I remember reading (probably from one of his books) that Sagan's idea for a life-detecting experiment on Mars was never actually sent there (apparently this experiment went instead). IIRC, it was basically to put a sample in a box and just watch it to see if anything changed at all in a way that indicates that some chemical process is happening.
Microscopy could also be a good route. Microbial life should look pretty distinct from inorganic matter, even if everything in the soil sample were dead by the time it was imaged. As far as I know, we have not sent a microscope up capable of resolving even a large mammalian cell, let alone resolve 1 micron bacteria (if these microbes are even to be similar in size as those on Earth). I suspect the vibrations during launch make it especially challenging to actually get a powerful microscope out to Mars unharmed.
It's very important to NASA to never send anything to Mars that could definitively rule out the presence of life or water.
Something I noticed a few years ago is that NASA publishes a press release every month or so with the title "possible hint of water found on Mars". There are literally thousands of such web pages on their site:https://www.google.com/search?q=site%3Anasa.gov+"hint"+"wate...
Nobody ought to be this obsessed with something, unless there's an agenda. It's like cigarette companies going on and on about how their latest product is "more healthy".
What's going on is that NASA has had a lot of trouble in recent decades maintaining their funding. There's not a lot in space that excites US senators. There's no oil, no resources that can be practically mined, etc...
So they have to have some sort of goal, something they have to get funding for so that they can go "look for it".
Some NASA administrator picked "water on Mars". Now it has morphed into a reason for the agency to exist, which means if it was ever shown not to exist, then NASA would face a real existential risk itself.
So they'll drag their feet as long as possible, sending every possible instrument they can pack into a rover, except for the one that could definitively rule out life and/or water.
This is why they didn't send a microscope, and most likely won't send one on the next mission either.
They are talking about cells, but must every form of life be built from cells?
It seems like all life on earth descended from one species, that was a cell. So all our life on earth is made out of cells. But couldn't life be completely different somewhere else?
A cell is fundamentally a structural division between an inside and an outside. This creates an energy gradient that does work. So a cell is simply a structure that maintains a gradient for the purpose of doing work.
It's a very simple object--kind of a thermodynamic primitive for resisting entropy. The organelles within cells are themselves cells. I'm not sure what life would look like without cells but it would probably rely on some type of otherwise naturally occuring gradient like a tide pool or mineral formation.
So, one the one hand all Earth life depends on proton gradients over membranes in some form or other for energy, as in the mitochondria powering us. But because prokaryotes and archea seem to share a common ancestor but use radically different cell membranes it looks like their common ancestor might not have generated its own membranes but used naturally occurring lipid membranes. And we'd probably want to call that common ancestor alive.
Cells (as in the bit that makes it a contained volume) are both a thing that forms spontaneously without biology, and very useful for isolating one blob of chemistry from others right next to it.
All the cells that can form spontaneously without biology are dead.
More precisely, they are just cell membranes, not cells. Cell membranes form spontaneously from many fatty substances, the root cause being that oil and water do not mix, i.e. fatty substances are hydrophobic.
A dead cell or cell membrane does not exchange chemical substances with the environment (except passively, i.e. when molecules or ions diffuse from high concentration towards low concentration).
A living cell has not only a cell membrane that separates the interior from the exterior, but it also has molecular pumps and ionic pumps embedded in the membrane, which selectively pump some substances in and other substances out. Without this controlled exchange between interior and exterior, the growth and multiplication that define life are impossible.
What is characteristic for life are the molecular pumps and ionic pumps. The cell membranes have only the passive role of preventing the substances that have been pumped in one direction to come back to the place from where they had been taken by the pump.
If extraterrestrial life were silicon-based, it may instead of cells have ceramic and metallic structures (like filaments) that grow via crystallization. I think that is what the parent is getting at - cells are part of our carbon/water based biology but maybe not all possible forms of life
Technically yes, but I think many people would say it seems likely that all life would have some sort of "exterior layer" like a cell membrane. Realistically this falls into the "unknown unknown" category of knowledge, where we have to speculate with very little concrete evidence.
It makes sense to think about an organisms like that.
But it would be really interesting, if there were other possibilities too we could think of.
A hundred years ago nobody thought something like quantum entanglement could be possible. Maybe there will be a similar eye opening surprise in extra terrestrial life.
But off course it’s reasonable to start looking for all the things we can already imagine, and make observations in a way we already know of.
