jump to navigation

Size comparisons, take two August 14, 2009

Posted by Jorge Candeias in Ceres, Mercury, Neptune.
Tags: , , , ,
add a comment

I’ve already shown you a comparison between the largest Solar System planets in each category, and then I thought, heck, for the sake of completeness let’s do the same with the smallest ones, also with the help of Celestia. So here you go:

Size comparison between Neptune and Mercury

Size comparison between Neptune and Mercury

Size comparison between Mercury and Ceres

Size comparison between Mercury and Ceres

Isn’t this cute? The proportions look very much like those of the largest planets in each group, and if you prefer some numbers here they are: Neptune is 10 times larger than Mercury, wereas Mercury is nearly 5 times larger than Ceres. If you go check the masses, you’ll find that Neptune is almost 290 times heavier that Mercury, and Mercury 375 times heavier than Ceres. Everything very similar to the proportions between the biggest planets in each class. It should be noted, though, that Neptune may be the smallest of the giants but is not the lightest; that is Uranus’ claim to fame. Or one of them, anyway.

And, again, there isn’t much of a point in this. It’s just a visual reminder that if you look at the objects without taking into consideration their positions relative to eachother, the differences between giant and terrestrial planets tend to be larger than the difference between the terrestrials and the dwarfs.

Why are 8 planets bad science August 12, 2009

Posted by Jorge Candeias in Definition of planet, Plutophiles.
Tags: , , , , , , , ,

Yesterday, there was a small rebellion of “plutophiles” on twitter. A hashtag, #bringbackpluto, made it to number one in the trending topics list, and the messages that came along with it were, in general, as silly as you might expect. People just don’t get it.

The people who took part in that particular hashparty vastly misunderstand the reasons why the whole business of Pluto’s “demotion” came about. And their revolt does nothing to further their case and actually “bring back Pluto” (as if Pluto went anywhere; as if it isn’t right where it has always been, going round the Sun beyond Neptune). Quite the contrary. By showing so eloquently that they don’t get it, they simply won’t sway any of the people who actually have some knowledge about this stuff. The only way to sway them is to play their game, which means learning the science and discuss it scientifically. And learning some history of astronomy as well. And remember my mantra: “this ain’t about Pluto!”

Hop aboard. I’m taking you in a small historical trip. A trip you may get from plenty of other sources, but in this there’s no such thing as too many sources of information. And besides, nobody tells it quite like I do. In the end of this necessarily long text, I’ll tell you the main reason why I think that to speak about 8 planets is bad science. You can jump immediately to that point, if you think you already know all the historical stuff, but you’ll be missing my emphasis, on which I base my conclusions. It’s up to you.

Ready? Allright then. Fasten your seatbelts and let’s go visit the ancient Greeks.

Not that those were the guys who discovered the first planets. Ever since the first records of celestial movements were made, probably by the very first astrologers, people knew that there were some lights in the sky that stayed put, wereas other lights walked about. The Greeks were simply the guys who came up with the word “planet”. It means, aptly enough for the level of their understanding, wanderer.

Back then there were two different kinds of wandering celestial objects: those with an obvious disc, and those that looked like point sources of light, like moving stars. The first kind encompassed the Sun and the Moon, and there were all kinds of legends about them; the second kind was composed by 5 objects: Mercury, Venus, Mars, Jupiter and Saturn. These five were always thought of as planets, the Moon and the Sun kept coming and going from that category. The Earth, of course, at first was not thought of as a planet like the others, being as it was the center of it all (and flat). But whatever the actual numbers and groupings were, one thing remained constant: planets were special. Worthy of being used as characters for all sorts of myths and stories. How could they not be special? They were a handful of wandering lights in an otherwise static sky! They had to be pretty important and unique indeed! Right?

Then happened the first revolution in our understanding of these things, when the geocentric models of the Universe gave way to Copernicus’ vision of a universe centered in the Sun, a heliocentric vision. Planets, once rotating around the Earth, were now circling the Sun.

And the Earth with them.

This meant that planets were not point sources of light after all, but (probably) solid, round worlds like our own, maybe even with their own inhabitants. It also meant that the Moon was not a planet, but a satellite, for it circles not the Sun, but the Earth. The Sun? Ah, not a planet either. The Sun now became the center of everything. Not a star, as yet, but so unique it had no category to belong to. It was just the Sun.

This was a complete turnaround in our understanding of what a planet is. But, despite that, the now 6 planets remained very special places indeed. Think about it: thousands and thousands of stars, and only six worlds like our own? They’re special, no question about it!

