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.

Monday, March 10, 2014

2015: Tell People Both Sides about Dwarf Planets

Like Planetary Society blogger Emily Lakdawalla, I and many others can hardly wait to see objects like Ceres, Charon, and Pluto, that have long appeared to us as tiny dots, finally be revealed as complex worlds with geology and geography—in other words, real physical places we can explore.

And as she recommends, I am spreading the word as far and wide as I can about just how awesome 2015 will be.

But the backdrop and the story I am telling are a bit different from Lakdawalla’s—not about the facts but about the different ways we can interpret those facts.

Unfortunately, Lakdwalla approaches the flybys of Ceres and Pluto-Charon from the vantage point that the IAU demotion of Pluto is a done deal, that our solar system has only eight planets, when this is far from the case.

She is completely wrong in claiming NASA is not promoting its own planetary missions. Nothing could be further from the truth. The New Horizons team has been releasing videos promoting the flyby, marking milestones such as the time the spacecraft crosses the orbit of each planet on its way to Pluto, and planning major outreach campaigns as part of its year-long Pluto Eve designation.

After hosting a five-day Pluto Science Conference last summer, the New Horizons team is meeting for two-day seminars four times this year. The first, held in January, did include an extensive discussion on public outreach about the mission.

Likewise, the Dawn mission did a thorough job promoting the Vesta flyby, providing analyses of the data that ultimately led some on the mission to label Vesta “the solar system’s smallest terrestrial planet.” Dawn continues to publicize updates as its spacecraft heads for Ceres, and there is every reason to believe those on the mission will do as thorough a job of public outreach with Ceres as they did with Vesta.

But maybe there is a reason Lakdawalla does not acknowledge these efforts—specifically the fact that so many scientists on the New Horizons team, and some on the Dawn team, want the public to know that these missions are visiting planets because that is what dwarf planets are—smaller versions of the larger planets. This is based on their legitimately scientific view that by virtue of being rounded by their own gravity, these worlds “count” as a subclass of planets based on the type of objects they are.

So she ignores the position of Dr. Alan Stern, Principal Investigator of New Horizons and someone who literally fought for a mission to Pluto for more than 20 years. Dr. Stern says, "And I can’t think of a single distinguishing characteristic that would set apart Pluto and other things that you’d call a planet, other than its size. So I like to say, a Chihuahua is still a dog."

Yes, this means that large, round moons like Europa, Io, Ganymede, Callisto, Titan, Enceladus, and Triton, are planets too. Compositionally, they are planets. They are worlds we could someday explore and even possibly colonize. They are places on whose surfaces we can land a rover. Several of them, along with Ceres and Pluto, may very well harbor subsurface oceans that could host microbial life. The only difference between the objects listed above (excluding Ceres and Pluto) is that they orbit other planets instead of orbiting the Sun directly. That makes them, according to the geophysical planet definition, secondary or satellite planets.

If that seems strange, consider that astronomers have already noted that exo-moons (moons of exoplanets) could harbor life and should be considered for possible future settlement. No one can live on a gas giant, but a rocky moon, for all practical purposes is a complex, potentially habitable world—in other words, a planet.

Yet Lakdawalla draws an artificial boundary between these worlds and the solar system’s four terrestrial and four jovian primary planets. She says, “When you include the planets it's striking and surprising how big and varied the solar system's large moons are; they're quite planet-like, and you'll often hear planetary scientists slip up and call them "planets" when they're discussing geology of the planet-sized moons.”

The last sentence seems to be a response to a video released by the New Horizons mission containing clips of astronomers at last summer’s Pluto Science Conference referring to Pluto as a planet. These were not “slip ups,” and referring to them as such is a clear and direct insult to those scientists whose words were quoted. Far from “slipping up,” these scientists were, whether consciously or not, acknowledging that spherical moons and spherical primary objects orbiting the Sun are planets.

At times, Lakdawalla seems to be talking down to readers, with comments such as, “…it's very hard to talk people into funding a space program whose destinations seem to be places nobody ever heard of. Ceres, Pluto, Charon; and I'll add Europa, Ganymede, Titan, Enceladus, and Triton: how important can they be, if they're not on that list of eight planets.”

That list limited to eight planets does not exist, except in some people's minds.

And on what does she base the assumption that most people never heard of these worlds?

Her biggest blunder is the presupposition that all scientists simply accept the controversial 2006 IAU planet definition and demotion of Pluto. This is misleading and is a disservice to the public because it simply is not true.

Hundreds of planetary scientists signed a formal petition rejecting the IAU’s “nomenclature” change and still hold the same position today, seven years later. Lakdawalla says, US teachers “…don't seem to understand what Pluto is now thought to be.” The real truth is that there is no consensus even among astronomers as to what Pluto is. How an astronomer views Pluto depends on whether he or she adheres to the dynamical view, the one taken by four percent of the IAU, or to the geophysical view, the equally scientifically valid position that Stern and like-minded scientists take.

