Dragonfly is powered by an RTG (with batteries), but higher performance nuclear aircraft should be possible on Titan also. It's possibly the best place in the solar system for nuclear energy (although the fuel has to be imported). The dense, cold atmosphere makes open cycle nuclear gas turbines very easy to build, even at modest core temperature.
That should be just a gas turbine where the gas is heated through a heat exchanger and where the heat source happens to be a nuclear reactor.
Normally such gas turbines with external heating use their gas in a closed cycle, because air is not a suitable working gas (one of the reasons is that it is too oxidizing at high temperatures, which can damage the turbine; another reason is that it is preferable if the working gas can be transformed into a supercritical fluid at a low enough temperature and low enough pressure, like carbon dioxide).
In a place where the atmosphere would be an acceptable working gas, the cost of the turbine could be reduced by using the atmosphere as the working gas in an open cycle.
The big reason for this cycle on Titan is that at a given pressure ratio, the necessary absolute temperature in the hot part of the engine is proportional to the absolute inlet temperature. So, if the absolute inlet temperature is 1/3rd that of Earth's atmosphere, the peak temperature is also drastically reduced. All the hot parts could be made from cheap materials. The turbine blades wouldn't have to be cooled. Lower temperature also reduces the speed of sound in the gases, which reduces the velocity (and therefore stress) of the compressor and turbine blades.
Well, if operated on Titan and the gas was heated by routing it through the reactor, the nitrogen would make carbon-14. Would we care about that, though?
Given there's literal seas of hydrocarbons on Titan I wonder if there's a source of oxygen that could be liberated, allowing probes to operate without the need for fuel from Earth?
Depends how tightly bound the oxygen is. If the reaction is exothermic then you capture the liberated oxygen to make far more oxygen in a feedback loop.
I don't get it, are you thinking Titan's just a bomb ready to go off? I'm pretty sure that at least one meteor has hit Titan in the past with the energy of a nuclear weapon, and it's still there. Calculations trying to see if a nuclear bomb would ignite Earth's atmosphere were interesting, but it feels hubristic to think that any nuclear weapon would compare to Chicxulub.
Chemically, things are usually pretty much at equilibrium and if there's a giant energetic cliff, they'll fall off eventually. Nuclear-wise, sure, all the light elements could fuse (hydrogen, helium, carbon, oxygen...) and release energy, but that requires some fairly exotic conditions.
It would mostly be in the form of CO2, water, with lesser amounts of CO and acetonitrile. I suppose there's some chemical energy in the CN groups (also in acetylenes) but I don't see how that could give free oxygen.
Titan is actually high on my list of places that could harbor life.
I’m not talking about subsurface water though that’s possible. I mean chemically alien life.
The reason I suspect this is a phenomenon understood in theory of complexity and evolutionary informatics circles called the “edge of chaos.” Oversimplifying a bit you get universal computation in the vicinity of a phase boundary.
Titan is loaded with phase boundaries: solid, liquid, gas, dynamic changes between them, rain, dissolving and crystallizing solids, etc. The solvent is just light hydrocarbons not water.
Life on Titan would be slow and low metabolism compared to us (probably). We should be aware of this likely difference when looking. What looks like minerals, rocks, weird films of chemicals, etc may be alive. We should look for structure, metabolism, isomer preferences, etc.
Of course life on Titan is convinced there could never be life here. The third planet is a literal hell where it rains molten dihydrogen monoxide in an atmosphere of corrosive oxygen. Any life there would vaporize and oxidize instantly.
Rumors of a strange disc shaped object being recovered with material and isotope ratios pointing to the third planet are entirely unfounded, as are rumors of amateur radio enthusiasts picking up signals from there.
> Life on Titan would be slow and low metabolism compared to us (probably).
On the other hand, maybe the chemistry there could be using less stable chemicals where less energy is needed to change them. It's at a much lower temperature, after all.
I suspect we'll find nothing, though, due to Fermi. If two different Origin of Life events happen in the same system, OoL (of at least one of those kinds) must be common in the universe, and that would remove what I consider the big potential obstacle to abundant intelligence in the universe. Just an intuition without more data, of course.
Its wholly possible for the universe to be teeming with single-celled life, but I think the jump to multicellular, intelligent, civilization, and space-faring (at least signals wise) could still cut it to a factor 1/1000 stars. And we're relatively early in the life of the universe still.
