Cosmos 10: The Immortals

I'm going to start threads on Cosmos, to see if people have reactions, and to answer questions.

My reaction: The ninth show was the best so far--absolutely riveting storytelling. The tenth was meh.

My Q: How accepted is it that primitive bacteria survived multiple impact-sterilizations by being bounced off earth and back again?

Got a link where that can be streamed??? I am on rabbit ears and internet streaming for sources ;-) I have not seen any of the series, been catching up on Game of Thrones.

Google Hulu--you can get it on regular Hulu, not just Hulu plus.

Or go to http://www.cosmosontv.com

The first one left me too disappointed to watch any of the rest. Glad to hear the others were good.

Really?! God, some of them have been great. What didn't you like about the first?

I hated the whole Bruno segment in the first episode. And was a little irritated at all the shiny graphics.

Meh. I disliked the careless subtext of the Bruno bit, but it didn't spoil it for me. The end, with Carl Sagan's book, appealed to me. You should check out more. They're really rather good.

It might help to have a kid. I am to some degree watching them through his eyes. It's clearly a formative moment for him.

Tim,

You are not the first person to recommend I give the series another look. My apologies for the comment above. Should not have been made.

I hope others will comment about the good aspects.

BTW, I heard deGrasse Tyson speak a couple years ago, in Chattanooga. A very good talk. It was about the time that Pluto was demoted and those pesky super neutrinos were running around faster that light.

>8 richardbsmith:

He has a good zinger at the end of this video from a while back -- there was a lot of unpleasant... commentary about the demotion. He says "I blame Disney for the whole thing."

I'm not even sure what comment. Either way, no foul.

Tyson has a great single-episode show called "The Pluto Files" on the demotion.

Mostly, there were a lot of unhappy schoolkids. It turned out to be a largely USian thing, despite the fact that few USians knew that it was a USian who discovered Pluto in the first place.

I still defend it. David Weinberger has a good bit on the strangeness of the classification theory at stake.

Pluto is just not a planet. Once more and more was discovered about the Kuiper Belt the more Pluto was seen to be Kuiper Belt object.

What criterion can you come up with that isn't circular or just a gut opinion? We aren't Kuiper belt "objects" planets? What is a planet, exactly? Does the definition have any underling reality to it--a reality that somehow embraces both the gas giants and tiny Mercury, and which of necessity must exclude Pluto and its confreres? Is the definition useful? Does it predict something? Explain something? Or are we just drawing lines around seemingly different entitles, and between other entities, for the sake of it?

>14 timspalding: What criterion can you come up with that isn't circular or just a gut opinion?

"Clears its orbit" is a criterion that makes sense.

(Why) aren't Kuiper belt "objects" planets?

They fail to clear their orbits.

What is a planet, exactly?

http://en.wikipedia.org/wiki/IAU_definition_of_planet

Does the definition have any underling reality to it--a reality that somehow embraces both the gas giants and tiny Mercury, and which of necessity must exclude Pluto and its confreres? Is the definition useful? Does it predict something? Explain something? Or are we just drawing lines around seemingly different entitles, and between other entities, for the sake of it?

Yes, Yes, Yes, Yes, and No.
(Well - - no more arbitrarily than any other taxonomy. Taxonomies are mostly a mechanism for producing edge cases.)

Wiki:

Starting in 2000, with the discovery of at least three bodies (Quaoar, Sedna, and Eris) all comparable to Pluto in terms of size and orbit, it became clear that either they all had to be called planets or Pluto would have to be reclassified. Astronomers also knew that more objects as large as Pluto would be discovered, and the number of planets would start growing quickly. They were also concerned about the classification of planets in other planetary systems. In 2006, the matter came to a head with the measurement of the size of 2003 UB313. Eris (as it is now known) turned out to be slightly larger than Pluto, and so was thought to be equally deserving of the status of 'planet'.

Historical parallel
The refining understanding of Pluto echoed a debate in the 19th century that began with the discovery of Ceres on January 1, 1801. Astronomers immediately declared the tiny object to be the "missing planet" between Mars and Jupiter. Within four years, however, the discovery of two more objects with comparable sizes and orbits had cast doubt on this new thinking. By 1851, the number of "planets" had grown to 23, and it was clear that hundreds more would eventually be discovered. Astronomers began cataloguing them separately and began calling them "asteroids" instead of "planets".

