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  Researchers find evidence for 'Planet Nine'

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Author Topic:   Researchers find evidence for 'Planet Nine'
Robert Pearlman
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posted 01-20-2016 12:56 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
California Institute of Technology release
Caltech Researchers Find Evidence of a Real Ninth Planet

Caltech researchers have found evidence of a giant planet tracing a bizarre, highly elongated orbit in the outer solar system. The object, which the researchers have nicknamed Planet Nine, has a mass about 10 times that of Earth and orbits about 20 times farther from the sun on average than does Neptune (which orbits the sun at an average distance of 2.8 billion miles). In fact, it would take this new planet between 10,000 and 20,000 years to make just one full orbit around the sun.

The researchers, Konstantin Batygin and Mike Brown, discovered the planet's existence through mathematical modeling and computer simulations but have not yet observed the object directly.

"This would be a real ninth planet," says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy. "There have only been two true planets discovered since ancient times, and this would be a third. It's a pretty substantial chunk of our solar system that's still out there to be found, which is pretty exciting."

Brown notes that the putative ninth planet — at 5,000 times the mass of Pluto — is sufficiently large that there should be no debate about whether it is a true planet. Unlike the class of smaller objects now known as dwarf planets, Planet Nine gravitationally dominates its neighborhood of the solar system. In fact, it dominates a region larger than any of the other known planets — a fact that Brown says makes it "the most planet-y of the planets in the whole solar system."

Batygin and Brown describe their work in the current issue of the Astronomical Journal and show how Planet Nine helps explain a number of mysterious features of the field of icy objects and debris beyond Neptune known as the Kuiper Belt.

"Although we were initially quite skeptical that this planet could exist, as we continued to investigate its orbit and what it would mean for the outer solar system, we become increasingly convinced that it is out there," says Batygin, an assistant professor of planetary science. "For the first time in over 150 years, there is solid evidence that the solar system's planetary census is incomplete."

The road to the theoretical discovery was not straightforward. In 2014, a former postdoc of Brown's, Chad Trujillo, and his colleague Scott Sheppard published a paper noting that 13 of the most distant objects in the Kuiper Belt are similar with respect to an obscure orbital feature. To explain that similarity, they suggested the possible presence of a small planet. Brown thought the planet solution was unlikely, but his interest was piqued.

He took the problem down the hall to Batygin, and the two started what became a year-and-a-half-long collaboration to investigate the distant objects. As an observer and a theorist, respectively, the researchers approached the work from very different perspectives — Brown as someone who looks at the sky and tries to anchor everything in the context of what can be seen, and Batygin as someone who puts himself within the context of dynamics, considering how things might work from a physics standpoint. Those differences allowed the researchers to challenge each other's ideas and to consider new possibilities. "I would bring in some of these observational aspects; he would come back with arguments from theory, and we would push each other. I don't think the discovery would have happened without that back and forth," says Brown. " It was perhaps the most fun year of working on a problem in the solar system that I've ever had."

Fairly quickly Batygin and Brown realized that the six most distant objects from Trujillo and Shepherd's original collection all follow elliptical orbits that point in the same direction in physical space. That is particularly surprising because the outermost points of their orbits move around the solar system, and they travel at different rates.

"It's almost like having six hands on a clock all moving at different rates, and when you happen to look up, they're all in exactly the same place," says Brown. The odds of having that happen are something like 1 in 100, he says. But on top of that, the orbits of the six objects are also all tilted in the same way — pointing about 30 degrees downward in the same direction relative to the plane of the eight known planets. The probability of that happening is about 0.007 percent. "Basically it shouldn't happen randomly," Brown says. "So we thought something else must be shaping these orbits."

The first possibility they investigated was that perhaps there are enough distant Kuiper Belt objects — some of which have not yet been discovered — to exert the gravity needed to keep that subpopulation clustered together. The researchers quickly ruled this out when it turned out that such a scenario would require the Kuiper Belt to have about 100 times the mass it has today.