I agree with your sentiment but not your specific number. The leap from uni- to multi-cellular life might be a "great filter" in Fermi-paradox parlance.
But I think it would need to be more like one in a million or one in a billion. I think even one civilization becoming a slow interstellar (less than 0.1C ships for their) civilization could colonize the galaxy in less than a million years.
Consider what we could do if we could get a slow ship to Alpha Centauri in some absurd time like 1000 years and actually settle there. Maybe we try ever If us here on Earth and Sol could only do that once every thousand years and then if each colony could too. We would only be doubling the amount of stars we inhabit every thousand years. Presuming this slow pace we would also be adding 5~10 light years to our civilization in that time too. But in a million years that 5k to 10 light years would be a sphere with diameter about 10% to 20% the diameter of the galaxy. Allow those jumps to be 50ly and we could get a whole Milky Way galaxy in that time.
That is all predicated on very slow stuff, no FTL, slow ships or project taking massive time. And since the dinosaurs died we had 65 such time periods and another 300 while the dinosaurs lived...
And I could go on for hours about this stuff. But my point is that if unicellular life is common and there is a single great filter and that is the jump to multicellular life then the odds of that event dictate how often we would see other civilizations. A 1 in 1000 we would see civilizations all over the place. We would certainly be withing radio range of at least a few. So it would need to be much worse odds.
I don't think multicellularity is a plausible Great Filter, since it's easy to achieve in laboratory evolution experiments -- just get cells to stick together after fissioning.
The assumption that colonisation and endless population growth are inevitable goals of any intelligence is a flaw of the paradox, in my opinion. I see it as something we just haven’t outgrown yet as a species.
That colonisation could of course be in the form of probes simply exploring, but there are timescale and resource issues with that which make me question if it would be worthwhile for a civilisation considering the limited energy in any given system and tremendous effort involved in getting to another once it runs out.
It isn't an assumption. Not every civilization needs to expand but the ones that do will expand more than the ones that don't. And the expansionist subset of any civilization will wind up representing the whole of that Civilization on the larger scale.
Any proposed great filter to the Fermi paradox needs to be non-exclusive. As in it can't be something that will only impact some of the group, it needs to impact all or very near to all in a statistically significant way.
In the previous example if even just 1% of civilizations wind up having just a subset that go out and explore we would still expect to be able to have seen some here in the Milky Way because that would be 100,000 or so planets or Stars producing multicellular life and with the presumed odds we were discussing civilizations that expand. We presumed for the ease of math, because we're not pulling out the whole Drake equation, that the one in 1000 was just for the one filter. Of course you can do the math with whatever percentages you like at any filter. And each set of numbers you plug in means something slightly different with regards to what we're seeing and why we're seeing it out here in the real world.
I’m a multicellular rare Earther. We’ve had on the order of 10^40 cells, ever [1]. Symbiogenesis occurred, from what we can tell, once [2]. (For comparison, there are 10^11 stars in the Milky Way [3] and 10^24 in the observable universe [4].)
We might be able to argue that factor should be cut, since any late symbiogeneses would be outcompeted into oblivion. But that still, optimistically, puts us in the realm of the Milky Way’s star count.
The basic idea of rare Earth as an answer to Fermi is that if the frequency of advanced life is around 1 per galaxy per billion years or something like that then we'd likely never meet any aliens.
Intergalactic travel is borderline impossible barring unknown physics or travel very close to the speed of light. Even at speeds like 0.5c (50% the speed of light) the trip would take so long you'd have problems like cosmic rays tearing you apart over such long spans of time, and in the vastness of intergalactic space there's no place to pitch a tent and chill and repair things. 0.5c would get you to the stars but not the galaxies.
Intergalactic flight would require something more like 0.95c to 0.99c. The energy requirements for that are insane and possibly unachievable, and if you hit a dust particle at that speed the yield will be like a thermonuclear bomb. The cosmic microwave background also becomes a beam of hard gamma rays aimed at your head. All kinds of crazy extreme physics things happen.
Lastly, why do it? Galaxies are huge and if you're alone then it's all yours. The only conceivable reason would be to flee some galactic-scale super-catastrophe like your galaxy's central black hole behaving badly and frying everything with gamma rays. Even for that it might be easier to burrow deeply into planetary bodies instead.
