A Plethora of Alien Seas

[King Kong]

If life on Earth did indeed spring forth within our vast oceans, then it also might be teeming on thousands of other worlds. New models suggest that as many as one-third of the solar systems in the galactic neighborhood might contain terrestrial planets with oceans of water that could harbor life.

The new findings counter previous hypotheses on planetary formation, which have claimed that few solar systems contain Earth-like worlds. Part of the problem has to do with so-called hot Jupiters. These gas giants, which orbit closer to their parent stars than Mercury does to the sun, form relatively quickly from the gas in the protoplanetary disk. Astronomers assumed that as these hot Jupiters plow through disk material, they "vacuum up" a lot of the dust and rock or eject it from the solar system. That would leave little material left with which to make water-logged planets.

But "the new models indicate these early ideas were probably wrong," says planetary scientist Sean Raymond of the University of Colorado, Boulder. Reporting in today's issue of Science, Raymond and colleagues say they ran simulations lasting more than 8 months each on more than a dozen desktop computers. They observed how nascent solar systems evolved over about 200 million years, basing the initial conditions on current theories of how planets formed in our own solar system. The researchers found that when gas giants migrate, they fling lots of rocky debris away from the star and into the habitable zone, where liquid water can exist on a planet's surface. There, the debris frequently coalesces into Earth-sized planets.

This kind of early evolution also perturbs the disk, causing comets outlying billions of kilometers away to dive toward the star. Enough of these ice balls hit the terrestrial planets to deliver large quantities of water. "We were very surprised to learn that these planets are water-rich and probably covered in global oceans," he says.

The findings suggest that thousands of planetary systems within the Milky Way could harbor Earth-like planets, says Rory Barnes, a planetary scientist at the University of Arizona in Tucson. Still, he cautions that the key question is how many planetary systems have hot Jupiters. The current figures could be an overestimate: Existing exoplanet detection methods are "strongly biased toward" this type of planet, he says, but "strongly biased against" finding solar systems like our own, in which gas giants settle farther away from their parent star.

The Abstract

NASA pdf actually showing a few examples of the simulated star systems with Earthlike planets and 'Hot Jupiters'.

[Guardsman Bass]

We'll have to wait and see until we get more advanced detection capabilities to pick up the earth-sized planet, but hopefully this puts a nail in a coffin for the Rare-Earth groups (I remember the "Hot Jupiter" argument was used as an example of why earth-like planets could be very rare in Peter Ward's book Rare Earth).

[darthkommandant]

Still could sentient life evolve in the ocean? Also would impacts be more frequent since there is no jupiters to block the comets and asteroids that fall in from the outer reaches of ther star system? Still this puts another nail in the rare earth thoery which in my mind is a good thing.

[CaptainChewbacca]

Still could sentient life evolve in the ocean? Also would impacts be more frequent since there is no jupiters to block the comets and asteroids that fall in from the outer reaches of ther star system? Still this puts another nail in the rare earth thoery which in my mind is a good thing.

Why do you think most solar systems don't have gas giants capable of absorbing meteor impacts?

[Guardsman Bass]

This raises a question. Suppose the gas giants pull a large number of asteroids inward. Would they generally pull the asteroids away from the planets in the habitable zone, or would it just mean extra bombardment?

As for bombardment, it wouldn't completely ruin advanced life on a planet as long as it wasn't too frequent (like getting Dino-killing size impacts every 10 million years). Intelligent life could still arise, and they might get some interesting eclipes if they were close enough to the gas giants so that the giants occasionally eclipsed their suns.

[King Kong]

This raises a question. Suppose the gas giants pull a large number of asteroids inward. Would they generally pull the asteroids away from the planets in the habitable zone, or would it just mean extra bombardment?

The NASA pdf says that asteroid belts would likely form interior to the terrestrial planet in a system with a hot Jupiter. A terrestrial planet in this type of a system would be almost guaranteed to have greater bombardment than Earth, simply because of the extra gravitational effect of the large gas giant. In fact, the reason that these planets are likely to be water-rich is because the formation of the inner gas giant makes cometary impacts more likely during the formation of these terrestrial planets.

