Comments on Mike Brown's Planets: What's in a name?
Or how about this for the classification of bodies...Or how about this for the classification of bodies, whether in the Solar System or interstellar?<br /><br />Class Type Mass Example<br /><br />Major bodies<br /><br />A Titan star 50.32+ Sols Eta Carina<br />B Giant star 6.29+ Sols Betelgeuse<br />C Medium star 0.786+ Sols Alpha Centauri<br />D Dwarf star 103+ Jupiters Proxima Centauri<br />E Midget star 13+ Jupiters Luhman 16<br />F Titan planet 512+ Earths <br />G Giant 64+ Jupiter<br />H Huge 8+ Neptune<br />I Large 1+ Earth<br />J Small 1/8+ Venus<br />K Tiny 1/64+ Mars<br />L Dwarf 1/512+ Pluto<br />M Midget 1/4096+ Makemake<br /><br />Minor bodies<br /><br />N 1/32768+ Ceres<br />O 1/262144+ Juno<br />P 1/2097152+ Phoebe<br />Q 1/16777216+ Amalthea<br />R 1/134217728+ Eros<br />S 1/1073741824+ Phobos<br />T 1/8589934592+ Deimos<br />U 1/68719476736+ Phaethon<br />V 1/549755813888+ Halley's Comet<br />W 1/4.3980465e+12+ Apollo<br />X 1/3.5184372e+13+ Aten<br />Y 1/2.8147498e+14+ Apophis<br /><br />Micro bodies<br /><br />Z 1/2.8147498e+14 or less<br /><br />In what class is your favorite body?
Excellent post. Thank you.Excellent post. Thank you.
If we allowed moons (secondary planets) to be plan...If we allowed moons (secondary planets) to be planets:<BR/><BR/>Earth: 1 Planet (The Moon aka Luna)<BR/>Jupiter: 4 Planets (The Galilean Moons Io, Europa, Ganymede, Callisto)<BR/>Saturn: 7 Planets (Mimas*, Enceladus*, Tethys, Dione, Rhea, Titan, Iapetus)<BR/>Uranus:5 Planets (Miranda*, Ariel, Umbriel, Titiana, Oberon)<BR/>Neptune: 1 Planet (Triton. Triton is likely a captured plutoid that <A HREF="http://adsabs.harvard.edu/abs/2005ApJ...626L.113C" REL="nofollow">perturbed the natural moons, dispersing them through gravitational interactions</A>.)<BR/>Pluto: 1 Planet (Charon)<BR/><BR/>* May not be in hydrostatic equilibrium, though appear spherical.
To Mike Brown:A consequence of IAU's decision is t...To Mike Brown:<BR/><BR/>A consequence of IAU's decision is that now 2003EL61 ad 2005FY9 are considered as a dwarf planets and plutoids, "for naming purpose". In a concrete way, the IAU will use its two committees, including the one that is used to take classical names. For your proposed names, will you stick by your initial choice of Hawaiian gods or will you, as you did for Eris, switch to classical names?<BR/><BR/>Best regards.
Even in the 1868 the book, "Smith's Illustrated As...Even in the 1868 the book, "<A HREF="http://books.google.com/books?id=ZLgXAAAAIAAJ&pg=PA23&lpg=PA23&dq=%22secondary+planet%22+Herschel&source=web&ots=4hmJstEMT1&sig=yNU_6U4h_1GwfWg4gfFeGkqDnm0&hl=en&sa=X&oi=book_result&resnum=10&ct=result" REL="nofollow">Smith's Illustrated Astronomy</A>", moons were called secondary planets.<BR/><BR/>If astronomers used strictly a geophysical definition there would be <A HREF="http://en.wikipedia.org/wiki/List_of_moons_by_diameter" REL="nofollow">roughly 18 secondary planets</A>, including our moon.<BR/><BR/>The question is: "How inclusive do we want the term Planet to be?"
I disagree with the statement that having hundreds...I disagree with the statement that having hundreds of planets would take away from the magic of the word planet. In fact, most people already know that we have discovered nearly 300 planets orbiting other stars and find that extremely exciting. People actually enjoy finding out that there is more out there than we ever imagined. Therefore, I disagree that the dynamic definition is "better" for teaching and outreach to the general public.<BR/><BR/>Memorizing the names of planets is not really that important. What is more important is knowing the various subtypes of planets--for example, what the characteristics of a gas giant are compared with those of a terrestrial planet. <BR/><BR/>A major problem with the IAU definition is that it states that dwarf planets are not planets at all. It is obvious to people that this makes no sense, as can be seen from the National Geographic "Eleven Planets" book. In common practice, the eleven-planet scheme ends up being the one most frequently taught and utilized.<BR/><BR/>The conference this summer is not being held to determine a "scientifically correct" definition of planet but to study the process by which scientists and others arrive at such definitions. Obviously, that process has been problematic. The issue of who decides is critical. One can question whether the IAU should be be deciding which classification becomes "the" one taught and used, especially when its decision-making process excludes most of its members and other planetary scientists in the field.<BR/><BR/>If we can find a way to incorporate both geophysical and dynamic characteristics into a classification system, we would have the best possible situation and one that is easily teachable and understandable. For example, taking into account dynamical considerations, we could say that an object such as Ganymede, that is in hydrostatic equilibrium but orbits a planet instead of a star is a "secondary planet." That way we keep the overall term planet as broad as possible with multiple subcategories that take take all these characteristics into account. In popular usage, moons of planets will likely continue to be called moons or satellites; however, many are very similar to the primary planets (those orbiting the sun), and this too is important to acknowledge.