That left them with the idea of a planet. Their first instinct was to run simulations involving a planet in a distant orbit that encircled the orbits of the six Kuiper Belt objects, acting like a giant lasso to wrangle them into their alignment. Batygin says that almost works but does not provide the observed eccentricities precisely. "Close, but no cigar," he says.

Then, effectively by accident, Batygin and Brown noticed that if they ran their simulations with a massive planet in an anti-aligned orbit — an orbit in which the planet's closest approach to the sun, or perihelion, is 180 degrees across from the perihelion of all the other objects and known planets — the distant Kuiper Belt objects in the simulation assumed the alignment that is actually observed.

"Your natural response is 'This orbital geometry can't be right. This can't be stable over the long term because, after all, this would cause the planet and these objects to meet and eventually collide,'" says Batygin. But through a mechanism known as mean-motion resonance, the anti-aligned orbit of the ninth planet actually prevents the Kuiper Belt objects from colliding with it and keeps them aligned. As orbiting objects approach each other they exchange energy. So, for example, for every four orbits Planet Nine makes, a distant Kuiper Belt object might complete nine orbits. They never collide. Instead, like a parent maintaining the arc of a child on a swing with periodic pushes, Planet Nine nudges the orbits of distant Kuiper Belt objects such that their configuration with relation to the planet is preserved.

"Still, I was very skeptical," says Batygin. "I had never seen anything like this in celestial mechanics."

But little by little, as the researchers investigated additional features and consequences of the model, they became persuaded. "A good theory should not only explain things that you set out to explain. It should hopefully explain things that you didn't set out to explain and make predictions that are testable," says Batygin.

And indeed Planet Nine's existence helps explain more than just the alignment of the distant Kuiper Belt objects. It also provides an explanation for the mysterious orbits that two of them trace. The first of those objects, dubbed Sedna, was discovered by Brown in 2003. Unlike standard-variety Kuiper Belt objects, which get gravitationally "kicked out" by Neptune and then return back to it, Sedna never gets very close to Neptune. A second object like Sedna, known as 2012 VP113, was announced by Trujillo and Shepherd in 2014. Batygin and Brown found that the presence of Planet Nine in its proposed orbit naturally produces Sedna-like objects by taking a standard Kuiper Belt object and slowly pulling it away into an orbit less connected to Neptune.

Above: A predicted consequence of Planet Nine is that a second set of confined objects should also exist. These objects are forced into positions at right angles to Planet Nine and into orbits that are perpendicular to the plane of the solar system. Five known objects (blue) fit this prediction precisely. Credit: Caltech/R. Hurt (IPAC)

But the real kicker for the researchers was the fact that their simulations also predicted that there would be objects in the Kuiper Belt on orbits inclined perpendicularly to the plane of the planets. Batygin kept finding evidence for these in his simulations and took them to Brown. "Suddenly I realized there are objects like that," recalls Brown. In the last three years, observers have identified four objects tracing orbits roughly along one perpendicular line from Neptune and one object along another. "We plotted up the positions of those objects and their orbits, and they matched the simulations exactly," says Brown. "When we found that, my jaw sort of hit the floor."

"When the simulation aligned the distant Kuiper Belt objects and created objects like Sedna, we thought this is kind of awesome — you kill two birds with one stone," says Batygin. "But with the existence of the planet also explaining these perpendicular orbits, not only do you kill two birds, you also take down a bird that you didn't realize was sitting in a nearby tree."

Where did Planet Nine come from and how did it end up in the outer solar system? Scientists have long believed that the early solar system began with four planetary cores that went on to grab all of the gas around them, forming the four gas planets — Jupiter, Saturn, Uranus, and Neptune. Over time, collisions and ejections shaped them and moved them out to their present locations. "But there is no reason that there could not have been five cores, rather than four," says Brown. Planet Nine could represent that fifth core, and if it got too close to Jupiter or Saturn, it could have been ejected into its distant, eccentric orbit.