And more: there was an order to them, an order that was often used as an evidence of divinity, for only an allmighty God could create such perfectly harmonious structures. When Galileo peeked through his telescope and saw for the first time that the other planets were, indeed, discs, that seemed to confirm this notion, although shortly after two discoveries shook things a bit: the discovery of the four galilean moons of Jupiter (which were also called “planets” for a while, as were, later, the first moons of Saturn to be discovered), and a pair of strange “ears” protruding from the sides of Saturn, which even changed shape over time. It was only in mid XVII century that these ears were recognized as rings, and that the first moons of Saturn (starting with Titan, of course) became known. There was something else that also tainted these notions of divine astronomical perfection: the discovery, by Kepler, that the planets did not follow perfectly circular paths, as previously thought, but moved along ellipses.

In the next century two relevant things happened. First, some astronomers noticed that the planetary distances to the sun followed closely a mathematical relation which came to be known as Titus-Bode Law. There was a gap between Mars and Jupiter, though. And the law said nothing about ending the fun at Saturn. So everyone began looking for new planets in the gap and beyond Saturn, and Uranus was found right where the law said something should be. You can imagine by yourselves how that bolstered up its credibility and the notion that, despite some annoying facts, God really did have a finger in making an orderly and predictable universe, in which the planets had their very special parts to play.

When Ceres was found in 1801, again right where Titus-Bode predicted it, it all seemed to be proved beyond a doubt. And Ceres quietly became the 8th planet of the Solar System. But then, shortly after, 3 more planets were discovered in the same general area, and heads began to be scratched.

And then stranger things began to happen. Uranus wasn’t behaving: instead of peacefully following its path, it wobbled back and forth, as if something unseen was pulling it. So the astronomers crunched the numbers, determined the position where the perturbing object should be, pointed their telescopes to that position, and there was Neptune, yet another planet, just waiting to be discovered. This happened in 1846. Great news, right? Wrong. Neptune’s position deviated significantly from what was predicted by the old Titus-Bode Law.

Oops! Could it be that such a venerable law of nature was wrong?

To make things worse, the year before a 5th body had been found between Mars and Jupiter, and from 1847 on new discoveries around the same zone happened at a steady pace. By 1900 they were already 450. Things were a lot more chaotic than they had seemed to be. The neatly ordered plan of God was taking a beating from reality.

These were the signs of a revolution to come.

That’s when astronomers noticed two things: firstly all the chaos was restricted to the zone between Mars and Jupiter, where Titus-Bode predicted there should be a planet. Maybe it exploded, and what was being discovered were mere fragments? All the other planets seemed to behave, kinda. The divergence between Neptune’s position and Titus-Bode could perhaps be a fluke? A statistical outlyer? Astronomers also noticed that all of the well-behaved planets showed typical planetary discs. But the annoying rebels beyond Mars didn’t. Like the planets in the old days, they looked just like moving stars.

And so they were christened “asteroids”, a word that means “similar to stars”, and the number of planets was reduced to 8. And the order was preserved. And the planets continued to be special objects in the sky.

Ah! What a relief! Sometimes you need a revolution to keep things as they were.

Pluto came about in 1930 (although it had been detected much earlier), and deviated so much from Titus-Bode that effectively killed it for good. At first its size was greatly overestimated, but there was little question that it had to be called a planet, even though no disc could be seen and even though its orbit was weird. It was alone out there, very far from the area where asteroids dwell, and much bigger than asteroids were. But that weird orbit… many people found it really hard to swallow. It seemed too odd, too distant from the orderly display the other 8 showed. But, hey, 9 planets in such a large Universe are still pretty special, aren’t they? So they went with it anyway.

But then came the 1990’s. Astronomers began an amazing series of discoveries in the outer Solar System. Small and not so small icy bodies in orbits similar to Pluto’s became commonplace, a chaos of intersecting, eccentric, inclined orbits that seemed to mirror closely what happens in the Main Asteroid Belt. Those that were uncomfortable with Pluto’s oddity became increasingly more uncomfortable. And when finally an object larger than Pluto, Eris, was found, something just had to change again. It was inevitable. We just had to fundamentally rethink what makes a planet for the third time in our history.

It could be simple. Just make with Pluto the same that was made with Ceres, Pallas, Juno and Vesta in the XIX century, reduce once more the number of planets to 8, and get on with it. Keep the order. Keep the specialness of planetary status. That’s what the IAU astronomers did, and that’s the source of the current definition of planet.

