Planet X : Scientists have new evidence on Planet Nine

planet X

Caltech researchers have found mathematical evidence suggesting there may be a “Planet X” deep in the solar system.

This hypothetical Neptune-sized planet orbits our sun in a highly elongated orbit far beyond Pluto.

The object, which the researchers have nicknamed “Planet Nine,” could have a mass about 10 times that of Earth and orbit about 20 times farther from the sun on average than Neptune. It may take between 10,000 and 20,000 Earth years to make one full orbit around the sun.

The announcement does not mean there is a new planet in our solar system.

The existence of this distant world is only theoretical at this point and no direct observation of the object nicknamed have been made.

The mathematical prediction of a planet could explain the unique orbits of some smaller objects in the Kuiper Belt, a distant region of icy debris that extends far beyond the orbit of Neptune. Astronomers are now searching for the predicted planet.

In Depth

In January 2015, Caltech astronomers Konstantin Batygin and Mike Brown announced new research that provides evidence of a giant planet tracing an unusual, elongated orbit in the outer solar system. The prediction is based on detailed mathematical modeling and computer simulations, not direct observation.

This large object could explain the unique orbits of at least five smaller objects discovered in the distant Kuiper Belt.

“The possibility of a new planet is certainly an exciting one for me as a planetary scientist and for all of us,” said Jim Green, director of NASA’s Planetary Science Division.

“This is not, however, the detection or discovery of a new planet. It’s too early to say with certainty there’s a so-called Planet X. What we’re seeing is an early prediction based on modeling from limited observations. It’s the start of a process that could lead to an exciting result.”

The Caltech scientists believe Planet X may have has a mass about 10 times that of Earth and be similar in size to Uranus or Neptune.

The predicted orbit is about 20 times farther from our sun on average than Neptune (which orbits the sun at an average distance of 2.8 billion miles).

It would take this new planet between 10,000 and 20,000 years to make just one full orbit around the sun (where Neptune completes an orbit roughly every 165 years).

Scientists have discovered yet another marker on the trail toward the putative Planet Nine.

That clue is 2015 TG387, a newfound object in the far outer solar system, way beyond Pluto.

The orbit of 2015 TG387 shares peculiarities with those of other extremely far-flung bodies, which appear to have been shaped by the gravity of a very large object in that distant, frigid realm — the hypothesized Planet Nine, also known as Planet X.

“These distant objects are like breadcrumbs leading us to Planet X,” study leader Scott Sheppard, of the Carnegie Institution for Science in Washington, D.C., said in a statement.

“The more of them we can find, the better we can understand the outer solar system and the possible planet that we think is shaping their orbits — a discovery that would redefine our knowledge of the solar system’s evolution,” he added.

And 2015 TG387 is special among these bread crumbs, because it was found during a relatively uniform survey of the northern and southern skies rather than a targeted hunt for clustered objects in certain parts of the sky, Sheppard said.

Targeted hunts can produce biased results — for example, the appearance of clustering where none may actually exist, he explained.

2015 TG387 has two dwarf-planet companions in the low-bias class, Sheppard said:

2012 VP113, which he and his colleague Chadwick Trujillo (who’s a co-author of the new paper as well) spotted in 2014 as part of the same, ongoing long-term survey; and the relatively bright Sedna(because the whole sky has been searched to its level of brightness).

“And then if you bring in some of the other extreme objects — several of them were found in our survey as well,” Sheppard told “The statistics get better and better that this planet is likely out there.”

The discovery images of 2015 TG387 taken at the Subaru 8-meter telescope located atop Mauna Kea in Hawaii on October 13, 2015. The images were taken about 3 hours apart. 2015 TG387 can be seen moving between images near the center while the much more distant stars and galaxies are stationary.

Credit: Scott Sheppard

Sheppard and his colleagues first spotted 2015 TG387 in October 2015, using Japan’s 26-foot (8 meters) Subaru telescope atop the volcanic peak Mauna Kea in Hawaii. The researchers nicknamed the object “The Goblin,” because of the discovery date and the “TG” in the provisional designation.

