by Shannon Hall
April 05, 2016

from ScientificAmerican Website

Artist's impression of Planet Nine

(Planet Nine = Planet Ten = Planet X = Nibiru)

as an ice giant eclipsing the central Milky Way,

with a starlike sun in the distance.

Neptune's orbit is shown as a small ellipse around the sun.
Tomruen/Wikimedia Commons, CC BY-SA 4.0

Astronomers are homing in

on the whereabouts of a

hidden giant planet in our solar system,

and could discover the unseen beast

in roughly a year.


 

The hunt is on to find "Planet Nine" - a large undiscovered world, perhaps 10 times as massive as Earth and four times its size - that scientists think could be lurking in the outer solar system.

After Konstantin Batygin and Mike Brown, two planetary scientists from the California Institute of Technology, presented evidence for its existence this January, other teams have searched for further proof by analyzing archived images and proposing new observations to find it with the world's largest telescopes.

Just this month, evidence from the Cassini spacecraft orbiting Saturn helped close in on the missing planet.

Many experts suspect that within as little as a year someone will spot the unseen world, which would be a monumental discovery that changes the way we view our solar system and our place in the cosmos.

"Evidence is mounting that something unusual is out there - there's a story that's hard to explain with just the standard picture," says David Gerdes, a cosmologist at the University of Michigan who never expected to find himself working on Planet Nine.

He is just one of many scientists who leapt at the chance to prove - or disprove - the team's careful calculations.

Batygin and Brown made the case for Planet Nine's existence based on its gravitational effect on several Kuiper Belt objects - icy bodies that circle the sun beyond Neptune's orbit.

Theoretically, though, its gravity should also tug slightly on the planets.*

With this in mind, Agnès Fienga at the Côte d'Azur Observatory in France and her colleagues checked whether a theoretical model (one that they have been perfecting for over a decade) with the new addition of Planet Nine could better explain slight perturbations seen in Saturn's orbit as observed by Cassini.*

Without it, the other seven planets in the solar system, 200 asteroids and five of the most massive Kuiper Belt objects cannot perfectly account for it.*

The missing puzzle piece might just be a ninth planet.

So Fienga and her colleagues compared the updated model, which placed Planet Nine at various points in its hypothetical orbit, with the data.

They found a sweet spot - with Planet Nine 600 astronomical units (about 90 billion kilometers) away toward the constellation Cetus - that can explain Saturn's orbit quite well.*

Although Fienga is not yet convinced that she has found the culprit for the planet's odd movements, most outside experts are blown away.*

"It's a brilliant analysis," says Greg Laughlin, an astronomer at Lick Observatory, who was not involved in the study. "It's completely amazing that they were able to do that so quickly."

Gerdes agrees:

"That's a beautiful paper."

The good news does not end there.

If Planet Nine is located toward the constellation Cetus, then it could be picked up by the Dark Energy Survey, a Southern Hemisphere observation project designed to probe the acceleration of the universe.

"It turns out fortuitously that the favored region from Cassini's data is smack dab in the middle of our survey footprint," says Gerdes, who is working on the cosmology survey.*

 

"We could not have designed our survey any better."

Although the survey was not planned to search for solar system objects, Gerdes has discovered some (including one of the icy objects that led Batygin and Brown to conclude Planet Nine exists in the first place).

Laughlin thinks this survey has the best immediate chance of success. He is also excited by the fact that Planet Nine could be so close.

Although 600 AUs - roughly 15 times the average distance to Pluto - does sound far, Planet Nine could theoretically hide as far away as 1,200 AUs.

"That makes it twice as easy to get to, twice as soon," Laughlin says. "And not just twice as bright but 16 times as bright."

And the Dark Energy Survey is not the only chance to catch the faint world. It should be possible to look for the millimeter-wavelength light the planet radiates from its own internal heat.

Such a search (Cosmologists in Search of Planet Nine - The Case for CMB Experiments) was proposed by Nicolas Cowan, an exoplanet astronomer at McGill University in Montreal, who thinks that Planet Nine might show up in surveys of the cosmic microwave background (CMB), the pervasive afterglow of the big bang.

"CMB experiments have historically used solar system giant planets to calibrate their instruments, so we know that current and planned CMB experiments are sensitive enough to measure the flux from Planet Nine if it is as bright as we think it is," Cowan says.

Already, cosmologists have started to comb through data from existing experiments, and astronomers with many different specialties have also joined in on the search.

"I love that we can take this four-meter telescope and find a rock 100 kilometers in diameter that is a billion kilometers past Neptune with the same instrument that we are using to do extragalactic stuff and understand the acceleration of the universe," Gerdes says.

