Someone asked me the other day what it would take to surprise me. In other words, given the deluge of data coming in from all kinds of observatories, what one bit of news would set me back on my heels? That took some reflection. Would it surprise me, my interlocutor persisted, if SETI fails to find another civilization in my lifetime?
The answer to that is no, because I approach SETI without expectations. My guess is that intelligence in the universe is rare, but it’s only a hunch. How could it be anything else? So no, continuing silence via SETI does not surprise me. And while a confirmed signal would be fascinating news, I can’t say it would truly surprise me either. I can work out scenarios where civilizations much older than ours do become known.
Some surprises, of course, are bigger than others. Volcanoes on Io were a surprise back in the Voyager days, and geysers on Enceladus were not exactly expected, but I’m talking here about an all but metaphysical surprise. And I think I found one as I pondered this over the last few days. What would genuinely shock me – absolutely knock the pins out from under me – would be if we learn through future observation and even probes that Proxima Centauri b is devoid of life.
I’m using Proxima b as a proxy for the entire question of life on other worlds. We have no idea how common abiogenesis is. Can life actually emerge out of all the ingredients so liberally provided by the universe? We’re here, so evidently so, but are we rare? I would be stunned if Proxima b and similar planets in the habitable zone around nearby red dwarfs showed no sign of life whatsoever. And of course I don’t limit this to M-class stars.
Forget intelligence – that’s an entirely different question. I realize that my core assumption, without evidence, is that abiogenesis happens just about everywhere. And I think that most of us share this assumption.
The universe is going to seem like a pretty barren place if we discover that it’s wildly unlikely for life to emerge in any form. I’ve mentioned before my hunch that when it comes to intelligent civilizations, the number of these in the galaxy is somewhere between 1 and 10. At any given time, that is. Who knows what the past has held, or what the future will bring? But if we find that life itself doesn’t take hold to run the experiment, it’s going to color this writer’s entire philosophy and darken his mood.
We want life to thrive. Notice, for example, how we keep reading about potentially habitable planets, our fixation with the habitable zone being natural because we live in one and would like to find places like ours. Out of Oxford comes a news release with the headline “Researchers confirm the existence of an exoplanet in the habitable zone.” That’s the tame version of more lively stories that grow out of such research with titles like “Humans could live here” and “A Home for ET.” I’m making those up, but you know the kind of headlines I mean, and they can get more aggressive still. We hunger for life.
Here’s one from The Times: “‘Super-Earth’ discovered — and it’s a prime candidate for alien life.’” But is it?
Image: Artist’s depiction of an exoplanet like HD 20794 d in a conceivably habitable orbit. It may or may not be rocky. It may or may not be barren. How much do our expectations drive our thinking about it? Credit: University of Oxford.
That Oxford result is revealing, so let’s pause on it. HD 20794 d is about 20 light years from us, orbiting a G-class star like the Sun, which gives it that extra cachet of being near a familiar host. Three confirmed planets and a dust disk orbit this star in Eridanus, the most interesting being the super-Earth in question, which appears to be about twice Earth’s radius and 5.8 times its mass. The HARPS (High Accuracy Radial Velocity Planet Searcher) and ESPRESSO spectrographs at La Silla (Chile) have confirmed the planet, quite a catch given that the original signal detected in radial velocity studies was at the limit of the HARPS spectrograph’s capabilities.
Habitable? Maybe, but we can’t push this too far. The paper notes that “HD 20794 d could also be a mini-Neptune with a non-negligible H/He atmosphere.” And keep an eye on that elliptical orbit, which means climate on such a world would be, shall we say, interesting as it moves among the inner and outer edges of the habitable zone during its 647-day year. I think Oxford co-author Michael Cretignier is optimistic when he refers to this planet as an ‘Earth analogue,’ given that orbit as well as the size and mass of the world, but I get his point that its proximity to Sol makes this an interesting place to concentrate future resources. Again, my instincts tell me that some kind of life ought to show up if this is a rocky world, even if it’s nothing more than simple vegetation.
Because it’s so close, HD 20794 d is going to get attention from upcoming Extremely Large Telescopes and missions like the Habitable Worlds Observatory. The level of stellar activity is low, which is what made it possible to tease this extremely challenging planetary signal out of the noise – remember the nature of the orbit, and the interactions with two other planets in this system. Probing its atmosphere for biosignatures will definitely be on the agenda for future missions.