You have to separate low entropy volume from high entropy volume to do life. Btw cell internals are also full of membranes for the same reason. https://en.wikipedia.org/wiki/Organelle
That doesn’t mean your idea is wrong, but if we assume regular cold chemistry (i.e. not stellar insides or other exotic states/physics), membranes are just the sane and obvious default. Which conditions could make them less effective than something else?
> You have to separate low entropy volume from high entropy volume to do life
That's what I believed too, but I have doubts now after reading another comment that defines it as energy gradients. As far as I understand the concept, a crystal is low entropy as well. Or is it the same thing? Or the combination of the two (Use energy to keep entropy low)?
> membranes are just the sane and obvious default
The less sane one could be... Magnetic confinement fields I guess?
Exactly. Earth life requires organization (low entropy) to generate usable biological energy. Absent a division, that low entropy state reverts to the environmental mean.
I'm struggling to imagine what usable energy generation in a high entropy environment would look like.
I recall hearing this explicitly stated by a member of the current rover team. They said that we need to begin imagining completely different forms of life from our own - like completely outside the box thinking.
Thankfully plenty of hard sci-fi writers have done that for us.
It's something that I've been very interested in for a long time, especially the idea of "scale of life" - could there be a brain the size of a solar system? How would we even understand it? What about life which operates on a different time scale (in the solar-system brain example, it would operate on a different scale on two axis - space and time).
The box needs to be defined at some point, lest you start realizing you've defined it so broadly that natural phenomenon like fire, the wind, or the tides qualify.
There's an interesting theory that suggests Martian and Earth life have a common ancestor, and have exchanged life through material kicked up out of atmosphere due to asteroid or meteor impact.
Anything is possible, obviously, but in the current way we understand life, it's not likely.
I am unaware of any understanding of evolution or early life on Earth which supports an idea of some giant contiguous life-form.
That said, Mars is not Earth, and our definition of life is ever evolving (is a virus alive? is fire alive?) so, again anything is possible, but not everything is likely.
A cell is just literally an organic unit. It’s something organized that is alive. Any living thing would have to have cell’s otherwise it’s just not organized in any way which doesn’t make sense in the context of our universe
Still viruses are very specifically adapted to life on earth, everything contains DNA and RNA. Maybe this is the only form of life that is chemically possible, maybe there are many alternatives.
Folks, I don't usually do popularity contests, but I'm trying to figure out why I'm being downvoted into oblivion here. Earlier today I was upvoted a bunch, now I'm -3, and..
I don't really see much of controversy in what I said here?
They haven't bothered with labeled release or adding water to soil. Curiosity does have a similar oven+GCMS setup to Viking, which has indeed found funny organic chemicals in some soil samples: https://en.wikipedia.org/wiki/Sample_Analysis_at_Mars
It takes them seven months to fly a rover to mars. They could potentially devise a way to expose the rover to space during these months to sterilize it.
> As I have argued before, we need a new mission to Mars dedicated primarily to life detection to test this hypothesis and others. It should explore potential habitats on Mars like the Southern Highlands, where life could persist in salt rocks close to the surface
On a quick scan, I'm not seeing anything in your linked article that counters either your selected quote, or the thrust of the OP. Can you help me out by pointing to a section or summarizing the argument?
"It should explore potential habitats on Mars like the Southern Highlands, where life could persist in salt rocks close to the surface" is basically saying that we should throw away planetary protection guidelines in favor of studying places with potential for extant life, an argument that the author has been making repeatedly for a long time, and what the article I linked counters.
The discussion about Viking lander results was just build-up for that final paragraph making the argument for new life-searching mission.
OK, headline is more worrying that it needs to be - makes it sounds like we accidentally killed ALL life on Mars. It's actually referring to possible life in the soil sample the Viking lander poured water on.
Also, the part where they heated all (?) the samples before testing sounds more problematic than pouring water on some (especially since parts of mars hit 100% humidity, per the article).
This seems a bit hyperbolic. I suppose there is a tiny chance that we caused the extinction of the last vestiges of microscopic life on Mars. I doubt it though.
Science is about trying things and learning from our mistakes.
The best way to conduct a proper experiment is to either send a human, or a robot that is as adaptable as a human. This will let us run an effective experiment, react to intermediate results and continue based on that. Anything else is a waste of time, we'll never get anything conclusive.
Readit News
Here are some interesting slides I found while trying to figure out what his actual experiment idea involved: https://www.vanderbilt.edu/olli/archive/Life_On_Mars_Session...
Something I noticed a few years ago is that NASA publishes a press release every month or so with the title "possible hint of water found on Mars". There are literally thousands of such web pages on their site:https://www.google.com/search?q=site%3Anasa.gov+"hint"+"wate...
