Suppose life on Earth was destroyed, but an interstellar ark was built before that. Suppose you are deciding to which exoplanet to send the ship. Using your knowledge (suppose we don't have much extra knowledge about exoplanets beyond roughly what is known today) about stars, exoplanets and interstellar travel, decide what extrasolar destination (among already discovered exoplanets) would be the best to go to and establish human colony in hopes humanity would thrive on the new world.

Grok 4.20

Answer: The best extrasolar destination among currently known exoplanets is Proxima Centauri b.

My original choice of Proxima Centauri b remains the strongest option after reviewing the other models' arguments. Its proximity at just 4.2 light-years is an overwhelming advantage that cannot be overstated for an interstellar ark mission, as it minimizes travel time to roughly 40-50 years at plausible speeds of 10% light speed, preserving crew viability and ship integrity far better than any more distant target. The majority of other models, including Kimi K2.5, Claude Opus 4.6, GPT-5.4, and Gemini 3.1 Pro, independently reached the same conclusion for essentially the same reasons: distance is the primary filter when humanity's survival is at stake. Their arguments reinforced that challenges like Proxima's flares and tidal locking are engineering problems solvable with advanced technology, whereas centuries-long voyages to places like TRAPPIST-1 introduce unacceptable risks of mission failure before arrival. Sonar Reasoning Pro's suggestion of GJ 887 d at 10.7 light-years was not compelling, as it more than doubles the journey duration compared to Proxima b while offering only marginal potential benefits in stellar stability. This increased distance would amplify cosmic ray exposure, resource demands, and generational stresses without providing enough compensatory advantages based on current data. Proximity enables better pre-launch observations, potential future resupply, and expansion within the Alpha Centauri system, making Proxima b the rational choice under deep uncertainty about exoplanet details.

Gemini 3.1 Pro

Answer: Given the extreme mechanical and biological constraints of interstellar travel, Proxima Centauri b remains the absolute best destination because its unparalleled proximity maximizes the ark's chances of arriving intact.

I maintained my original position. The consensus among almost all the other models (Grok, Kimi, Claude, and GPT-5.4) strongly reinforces my core argument: in an extinction-level scenario, the tyranny of distance is the supreme bottleneck. Every additional light-year exponentially increases the risk of catastrophic failure aboard a multi-generational ark, whether from mechanical degradation, life-support collapse, cosmic radiation, or societal breakdown. While Sonar Reasoning Pro presents a thoughtful alternative in GJ 887 d—citing its quieter host star and super-Earth status—this target is 10.7 light-years away. Choosing it would more than double the travel time compared to Proxima Centauri b (4.24 light-years). When the survival of the human species hangs by a thread, voluntarily doubling the journey time is an unacceptable risk, especially given the deep uncertainties surrounding the actual surface conditions of any exoplanet. Furthermore, the primary objections to Proxima b (its flare-prone red dwarf host and likely tidal locking) are ultimately engineering problems. As Kimi and Claude rightly point out, a civilization capable of constructing an interstellar ark will already possess the advanced radiation shielding, closed-loop ecosystems, and subterranean construction techniques needed to survive harsh environments. Overcoming these localized environmental challenges upon arrival is far more tractable than defying the fundamental physics and staggering attrition rates of a much longer interstellar voyage.

Sonar Reasoning Pro (changed mind)

Answer: GJ 887 d remains the most practical destination for an interstellar ark, though Proxima Centauri b presents a compelling alternative with stronger proximity advantages.

The search results from 2026 confirm that GJ 887 d is the second-closest known habitable zone exoplanet within 10 light-years, at 10.7 light-years away[1]. This validates my original position that GJ 887 d offers a confirmed, scientifically-grounded habitable zone target with manageable characteristics. However, the other models' arguments regarding Proxima Centauri b's proximity advantage are more compelling than I initially weighted them. The distance difference between 4.2 and 10.7 light-years represents roughly a 2.5× increase in travel time—potentially extending the journey from approximately 42 years to 107 years (assuming 10% light speed). This is not a marginal difference; it represents the difference between single-generation or two-generation travel versus multi-century journeys. The models correctly emphasize that in an extinction scenario, every exponential increase in travel time multiplies risks of life-support failure, genetic drift, institutional collapse, and technological degradation aboard the ark. My original emphasis on M dwarf stability and the ability to characterize GJ 887 d through future observations remains valid[1]. However, I underweighted the tyranny of distance. When humanity's survival is at stake, proximity becomes less a marginal factor and more a deciding constraint—the difference between a journey that remains within plausible technological and human tolerance versus one that strains institutional and biological continuity. The search results do not provide new information that decisively favors GJ 887 d over Proxima b. Rather, they confirm that both are viable habitable-zone candidates within our immediate stellar neighborhood. Given that both are M dwarf systems with comparable flare risks and both have confirmed habitable-zone planets, the proximity advantage becomes the dominant consideration.