Obviously we don’t know enough about HD 20794 d to talk meaningfully about it in terms of life, but my point is about expectation and hope. I think we’re heavily biased to expect life, to the point where we’re describing habitable zone possibilities in places where they’re still murky and poorly defined. That tells me that the biggest surprises for most of us will be if we find no life of any kind no matter which direction we look. That’s an outcome I definitely do not expect, but we can’t rule it out. At least not yet.
The paper is Nari et al., “Revisiting the multi-planetary system of the nearby star HD 20794 Confirmation of a low-mass planet in the habitable zone of a nearby G-dwarf,” Astronomy & Astrophysics Vol. 693 (28 January 2025), A297 (full text).
I wouldn’t be shocked to not find life on any one habitable zone (and habitable) planet. I would be shocked to find none. Noting of course that proving a negative is difficult, especially from light years distance.
There were have to be something fundamentally important going on, and surprising, if life is so rare that we are alone or perhaps almost alone. Even if what we find is nothing more than primitive life. Abiogenesis should not be that difficult.
It is difficult to be surprised by something not happening, of course, so at least you will never be subject to a sudden shock, more like a slow realization!
Myself, I would be very surprised if we did discover extraterrestrial life, for one very simple reason:
There is no such thing as “simple life”. Anything we know that can grow and multiply is incredibly complex. There must have been simpler intermediates, once, but we don’t see them, today. We can only speculate about their nature.
I think that Mars is a bit of a litmus test.
We should get a LOT of data from there in the coming years and if there are zero signs of present or past life, I think we are likely looking at a barren universe rather than a fecund one.
Yeah, like if Mars had plate tectonics in its deep past.
If we assume life starts fast, as long as there are the precursors and conditions for life, then Mars likely had a sufficient window… The fact that it is not (obviously) present now is a worry and I wonder if it hints at a filter…
Either way there should be some hint of life there, past or present. If after 10 years of looking in caves and drill samples there is still no hint, it could imply that life is exceedingly rare.
My guess is that HD 20794 d is, at minimum, a waterworld with a planetary ocean at least 100km deep and possibly as deep as a 1000km. It will have a very thick, dense atmophere with a surface pressure of 100atm and possibly up to 1000atm. This is dense enough that the planet may not have a sharply definable surface. Rather, the atmosphere gradualy merges into the ocean, analogous to a mini-Neptune. I think it highly unlikely HD 20794 d is even remote habitable to humans.
An ocean that deep leaves little chance of the weathering and erosion that resulted in our oceans being salty. It is all the dissolved materials that make our seas salty that allows for lots of biomass to form. The planetary ocean of HD 20794 d is likely to be as pure as the distilled water you use in you Keurig coffee maker. This is not conducive to life. What life that exists on this planet, if any, will likely be limited to the areas around the hydrothermal vents it emerged from and will be prokaryotic.
We have to look much more to find real habitable planets.
One more thing. Does HD 20794 d have planet tectonics? Tectonics allows for the controlled release of all that energy and heat in the planet. No plate tectonics, no controlled release. Instead, you get the period crustal resurfacing that make Venus what it is. Does the rocky core of Neptune have plate tectonics? I’ve heard Neptune has winds of speeds up to 900 mph. Could period crustal overturn of the rocky surface be the source of energy for these winds?
Instead of HD 20794 d being a super-earth, it could be a super-Venus. Certainly not an abode of life as we know it.
Complexity seems to arise naturally, spontaneously, out of the fabric of space-time itself. As long as there is some pocket of energy available, entropy can be reversed. The question is, is this property limited to the tools and matter available, or can it manifest itself in alternative ways with alternative materials? To put it another way, is carbon-water life the only life, or are there biologies and communities of silicon, ammonia-breathers, cryogenic supercooled crystalline creatures, life forms of plasma or electromagnetic fields, perhaps entities composed of interfering gravity waves?
Are there other kinds of life? Are ‘other kinds of life’ possible? Are alternative biologies even necessary? Are alien ecosystems and communities, if they exist, a lucky accident due to the same physical laws operating on the periodic table? Or are these alternatives inevitable, due to some fundamental property of space-time itself?
I am taking a beginner’s course now in molecular biology and I find it inconceivable that the subtle processes of life could be carried out in any other way than the familiar reactions we are now familiar with. But I I also know enough about the history of science to realize what a hopelessly provincial and short-sighted statement that is!