Is it fair to readers to stifle debate by closing off all discussion and simply declaring the issue decided when this is not the case? Is it in the best public interest to tell a story but hold back from telling readers that your story is really only one part of something much bigger?

I too oppose any redaction of Pluto from science education, but at the same time, am happy to report that many teachers, unlike Lakdawalla, do not accept the IAU decision at face value. Many continue to include Pluto with the planets, and the best ones teach the controversy, an exercise that centers on teaching children how to think rather than what to think. The best teachers inherently understand that Pluto’s status is an essay question, not a true or false one.

It isn’t clear what Lakdawalla means when she asks whether Pluto will look more “planet-ish” or “moon-ish.” That is because the division of spherical solar system objects and planets is artificial. Titan is often viewed as an analogue of early Earth, and Triton likely is very similar to Pluto. Other than their orbiting a primary planet, there is no distinguishing overall characteristic that separates spherical moons from full-fledged planets. They all are planets, and they all should be taught. Our solar system is a lot bigger and filled with far more planets than we were taught as kids.

Lakdawalla also errs in saying, “The reason Pluto was demoted was because we discovered other worlds out there that form a whole population of bodies, analogous to the asteroid belt, that occupy the same region of space. But we never talk about these other worlds. That's natural, because we don't know a lot about them; but the focus on Pluto tends to make us dismiss the rest as another belt of lumpy cratered rocks.”

First, the Kuiper Belt Objects that are spherical do not occupy the same region of space as Pluto. We are not talking about a crowded asteroid field like the one Luke Skywalker flies through in “The Empire Strikes Back.” There are several small planets in the Kuiper Belt, but they are not located in Pluto’s orbit or “region of space”—they are quite a bit further out and separated from one another. Second, she blurs the distinction between asteroids—tiny, shapeless rocks—and complex objects with enough gravity to squeeze them into a round shape. The former are rubble piles or dirty snowballs (comets) while the latter are fully-developed planets.

This does not mean that asteroids and comets should be ignored and not studied. At the same time, it is hard to understand how a geologist could so accept a blurring of the important distinctions between two very different types of bodies.

The geophysical planet definition argues that we cannot define an object solely by what else is around it. Yes, other bodies, small and large, were found in the region beyond Neptune. But that alone cannot be used to determine what Pluto is. To do that, we have to study Pluto itself. What it is should be considered equally important, if not more so, than where it is.

If it did anything, the IAU vote compounded confusion over what Pluto is. As one scientist at the January 2014 meeting of the New Horizons Science Team noted, that decision in some cases led to Pluto being removed entirely from lessons on the solar system (thankfully, many individual teachers and school board members chose to reject the IAU vote and keep Pluto in). There is no consistency in how the solar system is now taught to kids—that pretty much depends on the preferences of individual teachers.

It also generated a great deal of confusion among people of all ages. In various discussions, I have heard Pluto referred to as not only a star but an exoplanet, an asteroid, a moon of Neptune, etc.

Pluto isn’t “the end of the planets.” We haven’t completed our reconnaissance of the planets, and we won’t complete it with New Horizons because there are still more out there. New Horizons is visiting a third zone of planets, that of the dwarf planets. It will hopefully also explore one or two small KBOs that are not planet size. No one is arguing that either Kuiper Belt planets or tiny KBOs should not be studied.

A scientist should know better than to take a dictate by a self-appointed authority and pass it on as some sort of gospel truth. Unfortunately, Lakdawalla seems to have an agenda here. She has been close to Mike Brown for a long time and seems to be using her Planetary Science blog as a way of promoting him and his strange obsession with “killing” Pluto, which he has used to “brand” himself and leverage into money and fame. It is noteworthy that in December 2009, Lakdawalla attended a “Pluto-hating dinner” Brown held at his house, complete with a table centerpiece of a beheaded rubber Disney dog—this in front of a four-year-old. Brown gleefully posted pictures of the event via his Twitter account.

I also have an agenda, and that is to keep the debate going and make sure the public hears both sides of this issue so they can ultimately decide for themselves. The difference is, I hold to the geophysical planet definition, am honest about that agenda and don’t pretend to be giving people the objective truth while pretending there is no debate and or other side and doing everything possible to squelch that debate.

By all means, let’s spread the excitement about how awesome 2015 is going to be. New Horizons will visit the solar system’s only binary planet system, Pluto-Charon. Three new small planets will be revealed to us. Don’t tell people about “places that aren’t planets that we have yet to explore.” Tell them our solar system has so many more planets and types of planets than we ever thought, and that three of those planets will become real to us next year.