But it really is everything but simple. At the same time trans-neptunian objects were being found everywhere, exoplanets were also being found by the hundreds. Around “normal”, sun-like stars, around stars smaller and larger, around red dwarfs, around pulsars, even free-floating, roaming alone the empty spaces between the stars. Other planetary systems were found that didn’t look anything like our own. Systems with planets larger than Jupiter in orbits much more eccentric than those of any Solar System dwarf planet. Systems with 2, 3 or more giant planets packed inside what in the Solar System would be the orbit of Mercury. Systems with resonant giant planets. A wide variety of outcomes of a process that is apparently universal: planetary formation.

And all of a sudden there’s no order, only different outcomes of a process that is inherently chaotic. And all of a sudden planets are no longer special: we already know where are hundreds of them, and it’s now clear that we’ll end up finding many billions in our galaxy alone. Planets are literally everywhere.

And this is why 8 planets are bad science.

By insisting on a small number of planets, the astronomers are trying to perpetuate a notion that science itself has already defeated: that planets are rare and special bodies, that they are well-behaved and orderly, that it’s still possible to find in them the music of the spheres. When none of this is true.

This time, no revolution can leave things as they were. This time, we simply cannot avoid a true, paradigm-shifting revolution.

As Mark Sykes puts it, “we are in the midst of a conceptual revolution […], shaking off the last vestiges of the mythological view of planets as special objects in the sky – and the idea that there has to be a small number of them because they’re special.” That’s exactly it. And that’s why the most amazing part of all this is, to me, that the IAU definition was already obsolete when it was created and approved.

Which is to say, bad science.

This is also why I’m absolutely certain that it will end up being defeated. This definition will not stand. Not because thousands of “plutophiles” go do some agitprop to twitter, but because it just doesn’t fit reality. Not because people are annoyed by the “demotion” of Pluto, but due to the wide diversity of planets that exist out there. In the end, the only possible outcome of all this is a broad definition of what planets are, as broad and inclusive as planets are varied in this vast universe we live in, and a classification scheme that sets up categories within that definition. They are already emerging, even. The literature is crawling with “jupiters”, “neptunes”, “super-earths”, “hot neptunes”, “gas giants”, “ice giants”, “terrestrial planets”.

And, yes, “dwarf planets”, why not?

Stop it already August 7, 2009

Posted by Jorge Candeias in Plutophiles.
Tags: , ,
add a comment

Enough is more than enough.

Just saw, on twitter, someone calling Mike Brown a “twit” because he is, says the guy, “against Pluto” and “names a planet after a teevy (sic) show”. Really? A twit?

Yes, Mike Brown is a provocateur, otherwise he wouldn’t have chosen the alias “plutokiller” for his twitter account. But just how dumb and hysterical do you think calling him names makes you look like?

Can this nonsense stop? Can we please talk about planets and what distinguishes them from other objects in the vast Universe without this kind of childishness? And can we please put Pluto aside while we do that?

You too, Mike.

Some size comparisons August 7, 2009

Posted by Jorge Candeias in Earth, Eris, Jupiter.
Tags: , , , , ,

Well, I think it’s about time this blog includes a few pictures. And, since posts with pictures tend to require less words, it’s also a great way to give it content without spending in it too much time. So here are two quick renditions I made with Celestia, showing side by side the largest of the Solar System’s giant, terrestrial and dwarf planets:

Size comparison of Jupiter and the Earth

Size comparison of Jupiter and the Earth

Size comparison of the Earth and Eris

Size comparison of the Earth and Eris

The Earth in the bottom image is slightly larger than Jupiter in the top image (it isn’t easy to get this just right in Celestia without doing some math, which I didn’t), but I think the comparisons are effective even so. Eris (which doesn’t look like that, by the way; since we’ve never seen its surface, Celestia uses by default a generic texture, the same for all bodies in the same situation) is closer to the size of the Earth than the Earth is to the size of Jupiter. If you need numbers, then they are approximately as follows: the diameter of Jupiter is 11 times that of Earth. The diamater of the Earth is 5 times that of Eris (and no, the rather large uncertainties in Eris data don’t change this by much; at most they may drop that number to 4). More interestingly, if you compare not sizes but masses, which are actually more relevant, you get a couple of very similar numbers: Jupiter is about 320 times more massive than the Earth; the Earth is approximately 360 times more massive than Eris.