Batygin and Brown continue to refine their simulations and learn more about the planet's orbit and its influence on the distant solar system. Meanwhile, Brown and other colleagues have begun searching the skies for Planet Nine. Only the planet's rough orbit is known, not the precise location of the planet on that elliptical path. If the planet happens to be close to its perihelion, Brown says, astronomers should be able to spot it in images captured by previous surveys. If it is in the most distant part of its orbit, the world's largest telescopes — such as the twin 10-meter telescopes at the W. M. Keck Observatory and the Subaru Telescope, all on Mauna Kea in Hawaii — will be needed to see it. If, however, Planet Nine is now located anywhere in between, many telescopes have a shot at finding it.

"I would love to find it," says Brown. "But I'd also be perfectly happy if someone else found it. That is why we're publishing this paper. We hope that other people are going to get inspired and start searching."

In terms of understanding more about the solar system's context in the rest of the universe, Batygin says that in a couple of ways, this ninth planet that seems like such an oddball to us would actually make our solar system more similar to the other planetary systems that astronomers are finding around other stars. First, most of the planets around other sunlike stars have no single orbital range — that is, some orbit extremely close to their host stars while others follow exceptionally distant orbits. Second, the most common planets around other stars range between 1 and 10 Earth-masses.

"One of the most startling discoveries about other planetary systems has been that the most common type of planet out there has a mass between that of Earth and that of Neptune," says Batygin. "Until now, we've thought that the solar system was lacking in this most common type of planet. Maybe we're more normal after all."

Brown, well known for the significant role he played in the demotion of Pluto from a planet to a dwarf planet adds, "All those people who are mad that Pluto is no longer a planet can be thrilled to know that there is a real planet out there still to be found," he says. "Now we can go and find this planet and make the solar system have nine planets once again."

The paper is titled "Evidence for a Distant Giant Planet in the Solar System."

fredtrav
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posted 01-20-2016 01:02 PM     Click Here to See the Profile for fredtrav   Click Here to Email fredtrav     Edit/Delete Message   Reply w/Quote
The New York Times:
Dr. Brown said he began searching for the planet a year ago, and he thought he would be able to find it within five years — perhaps sooner, with luck. Now it is likely that other astronomers will scan that swath of the sky.

If the planet exists, it would easily meet the International Astronomical Union's requirements, Dr. Brown said.

"There are some truly dominant bodies in the solar system and they are pushing around everything else," Dr. Brown said. "This is what we mean when we say planet."

Robert Pearlman
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posted 01-20-2016 01:15 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Mike Brown as begun a blog devoted to The Search for Planet Nine.

cspg
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posted 01-20-2016 02:53 PM     Click Here to See the Profile for cspg   Click Here to Email cspg     Edit/Delete Message   Reply w/Quote
Cool!

mode1charlie
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posted 01-20-2016 03:27 PM     Click Here to See the Profile for mode1charlie   Click Here to Email mode1charlie     Edit/Delete Message   Reply w/Quote
WOW. (If it turns out to be true.)

pupnik
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posted 01-20-2016 04:46 PM     Click Here to See the Profile for pupnik     Edit/Delete Message   Reply w/Quote
Since he helped get Pluto demoted I feel I have to give him a hard time here and point out being "gravitationally dominant" doesn't make it a planet by the accepted definition. Having cleared its neighborhood is part of it though, and Planet 9 shares its neighborhood with other dwarf planets so I guess that makes it a Giant Dwarf Planet?

canyon42
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posted 01-20-2016 06:51 PM     Click Here to See the Profile for canyon42   Click Here to Email canyon42     Edit/Delete Message   Reply w/Quote
Would obviously be very cool if something is found; however, there is a LONG and distinguished history of theorizing additional planets in the vast dark. For him to be describing it as a "discovery" seems rather premature at this point.

Grounded!
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posted 01-21-2016 01:40 AM     Click Here to See the Profile for Grounded!   Click Here to Email Grounded!     Edit/Delete Message   Reply w/Quote
Here's what I would like to see...
  1. Pluto reinstated as a planet (as I was taught in grade school).
  2. Eris named our 10th planet.
  3. Then talk to us about this new theoretical "planet."

