This study seems rather self limiting (but then again I'm no biologist)... what if there are non-carbon based life that does not care about carbon dioxide or carbon monoxide?
The study doesn't dispute that. Any planet with any conditions could host complex life that's beyond our understanding. That's not helpful in a search. If we're going to go looking for extraterrestrials then we need to narrow the search to parameters we can recognise, and looking for "life as we know it" seems a reasonable starting point.
Essentially the point is to be self-limiting. No one is saying "Planets outside of these parameters can't have complex life." but instead "Planets outside of these parameters could not give rise to what we know as complex life."
It's really pushing the envelope to assume that "life as we know it" consists on animals with a circulatory system that uses hemoglobin and blood with neutral PH.
Why would life depend on the low concentration that is not even toxic to all of the life here on Earth?
Why would life depend on the low concentration that is not even toxic to all of the life here on Earth?
It wouldn't, and the study isn't saying that it would.
The point is about narrowing the search space. An analogy would be guessing passwords. If I want to guess the passwords of the people I work with I can start with the assumption that it could be anything, which doesn't narrow the space and makes the task impossible, or I can start with the assumption that it'll be based on a dictionary word with some numbers because all my passwords are like that. I'll definitely miss some passwords that don't fit my assumption but I'm far more likely to get some positive results (assuming my way of generating a password is common in the universe.)
Fair enough, but it would be counter-productive to have too restrictive a filter.
Take the CO criterion, for example. While it is reasonable to point out that CO may be present in high concentrations in many planetary atmospheres, at levels that would be toxic to life evolved on earth, one must consider that life might evolve in a way that tolerates or even exploits it. Oddly, the authors acknowledge this, yet, apparently without any counter-argument, still include CO as a probable show-stopper.
As the way to search for life beyond the solar system is to look at atmospheric composition, an alternative way to look at the 'CO problem' is to say that an abnormally low CO level on these planets might be a hint of life.
What about intelligent life? How much more does that narrow the parameters, and how many planets are estimated to exist that could support intelligent life as we know it?
Very interesting, I'm happy someone finally did a more statistically rigorous analysis of the Drake equation. Now I know where the aliens are hiding: in the long tail of an extremely skewed probability distribution!
The wide range of extremophiles here on earth makes me think that this paper is parochial, at best. Carbon is versatile and oxygen is a great source of energy, but that doesn't preclude other biochemical systems.
Given the amount of real estate in the universe that is "out in the cold" (Oort cloud equivalents, way beyond the snow line) it may be that we are the oddballs, and there are scientists out there wondering how life would be possible with molten ice and burning things with something as hellishly reactive as atomic oxygen. Free-floating planets might be where the really good parties are in our galaxy.
Wouldn't the best place to look for life be right here on Earth? I mean, if it could be demonstrated that life has or had more than a single origin on Earth, then we'd have 2 data points, and it would suggest that under the right conditions the emergence of life is not an anomalous occurrence.
In terms of life that is made out of 'normal matter' like we are, there are a few different universal solvents that could make this work [0]. Wikipedia's entry there is fairly facinating stuff. The really big take-away is that there is a limited number of universal solvents and we know what the temperature and pressure ranges of those solvents are; there are defined 'Goldilocks Zones'.
Outside of the matter that we are made of, who knows. It's not impossible that dark matter could somehow be set-up to create life, but we've no idea if it's feasible. The same goes for dark energy, only more so as we have basically no clue what dark energy is, even though it makes up the majority of the 'stuff' in the cosmos.
Voyager is also very slow and will soon be very cold. I wouldn't worry. The book's premise relies on fictional physics pretty far from anything we know in the real world --- things that would cause all sorts of thermodynamic and information-theoretic havoc --- so I wouldn't worry.
There is plenty of life that doesn't care about carbon dioxide and monoxide here on Earth.
When life started here CO2 was from hundreds of thousands to many millions of times more abundant than it's now. Tens of thousands more of it won't probably even make oxygen respiration impossible.
I don't think it is just the valency but also that the strength of the bonds it forms with many other elements fall into a 'goldilocks' range.
Between them, carbon and water have a bunch of unique properties. AFAIK, its hard to come up with any other suite of materials offering the same prospects for complexity, at any temperature.
I had a debate about this with a friend - is there a chemical cycle using silicon that could work like respiration does for organic life? Silicon dioxide is, well, glass...
Are you referring to it being a solid? Silicon dioxide would be a gas at some temperature - likewise CO2 is solid below -78.5c. Extraterrestrial life doesn't have to be anywhere near the same temperatures as us.
Also I don't see why you couldn't have an organism that "breathes" solid material.
I researched this topic for a while, and I came to conclusion that Si-based life is nearly impossible for several reasons.
> Silicon dioxide melting point: 1710 °C
No complex chemistry can survive these temperatures.
SiO2 is only soluble in HCl and HF, which are very reactive, so no solubility either.
> Also I don't see why you couldn't have an organism that "breathes" solid material.
All of known biological chemistry relies on some sort of solubility for reagents. I don't think there's any known organism that can get rid of solid waste from the entire volume of the organism.
You could react silicon with fluoride instead of oxygen. Silicon tetrafluoride melts at −90 °C (and boils at -86).
You can also have chlorine as your oxidizer and make Silicon tetrachloride which melts at −68.74 °C and boils at 57.65 °C, that temperature range is perfect.
What else will change by having a chlorine instead of oxygen atmosphere?
But this study does not do that. What we know is that life on this planet evolved to the conditions of this planet. As the conditions of the planet changed, which they have and quite radically, so too did the life.
Life didn't evolve to breathe nitrogen, oxygen, etc which we just coincidentally had - it evolved to breathe and utilize what was already present on our planet. And this should be the assumption for all life, which means that restricting stuff because it would be inhospitable to us is completely nonsensical.