And the point is?

There isn’t much of a point, really. This just goes to show you that when it comes to compare sizes we’re not all that gifted. The big boys in the block are really big. And if you look at them from this perspective, the dwarfs don’t seem all that insignificant anymore.

And remember: if you look beyond the Solar System you’ll find other big boys that are even bigger than the big boy from our own neighbourhood, making our planet seem even more puny and helpless. HD 139357 b, for instance, is a behemoth 9.76 times more massive than Jupiter, which is to say 3100 times more massive than the Earth. Yes, that’s three thousand Earths needed to make only one gas giant.

Good thing that it strolls around almost 400 light years away, huh?

OK, I’m in August 5, 2009

Posted by Jorge Candeias in Blog stuff.
add a comment

In the previous post, I promised I’d tell you what I decided regarding the future of this blog. Thanks to Astroengine‘s (and Discovery Space‘s) Ian O’Neill, who tweeted overjoyously my coming back from the dead as a space-oriented english-language blogger and hastily linked this tiny little blog from his heavyweight one, and to the guy behind Exoplanetology, who retweeted Ian’s tweet, leading to more hits and comments in one day than in the previous three years, I was left with only one option: give a new breath of life to this little Frankenstein of mine.

So OK, fellas, I’m in.

Now, don’t expect this blog to be anywhere near as active as those blogs linked above. I don’t have that much to say, in truth, nor do I have the first hand access to sources major league space bloggers have. Plus I spend a lot of time writing each post in an English that wouldn’t embarrass me too much. Not my mother tongue and all that, you know? I’m likely to go through weeks without posting anything (particularly whenever the deadlines in my day job start to tower over me, which is something that does happen relatively often), although in some occasions I may put out two or three posts in a row. The word is erratic. Expect this blog to be just that.

To stay in the loop without having to come back regularly just to see that nothing has changed, you have, of course, my RSS feed. I toyed with the idea of creating a new twitter account just for this baby, but the two email addresses I check regularly were already taken, and it may not be worth the effort of creating a new one or paying closer attention to the ones I basically ignore. You can, if you will, follow my main twitter account, where I’ll post update notices under the hashtag #1000plans, but be advised that I tweet mostly in Portuguese and on other, non-space, issues, so you may find my twitter feed quite uninteresting.

But do follow @astroengine and @exoplanetology. Those two are most certainly worth it.

One last thing on commenting policy: to avoid spam and the hassle of captchas and logins, everyone’s first comment is moderated. That means that it may take a while to show up, especially if you’re commenting while I’m sleeping or otherwise away. Rest assured, though, that it will show up (unless it’s some sort of spam or particularly trollish), and once you have one comment cleared, you’re free of moderation and your comments will show up as fast as wordpress allows. Just so you know.

See you soon.

Yaya! I’m here! August 5, 2009

Posted by Jorge Candeias in Blog stuff.
1 comment so far

Hello, everyone.

As the very few who have visited may have noticed, this blog has been pretty much abandoned for the last three years. The reason is simple, even if somewhat embarrassing: I had misplaced the password for my wordpress account and had a few email issues as well which didn’t make it easy to recover it. Silly, huh? That’s life, the universe and everything for you.

But now, hurray, I found it. Just popped up suddenly, like an old friend who decided to renew an old friendship all of a sudden. Go figure.

So. What to do? I still have to say all those things I promised three years ago, but quite a few were said already by other, more knowledgeable people, people with much better reps than I when it comes to these issues. And even so, I myself kinda spread bits and pieces of them here and there, in the comment boxes of places such as Astroengine or Universe Today. I could go fish out those comments and use them as source for a whole series of posts, but is it worth it? Weren’t those things already said? Could a blog that has been abandoned for so long find any new readers for my thoughts, readers that don’t know all about them already?

Decisions, decisions… Life is made of decisions.

Stay tuned; I’ll let you know what I decide to do. In the meanwhile, if you wish you may tell me your opinion: the comment boxes are open, as they have been all along.


Pluto? Who cares? August 29, 2006

Posted by Jorge Candeias in Definition of planet, Pluto.
Tags: ,

One of the things that has surprised me the most in all this debate on what is a planet is the obsession that so many people seem to have with Pluto. I expected it from people who didn’t know about the Solar System much more than the names of the “nine planets”, but the passion so many of the scientists involved, even those that qualified the whole debate as silly, seemed to have about the status of Pluto frankly amazed me. People seemed to decide first if they thought that Pluto was a planet or not and only then chose a definition for planet that placed Pluto where they thought it should be.

