Ice Volcanoes on Ceres May Provide Replicators Means of Spreading

Extraterrestrial replicators (be they naturally-evolved, or von Neumann probes or the mutant descendants thereof) are at least as likely to be based on organic chemistry as on clanking iron-age technology, as is often imagined. Material returned from comet Wild-2 showed that it was actually an extraterrestrial comet, and had amino acids on it. Other investigations have shown the presence of nucleobases (the components of DNA and RNA.)

Even Arrhenius-style "panspermia" spread by passive diffusion on astronomical timescales is not implausible, as our Oort Cloud has mixed with close-passing stars' clouds on the order of once every 0.1 MA (and we should assume this happens to other stars as well.) However, for passively spreading replicators, higher-gravity bodies like planets or large moons are dead ends because they have no means of escaping the gravity well.



Water geysers on Enceladus, from space.com
This is why comets and wet carbonaceous asteroids are the best places to look, and why the Hayabusa-2 probe on Ryugu is so important. Same for the Dawn probe. Europa and even Enceladus may be a tough sell as passively escapable gravity wells, but now we see evidence of active water volcanoes on Ceres through its life span.

The Fermi Paradox Thickens: More on Colonization Times for Von Neumann Probes

In a previous post I discussed the possibilities of replicators being aided in their diffusion between star systems by close passes; I also pointed to an interesting paper by Forgan et al looking at projected travel times of interstellar probes, based on powered vs. gravity-assist travel. A new paper (on which Forgan is the senior author) looks again at this problem using a Monte Carlo simulation approach, and gets an interesting but as always frustrating answer.

First, the paper would be valuable if all it contained was the excellent review of prior work done on this NP-hard version of the traveling salesman problem. (You think planning your road trip taxes a server?) In particular, they point to a prior paper arguing that von Neumann probe expansions could be slowed or stopped by mutant probes where a predator-prey dynamic evolves in the population and the probes hunt themselves to extinction. I had previously written about self-replicating probes becoming cancerous (a statistically more likely outcome) and turning to expansion above any other mission they previously had; but this only makes the Fermi Paradox more vexing rather than solving it.

Their approach was to simulate the galaxy as having 1 star per cubic parsec (so no local "backwaters"), with self-replicating probes moving at approximately the speed of Voyager I, 1000 m/s. They then compared replicating and non-replicating probes; not surprisingly, self-replicators were much much faster, exploring 100% of a box of 100,000 stars in at most 30 million years. In the replicator condition, the number of probes is no longer the constraint, and contact can occur in (possibly massive) parallel rather than serially. Of note: the authors also include a requirement for communication of which stars have already been explored, although if we assume a robustly replicating probe, this is unnecessary. ("Robust" means that the time and ability to replicate enough probes to successfully reach the neighboring stars are small relative to travel time.)

The authors correctly note that this short time frame makes the Fermi Paradox more vexing. So the alternatives with respect to self-replicating probes are:

1. They're here and we haven't found or noticed them yet.

2. They're not here, because
2a. Replicating probes are not possible or not effective (they can't be made at all, or they mutate)
2b. intelligence capable and willing to build such probes appears more rarely than once every 30 million years in a volume of 100,000 stars (they choose not to, or they don't evolve in the first place, or they wipe themselves out before they create them)

2a seems unlikely because we already know that replicators can develop through natural selection. This leaves us with 1 and 2b. It is certain that we have only the barest knowledge of the rest of our solar system, and gravity wells are expensive to get out of. My prediction is that we'll find evidence of such probes on low gravity bodies (asteroids, comets, small moons) as we continue to explore, but that once we find something strange, it will take time for us to understand what we're looking at.

Hat tip to Ben Weaver.

Asteroid Mining and Detecting Others' von Neumann Probes

With the announcement of "firefly", 3D-printing spacecraft to mine asteroids, we're getting closer to exploring space with multiple smaller craft, as well as more immediately economically rewarding activities, which is what will drive space exploration faster.



Of course it's also exciting because I think exploration of low-gravity bodies will give us more information about life elsewhere in the universe than we expect it to. While reasoning about extraterrestrial life invariably means making assumptions we don't even know we're making, based on what we know about the evolution of life on Earth and the number of planets in the rest of the universe, the development of some kind of replicators outside the solar system seems overwhelmingly likely. If we think at least partly self-reproducing probes are possible - and notice above that investors right here on 2013 Earth are trying to convince people they are - then we might be better off trying to get information about extraterrestrial life from artifacts already here in the solar system than from signals.

It is also likely that lower gravity bodies are better for any entity that wants to continue spreading, since gravity wells are energetically expensive to get in and out of. If you can get matter without descending onto a high gravity surface, you should. (Yes, "but what if aliens have antigravity" - but if we're going to bother thinking about it, we have to make guesses with what we know now. Otherwise maybe they'll ride unicorns. More seriously, if they don't care about gravity, why would they waste time with small gravity bodies like Earth? Mine the cores of gas giants. Hide just outside event horizons to evade detection.)

I've given previously in detail my arguments for why these artifacts might already be here, and where we might look. Comets and asteroids was the answer, so of course I'm excited that these mining probes may explore a number of asteroids during my lifetime. If there's something obvious, excellent (and frightening).