With regard to darthkommandant's questions, many of the example systems shown in the NASA pdf include a large gas giant planet at Jupiter's distance, but, as explained above, impacts would still be more likely. Personally, I think that intelligent life is extremely unlikely to evolve in the ocean, if only because sea life has been around much longer than land life, but has yet to produce a species on par with our intelligence. And even if they are intelligent, the evolutionary pressures to streamline sea life would likely prevent the evolution of limbs for tool use and construction.

However, I'm just psyched that life (intelligent, muticellular, or even just bacteria) could be more common in the universe than previously thought.

[darthkommandant]

Jsut to clear things up the second questions were based on those systems that lacked a large gas giant at that distance.

[RedImperator]

How long would these hot jupiters last? I was under the impression that being so close to the star would cause them to eventually lose most of their mass, with the solar wind sweeping away their mostly hydrogen atmospheres. It would be an exponential process, too: as the outer layers are swept away, the planet's mass falls, making it easier for the solar wind to blow away more hydrogen. Or are these things so massive they can hold onto a hydrogen/helium atmosphere despite being so close in?

[GrandMasterTerwynn]

How long would these hot jupiters last? I was under the impression that being so close to the star would cause them to eventually lose most of their mass, with the solar wind sweeping away their mostly hydrogen atmospheres. It would be an exponential process, too: as the outer layers are swept away, the planet's mass falls, making it easier for the solar wind to blow away more hydrogen. Or are these things so massive they can hold onto a hydrogen/helium atmosphere despite being so close in?

A Jupiter-sized, or larger, world is a pretty hefty proposition. Ours is more than twice the mass of the rest of the non-Solar bodies in the solar system put together. They have plenty of grunt with which to hold onto their gasses with. In fact data suggests that such a world would only lose, perhaps, 5% of its mass over the lifetime of its parent star.

[darthkommandant]

This atricle says that stars might eat hot jupiters in addition to evaporiting them. Other than thad I havent found anything about how long they last.

[darthkommandant]

Also this wiki article has this interisting quote about the hot jupiter planet HD 209458_b:

It is thought that this type of atmosphere loss may be common to all planets orbiting Sun-like stars closer than around 0.1 AU. HD 209458b will not evaporate entirely, although it may have lost up to about 7% of its mass over its estimated lifetime of 5 billion years.

[RedImperator]

How long would these hot jupiters last? I was under the impression that being so close to the star would cause them to eventually lose most of their mass, with the solar wind sweeping away their mostly hydrogen atmospheres. It would be an exponential process, too: as the outer layers are swept away, the planet's mass falls, making it easier for the solar wind to blow away more hydrogen. Or are these things so massive they can hold onto a hydrogen/helium atmosphere despite being so close in?

A Jupiter-sized, or larger, world is a pretty hefty proposition. Ours is more than twice the mass of the rest of the non-Solar bodies in the solar system put together. They have plenty of grunt with which to hold onto their gasses with. In fact data suggests that such a world would only lose, perhaps, 5% of its mass over the lifetime of its parent star.

Well, so much for my stunning mental image of a Jupiter sized world boiling away like a giant comet. Too bad: that would be completely awesome to see.

[darthkommandant]

Well the wiki article does have this artists immpression of this happening.

[Molyneux]

So...if Earthlike planets with water oceans are a fairly common occurrence...where are the radio signals?

[ThatGuyFromThatPlace]

just because we haven't detected them doesn't mean they aren't out there.
We're looking for signals originating near stars on certain frequencies and containing certain patterns, trouble is, an Alien might be sending out signals that are completely different from what we're looking for.

So far, all we've been looking for are signals that we believe aliens would send out if they were trying to contact other species, but we haven't been really looking for the sort of signals that WE have been sending out, like Radio and television. and even given the ridiculously narrow parameters, we've recieved several that matched almost exactly that were ignored simply becasue the messges were never detected again.

[RedImperator]

So...if Earthlike planets with water oceans are a fairly common occurrence...where are the radio signals?

