Thursday, March 27, 2014

Solar System's Most Distant Planet Discovered

An object estimated to be large enough to be in hydrostatic equilibrium and therefore rounded by its own gravity, has been found orbiting in the inner Oort Cloud, beyond Sedna, what until now was known as the solar system's furthest planet/

Known as 2012 VP113, this likely dwarf planet is somewhere between 300 and 1000 km in diameter. It was discovered by Dr. Chad Trujillo, one of the three astronomers who discovered Eris, and by Dr. Scott S. Shepard.

Here is the article announcing the discovery:
“NASA Supported Research Helps Redefine Solar System's Edge”

The Oort Cloud is a hypothesized sphere believed to be the source of long-period comets (those with orbits of 200 years or longer). The Kuiper Belt, source of short-period comets, is located 30-50 Astronomical Units (AU) from the Sun. One AU equals 93 million miles, or the distance between the Sun and the Earth.

Pluto orbits at the inner edge of the Kuiper Belt, with its perihelion (closest point to the Sun) at 29.7 AU and its aphelion (furthest point from the Sun) at 49.3 AU. The Kuiper Belt is located in the area between 30 and 50 AU.

Sedna, discovered in 2003, is almost certainly large enough to be in hydrostatic equilibrium and therefore a dwarf planet, even though the IAU has not recognized it as such. Its orbit is highly elliptical, and its closest point to the Sun is 76 AU; being that far beyond the Kuiper Belt, it has been classed as an inner Oort Cloud Object.

This new discovery, nicknamed “Biden” due to the VP initials in its name, orbits beyond Sedna, with a perihelion of 80 AU.

The inner Oort Cloud is estimated to be significantly larger than both the asteroid belt between Mars and Jupiter and the Kuiper Belt. And now, some astronomers believe this distant region could host up to 900 dwarf planets with diameters of 1000 km (621 miles) or larger. Sheppard emphasized some of these objects could rival the sizes of Mars or even Earth.

Why have they not yet been detected? The answer is their extreme distance from the Sun. Both Sedna and 2012 VP113 have highly elliptical orbits that at aphelion take them hundreds of AU from the Sun. That makes them extremely hard to detect even with our best telescopes, even more difficult to find than large exoplanets that orbit closer to their stars or giant exoplanets orbiting their stars at a great distance.

And this is not all. Some astronomers believe that the similarity in the orbits of Sedna, 2012 VP113, and other objects at the outer edge of the Kuiper Belt is due to the presence of a still undiscovered giant planet that could be as large as 10 times the size of Earth.

A second discovery in the outer solar system was also announced today. The centaur (an object that appears to be part asteroid and part comet) Chariklo was revealed have a ring system! The tiny object is surrounded by two dense and narrow rings. Until now, the only solar system objects known to have rings were the four gas giants Jupiter, Saturn, Uranus, and Neptune. One of the discovery team’s members is none other than Dr. Chad Trujillo, a co-discoverer of Eris.

More information on this discovery can be found here:
“ESOcast 64: First Ring System Around an Asteroid”

Not too long ago, Pluto was viewed as the outermost planet and the edge of our solar system. Then Eris and Sedna were discovered, and the frontier was expanded much further. Now, that boundary has been pushed even further back. Who knows how many more planets exist beyond even this new one? If the astronomers predicting 900 or more dwarf planets in the Oort Cloud are correct, our solar system may very easily have more than 1,000 planets.

A Mercury- or Mars-sized planet in the inner Oort Cloud would throw the IAU planet definition in complete disarray because such an object would not clear its orbit of surrounding comets and tiny iceballs, leading to the absurdity where two objects of the same size are classed differently, one a planet, and one not a planet, simply because the second orbits so much further away.

What about a giant planet that could be 10 times the size of Earth? The Oort Cloud is huge. Such a planet could very well be perturbing the orbits of smaller Oort Cloud dwarf planets, but it would not necessarily clear its neighborhood of these or of tiny comets. According to the IAU definition, if it doesn’t “clear the neighborhood of its orbit,” an object is not a planet.

The Chariklo discovery, along with Dawn’s findings at Vesta, suggest we may not understand asteroids as well as we think we do. They too might require subdivisions into various subclasses depending on their individual features and nuances. Complex objects like Vesta are very different from the majority of asteroids and are not really asteroids at all in the sense that they are not rubble piles but far more complex objects, something between asteroid and dwarf planet.

Didn’t an astronomer recently say that there likely aren’t any more large, planet-sized Kuiper Belt Objects out there since none have recently been found? Maybe that astronomer spoke too soon. Or maybe the worlds waiting to be found lurk beyond the Kuiper Belt, out in the nether regions of the Oort Cloud.

There is an 80s song with a refrain, “The frontier is forever shifting. Move on to the virgin lands.” In our solar system, every time we think we have found the outer edge, the frontier moves further, and another region opens up. That is what makes studying it so intriguing.

And yes, it’s looking more and more like we’re going to have to get used to our solar system having not 9, not 50-100, but possibly as many as 1,000 planets. That does not “devalue” the term planet any more than the existence of billions of stars and billions of galaxies “devalue” those terms. Ours is a bigger solar system than we thought. Children—and adults—don’t need to memorize a list of names; they need to understand the characteristics of each subclass of planets, the difference between primary and secondary or satellite planets, and the different regions where planets exist, including the Kuiper Belt and Oort Cloud. And yes, they also should learn about asteroids and comets and the ways they are different from small planets.

The frontier is forever shifting, and the best discoveries may very well be yet to come.

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