Robert Pearlman
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posted 01-21-2016 11:43 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
I think the ship has sailed on Pluto being (officially) categorized as a planet by the IAU. I could be wrong, but I don't see why they would reverse their decision, even if it was controversial.

That would also mean that Eric (and Ceres) will likely remain dwarf planets, too.

As for "Planet Nine," NASA's planetary sciences director Jim Green cautions it is too early to say it exists.

Wehaveliftoff
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posted 01-21-2016 04:31 PM     Click Here to See the Profile for Wehaveliftoff   Click Here to Email Wehaveliftoff     Edit/Delete Message   Reply w/Quote
Or this is just another pitch for more funding? The only evidence is 'rock solid'
Clyde Tombaugh 'I found it' evidence, other it's just a bunch of hot/cold air (pun intended).

Robert Pearlman
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posted 01-21-2016 04:36 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
It's not a pitch for funding, but rather for astronomers to begin a Tombaugh-like search for what the data suggests could/should exist.

AstronautBrian
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posted 01-22-2016 09:02 PM     Click Here to See the Profile for AstronautBrian   Click Here to Email AstronautBrian     Edit/Delete Message   Reply w/Quote
It's Skaro!

Glint
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posted 01-23-2016 09:28 AM     Click Here to See the Profile for Glint   Click Here to Email Glint     Edit/Delete Message   Reply w/Quote
Let's get a grip. The consensus is not unanimous.

Guy Ottewell offers a view in his blog. Although tantalizing, bear in mind at this point the most recent "planet 9" remains a hypothesis and has not yet been viewed.

Blackarrow
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posted 01-23-2016 12:26 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by AstronautBrian:
It's Skaro!

No, it's Mondas.

Robert Pearlman
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posted 01-26-2016 08:53 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Glint:
Let's get a grip. The consensus is not unanimous.
Mike Brown discusses why Planet Nine might not exist in his latest blog.
...I think Planet Nine is really out there. But that doesn't mean you should think it is out there. You might be skeptical. In fact, I would prefer that you were skeptical. I would prefer that you read the scientific paper, looking for potential flaws, caveats, and places where we might have been led astray. But, OK, I understand that the actual scientific paper is on the weighty side, so, rather than make you wade through it finding the potential pitfalls, instead, I will give you my top list of things that might be wrong.

Philip
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posted 01-30-2016 07:23 AM     Click Here to See the Profile for Philip   Click Here to Email Philip     Edit/Delete Message   Reply w/Quote
It's exciting it can explain the orbits of five well-known TNO — Trans Neptunian Objects... and let's not forget how planet Neptune was discovered; first mathematics then astronomy.

SpaceAholic
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posted 02-25-2016 02:21 PM     Click Here to See the Profile for SpaceAholic   Click Here to Email SpaceAholic     Edit/Delete Message   Reply w/Quote
The search narrows:
A study done by a team of French scientists may help narrow the search. In a recent paper appearing in Astronomy and Astrophysics, astronomer Agnes Fienga and colleagues looked at what effect a large Kuiper Belt planet would have on the orbits of other planets in the Solar System, focusing their study on Saturn. Thanks to NASA's Cassini orbiter, which has been orbiting Saturn since 2004, we can precisely calculate Saturn's position along its orbit.

Based on the planet's "residuals", the difference between the calculated position of Saturn versus what was actually observed, the team was able to exclude two sections of its potential orbit and home in on "probable" swath and a much larger "possible" section of the orbit.

SpaceAholic
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posted 04-20-2016 04:59 PM     Click Here to See the Profile for SpaceAholic   Click Here to Email SpaceAholic     Edit/Delete Message   Reply w/Quote
Further leveraging of Cassini data has helped to again narrow the likely location.
The research indicates that the most probable location for Planet Nine is towards the constellation of Cetus, in a patch sky with a 20-degree radius near Aires and Pisces, centred at the celestial coordinates right ascension 40 degrees, declination -15 degrees.