"Clears its orbit" is a criterion that makes sense.

If Pluto doesn't clear its orbit, Neptune doesn't either. But, like many other bodies, they are in orbital resonance with each other, and will neither clear each other out of the way or collide. Besides, are we saying that if Mars were knocked out of its orbit in some ways--but not others--it would no longer be a planet?

Well - - no more arbitrarily than any other taxonomy. Taxonomies are mostly a mechanism for producing edge cases.

Bad taxonomies are useless. Good taxonomies aren't. One could split up the physical world in a variety of arbitrary ways, but classification by elements and elements by atomic number is useful. It predicts and it explains--so much so that it predicted and explained things that weren't understood before the classification. One could similarly split up the natural world in many ways. Bats have wings, so do birds--so bats are birds. But modern biology cleaves to a classification based on an underlying genetic reality closely tied--again--both explanatory and predicative value. And on and on through science. The best classifications aren't just line drawing. They do something useful.

What does this do that's useful? What does it explain to say that Pluto isn't a planet because it doesn't clear it's orbit? Well, it explains that clearing its orbit is what makes a planet, unless you're Neptune. And it predicts that clearing its orbit is the usually right answer to what makes a Planet. Anything else? No.

At best it mirrors a sort of gut feel--the sort of classification at work when some members say a book is a thriller, but some others don't agree. That fits with how it was decided, by majority vote, with 57% in favor--just shy of what Herbert Hoover got! I'm not sure where that model of classification fits with science.

As for the historical parallel, I propose we extend the thinking. Since it is apparently a scientific principle that the number of planets be about the same number that we could see with the naked eye in 5,000 BC and called gods--a hoary tradition and what is science without tradition?--we should de-list our planets as larger extra-solar planets are discovered.

Yeah, I guess I'm just not getting the outrage.

There's a cloud of minor thingies out there. Pluto looks more like them than it looks like the major planets. We found a thing in 1930, and at first, we called it a "planet"; but after a while, as we learned more about the outer system - and learned that there's a whole swarm of them - we decided it was more accurate to call it a "minor planet".

Is this just a liberal/conservative split?
"As knowledge improves , our description of the world will change" vs. "Things must ALWAYS stay the way I learned them" ?

It does fit in with science. Ideas of planetary formation begin with coagulation of dust, then at a certain size gravity is sufficient to clear out it immediate orbit either by ejection of small bodies or by attraction and collision.

The process, gravitational focusing, slows down the planet and speeds up the smaller bodies, increasing their inclination and eccentricity. This process puts the planets into nearly circular orbits. They reach a size of around .1 Earth mass (an isolated body - nothing else near) , and several of these objects in similar orbits eventually combine gravitationally to clear out the orbit of other isolated and smaller objects.

Asteroid belt and Kuiper Belt objects were impacted by Jupiter and Neptune gravity such that this process of gravitational focusing did not complete for Pluto and Eres in the Kuiper Belt or for Ceres in the asteroid belt.

I think they differentiated, evidenced by the round shapes, hence dwarf planet. They did not complete the last step of planet formation, as evidenced by their small size.

Comparing a chart of relative sizes and location, I think it seems obvious that Pluto and Eres belong with the Kuiper Belt, but in addition there has been refinement of planetary formation theory as a result of discoveries in the Kuiper Belt and exoplanets.

>18 richardbsmith: They did not complete the last step of planet formation, as evidenced by their small size.

AND as demonstrated by Pluto's crazy-ass, eccentric, inclined orbit.

Go home, Pluto. You're drunk.

Lowell and Tombaugh were looking for a Planet X. A planet much larger that Pluto was eventually proven to be, that affected Neptune's orbit. I think Tombaugh did not find Planet X, a planet that was supposed to be much larger than Earth. He just happened to find something that could pass for a planet. Pluto did not meet the predictions of the object they were looking for.

When they found Pluto instead, it was thought to be much larger. Some estimates as large as Jupiter.

I think even there were some large estimates of Pluto's size until Charon was discovered - establishing Pluto's mass as slight.

"Hey, the IAU voted to reclassify Pluto as a minor planet."

Response one: "Oh. That's interesting."
Response two: "OMG!!! This OUTRAGE SHALL. NOT. STAND!!!!!!11!!"