Possible reasons:

1. The model is wrong. Earthlike planets are rare.
2. Earthlike planets aren't rare, but life requires some overlooked X factor present on Earth but not common elsewhere.
3. Life is common, but multicellular life requires some overlooked X factor present on Earth but not common elsewhere.
4. Multicellular life is common, but complex nervous systems required for intelligence to evolve require some overlooked X factor present on Earth but not common elsewhere.
5. Animals with complex nervous systems are common, but intelligence requires some overlooked X factor present on Earth but not common elsewhere.
6. Intelligence is common, but the kind of intelligence required for technology requires some overlooked X factor present on Earth but not common elsewhere.
7. Tool-making intelligence is common, but the social and environmental conditions behind the feedback loop that leads to rapidly advancing technology requires some overlooked X factor present on Earth but not common elsewhere.
8. Rapidly advancing technology is common, but scientific thinking, necessary for making the leap from improvements in tools that work on easily understood mechanical principals to radio requires some overlooked X factor present on Earth but not common elsewhere.
9. Science is common, but widespread use of radio communications requires some overlooked X factor present on Earth but not common elsewhere.
10. Radio is common, but widespread use of powerful, omnidirectional broadcasts that can be detected light years away requires some overlooked X factor present on Earth but not common elsewhere.
11. Broadcasting civilizations have a short lifespan, because A) broadcasting becomes obsolete quickly, B) broadcasting civilizations acquire the means to destroy themselves and procede to do so, or C) broadcasting civilizations are immediately destroyed once detected by other civilizations that don't want competition.
12. We're not listening on the right frequencies.
13. We're not listening at the right time.
14. We're listening, but we're too stupid to realize what we're hearing.
15. We're listening, but their thinking is so alien we don't realize what we're listening to.
16. We're listening at the right frequences, at the right time, we know what we're hearing and can understand it, but the government is keeping it a secret because they're afraid the whole world will go apeshit if it finds out.

I'm sure there are more, but that's what I could think up on short notice.

[Ariphaos]

Well, so much for my stunning mental image of a Jupiter sized world boiling away like a giant comet. Too bad: that would be completely awesome to see.

Don't mistake it, 1% of Jupiter over a billion years still amounts to some 2x10^17 kilograms of material over the course of a given year. Granted, only ices (for our purposes, methane, ammonia and water, for the most part), cause the cometary display.

Even still, with an average molecular weight of 16 or so, this makes them only 1/4th as likely to escape the planet (excluding the effects of brownian motion - a lot of matter is getting stripped off) as hydrogen (particle velocity goes up with the square root of temperature/mass). Given a relatively modest amount of ices at say, .2% (a bit less than Jupiter, likely, this number is going to be higher), that's still .05% of the above mass, or 1x10^14 kg each year.

Halley's comet, including the non-ice parts that make up most of its mass, weighs only an estimated 8x10^13 kg.

No comet inside the Solar System would be so stunning.

----

As to the article, it's important to note that there is a rather extreme selection bias involving hot jupiters. We've only recently developed accurate enough technology to detect Jupiter around our own star at any reasonable distance, so another decade or so will bring about a better census of ice giants and other jovian worlds in our neighborhood.

I'm also a bit skeptical. It's pretty clear that, in our Solar System alone, Jupiter, which has a smaller mass than many of these hot jupiters, has disrupted planetary formation within 4 AU of its orbit. Before I accept an orbit-crossing gas-giant as healthy for such formation I would like to see more than one team running through their own little model, thank you.

[Ariphaos]

1. The model is wrong. Earthlike planets are rare.

It's also a bit spurious - so are hot and eccentric Jupiter systems, it's doubtful that they, combined, account for even 15% of star systems (I don't have many figures on the commonality, but we're talking single digit percentages for each and this is the majority of what we've found so far due to selection bias).

2. Earthlike planets aren't rare, but life requires some overlooked X factor present on Earth but not common elsewhere.

I have this visage of planets around Tau Ceti composed almost entirely of immensely vast, and deep, oceans of ammonia, water, methanol, and/or methane. There are other particles there, and in theory life could form in them, but the needed quantity of heavier elements simply isn't present.