Of course one can imagine ultra-far-future scenarios like: what if Andromeda hosts some galactic-scale super civilization by the time it hits the Milky Way which by then also hosts such a thing. That'd be a hoot.
> Intergalactic flight would require something more like 0.95c to 0.99c
Why would it require speeds that high? Sure, it's going to take a very long time, but why is that an insurmountable obstacle?
There are enough isolated stars in intergalactic space that one can even imagining making the trip in smaller steps, with colonization in between. At a stellar density nine orders of magnitude lower than our galaxy stars are still within thousands of light years of each other.
Because most people go nearly insane in solitary confinement? and that isn’t even really solitary.
And gov’ts and social structures rarely last a few generations, let along 100 of them.
Not to mention inbreeding.
What makes you think any humans stuck in something the size of even the most generously sized starships won’t go full lord-of-the-flies and be unable to effectively maintain the ship long before it ever arrives?
Of course I see this as a conflation of life versus intelligence.
Do I suspect we'll see life commuting between galaxies, seems unlikely life as is fragile compared to how damned harsh space is.
But intelligence is a completely different story. We send rudimentary intelligences to space and have racked up billions of miles on them. It seems far more likely that any space faring civilization would look like the following.
1. They would ship the instruction to build life when the reach the destination they are heading too. Machines with error correction seem much more resilient would be much more likely to reach a destination if they had enough energy for the trip so they could refurbish themselves over time.
2. Getting rid of the bodies/life part in the first place. Who cares if it's a million years if you can just pause yourself?
Of course the fact the entire universe isn't filled with Von Neumann probes (at least that we see) points out that this hasn't happened yet.
1) that seems to be a lot harder than it seems. Entropy is a nightmare, and data corruption is a big problem.
And having a general purpose
system capable not only adapting to all the various situations and challenges likely to be faced, that also would have the reserves to deal with them usefully AND reproduce is something we can only hope for in our dreams right now.
And until such a thing exists, it’s only speculation it wouldn’t have similar types of problems, eh?
Humans are the most adaptable and intelligent anything we have yet run across, and we still regularly struggle to solve the problems we run across even in our comfy and well known existing biosphere which is right here, and that we’re quite well adapted to.
And that is assuming a one way trip. Energetically, what could it hope to return to us that would be worth the cost we’d sink into it to try?
Panspermia/species wide genetic reproductive drive, maybe - but then sending a robot doesn’t scratch that itch does it?
2) opportunity cost of time is a thing. Some would argue even that time itself is the most valuable thing we have. Pausing yourself for a million years while your competitors don’t, could be a real problem. Also, think of all the new TV shows you’d miss!
Agree on the von neumann probe problem. The lack of them doesn’t lend credence to it actually being straightforward or even possible solution for sure.
But hey, maybe all the UFO folks are onto something, warp drives/wormholes exist and are cheap, etc.
In which case, disclose it already assholes so we can start doing cool stuff with it!
We're not talking about sending a single person, so I don't know where the solitary confinement comment comes from.
A colonized galaxy will have people mostly living in artificial habitats. A starship of sufficient size is just an artificial habitat moving at high speed.
One would get around the issues you discuss by just sending multiple vehicles. And anyway, this is in rebuttal to the idea that intergalactic colonization is impossible. The onus on that argument is to show it can't work, not argue there are obstacles that would make it uncertain in any particular case.
Your claims that all this is easy and entirely possible - has no evidence, because near as we can tell we haven’t seen anyone visiting us or anywhere we’ve seen with any of these setups. And we haven’t successfully gone even beyond our moon with a manned mission.
I don’t think anyone is claiming intergalactic colonization is impossible.
All I’m saying is it doesn’t seem worth the cost, by any metric we currently have, or
straightforward to actually do, based on our current understanding of physics.
And that there are a lot of real issues with trying to do it that would make it unlikely to succeed if we tried right now, without making it even more costly.
> I don't think anyone is claiming intergalactic colonization is impossible
Let's look at what they actually said:
> Intergalactic travel is borderline impossible barring unknown physics or travel very close to the speed of light.
And I was arguing against that claim, which I believe is clearly spurious. You seem to agree with me on that.
> All I’m saying is it doesn’t seem worth the cost,
I don't see it as fundamentally different from interstellar colonization in that respect. Anyway, lots of things are done for the hell of it, and on the scale of a galactic economy an intergalactic colonization program would be less than pocket change.