Newton’s Laws of Gravity are remarkably concise, and yet we are discovering highly subtle processes and structures visible in orbital resonances which (although an obvious result of those Laws) were totally unexpected. Its almost as if the universe has a built-in property that allows, or even forces, it to create complex relationships and events from simpler ones And Newton’s Laws, although now supplanted by Relativity, can easily explain and describe these resonances.
The search for extra-terrestrial life isn’t just about whether or not evolution has created critters on other planets. It is an inquiry into the nature of reality itself.
How sure are you that you’re not mixing up disappointment with surprise? Study on the start of life seems to have a very long way to go, I personally wouldn’t be surprised not to see quick signs of primitive life.
If in the next decade or so, if we do not detect fairly unambiguous biosignatures, I won’t be surprised, but I will be disappointed, especially regarding the implications. IMO, it would indicate that the fanciful idea of finding other homes for humanity in “Earth-like” worlds is a no-go without extensive terraforming. It should increase the emphasis on preserving Earth, although there is little sign of that currently.
What would surprise me is alien ships appearing in Earth’s skies, or landing in places near various major national government buildings and wishing to address their nations. [If they claim they have been visiting us for centuries in their ships and with their probes, I will apologize to the Ufologists.]
Given our current understanding of physics, I would be [very] surprised if we make a sudden breakthrough allowing FTL flight. That could be a game-changer.
Proxima b may have had its atmosphere blown off by solar flares and its oceans evaporated as part of the process. If, as seems highly likely, it has synchronous rotation then, once the atmosphere thins down to < 100 mbar, the last dregs of the planet’s volatiles will collapse onto an ice cap of water, CO2, and nitrogen ice on the dark side. So, we are left with a barren and hot light side, an an extremely cold dark side. Possibilities are left for microbes to survive somewhere, but we may never know unless we actually visit, land, and drill down deep. Thus, I would not be surprised at all if no life is discovered on Proxima b.
An interesting paper utilizes DYNAMITE analysis of the 82 G. Eridani (HD 20794) system, revealing a candidate planet referred to as planet f, which is located in the habitable zone.
The title of the paper is “An Integrative Analysis of the Rich Planetary System of the Nearby Star e Eridani: Ideal Targets for Exoplanet Imaging and Biosignature Searches.” https://arxiv.org/abs/2205.06250
The concept of panspermia suggests that life could be common, particularly in ocean worlds, as this scenario would create optimal conditions for the evolution of life. Colonies on such worlds might evolve rapidly, much like Homo sapiens, who took only 300,000 years to develop into the diverse range of humans we see today.
With current technology, large ships would require at least a hundred years to reach 82 G. Eridani. This raises the question: would such long journeys lead to the emergence of many evolving worlds for any civilizations that choose to advance their genes beyond their home planet?
“What Would Surprise You?” when I saw that title I thought you were referring to current events around the world and in that case due to the last few years nothing much does surprise me these days.
I actually agree with Martyn here and a lot of these Planets around smaller red dwarfs are going to be hot on the day side with a giant ice cap on the night side, perhaps under a deep side night cap a layer of water could exist where you might find an ecosystem like lake Vostok, there is no chance of an Earth like biosphere.
Abelard Lindsey has it right too I’ve had the same opinion that these super earths are not the ideal places for life to arise.
For an advanced civilization from another star system could be an ideal place to build a habitat in a rind around the terminator.
I did read the paper on this planet, its size and mass place it in the Super earth Ocean type of world So its not going to be earth like and One could assume the ocean and atmosphere moderate the temperatures on the orbit.
Cheers Edwin
I would be very surprised if any of our current models for exoplanet habitability (and uninhabitability) survive contact with reality.
What will surprise almost everyone but me: benchtop abiogenesis. I don’t think the chemical compounds needed to initiate life were stable enough for the process to take long, so I think that if you bring together the right components (I’m guessing hydroxylapatite, maybe polyphosphates, formaldehyde, ammonia … and some things I don’t know about!), you can create a whole new origin of life – a genuinely “alien” life form! – in an afternoon. Understanding abiogenesis – the conditions needed, how hard it is, and especially, the range of different self-replicating nucleic acids that can result – well, that gives us a much clearer idea of the conditions needed for life to originate in the cosmos.
What will surprise me and everyone is communication with another species. We’ve been trying to do this for ages, since the first nominal member of the human genus tried to talk to a crow. We’re starting to see some claims of minor success. Question is … can AI-level resources really make it possible for us to understand such conversations as much as they can be understood? Inevitably we’ll be surprised by what animals either know or don’t know, think or don’t think, and it will help us prepare a bit for what lies beyond.