The Fight for Dwarf Planets Continues

Check out this excellent interview with Dr. Alan Stern, Principal Investigator of NASA's New Horizons mission to Pluto, by Space.com here:

http://www.space.com/scienceastronomy/pluto-planet-debate-stern-qanda-101129.html

I want to commend Space.com for presenting both sides of the Pluto debate rather than just one. Stern's argument makes sense because it is based on what an object is rather than where it is. Gravitational dominance is addressed if we class these small planets as "dwarf planets." It means they are planets but not large enough to gravitationally dominate their orbits.  Arguments that "we cannot have too many planets" because kids won't be able to memorize them or because then the term planet won't be "special" have no scientific merit. We might as well limit Jupiter to four moons instead of 63 for the same reason. The same is true for arguments that there are only two kinds of planets, terrestrials and jovians. Just because an object is not a terrestrial or a jovian doesn't make it not a planet--it makes it a different kind of planet. We very well may discover objects in other solar systems that require adding a fourth, fifth, etc. category of planets. As for eccentric orbits, many giant exoplanets, some with several Jupiter masses, have orbits far more eccentric than that of Pluto. There are at least two cases of systems with two giant planets orbiting their stars in a 3:2 resonance just like Neptune and Pluto. If these objects are not planets, what are they?

Similarly, spherical moons of planets are compositionally akin to planets themselves, which is why Stern and others have proposed calling them "satellite planets." If we ever land rovers on Triton and Pluto, the challenges and circumstances will be very similar in spite of the fact that one orbits a planet and the other orbits the Sun directly.

Brown's argument that there are only a few astronomers left who view dwarf planets as planets and that they are all on the New Horizons mission was a cheap shot and is blatantly untrue. How many of the 300 professional astronomers who signed the petition rejecting the IAU decision are on the New Horizons mission? The answer is very few. New Horizons is already fully funded and unaffected by whatever resolutions the IAU passes. In fact, the Dawn mission to Ceres and Vesta, launched to a dwarf planet and an asteroid, receives no less credibility than any planetary mission. The reality is many astronomers know that the IAU decision was politically motivated and done surreptitiously in a way that violated the group's own bylaws. Rather than accept it, most planetary scientists are simply ignoring it. Most of the 424 IAU members who voted on the 2006 resolution are not planetary scientists but other types of astronomers. Why should they and not those who study planets be the ones who determine what a planet is?

A Thanksgiving Message

On February 22 of this year, I posted an entry in this blog asking for help to save the observatory of my beloved astronomy club, Amateur Astronomers, Inc. Last December, we were sent an eviction notice by Union County College, where our observatory is located. This is a very belated thank you to all those people who took the time to call and write to the Union County Board of Chosen Freeholders and the Trustees of Union County College asking to save Sperry Observatory, which has been on the site for over 40 years. We were blessed with an outpouring of support from the public and the media, which ended up making a real difference. We were especially blessed by the support of State Senate Majority Leader Barbara Buono, who publicly stood up and spoke on behalf of our observatory.

During the spring, negotiations with the college administration were re-opened, and a new two-year agreement with the college was reached, granting us a reprieve. The announcement of the agreement can be read here: http://www.asterism.org/ . Click on "Special Notices."

Writing only as an individual, not representing anyone but myself, I want to thank everyone who took action on behalf of our club and our observatory. That little building has been like a second home to me for over three years. Thanks to your efforts, we can continue to share our love of astronomy and the beauty of the universe with the public from our beloved home of more than four decades.

On a similar note, I want to thank the many individuals--lay people, amateur astronomers, and professional astronomers--who have not only stood by planet Pluto, but have given me moral support on several occasions when I received some very nasty emails by a few meanspirited people opposed to my advocating for Pluto. Those who sent these messages, which were filled with personal attacks and not legitimate arguments DO NOT represent the majority of astronomers or lay people who support the IAU decision. I have had many friendly, respectful conversations with those on the "other side" of this debate, including the late Dr. Brian Marsden, who died too young this month and will most certainly be missed. How sad that he won't be here to see the images from Dawn and New Horizons, which certainly would have been of tremendous interest to him.

This is also an appropriate time to make an announcement concerning my book The Little Planet That Would Not Die: Pluto's Story. Yes, the book is still coming, but unfortunately, not by the end of 2010, as I had hoped for so much. In past entries, I have reported that I am taking classes in astronomy at Swinburne University with the goal of obtaining a Graduate Certificate of Science in Astronomy. These classes have been rewarding but also extremely challenging--challenging to the point that I realized I could not adequately complete the classwork and at the same time do justice to a project as important as a book about Pluto. The book is a work in progress, but with the last Swinburne class assignment, a research project, due on December 4, that progress has had to be put on hold.

Once that project is submitted, I will be back at work on the book full speed ahead. I will be taking a break after four classes at Swinburne with the goal of resuming studies toward the Masters in Astronomy after the book is completed, published, and promoted, hopefully with a book tour.

Also coming after the classwork is done will be the promised review of the DVD "Naming Pluto" and a book review of Pluto: Sentinel of the Outer Solar System by Dr. Barrie W. Jones.

Here's wishing a Happy Thanksgiving to all who celebrate and a big thank you to all of Pluto's loyal fans!

It Was Never "Eris vs. Pluto"

When Eris was observed occulting (passing over) a faraway star late last week, astronomers realized that their conclusion of Eris being bigger than Pluto was likely premature. No sooner had the information been released than the media began referring to a demotion for Eris equaling a victory for Pluto. And once again, they have it wrong.