In reality, Pluto shouldn’t matter at all. The debate should be centered on what should be the criteria for an object to be qualified as planet regardless of what would happen to Pluto or any other planet in the Solar System or elsewhere. The questions that must be answered are not “is Pluto a planet?”, but “what is a planet?” and “is there any good difference between what’s a planet and what isn’t?” and “of all the things that could be used to set apart planets from non-planets which are the best ones?” It should be only after finding a good answer to these questions that the one about the status of Pluto (or any other planetary object, really) must be answered.

In science, prejudice should not have a place. Whenever it does find its way into scientific theories the result goes from simply wrong to disastrous. We’ve seen it happen over and over again, particularly in human studies, in theories about racial superiority, or about the intrinsic intellectual inferiority of women, or about sexual minorities. But we’ve also seen its nasty work in astronomy, and I’m not talking about those astronomers that were imprisoned or killed by other people, for defending “blasphemous” cosmological theories, for instance, such as Galileo or Copernicus: I’m talking about the astronomers that spent their entire life, or a good portion of it, trying to fit data to their particular pre-conceived ideas on how the universe should work. The great ones, such as Kepler, who spent long years trying to fit planetary movements in circular orbits due to a religious notion that the work of god should result in the perfection of the circle, managed to rise above their prejudice and abandon it at some point. The lesser ones persisted… and were forgotten.

I would like to see Pluto being put aside for a while. I would like to see people discussing the characteristics of the planets regardless of the characteristics of Pluto or its orbit. That would be good science. To decide first if Pluto is a planet or not and only then trying to find a formulation that fits is not.

A definition of planet must be universal August 28, 2006

Posted by Jorge Candeias in Definition of planet.
Tags: ,
add a comment

After writing a couple of pages where I explain the purpose of this blog and the definitions of planet that will be used in it (the one the IAU proposes and the one I’m using), linked from the header (go check them out) here’s the first post proper. It’s more an ideological post than a scientific one in the sense that I think that a true definition for what a planet is has to be universal. There’s not really too much science in the reasons for my thinking so and that’s why I’m saying it’s ideological. You could think otherwise and your thoughts would be just as meritable. Still, I hope to persuade you I’m right.

So, why do I think that a definition for planet must be universal? And what does it mean “universal”?

Universal means that it must be adaptable to and usable in any place in the Universe. That’s a common thing in science: when things are defined, they are usually defined for the whole wide wilderness out there. A prime number isn’t one thing here and something else an Alpha Centauri; An orbit as an ellipse here and in M31, the Andromeda Galaxy; A fatty acid is composed of the same atoms in your body and in the Orion Cloud Complex; A star is a star if it shines above your head in a sunny day or in some globular cluster in the galactic halo or in one of the Magellanic Clouds; The quarks in the nail of your left thumb are just like the ones produced or released in the Big Bang.

The only situation where we admit the possibility that something we know here may not be defined in such a way that it can be applicable elsewhere is when we don’t know any other example of it out there. Such is the case of life. We’ve only met life in our planet, and therefore our hands and feet are tied: we must define it within the limits, that may be quite narrow, of what we know on Earth. But once our understanding expands, assuming it ever will, we’ll probably gain a new insight of what life is and will have to adapt our definitions accordingly.

Now, we had a similar problem with the planets until some 15 years ago: we assumed that there must be tons of them out there, it was even a given in science fiction, but we really didn’t know because we hadn’t detected a single one. If this issue had arisen back then, we would have to look only to what we have here in our cosmic backyard in search for information and some orientation.

That, however, has now changed. The same technologies that allowed us to detect the planets in the outer system that led to the need for a redefinition of what a planet is gave us also the information that other planetary systems exist around other stars as well (well, some of the same technologies, at least). And that’s why I believe that any definition of planet has now to take into account not only the populations of planetary objects that orbit our sun, but also all the planets found around other stars… and other objects.

Here lies the first, but huge, flaw in the “IAU planets”: the definition adopted in Prague is limited to the Solar System and to the Solar System alone and cannot be applied to any other system, not only because the word “Sun” is explicitly stated in the definition, but also due to its very nature. That, alone, is more than enough to reject that definition as far as I’m concerned.

Convinced? Not yet? Then wait until I add more stuff to the blog. I strongly recommend the RSS feed, in case you’re interested. See ya.