In the meantime Batygin and Brown are proposing a dedicated survey of their own.

In a recent study (Observational Constraints on the Orbit and Location of Planet Nine in the Outer Solar System) they searched through various sky maps to determine where Planet Nine cannot be.

"We dumpster-dived into the existing observational data to search for Planet Nine, and because we didn't find it we were able to rule out parts of the orbit," Batygin says.

The zone where the planet makes its farthest swing from the sun as well as the small slice of sky where Fienga thinks the planet could be now, for example, have not been canvassed by previous observations.

To search the unmapped zones, Batygin and Brown have asked for roughly 20 observing nights on the Subaru Telescope on Mauna Kea in Hawaii.

"It's a pretty big request compared to what other people generally get on the telescope," Brown says. "We'll see if they bite."

If they do, Brown is convinced he will have his planet within a year.

"I really want to see what it looks like," says Batygin, who adds that his aspiration drives him to search for the unseen world.

But Laughlin takes it a step further:

"I think [the discovery] would provide amazing inspiration for the next stage of planetary exploration," he says.

We now have another opportunity to see one of the worlds of our own solar system for the first time.

"If Planet Nine isn't out there, we won't have that experience again."

* Editor's Note (April 08, 2016):

The headline and asterisked sentences in this story were edited after its original posting to correct an error.

The original stated that perturbations in the Cassini spacecraft's orbit around Saturn could be caused by Planet Nine. It is not Cassini's orbit, however, but perturbations of Saturn's orbit around the sun that may be explained by the presence of Planet Nine.
 

 


Strong Evidence Suggests a...

'Super Earth' Lies beyond Pluto
by Michael D. Lemonick
January 20, 2016

from ScientificAmerican Website

Spanish version

Artist's rendering of what Planet Nine might look like.
Caltech/R. Hurt (IPAC)

Astronomers have found

compelling hints of a huge, unseen world

that may reside in the murky reaches

of the Kuiper Belt

"New Planet Found" is about as exciting a headline nowadays as "Dog Bites Man," which is to say, not very.

Thanks largely to the space-based Kepler Mission, astronomers have identified about 2,000 new worlds, orbiting stars that lie tens or even hundreds of light-years from Earth, in the last two decades.

Collectively, these are scientifically important, but with so many in hand no single addition to the list is likely to be much of a big deal. But a new planet announcement today from the California Institute of Technology is a very different proposition, because the world it describes does not circle a distant star.

It is part of our own solar system - a place you would think we had explored pretty well by now.

Evidently not: in an analysis accepted for publication at The Astronomical Journal (Observational Constraints on the Orbit and Location of Planet Nine in the Outer Solar System), California Institute of Technology planetary scientists Konstantin Batygin and Mike Brown present what they say is strong circumstantial evidence for a very large undiscovered planet, perhaps 10 times as massive as Earth, orbiting in the solar system's outer darkness beyond Pluto.

The scientists infer its presence from anomalies in the orbits of a handful of smaller bodies they can see.

"I haven't been this excited about something in quite a while," says Greg Laughlin, an expert on planet formation and dynamics at the University of California, Santa Cruz, who was not involved in the research.

The object, which the researchers have provisionally named "Planet Nine," comes no closer than 30.5 billion or so kilometers from the sun, or five times farther than Pluto's average distance.

Despite its enormous size, it would be so dim, the authors say, that it is unsurprising that nobody has spotted it yet.

If it exists, that is.

"Sadly," Brown says, "we don't have an actual detection yet."

But the evidence is strong enough that other experts are taking very serious notice.

"I think it's pretty convincing," says Chad Trujillo of the Gemini Observatory in Hawaii.

David Nesvorny, a solar system theorist at the Southwest Research Institute (SwRI), in Boulder, Colo., is impressed as well.

"These guys are really good," he says. "They make a good case."

THE ANIMATION WAS CREATED USING WORLDWIDE TELESCOPE.
CALTECH/R. HURT (IPAC)

 

Strange orbits

Batygin and Brown are not the first to argue for an extra planet in our solar system.

In 2014 Chad Trujillo and Scott Sheppard, of the Carnegie Institution for Science, argued in Nature (A Sedna-like Body with a Perihelion of 80 Astronomical Units) that their own discovery of a much smaller object, called 2012 VP113, along with the existence of a handful of previously identified bodies in the outer solar system, hinted that there might be something planet-size out there.

The evidence lay with their orbits, specifically with an obscure parameter called the "argument of perihelion" - the relationship between the time a body makes its closest approach to the sun and the time it passes through the plane of the solar system.