SpaceAholic
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posted 07-08-2016 10:21 AM     Click Here to See the Profile for SpaceAholic   Click Here to Email SpaceAholic     Edit/Delete Message   Reply w/Quote
New clues:
"The argument that a planet is there is not ironclad," cautions Renu Malhotra, a planetary scientist at the University of Arizona in Tucson. "I think it's worth studying. There's enough there to not ignore this evidence," she adds. "We just shouldn't get depressed if the planet's not there."

Malhotra and colleagues have been looking for independent evidence for a ninth planet. And they think they've found another clue: The orbital periods of those six bodies are roughly synced to one another, her team reports in the same journal. For example, the most distant one, the dwarf planet Sedna, goes around the sun five times in about the same amount of time that its neighbor, 2010 GB174, completes eight orbits. Such synced orbits usually hint at some gravitational link among all the bodies involved. But these minuscule worlds are too tiny to affect one another, says Malhotra, suggesting there's a more massive culprit.

A planet at least 10 times as massive as Earth and orbiting the sun once every 17,117 years would be in sync with four of these bodies, Malhotra and colleagues find. That puts Planet Nine, on average, about 100 billion kilometers from the sun, or roughly 665 times the distance between the sun and Earth.

SpaceAholic
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posted 10-20-2016 10:24 AM     Click Here to See the Profile for SpaceAholic   Click Here to Email SpaceAholic     Edit/Delete Message   Reply w/Quote
The putative "Planet Nine" may have tilted the entire solar system, researchers say.
"Planet Nine may have tilted the other planets over the lifetime of the solar system," said study lead author Elizabeth Bailey, an astrophysicist and planetary scientist at the California Institute of Technology in Pasadena.

Prior work found that the zone in which the eight major planets orbit the sun is tilted by about 6 degrees compared to the sun's equator. This discrepancy has long been a mystery in astronomy.

Glint
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posted 10-20-2016 12:30 PM     Click Here to See the Profile for Glint   Click Here to Email Glint     Edit/Delete Message   Reply w/Quote
Out of respect for Clyde Tombaugh, and the many decades that Pluto was actively in the club of [major] planets, can we just retire the "9th planet" jersey and go back to looking for Planet X?

SpaceAholic
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posted 02-17-2017 10:24 AM     Click Here to See the Profile for SpaceAholic   Click Here to Email SpaceAholic     Edit/Delete Message   Reply w/Quote
Zooniverse release
We need your help searching for new objects at the edges of our solar system. In this project, we'll ask you to help us distinguish real celestial objects from image artifacts in data from NASA's Wide-field Infrared Survey Explorer (WISE) mission. The real objects are brown dwarfs and low-mass stars, the Sun's nearest neighbors. You may find an object closer than Proxima Centauri (the closest star to the Sun) or even discover the Sun's hypothesized ninth planet, which models suggest might appear in these images.

Wehaveliftoff
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posted 02-17-2017 03:40 PM     Click Here to See the Profile for Wehaveliftoff   Click Here to Email Wehaveliftoff     Edit/Delete Message   Reply w/Quote
Now, THAT's the Spirit! because this is A LOT of work.

Mike Dixon
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posted 02-17-2017 03:56 PM     Click Here to See the Profile for Mike Dixon   Click Here to Email Mike Dixon     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Glint:
Out of respect for Clyde Tombaugh, and the many decades that Pluto was actively in the club of [major] planets, can we just retire the "9th planet" jersey and go back to looking for Planet X?
Thanks for saying what many people think.

Robert Pearlman
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posted 03-01-2017 09:57 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
National Air and Space Museum release
Planet Nine From Outer Space

Exploring Space Lectures
Lecturer: Mike Brown, California Institute of Technology
May 2, 2017 | 8:00pm
National Air and Space Museum, Washington, D.C.

(This lecture will also be presented online.)

The recent suggestion of evidence of a massive ninth planet in the outer solar system has set off a worldwide search to find this latest member of our planetary family. Mike Brown, professor of planetary astronomy at California Institute of Technology and discoverer of several Kuiper Belt objects, will explore the evidence of Planet Nine and the prospects for the search now underway.