Eh, the biggest blocker IMO is far more esoteric. Money.
There is nothing we are aware of that is even close to expensive/worthwhile enough (except perhaps information) to justify the cost in energy to move it that distance. Even if the energy is essentially free.
Do the math - rocket fuel isn’t very expensive in bulk, but even moving ‘free’ gold, platinum, iridium, etc. is not even close to worth it.
And information can be gathered with telescopes or transmitted with lasers or radio at faster speeds, so why bother with the trek?
> Do the math - rocket fuel isn’t very expensive in bulk, but even moving ‘free’ gold, platinum, iridium, etc. is not even close to worth it
What math are you on? The entire reason moving the "free" ore in the asteroid belt to Earth is expensive is propellant. If we had cheap interplanetary transport, it would absolutely make sense to mine and return matter.
Which we don’t. And how do you expect to get it? Especially when the ‘cheap’ part is already too expensive to make it cost effective even within our own neighborhood?
That’s the point!
You might as well complain there is no point in being poor when you could just be rich. Or that I could take all
vacations I wanted if it was free to take vacations. Thanks?
And do the calculations for the energy required. It’s monstrous.
Then think for a moment about all the other things we’d probably prefer to do with such a monstrous amount of energy. That’s the opportunity cost, even if that energy is free.
We’re entirely speculating on that colonization part - we’ve never tried it.
The energy required is utterly trivial compared to the energy available. If you scale up current society to use the entire output of the Sun, the energy cost of interstellar colonization would be (proportionally) less than a Kickstarter project.
And if I had infinite energy, I'd have infinite energy. But we don't, and near as I can tell, it's just a fantasy.
A fantasy that even if it happened, would be competing with other things - like powering future air conditioning, or the equivalent of 3D porn, or solving world hunger, or building more aircraft carriers, or the like.
So will never be free or actually infinite eh? That’s the opportunity cost part of the equation.
It does get down to the central question behind all of this: can we assume growth indefinitely, or at least up to hard limits?
I propose we should, since any subgroup that doesn't grow will be overshadowed by groups that do. If propensity to reproduce has a genetic component it will be selected for.
I think the underlying question is ‘when would such a course of action (interstellar travel) be more preferable than the alternative’.
We could have growth to near infinity and still have interstellar travel be inferior to all our other options, based on our current understanding of physics.
I don't see how that consideration has any relevance. How does preference get enforced across time and space? Your argument seems to be "this outcome will occur because it is preferable" which seems like a canonical example of wishful thinking.
Rather the opposite isn’t it? What you’re saying is ‘regardless of relative benefit or cost, humanity would make the decision to do interstellar travel - because reasons’.
I’m pointing out that relative benefit and cost matter and tend to drive decisions - and that the massive cost with (currently) no plausible benefit which could outweigh it, makes it unlikely we would end up taking that course.
Unless we discover new physics, or new ‘value’ somewhere which would justify it.*
Energetically, for instance, even if we found a planet of pure most expensive thing we can think of (except perhaps for antimatter, though that is a more complicated discussion) just a few light years away, it would never be economic to go get it based on our current understanding of physics.
Even sending a physical probe would be of dubious value, especially considering everyone who would be alive or benefit from anything it could ever provide (including information) would be long dead before we could even find out if it could talk to us over those distances or had arrived.
This is so obvious, btw, that sci-fi writers always have to come up with new physics (or outlandish extrapolations of current thoughts on potential physics - see the Expanse’s Epstein drive, or Star Trek warp tech and subspace communications) for the story to be even a little plausible or interesting. [http://toughsf.blogspot.com/2019/10/the-expanses-epstein-dri...]
And it always has to be a mcguffin, because otherwise the whole story falls apart.
For example, in The Expanse, the Rocinante’s drive would have to output 60+ TW of power for even a moderate burn (2G). Something even the most basic mining rockhopper is supposedly capable of, and folks are regularly shown in poverty type living conditions while being those rock hoppers.
The amount of power produced from just that one engine in that universe in an hour or less would be sufficient to distill enough water, power enough hydroponic grow farms, and synthesize enough chemicals, to feed and hydrate literally hundreds of millions of people. Maybe a billion, if sufficiently efficient.