Sorry, just not getting response two.

"Is it at least possible that the initial 1930s classification of the object Pluto was a mistake?"
"NO! and we must NEVER revise our theories in the light of new evidence!"

Yeah, I'm just not getting it.

>7 timspalding: The end, with Carl Sagan's book, appealed to me. You should check out more. They're really rather good.

That was my favorite part. I also liked the whole evolution of the eye bit.

It might help to have a kid. I am to some degree watching them through his eyes. It's clearly a formative moment for him.

I watched the pilot with a friend who has absolutely zero science knowledge or background, and she loved it. All that effort to get across the scale of the universe, the "calendar" that placed mankind within the last five minutes of all of time....she ate that stuff up. I grew up on things like the film The Powers of Ten, so it was not new to me. I think I just wasn't exactly the audience the show was aimed at. Plus, I felt De Grasse Tyson's natural ebullience was a little clipped.

But I'll go back and watch some of them. I shouldn't have given it up so quickly.

>11 AnnaClaire: Mostly, there were a lot of unhappy schoolkids.

Tyson's appearance on The Daily Show when he was promoting The Pluto Files was hilarious. "I got hate mail from third graders! In crayon!"

I joke about how Pluto will always be a planet to me, but I really don't have a beef with the reclassification.

Yeah, I guess I'm just not getting the outrage.

There's no outrage on my part. I am, however, amused at the unreflective nature of much of the advocacy here. It's too easy to conflate reality with the classificatory schemes we throw over reality, and forget what classification is for and what it's not for.

I think your historical explanation is about right. When we learned there were a lot of them, a majority (i.e., 57%) of astronomers shrank back. Although "planet" had never really been defined, the prospect of finding many more just didn't fit their gut sense of planets. But the whole concept is questionable. What's a planet, really? It's a concept from ancient observation--a dot that "wanders" in a sky that--to the premodern eye--seems to move together. To those early eyes, Jupiter and Mars seemed the same. After all, they have (from Earth) almost the same brightness in the sky, and nobody knew that the the latter had 1% of 1% the volume of the other, was composed of very different stuff, etc. If we had grown up in the dark of space, and only just come to the solar system, would we decade that Mercury and Jupiter are one thing, and Pluto is the other? I don't think so.

"As knowledge improves , our description of the world will change" vs. "Things must ALWAYS stay the way I learned them" ?

Exactly the opposite. As we discover planets, I'm okay with that. You're the one who wants to keep the number down to about what it was when we thought planets were gods. Next thing, you're going to insist that Venus makes people horny.

>16 timspalding: If Pluto doesn't clear its orbit, Neptune doesn't either.

I suspect, but don't really know, that to an astronomer Neptune and Pluto are not in the same orbit even though they cross. And, no, I don't know how that differs from the asteroid belt where not all of the objects could be in exactly the same orbit. Isn't Pluto's orbit highly tilted though?

ETA: I just read that again and you didn't say what I thought you said. I'll have to come back to this later.

CGP Gray did a video explaining why Pluto got reclassified.

Just as an aside - there's a spacecraft* headed to Pluto with closest approach next summer. http://pluto.jhuapl.edu

*Disclosure: I worked on the team that built and launched it, so I think it's the coolest spacecraft ever. :)

I think the vote came down to a definition of planet.

Whether differentiation is enough.

The vote was less about Pluto's status than about the phenomena of a planet. Previous to 2000, there was little need to refine that definition.

By 2000 and after, there was a real need.

Is differentiation enough? No, according to your 57% number. It was possible to have a planet defined by its shape, there is real physics in that. But there is more real physics with the further development to form a planet, additional real physics that Pluto and Eres did not experience because the Kuiper Belt was disturbed by Neptune, a disturbance that prevented further consolidation and even ejected a very large amount of available gas and ice from that orbit. Giving final end to any possibility of that last bit of planetary formation ever taking place.

But I argue against your characterization of these comments as unreflective advocacy.

drneutron,

A real expert.

Pluto a Kuiper Belt object or a planet. Your vote please. : )

No comment. :)

I'm an engineer, not a scientist, so I'll defer to the experts.

What is funny is that our bunch is debating this, and a real expert is no comment. : )

Exactly the opposite. As we discover planets, I'm okay with that. You're the one who wants to keep the number down to about what it was when we thought planets were gods.