It took the team three additional years to nail down The Goblin’s orbit, which they did with the aid of observations by the Las Campanas Observatory in Chile and the Discovery Channel Telescope in Arizona.

2015 TG387 loops around the sun on an extremely elliptical path, coming within about 65 astronomical units (AU) of the sun at its closest point (known as perihelion) and getting about 2,300 AU away at its most distant (aphelion).

One AU is the average Earth-sun distance — about 93 million miles (150 million kilometers). So 2015 TG387 is way, way out there. Indeed, it takes about 40,000 Earth years for the newfound object to complete one lap around the sun.

Only two known solar system bodies have more-distant perihelia than The Goblin does (2012 VP113 and Sedna), and only one (2014 FE72) has a greater aphelion distance. (For perspective: Pluto never gets closer to the sun than 29.7 AU, or farther away than 49.3 AU.)

The orbits of the newfound extreme dwarf planet 2015 TG387 and its fellow Inner Oort Cloud objects 2012 VP113 and Sedna, as compared with the rest of the solar system.

The orbits of the newfound extreme dwarf planet 2015 TG387 and its fellow Inner Oort Cloud objects 2012 VP113 and Sedna, as compared with the rest of the solar system.

Credit: Roberto Molar Candanosa and Scott Sheppard, courtesy of Carnegie Institution for Science

Sheppard and his colleagues think 2015 TG387 is about 186 miles (300 km) wide and probably spherical, in which case it would qualify as a dwarf planet. But that’s all they can really say about The Goblin’s physical characteristics.

“It’s pretty faint, so we can really just see that it’s there,” Sheppard told “We don’t even know the color of the object; we haven’t gotten any spectroscopy on the object yet, or anything like that.”

(The 186-mile diameter is not a measurement but rather an estimate, assuming a “moderate” reflectiveness for 2015 TG387.)

But going back to the orbit: The Goblin’s is similar in key ways to those of some other extremely distant bodies — particularly in an element called “longitude of perihelion.” Basically, the elongated parts of their elliptical orbits are clustered in the same part of the sky, which is consistent with gravitational shepherding by Planet X.

The existence of Planet X was first seriously proposed in 2014 by Sheppard and Trujillo, to potentially explain oddities in the orbits of 2012 VP113, Sedna and a few other trans-Neptunian objects.

In 2016, astronomers Konstantin Batygin and Mike Brown presented more evidence for such an unseen “perturber,” which they called Planet Nine. Batygin and Brown have suggested that this world may be about 10 times more massive than Earth and orbit about 600 AU from the sun on average.

Artist's impression of the hypothetical Planet Nine, a roughly Neptune-mass world that may lie undiscovered in the outer solar system.

Artist’s impression of the hypothetical Planet Nine, a roughly Neptune-mass world that may lie undiscovered in the outer solar system.

Credit: R. Hurt (IPAC)/Caltech

In the new study, the researchers also performed computer simulations to test how Planet X’s gravitational tug might influence the orbit of The Goblin. They found significant shepherding akin to that inferred for other distant objects — and determined that 2015 TG387’s orbit remains stable for the age of the solar system nonetheless.

“What makes this result really interesting is that Planet X seems to affect 2015 TG387 the same way as all the other extremely distant solar system objects,” Trujillo, who’s based at Northern Arizona University, said in the same statement. “These simulations do not prove that there’s another massive planet in our solar system, but they are further evidence that something big could be out there.”

Sheppard puts the odds of Planet X’s existence at around 85 percent. And he says it’s not at all surprising that astronomers haven’t spotted it yet.

“Where we think the planet is — hundreds of AU away, if not 1,000 AU — something even as big as Neptune would be fainter than most telescopes could see,” Sheppard told (In case this sounds odd or incongruous: The Goblin was discovered near perihelion, at about 80 AU from the sun.)

“And most of our surveys to date do not go that faint, do not go that deep. We’ve covered very little of the sky to the depth that’s needed to be covered to find something this faint,” he added. “You can hide a very big thing in the outer solar system very easily.”

The paper describing the discovery of 2015 TG387 has been submitted to The Astronomical Journal.


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