits of the two objects along with 10 other oddballs. They noticed that, at perihelion, all came very near the plane of solar system in which Earth orbits, called the ecliptic. In a paper, Sheppard and Trujillo pointed out the peculiar clumping and raised the possibility that a distant large planet had herded the objects near the ecliptic. But they didn't press the result any further.
Later that year, at Caltech, Batygin and Brown began discussing the results. Plotting the orbits of the distant objects, Batygin says, they realized that the pattern that Sheppard and Trujillo had noticed "was only half of the story." Not only were the objects near the ecliptic at perihelia, but their perihelia were physically clustered in space (see diagram, above).
For the next year, the duo secretly discussed the pattern and what it meant. It was an easy relationship, and their skills complemented each other. Batygin, a 29-year-old whiz kid computer modeler, went to college at UC Santa Cruz for the beach and the chance to play in a rock band. But he made his mark there by modeling the fate of the solar system over billions of years, showing that, in rare cases, it was unstable: Mercury may plunge into the sun or collide with Venus. "It was an amazing accomplishment for an undergraduate," says Laughlin, who worked with him at the time.
Brown, 50, is the observational astronomer, with a flair for dramatic discoveries and the confidence to match. He wears shorts and sandals to work, puts his feet up on his desk, and has a breeziness that masks intensity and ambition. He has a program all set to sift for Planet X in data from a major telescope the moment they become publicly available later this year.
Their offices are a few doors down from each other. "My couch is nicer, so we tend to talk more in my office," Batygin says. "We tend to look more at data in Mike's." They even became exercise buddies, and discussed their ideas while waiting to get in the water at a Los Angeles, California, triathlon in the spring of 2015.
First, they winnowed the dozen objects studied by Sheppard and Trujillo to the six most distant-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.
Batygin began seeding his solar system models with Planet X’s of various sizes and orbits, to see which version best explained the objects’ paths. Some of the computer runs took months. A favored size for Planet X emerged-between five and 15 Earth masses-as well as a preferred orbit: antialigned in space from the six small objects, so that its perihelion is in the same direction as the six objects' aphelion, or farthest point from the sun. The orbits of the six cross that of Planet X, but not when the big bully is nearby and could disrupt them. The final epiphany came 2 months ago, when Batygin's simulations showed that Planet X should also sculpt the orbits of objects that swoop into the solar system from above and below, nearly orthogonal to the ecliptic. "It sparked this memory," Brown says. "I've seen these objects before." It turns out that, since 2002, five of these highly inclined Kuiper belt objects have been discovered, and their origins are largely unexplained. "Not only are they there, but they are in exactly the places we predicted," Brown says. "That is when I realized that this is not just an interesting and good idea-this is actually real."
Sheppard, who with Trujillo had also suspected an unseen planet, says Batygin and Brown “took our result to the next level. …They got deep into the dynamics, something that Chad and I aren’t really good with. That's why I think this is exciting."
Others, like planetary scientist Dave Jewitt, who discovered the Kuiper belt, are more cautious. The 0.007% chance that the clustering of the six objects is coincidental gives the planet claim a statistical significance of 3.8 sigma-beyond the 3-sigma threshold typically required to be taken seriously, but short of the 5 sigma that is sometimes used in fields like particle physics. That worries Jewitt, who has seen plenty of 3-sigma results disappear before. By reducing the dozen objects examined by Sheppard and Trujillo to six for their analysis, Batygin and Brown weakened their claim, he says. "I worry that the finding of a single new object that is not in the group would destroy the whole edifice," says Jewitt, who is at UC Los Angeles. "It's a game of sticks with only six sticks."