If they don't find anything it could mean:

1. There's really nothing there to find. Intelligent life is much rarer than we think. Replicator chemistry is either not as inevitable as it seems, or there's a Great Filter between algae and interstellar expansion, or life is just rare enough that we're isolated.

OR

2. Something is there to find, but we don't notice it at first.

Because we're looking for something alien - something completely outside our experience - it's hard to say what a gas chromatograph of chewed-up alien von Neumann probe chemistry would look like. (This is why I hope full rocks are towed back, so we can have people in Earth orbit doing real chemistry on them.)

So how to distinguish 1 from 2? Keep looking, and follow up any interesting chemistry we find, "interesting" meaning any low-entropy repeating patterns, either temporally or spatially, on low-gravity bodies. I very much doubt we're going to find a metal ship crouching amidst a flying rubble pile. I do think we'll find strange chemistry that's worth looking into, at least insofar as it's relevant to the origin of life on Earth, and at least with comets that's no longer controversial. I haven't yet seen a model which examines what fraction of asteroids we would expect to be colonized by theoretical replicators, so I'm not sure at what rate I should de-weight my expectation of finding alien artifacts on asteroids, as more asteroids are mined without the merest

Dawn Spacecraft Arrives at Vesta

The Dawn spacecraft is in orbit around Vesta as I type. Of the two bodies Dawn will explore, Vesta is the more boring in terms of possibilities for organic chemistry, since it's drier. For Ceres, McCord and Sotin estimate a water contentof 17-27% by mass. This means Ceres actually has more water than Earth's oceans. Of course much of this will be present in minerals and not sloshing around loose, but that's still a much bigger reaction vessel than Urey and Miller had. In fact, if we think water-mineral interface is what matters, which is what underlies the assumption that Earth's first RNA replicators appeared in shallow warm pools where they had surfaces onto which they could be immobilized for more reactions, then most of the volume of early Earth's deep seas could have been an organic chemistry desert, by comparion to Ceres.

Unfortunately we won't know, because Dawn only has EM detectors. My wish for a landing or at least a gas chromatograph on board Dawn stems from my argument that it's exactly on small wet bodies like Ceres that we should expect to find evidence of von Neumann probes, or their descendants.


Above: gas chromatogram of amino acids found in the Murchison meteorite. The organic chemistry of small bodies, even including nucleic acid bases as in the Murchison meteorite">this paper, is usually discussed in the context of being a possible source of early replicator chemistry on Earth; this is not mutually exclusive with these materials being von Neumann probes, mutant or otherwise. Figure from Engel MH and Macko SA, Nature 389, 265-268(18 September 1997).

Both Vesta and Ceres are big enough that you can't reach escape velocity just by running (Vesta's escape velocity is a little less than a jet's at cruising altitude, and for Ceres it's a little more than Mach 1); so they still aren't trivial gravity wells (a criterion for being a good place for replicator activity). However, it looks like water vapor has already been observed escaping Ceres, a necessary step in the spread of an organic-molecule model of von Neumann probes. But I hope that Vesta surprises us, because we have to wait until February 2015 for Dawn's efficient but not-flashy ion thrusters to get it there.


Dawn's launch.

What would be really ironic is if we didn't find anything until we towed a smaller asteroid back to Earth orbit for mining.

Manned Exploration of Asteroids

The U.S. President has announced his plan to have American astronauts "land" on an asteroid by 2025. This is cool for several reasons:

1) It means that rule-makers are finally taking seriously the idea of asteroid defense.

2) If space exploration is going to continue it must become sustainable; that is, materially profitable. The most expensive thing about space travel is getting out of gravity wells. Raw material from small bodies, i.e. that's already in microgravity is therefore orders of magnitude cheaper than material that has to be brought up. (First organization who can make a self-printing 3D printer mostly out of materials to be found in asteroids wins. Template information up by sat phone, finished products down by parachute.) Asteroids are better candidates than comets because objects in stable, closer orbits are slower than objects that fall in from far away and whip around the sun in a matter of days.

3) We'll get a more in-depth look at an asteroid, and we'll find evidence of alien life. Leaping to conclusions there? I've written before that I think that we can't rule out von Neumann probes or replicating non-terrestrial entities of some kind in our own solar system, and that we haven't seen them yet because we're looking in the wrong places. (This probably also qualifies as one of my most absurd beliefs.) Interestingly, one of the greatest science fiction series of all time begins with an astronaut planting a nuclear bomb on an asteroid, and in the process discovering our first evidence of alien life. I don't think we'll be finding any doorways carved into canyons as in this novel, but I do think we'll find the kind of highly monodisperse heteropolymers - with nitrogen isotope ratio suggesting an extrasolar origin - that are an unmistakable sign of high-fidelity replication systems.

In other impactor-related news, I'm planning a trip to Siberia and Central Asia and I was trying to get to the Tunguska site. But it's way off the Siberian railroad and really hard to get to (a week out of my itinerary?) and Black Oil Aliens notwithstanding, there's nothing obviously special about the site; i.e. you want a crater, go see Winslow, and it's fifteen minutes off I-40 east of Flagstaff. I would still love to go - so, if you happen to have seen this on your Google News feed for Tunguska, and you're looking for someone to collect samples from the site but can't find any hearty risk-takers, why not let a hard-working medical student help you out by funding my extra week to get out there and get your work done for you!