Tickets for this lecture are free and must be reserved in advance

SpaceAholic
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posted 04-05-2017 06:04 AM     Click Here to See the Profile for SpaceAholic   Click Here to Email SpaceAholic     Edit/Delete Message   Reply w/Quote
Four objects detected by Australian National University and crowd sourced volunteers are being further assessed as possible candidates for Planet 9.
Lead researcher Dr Brad Tucker said about 60,000 people from around the world had classified over four million objects in space as part of the ANU-led citizen search for the so-called Planet 9.

"We've detected minor planets Chiron and Comacina, which demonstrates the approach we're taking could find Planet 9 if it's there," said Dr Tucker from the ANU Research School of Astronomy and Astrophysics.

spaced out
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posted 04-05-2017 08:49 AM     Click Here to See the Profile for spaced out   Click Here to Email spaced out     Edit/Delete Message   Reply w/Quote
As I understand it they're pretty confident none of the four objects is likely to be Planet 9 but finding out what they are should be interesting anyway.

Whatever the findings it's still a huge achievement as they processed something like 13 man-years of data in three days thanks to crowd-sourcing and I'm proud to say I was a small part of that crowd.

Even a negative result is important as they can now say with some confidence that Planet 9 can't be found in a significant chunk of its possible locations. That helps narrow down the possible orbits.

Wehaveliftoff
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posted 04-19-2017 12:31 PM     Click Here to See the Profile for Wehaveliftoff   Click Here to Email Wehaveliftoff     Edit/Delete Message   Reply w/Quote
Surprise, surprise. That huge object lurking at the edge of the solar system? May not be a ninth planet after all, Newsweek published today.
Ever since enthusiasm started growing over the possibility that there could be a ninth major planet orbiting the sun beyond Neptune, astronomers have been busy hunting it. One group is investigating four new moving objects found by members of the public to see if they are potential new solar system discoveries. As exciting as this is, researchers are also making discoveries that question the entire prospect of a ninth planet.

SpaceAholic
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posted 04-19-2017 12:56 PM     Click Here to See the Profile for SpaceAholic   Click Here to Email SpaceAholic     Edit/Delete Message   Reply w/Quote
Or it may be...if your referring this originally sourced article the author is offering a theoretical alternative explanation that may account for displacement of some trans-neptunium objects (but the theory does not address all the observational evidence otherwise supporting the existence of Planet 9).

SpaceAholic
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posted 06-24-2017 11:41 PM     Click Here to See the Profile for SpaceAholic   Click Here to Email SpaceAholic     Edit/Delete Message   Reply w/Quote
Planet X? Another Earth-Size World May Lurk in the Outer Solar System
Scientists at the University of Arizona's Lunar and Planetary Laboratory (LPL) have determined that an unseen object with a mass somewhere between that of Earth and Mars could be lurking in the Kuiper Belt, a region beyond Neptune filled with thousands of icy asteroids, comets and dwarf planets.

In January 2016, a separate group of scientists predicted the existence of a Neptune-size planet orbiting the sun far, far beyond Pluto — about 25 times farther from the sun than Pluto is. This hypothetical planet was dubbed "Planet Nine," so if both predictions are correct, one of these putative objects could be the solar system's 10th planet.

The so-called "planetary-mass object" described by the scientists from LPL appears to affect the orbits of a population of icy space rocks in the Kuiper Belt. Distant Kuiper Belt objects (KBOs) have tilted orbits around the sun.

SpaceAholic
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posted 10-16-2017 11:51 AM     Click Here to See the Profile for SpaceAholic   Click Here to Email SpaceAholic     Edit/Delete Message   Reply w/Quote
NASA release
The Super-Earth that Came Home for Dinner

It might be lingering bashfully on the icy outer edges of our solar system, hiding in the dark, but subtly pulling strings behind the scenes: stretching out the orbits of distant bodies, perhaps even tilting the entire solar system to one side.