This is a very good point you make in this blog en...This is a very good point you make in this blog entry - finally, the whole debate is about which of the classification schemes will have ownership over the magical word "planet". <BR/><BR/>And yes, the public plays indeed an important role here. As we all learn the names of the planets (and maybe some of their properties) at school, the planets are to many the very first contact with astronomy, maybe even with science. I feel that having hundreds of planets, most of them being small, distant iceworlds you never going to see in your backyard-telescope, will take much of the magic away from the word planet. What point is there in learning the names of all the planets, if there are a few dozen more detected every year? Therefore, in my opinion, we should let the "dynamical" definition of the planet win the debate, to make sure that the planets stay the "one-of-a-kind", individual, diverse, fascinating worlds they are. <BR/><BR/>As a geologist, I certainly like the "dwarf planet" definition, although personally I would have prefered it to be called "planetoids" oder "planetary objects". But for the case of spreading science to the public and teaching it, I strongly favor the "dynamic" definition of the term.
I agree with you, in that we have two different, p...I agree with you, in that we have two different, perfectly rational planetary classification systems: one based on geology, and the other on dynamics. I tend to favor the geological model with its myriads of "planets", but the other has merit as well.<BR/><BR/>The crux of the controversy, as I see it, in the IAU's definition of "dwarf planet" and "plutoid" is the other comment you made: that there is no <I>scientific</I> way to decide who gets to use the term "planet".<BR/><BR/>Inherently, the issue among the general public isn't one of science, but rather one of culture and tradition. I believe you used the terms "cultural planet" and "historical planet" in your page on Eris when it was first discovered, and they're good expressions. How do we reconcile these two classification systems with what the layman thinks of as a "planet"? People like their shortlists of easily memorized planet names, and lots of people, for whatever reason, are attached to Pluto.<BR/><BR/>(Astrologers, I gather, don't have this problem. They stick with the ancient definition of "planet", which includes the Sun and the Moon, and they have no problem dealing with dozens or even hundreds of "planets".)<BR/><BR/>I've thought all along that the IAU needs to recognize this public need and come up with a "cultural planet" category. Let them define "cultural planet" the way we always did implicitly before August of 2006: any body which orbits the sun and is at least as large as Pluto (or at least 2000 KM in diameter, if they prefer a nice, round number). Any newly discovered object in this size range could then be named as a major planet, from a cultural standpoint. Since the IAU is involved in naming these celestial objects, they'd have to be the ones to define "cultural planet".<BR/><BR/>Is this scheme somewhat arbitrary? Of course. But it's also not "scientific", so as long as we recognize the fact, we should be OK with it.<BR/><BR/>Perhaps this would resolve some of the recent confusion in textbooks. As one example, I've noticed that National Geographic has a book called "11 Planets", which numbers the three official dwarfs in with the eight bigger planets. Introductory text books could stick with the "cultural planet" category for memorization purposes, and in due time astronomy students can be introduced to the more nuanced classification schemes.<BR/><BR/>It might be useful to grandfather in Ceres, simply because it's the largest member of the asteroid belt and as historically important as Pluto and Eris. A planetary list including Ceres would give a pretty good cross-section of the major orbital zones in the Solar System. But that's an argument for another day.<BR/><BR/>Just my two cents, for what it's worth.<BR/><BR/>Bob Shepard
I like it. But I will risk answering the last que...I like it. But I will risk answering the last question: Had Pluto been closer to us, our first prejudice estimate at it's size may not have been 9000km and might have been closer to 3000km. <A HREF="http://aa.usno.navy.mil/faq/docs/minorplanets.php" REL="nofollow">The first asteroids discovered were often estimated to be about 3000km in diameter</A>, and perhaps this would have made astronomers slower to call Pluto a Planet for fear of history repeating itself. For when Pluto was discovered it was truly just an asteroid (a star like object in the night sky.)<BR/><BR/>To Ponder: Should a Planet be defined by what it is (physical characteristics) or where it is (orbital dominance)? So I ask, "Is the Earth's moon a planet?"
To PlutoThe smaller you got, the thicker the plot,...To Pluto<BR/><BR/>The smaller you got, the thicker the plot,<BR/>Your story is quite convoluted.<BR/>A planet you're not, as potato you're hot,<BR/>While the atmosphere here is polluted<BR/>By astronomers' cant and commoners' rant.<BR/>For seventy years we saluted<BR/>You then all at once you're the one no-one wants,<BR/>From the heavenly nine you've been booted!<BR/>Oh Pluto, my dear, it's curtains, I fear,<BR/>You've been roundly and soundly demoted,<BR/>For failure to clear your orbit, I hear,<BR/>Is a sin that's been newly promoted<BR/>As the means to an end which - Heaven forfend!<BR/>Meant millions of us were outvoted.<BR/>And who would have dreamt your orbit's unkempt?<BR/>I think you've been badly Swift-boated.<BR/>As ultimate task I've a question to ask:<BR/>Were you closer to us, would there be such a fuss?<BR/><BR/> 23 June 2008