3. Life is common, but multicellular life requires some overlooked X factor present on Earth but not common elsewhere.

See above, to a degree, but given that even bacteria have functions that mimic multicellular effects I somewhat doubt this.

4. Multicellular life is common, but complex nervous systems required for intelligence to evolve require some overlooked X factor present on Earth but not common elsewhere.

Nervous systems evolved out of cilia. What triggerred this, and the likelihood of its occurance, is open to debate, but given that it:
1) Has only happenned once
2) Took four billion years to occur

Suggests that it is certainly not common.

5. Animals with complex nervous systems are common, but intelligence requires some overlooked X factor present on Earth but not common elsewhere.

Certainly, humanity has survived several serious beatdowns. A brain like ours is a very taxing organ and eventually reduced us to three strains of humanity, two of which were apparent dead ends and died out, the third of which, us, was knocked down to two thousand people at one point. Obviously, any land-based sentient species is going to be under extreme selection pressure.

6. Intelligence is common, but the kind of intelligence required for technology requires some overlooked X factor present on Earth but not common elsewhere.

Kinda doubt this, since our ancestors started making tools (however simple hand axes may be) quite early.

7. Tool-making intelligence is common, but the social and environmental conditions behind the feedback loop that leads to rapidly advancing technology requires some overlooked X factor present on Earth but not common elsewhere.

Seems possible. We had hand axes for millions of years, fire for half a million, then allthesudden we get one subspecies with: Bows, spears, atl atls, language, etc. Granted, there was a good period of 60k years of stagnation or so, but it's still significant.

8. Rapidly advancing technology is common, but scientific thinking, necessary for making the leap from improvements in tools that work on easily understood mechanical principals to radio requires some overlooked X factor present on Earth but not common elsewhere.

9. Science is common, but widespread use of radio communications requires some overlooked X factor present on Earth but not common elsewhere.

10. Radio is common, but widespread use of powerful, omnidirectional broadcasts that can be detected light years away requires some overlooked X factor present on Earth but not common elsewhere.

I rather doubt these, it seems a bit nonsensical, unless the species in question is incapable of sensing light for some reason, which would seem highly unlikely.

11. Broadcasting civilizations have a short lifespan, because A) broadcasting becomes obsolete quickly,

This would seem to only be the case if some sort of efficient FTL modus of communication is available, which does not seem likely.

B) broadcasting civilizations acquire the means to destroy themselves and procede to do so, or

Possible, I suppose, but humans are a pretty resilient species. It's not even certain that fullscale biological warfare would wipe us out. Any sapient species would no doubt be quite resilient as well.

C) broadcasting civilizations are immediately destroyed once detected by other civilizations that don't want competition.

This relates to part A for another counterargument.

Such civilizations are no doubt going to be dimming their stars. It would seem likely that we will notice this, eventually.

12. We're not listening on the right frequencies.

The water band is pretty sensible. Granted, outside of that we can't really sense anything more than 30-40 light-years away right now, for common transmissions.

13. We're not listening at the right time.

This falls in with 'destroying themselves', I suppose. A civilization's destruction by any means will qualify.

14. We're listening, but we're too stupid to realize what we're hearing.
15. We're listening, but their thinking is so alien we don't realize what we're listening to.

We're not looking for a language, we're looking for a signal that does not perfectly mimic random noise. These two points do not apply.

16. We're listening at the right frequences, at the right time, we know what we're hearing and can understand it, but the government is keeping it a secret because they're afraid the whole world will go apeshit if it finds out.

Heh.

[GrandMasterTerwynn]

So...if Earthlike planets with water oceans are a fairly common occurrence...where are the radio signals?

Aha, the well-known Fermi Paradox. "If life's so common, then why haven't we heard from it yet?" However, the answer to the question is simple. Just because the Galaxy is teeming with life, it doesn't mean that sapient, technological life has to be similarly common. After all, the sort of technology-using life with appreciable radio emissions has only existed on Earth for less than 100 years . . . out of 3.8 billion years of biological history on the planet. It's unknown how much longer we'll last, though one would have every right to expect that number to be on the low side.

