Monday, July 29, 2013

Do we search for habitable systems?

In the last few years we've heard a lot about the discovery of "habitable planets" - usually defined by their size, solidity, and a distance from their star that could maintain liquid water.

This is all well and good, but part of what makes Earth habitable (at least to the sort of organisms we're familiar with) is the solar system that we live in. I'm specifically thinking of the role that Jupiter plays in flinging comets out of the solar system before they hit us.

So my question is - does this sort of thing factor into the search for habitable planets at all? Presumably it would be straightforward to look for because if you want a planet with a Jupiter-effect it's going to by definition be big and exerting a lot of pull on its system. If we don't, presumably factors like this will be worked in once we have a bigger catalogue of habitable planets.


  1. The search for planets is biased towards gas giants in close orbits because they are the easiest to find.

    1. Right, but is there any work at all in characterizing systems that are more likely to be habitable. I don't know a standard for a "habitable system" other than this Jupiter effect but presumably there are also characteristics of stars, etc.

      Do we have additional information on this sort of stuff that we can use to prioritize the potentially habitable list (since presumably it's only going to grow bigger).

  2. I don't there's much sense in searching for habitable planets.

    There are two possible motivations.... The first is to find alien life and the second is to find places that could be colonized.

    The first doesn't make much sense because there's no way of remote-sensing the existence of life. Also, we have very little idea of what the environmental parameters for life actually are. Extremophile bacteria have shown that the limits are a lot wider than we think. It's not impossible that gas-giants could contain life. We should investigate extremophile life first, then come up with a environmental window rather than guessing.

    The second supposed reason makes even less sense. We have no way of travelling inter-stellar distances to earth-like planets. If we did short distances would be far preferable to long ones. A trip that takes only, say, four generations would be far better than one taking 30. Going somewhere with rocky planets or moons within which caverns could be built to inhabit would be the most practical (though, of-course, that's neither practical nor possible today). The discussions about terraforming are just as silly. We have no idea how to do terraforming. If a planet were close to Earths environment we have no idea how to change it so the environment is habitable. That may be very difficult indeed. It may be easier to start with a planet that's completely different to Earth than one that's like it.

    1. Right, this is the source of my caveat in the main post. But if we've got a telescope up there it seems silly to wait to find habitable planets given the parameters for Earth-like life that we do have. It's one of the most interesting things we can do with those telescopes and that data right now after all, so I don't see the logic of your first - etremophile studies, second - turn to the telescopes strategy. There's no guessing involved - it's the application of admittedly limited but clearly verified (verified in the case of Earth) parameters. To call that "guessing" is absurd unless by "guessing" all you mean is that we don't know for sure if any given planet has life - and if that's all you mean that seems obvious.

      I'd agree on your second reason but I'm not sure that's the principle goal. Anyone that thinks colonization outside of the solar system is something worth thinking about at this point is usually thinking about ships, not other planets. If we can actually make a ship we can survive on that can get to those planets, then we've solved the survivability problem and we can live anywhere.

      It's true we have no idea how to do terraforming (well... little idea). I don't see how "silly" follows from that. I didn't know how to do a lot of things a couple years ago. I still don't know how to do a lot of things. That might need a little explaining (at least to me).

    2. > It's one of the most interesting things we can do with
      > those telescopes

      I'm not sure about that, I expect Astronomers would have a better idea about that. If it's true that there's nothing better for them to do then you're right.

      > To call that "guessing" is absurd unless by "guessing" all
      > you mean is that we don't know for sure if any given planet
      > has life - and if that's all you mean that seems obvious.

      What I mean is we're guessing about the range of environments that support life. We're looking for places like Earth. But, we don't really have a good handle on the question. The likelihood is that many more planets could support life too, so we're ignoring most of the important ones at present. It's also quite possible that some parameters are more sensitive than we think, so planets that superficially appear similar to Earth actually aren't capable of supporting life.

      > It's true we have no idea how to do terraforming
      > (well... little idea). I don't see how "silly"
      > follows from that. I didn't know how to do a lot of
      > things a couple years ago.

      Until we know more about how to do it we can't speak about the conditions needed for a planet to be suitable. They may be exactly the opposite of what we think. I can imagine a terraforming engineer in 1000 years time telling the press something like "I'm looking for planets that are like Venus. Now Venus has been terraformed we know what's needed is lots of thermal energy on the surface and nice sulphuric acid rain."

      The way we engineer things isn't necessarily closely related to the way they occur naturally. Think of combustion engines and wheels compared to limbs and muscles, for example.

    3. The odds are that we would "terraform" earth like planets by seeding them with bacteria, lichens, plankton, grasses etc. and then waiting a LONG time for the atmosphere to be converted from CO2, methane and ammonia to Earth like. It is very unlikely we will ever get there to do it (although I once wrote a short story for my own amusement where a seriously dysfunctional individual flung frozen excrement into the void and wound up seeding Earth with life when some frozen turds fell to Earth.)

      The only reason to search for "habitable" planets is to try to determine if we are alone in the Universe. As Arthur C. Clarke said “Two possibilities exist: either we are alone in the Universe or we are not. Both are equally terrifying.”

    4. "It's one of the most interesting things we can do with those telescopes and that data right now after all..."

      They find planets in the circumstellar habitable zone* using doppler spectroscopy all the time. See HARPS:

      Starting around 2020 a third generation of doppler spectroscopy telescopes will come oneline and they will be able presumably to discover planets the size of the Earth or smaller (right now the technology only exists to find rocky bodies some magnitude larger than the Earth but far smaller than say a gas giant).

      *As with most terms it has been refined over the years (and obviously there is ongoing discussion of the matter) but currently it is generally understood to mean a region around a sun where water can subsist (in light of a number of factors like mass of the planet and how it effects an potential atmospheric pressure, etc.). Obviously what the term describes and how it is applied is going to be in a state of evolution for some time to come.

  3. Just saw this, covering research on habitability as it relates to the solar system...

    Earth will turn into a Venus-like hell earlier than previously thought

    ...especially cool at the end is the proposal to use asteroids to make periodic adjustments to Earth's positioning in the solar system.

  4. There are stellar classes that are stable enough to support life, and ranges of liquid water and size that might come close, but there are many other criteria that may be necessary or not and may be detectable or not. Jupiters may be common but not necessary while magnetic fields may be necessary but not detectable. A large moon to stabilize rotation might be necessary, while phase locking might be prohibitive, but there could be moons around close Jupiters. Clouds may extend the zone inwards a bit. It may not be that difficult to detect life, an O2 atmosphere would be sufficient, though a small target close in may be hard to separate. Right now collecting enough samples for statistics and analysis of those we can, will give us better ideas of what to expect and what to search for.


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