But that's exactly the problem: the thingies we're discovering in the outer reaches of the system are clearly NOT PLANETS. They're much like Pluto, though. Therefore...Pluto isn't actually a planet, either.

(And will YOU be composing the mnemonic for "Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto, Eris, Makemake, Haumea, Sedna, 2007 OR10, Quaoar, Orcus, Altjira, Varda, Manwë, 2002 RN109, 2005 VX3, 2012 DR30, 2013 AZ60, 2013 BL76, 2013 FY27, 2013 FZ27, etc.?".... Good luck with that. There are entirely reasonable first-principal reasons to keep the list of planets down to "mostly visible objects that you can walk outside and notice, plus a couple objects visible with less-than-professional-grade gear".)

Next thing, you're going to insist that Venus makes people horny.

(Well, it does, of course... you could probably draw up a pretty good positive correlation between "times when people have sex" and "times when Venus is visible in the sky"; but was that remark actually called for here?)

Obligatory xkcd:

http://xkcd.com/473/

Of course, Pluto should have been a planet.

Early it should have been a planet because it was believed to be Planet X and about Earth size or bigger
Later when it was shown to be tiny, it still should have been a planet because, what else could it be. It was not an asteroid or it would be in the asteroid belt. Planetary formation models could allow for small planets. If it is not a planet and not an asteroid, then it is just a Pluto.

Now it is not a planet because we have other objects that it shares similar properties and formation processes, and because of those objects we have a more complete model of planetary formation that shows and predicts how the planets' gravity and migrations kept these objects from becoming planets.

the thingies we're discovering in the outer reaches of the system are clearly NOT PLANETS

Why not? When Eris was discovered, many considered it one. It's big, round and floats around the sun. You could land on it. It has a horizon.

CGP Gray did a video explaining why Pluto got reclassified.

And it makes the point well:

"But this story is really less about Pluto than it is about realizing the word 'planet' isn't very helpful.

The first four planets are nothing at all like the next four, so it's even a little weird to group these eight together which is why they often aren't and are separated into terrestrial planets and gas giants…"

As he, others and I have noted, the definition seems to be dependent on the vicissitudes of measuring instruments. But rather than the number of planets growing as we found more, we've decided to keep the number constant and keep changing the definition to prevent expansion. This is a rather odd principle. What if, once we could see bacteria, we decided that "life" must be large or it's not life?

But we're running into problems as we look outside our solar system. We're discovering exoplanets now, but--really--we aren't. Because nobody has confirmed that these objects have or have not "cleared their orbit." Our tools don't allow us to say, so, if we were consistent, we would shut up about it and say only that we may have discovered planets.

The first four planets are very much like the other 4 planets. The difference is location. Same processes initially. More material available beyond the snow lines.

And now we can speak of gas giant planets, ice giant planets, terrestrial planets, and dwarf planets.

All of which have differentiated, and undergone the same processes up to different steps, according to the physics of their location wrt the Sun and the solar disk.

A similar argument can be had with stars. Is a brown dwarf a star?

The definition of planet has changed. We discovered a smaller class of objects, to which Pluto better belongs. Until those objects were discovered, planet was the only class available. Pluto is more like the rest of the Kuiper objects - size, formation, composition.

The difference is how far in the process Pluto and Eres and Ceres went. They were stopped early, to a great degree because the planets that had formed ejected most of the material.

When you have written all you can say, is it time to shut up? Or should you keep repeating? : )

>16 timspalding: If Pluto doesn't clear its orbit, Neptune doesn't either.

From http://en.wikipedia.org/wiki/Pluto#2006:_IAU_classification: Pluto fails to meet the third condition, because its mass is only 0.07 times that of the mass of the other objects in its orbit (Earth's mass, by contrast, is 1.7 million times the remaining mass in its own orbit).

So the "clearing it's orbit" criteria should maybe be stated as "almost completely cleared it's orbit".

ETA: From http://en.wikipedia.org/wiki/Clearing_the_neighbourhood

In the end stages of planet formation, a planet will have "cleared the neighbourhood" of its own orbital zone (see below), meaning it has become gravitationally dominant, and there are no other bodies of comparable size other than its own satellites or those otherwise under its gravitational influence. A large body which meets the other criteria for a planet but has not cleared its neighbourhood is classified as a dwarf planet. This includes Pluto, which shares its orbital neighbourhood with Kuiper belt objects such as the plutinos. The IAU's definition does not attach specific numbers or equations to this term, but all the planets have cleared their neighbourhoods to a much greater extent than any dwarf planet, or any candidate for dwarf planet.