The United States currently consumes a total of 4 trillion Terawatt hours a year [https://www.eia.gov/energyexplained/electricity/use-of-elect....], and at that engines moderate 60 TW power output level, it would produce energy equivalent to our current entire yearly electrical energy usage every 4 minutes. And they’re shown, in context, doing half that rate as a matter of course for weeks. Even if we converted that to electrical energy in the most absurdly inefficient way possible (boiling water to drive steam turbines), it would produce that degree of electrical power every 15 minutes.
Does the Expanse make any sense at all, if each individual ship is burning more than the energy equivalent of all the clean water, food, drugs, and electrical power the entire Earth needs for a year every single week they operate normally? Or for some of those ships, every minute? Especially when there are shown to be thousands or even hundreds of thousands of such ships operating at once, by a vast array of different powers and interests?
And that Earth, despite having access to all that tech, and building 1000s of those engines (at least), grows crops in open fields and suffers massive famines due to… winter conditions? Due to an asteroid impact? And sometimes just because? And has severe water rationing even for the political elite?
Earth is show to have a pretty dysfunctional (and neglectful) political system, but even they couldn’t pull that degree of insanity off.
And belters worry about using mirrors on Ganymede, when just going to and from Ganymede requires using 4+ orders of magnitude more energy than they would if they used enough grow lights to be getting complaints from Earth about the light pollution.
And a 10,000 year voyage at slow rates to go somewhere that has nothing that justifies the insane cost to do it, with no ability to communicate on timescales equivalent to even the whole of human recorded history, is not a very interesting story. Such a voyage, based on our current track record with technical reliability or social stability is even less likely to succeed.
It’s the economic equivalent of
heating your house by burning shovel fulls of
$100 bills in your fireplace - because you can’t pay your $150/month heating bill.
Even Mr. Musk eventually decided he’d rather buy Twitter than actually try to colonize Mars, yeah? And relatively speaking, Mars is right there and way friendlier and more interesting in every way than interstellar space.
Actual interstellar space travel seems more and more like the equivalent of the 50’s idealism around powering your hairdryer with a micro-nuclear reactor.
* Notably, sometimes ideology and propaganda can push society into doing really weird things. But even the Crusades had a real macroeconomic and sociological basis for why they needed to happen. So maybe at some point, sending politically problematic ‘colonists’ into space to die will be worth the cost. And some might even make it! Eventually. But chances are, we’ll find more cost effective ways to do it.
I mean, that's not a great backup plan. If you're not running a Redundant Array of Independent Planets then you're just one crash away from total data loss.
I mean just looking at the energy expenditure growth rate of Earth, you spend as much energy as kings used to in a day. And there is still an absolutely massive amount of solar energy left to harvest.
I'm highly sceptical of the Fermi paradox being a meaningful paradox at all. I don't think we have nearly enough data to make any conclusion at all about the frequency of intelligent life in our own galaxy, let alone the universe.
We've only started finding exoplanets in the last few decades, and the frequency of exoplanet detection was very low for most of that time and is still growing today.
The ability to learn much of anything about the environments of these planets is even more recent, just a few years since the launch of JWST, and still very limited. It's still only "reliable" for fairly large planets, mostly gas giants. And even for those planets our ability to model the data is an area of active, painstaking research. The number of planets whose atmospheres we have any data-backed information about is very very low.
So it seems like the only real argument for the Fermi paradox(certainly back in the 50s when Fermi proposed it) is that we haven't been visited or received any communication. But even that's worthy of doubt. Indeed, our ability to detect and characterise very small objects in or passing through the solar system is fairly limited even today, and was practically non-existent before. It seems very plausible that alien probes could have visited our solar system many times without us noticing. It could for instance be the case that this is only possible by way of technologies that can't easily decelerate and so they've only passed through. We'd have to be pretty lucky to spot something like that, at the size it would likely be, passing through only for a short time(given the speed it would have to move at).
As for radio signals, the amount of funding that goes into projects like SETI is not exactly earth-shattering and also hasn't been going on for very long. It's a pretty fringe area of research. The amount of interference from earth-based radio sources also makes this research quite difficult.
I'm not some UFO nut, btw. I'm not arguing for conspiracy theories involving the US government, alien abductions, yadda yadda. I'm just asking what do we really know? Not very much, it seems to me.
The Fermi paradox isn't a paradox, it's a strong constraint that models of ET life have to conform to. In particular, models with billions of ET civilizations in the galaxy appear to require strong (and I suggest implausible) assumptions about the unlikelihood of interstellar colonization.