If a planet is there, it's extremely distant and will stay that way (with no chance -- in case you're wondering -- of ever colliding with Earth, or bringing "days of darkness").It is a possible "Planet Nine" -- a world perhaps 10 times the mass of Earth and 20 times farther from the sun than Neptune. The signs so far are indirect, mainly its gravitational footprints, but that adds up to a compelling case nonetheless.

One of its most dedicated trackers, in fact, says it is now harder to imagine our solar system without a Planet Nine than with one.

"There are now five different lines of observational evidence pointing to the existence of Planet Nine," said Konstantin Batygin, a planetary astrophysicist at Caltech in Pasadena, California, whose team may be closing in. "If you were to remove this explanation and imagine Planet Nine does not exist, then you generate more problems than you solve. All of a sudden, you have five different puzzles, and you must come up with five different theories to explain them."

Batygin and his co-author, Caltech astronomer Mike Brown, described the first three breadcrumbs on Planet Nine's trail in a January 2016 paper, published in the Astronomical Journal. Six known objects in the distant Kuiper Belt, a region of icy bodies stretching from Neptune outward toward interstellar space, all have elliptical orbits pointing in the same direction. That would be unlikely -- and suspicious -- enough. But these orbits also are tilted the same way, about 30 degrees "downward" compared to the pancake-like plane within which the planets orbit the sun.

Breadcrumb number three: Computer simulations of the solar system with Planet Nine included show there should be more objects tilted with respect to the solar plane. In fact, the tilt would be on the order of 90 degrees, as if the plane of the solar system and these objects formed an "X" when viewed edge-on. Sure enough, Brown realized that five such objects already known to astronomers fill the bill.

Two more clues emerged after the original paper. A second article from the team, this time led by Batygin's graduate student, Elizabeth Bailey, showed that Planet Nine could have tilted the planets of our solar system during the last 4.5 billion years. This could explain a longstanding mystery: Why is the plane in which the planets orbit tilted about 6 degrees compared to the sun's equator?

"Over long periods of time, Planet Nine will make the entire solar-system plane precess or wobble, just like a top on a table," Batygin said.

The last telltale sign of Planet Nine's presence involves the solar system's contrarians: objects from the Kuiper Belt that orbit in the opposite direction from everything else in the solar system. Planet Nine's orbital influence would explain why these bodies from the distant Kuiper Belt end up "polluting" the inner Kuiper Belt.

"No other model can explain the weirdness of these high-inclination orbits," Batygin said. "It turns out that Planet Nine provides a natural avenue for their generation. These things have been twisted out of the solar system plane with help from Planet Nine and then scattered inward by Neptune."

The remaining step is to find Planet Nine itself. Batygin and Brown are using the Subaru Telescope at Mauna Kea Observatory in Hawaii to try to do just that. The instrument is the "best tool" for picking out dim, extremely distant objects lost in huge swaths of sky, Batygin said.

But where did Planet Nine come from? Batygin says he spends little time ruminating on its origin -- whether it is a fugitive from our own solar system or, just maybe, a wandering rogue planet captured by the sun's gravity.

"I think Planet Nine's detection will tell us something about its origin," he said.

Other scientists offer a different possible explanation for the Planet Nine evidence cited by Batygin. A recent analysis based on a sky mapping project called the Outer Solar System Origins Survey, which discovered more than 800 new "trans-Neptunian objects," suggests that the evidence also could be consistent with a random distribution of such objects. Still, the analysis, from a team led by Cory Shankman of the University of Victoria, could not rule out Planet Nine.

If Planet Nine is found, it will be a homecoming of sorts, or at least a family reunion. Over the past 20 years, surveys of planets around other stars in our galaxy have found the most common types to be "super Earths" and their somewhat larger cousins -- bigger than Earth but smaller than Neptune.

Yet these common, garden-variety planets are conspicuously absent from our solar system. Weighing in at roughly 10 times Earth's mass, the proposed Planet Nine would make a good fit.

Planet Nine could turn out to be our missing super Earth.

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Ultimate Bulletin Board 5.47a





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