ETA2: And then there's this from http://astronomyonline.org/aoblog/aoblog21.asp:

When looking at this definition, it would seem that Neptune has not cleared its orbit because Pluto overlaps; however, disk clearing occurs during Solar System formation. While there is some debate as to how the planets formed, it is agreed that the gas giant planets (Jupiter, Saturn, Uranus and Neptune) must have formed prior to the T Tauri phase of our Sun (i.e. the initiation of fusion at the core) so disk clearing must have occurred prior to this. It can be argued that Pluto was captured some time after planetary formation as Pluto would have been "consumed" by Neptune.

So objects that are gravitationally captured after Solar System formation don't count against the orbit clearing criteria.

>38 jjwilson61:

Look. I agree that it's possible to craft a definition that cuts Pluto out--although, as was noted at the time, the definition itself includes a list of the objects that meet the definition!

(1) A "planet"₁ is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

And the footnote 1? It is:

"1 The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

So, you can do it, somehow. The question is why one should craft one definition or another. My contention is that it's basically arbitrary. The definition doesn't do anything other than separate some stuff out into groups--groups which could easily be lumped or split further with equally persuasive justification. It has no added value--nothing it predicts or explains particularly well.

And again as noted, it's a heliocentric definition. This was explicitly stated at the time--that the definition only applies to objects orbiting around our sun. A second definition was adopted for extrasolar planets. It doesn't include anything about a planet clearing it's neighborhood because you can't tell if an extra-solar planet does so or not.

>36 timspalding:

What if, once we could see bacteria, we decided that "life" must be large or it's not life?

Nonsensical analogy. Size isn't one of the criteria for life and doesn't make sense as a criterion for life in view of what we know about living organisms.

In a completely different context, such as astronomy, size may indeed be judged to be a useful criterion of discrimination--and that too will depend on current state of knowledge and understanding.

I'm just wondering what Tim proposes we replace all of this with? The Platonic planet?

I think the easiest solution is planets—with subtypes for rocky planets, gas giants, dwarf planets, etc. (As it stands, Pluto is a "dwarf planet," but dwarf planets are not planets. Wikipedia proposes the analogy of the rocky-mountain oyster not being an oyster.) But either way, it should be understood that this is an essentially arbitrary convenience term, like definitions of "mountain" that draw a sharp line at 2,000 feet, and not really defensible or "true."

like definitions of "mountain" that draw a sharp line at 2,000 feet, and not really defensible or "true."

Isn't that just true of definitions?

Well some definitions are useful, some aren't. One may usefully distinguish the definition of an element--which is extremely useful--from that of what comprises paranormal romance.

>39 timspalding:

1) I was specifically addressing your question about why Neptune is considered a planet under the new definition.

2) I wouldn't call a footnote part of the definition. It's obviously there as more of a clarification.

3) I think there is a clear demarcation between the objects that orbit around the sun in paths almost entirely all to themselves and objects in the asteroid belt and the kuiper belt. As my final link alludes to there also seems to be a distinction in solar system evolution about when the various kinds of objects came about and how they came about.

4) I think its pretty safe to say given what we know about orbital mechanics that any object as large as those we are able to detect around other stars are going to be big enough that they'll have cleared their orbits of other bodies.

>39 timspalding: My contention is that it's basically arbitrary.

And so? What definitions, what taxonomies, AREN'T "arbitrary"?

>36 timspalding: Why not? When Eris was discovered, many considered it one.

The better analogy is with Ceres: when Ceres was discovered, many considered THAT to be a planet, too.
But then more and more Ceres-type objects were found, and astronomers realized that the definition of "planet" had to be modified to redefine "Ceres-types planets" as "asteroids".

And so? What definitions, what taxonomies, AREN'T "arbitrary"?

Well, precisely. Some are, and some aren't. There are classifications like species, manuscript traditions and elements and classifications like literary genres and hot dates.

Just an aside, are there any known largish objects in the Oort cloud?
And why do I know so little about it? :-)

ETA. Tö correct it to a "Cloud" :-)