(IMAGES) WIKIMEDIA COMMONS; NASA/JPL-CALTECH; A. CUADRA/ SCIENCE ; NASA/JHUAPL/SWRI; (DIAGRAM) A. CUADRA/ SCIENCE
At first blush, another potential problem comes from NASA’s Widefield Infrared Survey Explorer (WISE), a satellite that completed an all-sky survey looking for the heat of brown dwarfs-or giant planets. It ruled out the existence of a Saturn-or-larger planet as far out as 10,000 AU, according to a 2013 study by Kevin Luhman, an astronomer at Pennsylvania State University, University Park. But Luhman notes that if Planet X is Neptune-sized or smaller, as Batygin and Brown say, WISE would have missed it. He says there is a slim chance of detection in another WISE data set at longer wavelengths-sensitive to cooler radiation-which was collected for 20% of the sky. Luhman is now analyzing those data.
Even if Batygin and Brown can convince other astronomers that Planet X exists, they face another challenge: explaining how it ended up so far from the sun. At such distances, the protoplanetary disk of dust and gas was likely to have been too thin to fuel planet growth. And even if Planet X did get a foothold as a planetesimal, it would have moved too slowly in its vast, lazy orbit to hoover up enough material to become a giant.
Instead, Batygin and Brown propose that Planet X formed much closer to the sun, alongside Jupiter, Saturn, Uranus, and Neptune. Computer models have shown that the early solar system was a tumultuous billiards table, with dozens or even hundreds of planetary building blocks the size of Earth bouncing around. Another embryonic giant planet could easily have formed there, only to be booted outward by a gravitational kick from another gas giant.
It’s harder to explain why Planet X didn’t either loop back around to where it started or leave the solar system entirely. But Batygin says that residual gas in the protoplanetary disk might have exerted enough drag to slow the planet just enough for it to settle into a distant orbit and remain in the solar system. That could have happened if the ejection took place when the solar system was between 3 million and 10 million years old, he says, before all the gas in the disk was lost into space.
Hal Levison, a planetary dynamicist at the Southwest Research Institute in Boulder, Colorado, agrees that something has to be creating the orbital alignment Batygin and Brown have detected. But he says the origin story they have developed for Planet X and their special pleading for a gas-slowed ejection add up to "a low-probability event." Other researchers are more positive. The proposed scenario is plausible, Laughlin says. "Usually things like this are wrong, but I'm really excited about this one," he says. "It's better than a coin flip."
All this means that Planet X will remain in limbo until it is actually found.
Astronomers have some good ideas about where to look, but spotting the new planet won't be easy. Because objects in highly elliptical orbits move fastest when they are close to the sun, Planet X spends very little time at 200 AU. And if it were there right now, Brown says, it would be so bright that astronomers probably would have already spotted it.
Instead, Planet X is likely to spend most of its time near aphelion, slowly trotting along at distances between 600 and 1200 AU. Most telescopes capable of seeing a dim object at such distances, such as the Hubble Space Telescope or the 10-meter Keck telescopes in Hawaii, have extremely tiny fields of view. It would be like looking for a needle in a haystack by peering through a drinking straw.
One telescope can help: Subaru, an 8-meter telescope in Hawaii that is owned by Japan. It has enough light-gathering area to detect such a faint object, coupled with a huge field of view-75 times larger than that of a Keck telescope. That allows astronomers to scan large swaths of the sky each night. Batygin and Brown are using Subaru to look for Planet X-and they are coordinating their efforts with their erstwhile competitors, Sheppard and Trujillo, who have also joined the hunt with Subaru. Brown says it will take about 5 years for the two teams to search most of the area where Planet X could be lurking.
Subaru Telescope, NAOJ
If the search pans out, what should the new member of the sun's family be called? Brown says it's too early to worry about that and scrupulously avoids offering up suggestions. For now, he and Batygin are calling it Planet Nine (and, for the past year, informally, Planet Phattie-1990s slang for "cool"). Brown notes that neither Uranus nor Neptune-the two planets discovered in modern times-ended up being named by their discoverers, and he thinks that that's probably a good thing. It's bigger than any one person, he says: "It's kind of like finding a new continent on Earth."
He is sure, however, that Planet X-unlike Pluto-deserves to be called a planet. Something the size of Neptune in the solar system? Don't even ask. "No one would argue this one, not even me."