The objects Trujillo and Shepherd identified all had uncannily similar arguments of perihelion, which could mean they were being shepherded by the gravity of an unseen world.

"We noticed something curious," Trujillo says, "and said 'someone should go explore this further'."

(Scientific American is part of Nature Publishing Group.)

Several groups did, and agreed that the case for a hidden planet was plausible but still quite speculative.

The new analysis strengthens that case dramatically, however. The similarity of the arguments of perihelion turns out to be "just the tip of the iceberg," Batygin says.

The first thing he and Brown did, he says, was to analyze Trujillo and Sheppard's data with entirely fresh eyes.

"What we noticed," Batygin says, "was that the long axes of these objects' orbits fall into the same quadrant of the sky."

In other words, they point in the same direction. That outcome was not guaranteed; two bodies can have similar arguments of perihelion even if their orbits are not otherwise physically similar.

But when Brown and Batygin plotted the orbits of those outer solar system objects, they noticed that their highly elliptical orbit shapes were closely aligned.

"Shouldn't something like that be hard to miss?" Brown asks.

 

"Yes, you would think so. This a case where we had our noses buried in the data, never stepping back and looking at the solar system from above. I couldn't believe I'd never noticed this before," he says.

 

"It's ridiculous."

The directionality of the orbits was an even stronger hint that something was physically herding these distant objects.

"At first," Brown says, "we said 'there can't be a planet out there - that's crazy.'"

So they examined the most likely alternative - that the Kuiper Belt of icy objects beyond Pluto had formed all of its bodies into a clump naturally, much as galaxies pulled themselves into shape gravitationally out of the cosmic cloud of gas that emerged from the big bang.

The problem with that scenario, the authors realized, was that the Kuiper Belt lacks the mass to make it happen. When the scientists turned to the "crazy" notion of a planet, however, their simulations generated just the right kind of aligned orbits.

They also revealed something else:

The gravity of a giant planet should lead to an entirely independent set of objects whose orbits are not aligned with one another but are sharply tilted compared with the orbits of the planets - up to 90 degrees away from the plane of the solar system or even more.

"That seemed really puzzling," Batygin says. "But then Mike said, 'I think I've seen something like these in the data'."

Sure enough, observers have spotted a half dozen or so objects just like this and nobody had come up with a good explanation of how they might have gotten there.

Now Batygin and Brown's simulation was providing one.

"The fact that they're now marshaling two new, independent lines of evidence for a hypothetical planet," Laughlin says, "makes their case even stronger."

Super Earth

The planet that best fits the data would be on the order of 10 times as massive as Earth - putting it in the so-called "Super Earth" category, which includes many planets around other stars but none, until now, in our own solar system - and smaller than Neptune, the fourth-largest known planet orbiting the sun, which has about 17 Earth masses.

Its most probable orbit is a highly elongated one that brings it to within 35 billion kilometers of the sun at the closest ("that's where it does all the damage," Brown says) and between three and six times as far away at its most distant.

Even at that enormous distance, Planet Nine could in principle be spotted with existing telescopes - most easily with the Japanese Subaru Telescope in Hawaii, which not only has a huge mirror for trapping faint light but also a wide field of view that would allow searchers to efficiently scan big swaths of sky.

"Unfortunately, we don't own the Subaru," Brown says, "which means we're unlikely to be the ones who find it. So we're telling everyone else where to look."

Until they actually see it, astronomers cannot say definitively that Planet Nine is real.

"I tend to be very suspicious of claims of an extra planet in the solar system," says Hal Levison of SwRI.

 

"I have seen many, many such claims in my career, and all of them have been wrong."

The orbital alignment is genuine, he acknowledges.

"Something is creating it. But what that something is needs to be explored a bit more."

Overall, however, planetary scientists are clearly thrilled by the prospect that we might be on the verge of such a major discovery.

"When I was growing up," Sheppard says, "we thought the big planets had all been found. It would be very exciting and very surprising to learn that we were wrong."

The mood of the astronomical community is perfectly captured, Greg Laughlin says, by something British astronomer John Herschel said to the British Association for the Advancement of Science in a talk on September 10, 1846.

Irregularities had been spotted in the orbit of Uranus, suggesting that the gravity of an unknown, massive planet was tugging on it.

 

Referring to the mystery object, Hershel said:

"We see it as Columbus saw America from the shores of Spain. Its movements have been felt along the far-reaching line of our analysis with a certainly hardly inferior to ocular demonstration."

Just two weeks later Neptune was discovered, right where the theorists' calculations said it should be.