On November 5, several teams of astronomers in the Chilean Andes observed Eris pass in front of a 17^th magnitude star in the constellation Cetus. Many additional astronomers observed the efforts of one of these teams remotely, via the Internet. The best observation was made by Jose Luis Ortiz at the Institute of Astrophysics of Andalusia, Spain using a 16-inch telescope. Their occultation video can be found here: http://www.youtube.com/watch?v=HxQ0b8p4cGY

By viewing Eris pass over this star, astronomers can determine Eris’ diameter. What they discovered is that Eris has a diameter of 2340 kilometers or 1454 miles or less, making it a bit smaller than Pluto, which has a diameter of 2344 kilometers or 1456.5 miles, plus or minus 10 kilometers.

Because Eris’ discovery re-opened the already ongoing debate over the definition of planet, Eris is often portrayed as Pluto’s rival, the cause of its demotion. This viewpoint misses the mark completely because the two planets were never in competition. On the contrary, Eris’ existence confirms that Pluto is not a loner, that there is an entire class of small planets beyond Neptune, which share features with one another as well as with Neptune’s largest moon, Triton.

Small objects at such distances are difficult to measure under the best of circumstances. Eris is three times further from the Sun than Pluto. Previous Hubble images showed it to have a slightly larger diameter than Pluto, but even the best such measurements have a degree of uncertainty.

According to Kelly Beatty in Sky and Telescope magazine, Eris may have previously appeared larger than it really is because its axis is pointing toward the Sun, warming up the hemisphere facing the Sun and thereby leading to inflated infrared measurements. The article can be found here: http://www.skyandtelescope.com/news/106861063.html?loggedin=y

Eris’ mass is currently believed to be 2.5 grams per cubic centimeter, making it more massive than Pluto even if it is smaller. Pluto’s mass is estimated at 1.8 to 2.1 grams per cubic centimeter. Higher density likely means it is composed of more rock and less ice—another argument against classifying either Eris or Pluto as comets or “dirty snowballs,” given that the majority of their composition is rock. And Eris has a reflectivity of about 90 percent, significantly higher than that of Pluto, meaning it is highly reflective of sunlight falling upon it. This too could make the planet appear bigger than it really is.

The diameter numbers for Pluto and Eris are so close as to be almost identical. No one should be surprised if the “contest” over which is bigger goes back and forth many times as new data becomes available.

The fact that Eris and Pluto are so similar works against the mindset that demoted Pluto in the first place. The argument was we have four terrestrials, four gas giants, and one misfit, Pluto. Eris’ discovery illustrates that Pluto is not and never was, a misfit. It was the second (as Ceres was the first) of a third class of planets to be found in our solar system, small objects large enough to be planets because unlike asteroids, they are large enough for their own gravity to pull them into a round shape. Dwarf planets are simply small planets not large enough to gravitationally dominate their orbits. There is no rational explanation to label them as not being planets at all other than the artificial, convenience-based argument that our solar system cannot have too many planets, as children will never be able to memorize them.

Pluto and Eris are not rivals; they are two of a kind. Makemake and Haumea are likely similar in composition, mass, and density. Interestingly, all these objects also bear striking similarities to Neptune’s largest moon, Triton. Triton orbits Neptune backwards, meaning it revolves in the opposite direction as Neptune does around the Sun. It is in an unstable orbit, meaning it likely was once a planet with its own orbit around the Sun and was subsequently captured by Neptune.

With a diameter of 2700 kilometers, Triton has a composition strikingly similar to that of Pluto. Both have surfaces covered with frost of carbon dioxide, carbon monoxide, nitrogen, and methane, and both have a pinkish-red color. These similarities are enough to raise questions about whether Triton, Pluto, and Eris, as well as possibly Makemake and Haumea, have similar origins.

Anyone interested in more detail about Pluto’s troposphere (lower atmosphere) can find it at http://www.astro.ex.ac.uk/exoclimes2010/posters/1.7_Zalucha.pdf

Even among the four terrestrials and four gas giants in our solar system, no two planets are identical in size, composition, geology, number of moons, etc. The similarities and differences that we pick and choose to categorize these objects are largely subjective. Saturn has the lowest density of all the planets; it would float if we could find a large enough ocean in which to place it. Jupiter and Saturn have more in common with the Sun than with the Earth when it comes to composition, as the former are composed mostly of hydrogen and helium, and neither has a solid surface.

Astronomers determined Jupiter and Saturn are not stars, however, because they never conducted hydrogen fusion and therefore never produced their own light—neither is anywhere near massive enough to do this. Yet at the same time, they chose to put Jupiter and Earth in the same overall category of planet even though the two bodies have little in common. Earth actually has more in common with Pluto than with Jupiter. Both Earth and Pluto are rocky with solid surfaces; both have nitrogen in their atmospheres, and both have large moons believed to have formed via giant impacts with the original planet.

The next time you hear people use the argument that Pluto is “not like the other planets,” the old “one of these things is not like the others,” remember that inherent in this statement is a subjective choice of characteristics used to determine similarity and difference. A different choice of characteristics will yield a different categorization system. If we use hydrostatic equilibrium to classify an object as a planet, spherical moons of planets like Triton are essentially planets themselves and deserve their own category of secondary or satellite planets.

The best way to learn the specifics about these bodies is to go there. An Eris Express would take about 30 years, but if we can find a way to speed up that travel time and to fund such a mission, the returns would be priceless. The same is true for further exploration of Uranus and Neptune and their satellites, possibly through orbiters like Galileo did for Jupiter and Cassini is doing for Saturn.

Until we actually see these places up close, all conclusions should be understood to have a tentative quality about them. People want quick, easy answers, but that does not work for small objects at such distances. For the foreseeable future, we just have to learn to accept that there is no “final answer.”