Not a good assumption. If hypothetical Martial life is similar to ours, then it has certain requirements which are met almost nowhere on the surface of the planet. Such life could well be restricted to a few tiny enclaves where the temperature, humidity, and air pressure are all high enough, and we might just have missed those enclaves.
On the other hand, if life on Mars is substantially different from life here, we might have looked directly at it, but not recognized it. To say that it should be “detectable everywhere”, you must assume that it is both enough like terrestrial life to be easily recognizable, while simultaneously assume that it’s enough unlike terrestrial life to be able to survive everywhere.
In fact, we’re still finding new forms of life on our own planet in areas we’ve not previously though to look, in forms we didn’t believe could be stable, and in conditions we would consider uninhabitable. Any genuinely non-terrestrial form of life is almost certain to look like nothing we are familiar with and may not be recognizable as life at all without going back to thermodynamic principles and recognizing a systematic moderation in he flow of energy.
With regard to the propensity for life to spontaneously develop, it is either statistically somewhat likely–in which case, given that vast number of possible times it could develop over the lifespan of the universe, it is very, very common–or vanishingly unlikely, and therefore life on Earth is almost totally unique and we will never come across an extraterrestial lifeform. Since we have only our one cohort of data we cannot say anything definitive, but we can observe that the precursors for life–amino acids–have been found to spontaneously occur under frequently observed planetary conditions–even conditions that are found on other bodies in the Solar System–and even in interstellar space, which tends to argue that if the creation of life involves a statistical combination of conditions which occurred on primordial Earth, it is probably occurring elsewhere with a reasonable degree of frequency, and otherwise must require some kind of magically unique event. As scientists, we tend not to believe in uniqueness and certainly not magic in natural events, and if something can occur once under certain conditions it will occur again, a philosophy which underpins all of science.
About the probability of intelligent life, on the other hand, we can say almost nothing.
We really shouldn’t be asking about the probability of life, or intelligent life, elsewhere. What we should be asking about is its density. If the Universe is infinite, as it currently appears to be, then it’s out there somewhere, no matter what “it” is. But if our nearest neighbors are on the next planet over in our own Solar System, that’s a very different proposition from them being tens of lightyears away, which is in turn very different from them being in the next galaxy over.
The probability for life to spontaneously occur (under “common” conditions) is closely linked to the density. However, the other consideration I neglected to address is the persistence of life. If life pops into existance with great frequency but goes extinct with almost equal frequency, then you have to consider that in your probability of finding extant life.
I’m not an astrophysicist (and I don’t play one on TV) but I don’t think that they are testing Mars’ atmosphere for life , are they? After all, there could be airborne bacteria on Mars which survives in its harsh climate by being transported from one nutrient-rich area to another.
I have always had issues with humans looking for life like us when it’s clear that many types of life aren’t present in many areas around the Earth. There are no reptiles native to Antarctica. There are are only four types of marsupials found outside of Australia. There are few freshwater cetaceans anywhere on the planet.
Looking for what we have here elsewhere is probably looking to be disappointed,IMO.
The radiation environment on Mars’ surface does a pretty good job of breaking down organic chemicals, so there could still be subterranean life that doesn’t last long when the occasional impact or liquid upwelling exposes some of it temporarily.
The density at which life can be found, in response to Chronos’ comment above.
Nothing like Earth bacteria could survive on the Martian surface. It’s not because of the cold or thin atmosphere per se, but the radiation; despite being so much futher from the Sun, the lack of an ozone layer allows essentially all of the incident UV to reach the surface which is nhighly disruptive to organic molecules. If there is life based upon compounds built from amino acids it is almost certainly found under the surface. This isn’t to say that some other self-replicating and energy-moderating form that we could consider to be alive couldn’t exist on the surface in the manner you suggest, but it wouldn’t look anything like terrestrial bacteria.
I believe Apollo 12 (“that’s small step for Neal, but it’s a big on for me”, Pete Conrad) landed near one of the lunar probes and found bacteria on the arm. There was some question that it was contaminated after the return to Earth.
Ot was the camera enclosure from Surveyor 3, on which was found samples of Streprococcus mitis, a bacteria that frequents mammalian mucus tissues (mouth and sinus). As it was not directly exposed to UV radiation it is possible that bacterial spores may have survived for the almost theee year exposure on the Moon, but because the camera was not handled under sterile conditions upon return it could be easily due to contamination during disassembly.
As I said, it may be possible for Earth or Earth-like bacteria to survive in the soil of Mars or otherwise protected from UV, but I don’t think it could survivr on the exposed surface.
On what basis can you possibly declare this “likely”? We can certainly say that it’s virtually certain that life exists in some unknown density among the billions of stars in this galaxy and the billions of other galaxies, based on the universality of the laws of physics and chemistry and the large numbers of extra-solar planets that have already been found. But with a few relatively far-fetched exceptions, pretty much the whole of the solar system outside earth seems quite hostile to life in any conceivable form, and except possibly for Mars, has likely always been so.
Your hypothesis suggests that life is so common that it will likely form just about anywhere; if so, one should expect that it would have flourished and evolved in a major way in the kind of relatively benign environment that Mars probably once was. Yet although we can find evidence of such an environment even after a billion years, like ancient riverbeds, there’s no evidence at all that such life ever existed – though admittedly traces of long-extinct biologically primitive life would be very hard to find.
Marginally, I suppose. But which is more likely – (a) that life first evolved here, a planet which is by definition very hospitable to life, or (b) that it evolved first in a more hostile environment, and got ejected from that place via meteor strike, and survived the heat of impact and ejection, and survived the vacuum, temperature extremes, and radiation of outer space, and survived the heat of re-entry to earth, and then adapted its alien biology to earth’s environment and thrived. One can certainly hypothesize and even demonstrate life forms that survive extreme conditions, but let’s face it, one thing that most life generally does extremely well is die. (b) is not impossible, but (a) seems much more likely.
I agree, which is why I was careful to qualify it with ‘marginally’. I guess I was thinking about the moons of Saturn and Jupiter - which are essentially like a big, wet, energetic chemistry set - it may be, for example, that abiogenesis is more likely in conditions that turn out to be quite hostile to continued survival of the proto-life product - there could be places where life arises, and different places where life flourishes - and they might not intersect at all.
Even if we had millimeter-level photographs of the entire surface of the planet, short of crowdsourcing out to every human on the planet, looking through all the images and trying to find something that plausibly looks like a life form would be a considerable effort, and short of some truly developed creatures - like a leafy plant or animal - all you would end up with are millions of odd discolorations that had been pointed out, each of which would need to be checked out by actually driving out to that spot on Mars and taking a sample.
So basically no, life hasn’t been ruled out by our photographs. The majority of regions that have been captured probably haven’t even been looked at in any detail.
That is also possible. If the Universe is infinite, it’s probably impossible to prove it. It might be possible to prove it finite, if that happens to be true, but it hasn’t happened yet.