It's also an antidote to baseless presumptions that ETs (or even life of any kind) must be common outside our solar system.
I completely agree. We haven't been looking very long and very hard and we're not even that sure what to look for or where to look. All we can say right now is that we do not see any unambiguous signs of ETI, but space is called space for a reason. We are also searching the vastness of time.
I don't completely dismiss ET-origin UFOs. I don't think there's anywhere near enough evidence to make such a claim as anything more than a hypothesis, but remember that one possible answer to the Fermi paradox is that there isn't one.
> Of course life on Titan is convinced there could never be life here. The third planet is a literal hell where it rains molten dihydrogen monoxide in an atmosphere of corrosive oxygen. Any life there would vaporize and oxidize instantly.
What are some of the chemicals that would vaporize and oxidize instantly in Earth’s atmosphere which this hypothetical Titan life could be made of?
Almost any light hydrocarbon (4 carbons or smaller) vaporizes in the Earths atmosphere. Oxygen is pretty corrosive and we have all sorts of biological systems to slow or prevent this.
Triethylborane −20 °C (−4 °F): It looks like something that you could find in Titan, but I don't remember reading about that. The structure is not so weird, and there are some similar molecules with nitrogen instead of boron. I don't remember massive natural production of organic molecules with boron, but boron chemistry is very weird and well above my chemistry level.
Silane 21 °C (70 °F): It would be more strange to have too many organic molecules with silicon.
Phosphorus (white) 34 °C (93 °F): I don't think it's stable enough to be acumulated naturay. It's too energetic and I expect it to react with some of the molecules in Titan.
I'm not sure if this is what you meant, but the concept of an alien species with a totally different subjective perception of time would be interesting. As in all of our actions/movements/speech would be experienced as being on e.g. 10x fast forward to them, or vice versa.
The rest of the story, including almost the whole history of cheela civilization, spans from 22 May 2050 to 21 June 2050. By humans' standards, a "day" on Dragon's Egg is about 0.2 seconds, and a typical cheela's lifetime is about 40 minutes.
The most informative sentence was down towards bottom of page:
> The team mapped the shorelines of each Titan sea using Cassini's radar images, and then applied their modeling to each of the sea's shorelines to see which erosion mechanism best explained their shape.
(I feel like phys.org is repeatedly disappointing in reward-to-time relative to their headlines.)
Thats why Dr. Manhattan is my favorite superhero; he can appear anywhere he wants in the universe and observe the glorious interactions without any harm to him. What a grand universe and how little we can observe with our mortal eyes!
Liquid hydrocarbons? You'll sink like a brick. I don't know exactly what methane and ethane do at minus whatever but the density is at least 30% lower than water...
So nothing you could swim in, but it would be relatively easy to build a boat.
Hmm, come to think of it: Titan's gravity is 0.138 g. So you might be able to stay afloat in liquid methane by actively swimming upwards, even if you can't float.
Similar to how birds stay afloat in the air, despite being heavier than air.
You could perhaps build them out of ethanol or so?
Basically, you wouldn't want to build them out of materials that are useful at human room temperature, but you could perhaps build them out of materials that are liquid or even a gas on earth, but solid at Titan's temperatures. (No clue whether ethanol would be good, it solidifies at -114.1C, but I have no clue what kind of solid it would be.)
Stephen Baxter's SF nivel 'Titan' [0] has some astronauts build a sort of boat on Titan but the generally depressing story otherwise lacks any surfer vibes.
Well that’s depressing beyond belief. I don’t even have words for how sad the novel sounds. I think the best thing I can leave is “war pigs” by Black Sabbath
War pigs is positively cheerful compared with Titan! At least Titan sort-of avoided another Stephen Baxter trope that annoyed me when it kept appearing: how humanity's first star ship, last-chance rescue ark, etc always somehow gets taken over by a gang of lowlife characters who were included for bizarre plot reasons / sneaked onboard at the last minute / etc. Although in Titan, instead of stowaways, madness due to increased radiation exposure turns one of the crew into the deranged psycho who has to be managed by the others.
Many of his books also include a disgruntled ex-astronaut partnered with some all-knowing alien / robot / immortal / etc that provides exposition / info dumps as required when Baxter decides to 'tell' rather than 'show'.
https://en.wikipedia.org/wiki/Dragonfly_(Titan_space_probe)