Simply put, for the vast majority of the history of life, the most sophisticated organisms on the planet were plankton. Multicellular animal life didn't even appear until half a billion years ago, and up until 65 million years ago, the brightest animals on the planet were barely capable of ostrich-level intelligence. Animals with near-human intelligence didn't appear until a million years ago.

Not to mention even if every planet in the galaxy were the exact same age as Earth, they will have radically different histories. Technology-using life could've cropped up several tens of millions of years sooner had a certain asteroid occupied a slightly different orbit, or if the evolutionary cards had broken the right way sooner. Similarly, technology-using life could still be hundreds of thousands, or even millions of years in the future had the Toba catastrophe been more thorough at wiping out Homo Sapiens.

And one can't forget that habitable worlds don't stay that way forever. Mars was habitable for something like a few hundred million years after it first became possible for it to support life. Earth itself will only be habitable for several hundred million more years, a billion at the outside.

[Molyneux]

Aha, the well-known Fermi Paradox. "If life's so common, then why haven't we heard from it yet?" However, the answer to the question is simple. Just because the Galaxy is teeming with life, it doesn't mean that sapient, technological life has to be similarly common. After all, the sort of technology-using life with appreciable radio emissions has only existed on Earth for less than 100 years . . . out of 3.8 billion years of biological history on the planet. It's unknown how much longer we'll last, though one would have every right to expect that number to be on the low side.

Simply put, for the vast majority of the history of life, the most sophisticated organisms on the planet were plankton. Multicellular animal life didn't even appear until half a billion years ago, and up until 65 million years ago, the brightest animals on the planet were barely capable of ostrich-level intelligence. Animals with near-human intelligence didn't appear until a million years ago.

Not to mention even if every planet in the galaxy were the exact same age as Earth, they will have radically different histories. Technology-using life could've cropped up several tens of millions of years sooner had a certain asteroid occupied a slightly different orbit, or if the evolutionary cards had broken the right way sooner. Similarly, technology-using life could still be hundreds of thousands, or even millions of years in the future had the Toba catastrophe been more thorough at wiping out Homo Sapiens.

And one can't forget that habitable worlds don't stay that way forever. Mars was habitable for something like a few hundred million years after it first became possible for it to support life. Earth itself will only be habitable for several hundred million more years, a billion at the outside.

Thank you, I couldn't remember what that question was called.

[Junghalli]

So...if Earthlike planets with water oceans are a fairly common occurrence...where are the radio signals?

To add to what others have already said we couldn't detect the radio emissions of our own civilization unless it was very close to us cosmically (much less than 100 ly).

Intelligent life could still arise, and they might get some interesting eclipes if they were close enough to the gas giants so that the giants occasionally eclipsed their suns.

Even a superjovian planet would be much smaller than the star it revolved around so sorry, all you'd see was a little black dot moving across the face of the sun.
To have an eclipse like you describe the gas giant would have to be close enough to the habitable world that it would show a visible disc, like our moon does, when the planets were close together. Such an arrangement would almost certainly be very unstable, and I doubt such a planet would last long enough to develop life at all (unless it was captured by the gas giant and became a moon, the gas giant itself probably orbiting within the life zone if their orbits are that close).

[LaserRifleofDoom]

Xeriar, let's not jut arbitrarily say that radio is the end-all, be-all of communication until we invent FTL communications. Right now, there is significantly more traffic through fiber optics than through radio waves. And I wouldn't be surprized if a trend to eliminate most radio communication occurs.

[Ariphaos]

Xeriar, let's not jut arbitrarily say that radio is the end-all, be-all of communication until we invent FTL communications. Right now, there is significantly more traffic through fiber optics than through radio waves. And I wouldn't be surprized if a trend to eliminate most radio communication occurs.

Fiberoptics isn't going to let us talk to Mars, or probes to Alpha Centauri, etc.

[Dave]

That wasn't the point.

The point was that with more fiber-optic communicationa and the eventual elimination (banning?) of High-Power brodcast signals there would be very little coherent noise leaving the planet.

This could be one of the reasons we haven't heard from anyone...They all switched to land based communication.