Nobody ought to be this obsessed with something, unless there's an agenda. It's like cigarette companies going on and on about how their latest product is "more healthy".
What's going on is that NASA has had a lot of trouble in recent decades maintaining their funding. There's not a lot in space that excites US senators. There's no oil, no resources that can be practically mined, etc...
So they have to have some sort of goal, something they have to get funding for so that they can go "look for it".
Some NASA administrator picked "water on Mars". Now it has morphed into a reason for the agency to exist, which means if it was ever shown not to exist, then NASA would face a real existential risk itself.
So they'll drag their feet as long as possible, sending every possible instrument they can pack into a rover, except for the one that could definitively rule out life and/or water.
This is why they didn't send a microscope, and most likely won't send one on the next mission either.
It seems like all life on earth descended from one species, that was a cell. So all our life on earth is made out of cells. But couldn't life be completely different somewhere else?
It's a very simple object--kind of a thermodynamic primitive for resisting entropy. The organelles within cells are themselves cells. I'm not sure what life would look like without cells but it would probably rely on some type of otherwise naturally occuring gradient like a tide pool or mineral formation.
The local star, especially if close enough, creates lots of gradients.
Dead Comment
Cells (as in the bit that makes it a contained volume) are both a thing that forms spontaneously without biology, and very useful for isolating one blob of chemistry from others right next to it.
There is however life on earth with huge cells and multiple nucleuses: https://en.wikipedia.org/wiki/Plasmodium_(life_cycle)
But also, the Viking test was more general than "cells", it would have ben positive with anything that could, to simplify, eat the food it was given.
More precisely, they are just cell membranes, not cells. Cell membranes form spontaneously from many fatty substances, the root cause being that oil and water do not mix, i.e. fatty substances are hydrophobic.
A dead cell or cell membrane does not exchange chemical substances with the environment (except passively, i.e. when molecules or ions diffuse from high concentration towards low concentration).
A living cell has not only a cell membrane that separates the interior from the exterior, but it also has molecular pumps and ionic pumps embedded in the membrane, which selectively pump some substances in and other substances out. Without this controlled exchange between interior and exterior, the growth and multiplication that define life are impossible.
What is characteristic for life are the molecular pumps and ionic pumps. The cell membranes have only the passive role of preventing the substances that have been pumped in one direction to come back to the place from where they had been taken by the pump.
But it would be really interesting, if there were other possibilities too we could think of.
A hundred years ago nobody thought something like quantum entanglement could be possible. Maybe there will be a similar eye opening surprise in extra terrestrial life.
But off course it’s reasonable to start looking for all the things we can already imagine, and make observations in a way we already know of.
That doesn’t mean your idea is wrong, but if we assume regular cold chemistry (i.e. not stellar insides or other exotic states/physics), membranes are just the sane and obvious default. Which conditions could make them less effective than something else?
That's what I believed too, but I have doubts now after reading another comment that defines it as energy gradients. As far as I understand the concept, a crystal is low entropy as well. Or is it the same thing? Or the combination of the two (Use energy to keep entropy low)?
> membranes are just the sane and obvious default
The less sane one could be... Magnetic confinement fields I guess?
I'm struggling to imagine what usable energy generation in a high entropy environment would look like.
It's something that I've been very interested in for a long time, especially the idea of "scale of life" - could there be a brain the size of a solar system? How would we even understand it? What about life which operates on a different time scale (in the solar-system brain example, it would operate on a different scale on two axis - space and time).
I think the only wiggle room there is "nontrivial".
I am unaware of any understanding of evolution or early life on Earth which supports an idea of some giant contiguous life-form.
That said, Mars is not Earth, and our definition of life is ever evolving (is a virus alive? is fire alive?) so, again anything is possible, but not everything is likely.
Okay? People have no idea what pre-cellular life looked like so the entire earth being a giant cell is not out of the question.
Deleted Comment
But the only life we know... is cells. Unless you count viruses. Which most biologists don't.
I don't really see much of controversy in what I said here?
Making a lander where we know there are no earth microbes on it is quite difficult and certainly important for testing for life.
And the refutations to the authors original pleas are still as valid as they were then: https://www.liebertpub.com/doi/10.1089/ast.2017.1749
The discussion about Viking lander results was just build-up for that final paragraph making the argument for new life-searching mission.
passive aggressive subtitle vs. headline wars ftw
That's why we don't have one.
Dead Comment
Science is about trying things and learning from our mistakes.