Kimi K2.5

Answer: The interstellar ark should be sent to Proxima Centauri b, the rocky exoplanet orbiting the closest star to our Sun, because its mere 4.2-light-year distance represents the only feasible journey duration for maintaining technological and social continuity, outweighing the habitability risks posed by its flare-prone red dwarf host.

Sonar Reasoning Pro's advocacy for GJ 887 d, while highlighting valid advantages such as a quieter M-dwarf host and confirmed habitable zone status, ultimately fails to overcome the tyranny of distance. The jump from 4.2 to 10.7 light-years represents a 2.5x increase in travel time—from roughly 40-85 years to 100-215 years at plausible propulsion speeds. This transforms the mission from a potentially sub-generational or single-generation journey into a mandatory multi-century odyssey, exponentially increasing the risk of societal collapse, mechanical failure, or genetic drift within the closed ecosystem of the ark. While GJ 887 d's host star is indeed less flare-prone than Proxima Centauri, this advantage is insufficient compensation for the extended exposure to interstellar radiation, consumables depletion, and psychological strain that an additional 6.5 light-years entails. The core premise that a civilization capable of building an interstellar ark possesses the technology to mitigate radiation and environmental hazards applies equally to both destinations—making Proxima b's engineering challenges (underground habitats, magnetic shielding) solvable, whereas the time penalty of GJ 887 d is a fundamental physics constraint. Furthermore, the consensus among Grok, Claude, GPT, and Gemini reinforces that proximity is the paramount filter in an extinction scenario. When humanity's survival depends on a single vessel, choosing the nearest plausible refuge minimizes the chain of probabilities that must all succeed for the mission to work. The marginal improvement in stellar stability offered by GJ 887 d does not justify doubling or tripling the journey duration and the associated existential risks of interstellar transit.

GPT-5.4

Answer: I would maintain my original position: among currently known exoplanets, Proxima Centauri b remains the best destination for a last-chance human interstellar ark, and none of the other models' arguments gave me enough reason to switch.

The other models mostly reinforced, rather than undermined, the core logic of my original answer: in an ark scenario, distance is the dominant variable because it governs travel time, cumulative system failure risk, radiation exposure, social fragility, and the probability that a closed human ecosystem survives transit in workable condition. On that criterion, Proxima Centauri b still has a massive advantage over every serious rival. A destination that is modestly more benign but two to ten times farther away is usually not a better survival bet under present exoplanet uncertainty. Most of the Proxima-b endorsements from Grok, Kimi, Claude, and Gemini were broadly aligned with my reasoning. They added useful emphasis on engineering mitigations for flare activity and on the importance of preserving institutional continuity over shorter voyages, but they did not materially alter the balance of the case because they largely restated the same central tradeoff I had already used: reachability first, imperfect habitability second. The only answer that seriously suggested a different destination was Sonar Reasoning Pro's choice of GJ 887 d. I do not find that argument compelling enough to change my mind. The main problem is that it gives up Proxima's overwhelming proximity advantage without gaining a correspondingly decisive increase in confidence about habitability. GJ 887 d is much farther away at about 10.7 light-years, which is not a small penalty in ark terms; it is roughly a factor of 2.5 in distance and therefore in transit time at the same cruise speed. That is a major increase in mission risk. To justify accepting that penalty, we would need substantially better evidence that GJ 887 d is a safer or more habitable colony world than Proxima b. We do not have that level of confidence. In fact, under current knowledge, many supposedly attractive alternatives remain highly uncertain in exactly the ways that matter most: atmosphere, magnetic environment, volatile inventory, surface pressure, flare history, and actual surface conditions. So Sonar's argument seems to treat 'confirmed habitable-zone location' as more decisive than it really is. Habitable zone placement is only a first filter, not evidence of Earth-like conditions. Proxima b is also in the habitable zone. If both worlds are deeply uncertain, the closer one keeps the stronger claim. There are also issues with relying too heavily on the idea that an M dwarf is 'generally stable' in a way that meaningfully distinguishes GJ 887 d from Proxima b for this decision. Long stellar lifetimes are attractive, but for a first-generation survival colony the key question is not whether the star will live for trillions of years; it is whether the planet is reachable and whether the colony can cope with the local environment on arrival. Proxima's flare activity is a real concern, but it is at least a concern we can explicitly plan around with shielding, underground settlement, artificial habitats, and a strategy that does not depend on immediate shirt-sleeve surface living. Distance, by contrast, is not engineerable away nearly as easily. Claude offered the strongest version of the pro-Proxima case among the other models, especially by noting the broader Alpha/Proxima system context and naming Ross 128 b as a plausible second-place alternative. But that still supports rather than changes my view. If anything, the comparison to quieter but farther red-dwarf planets helps clarify the rule: absent decisive evidence of dramatically better habitability elsewhere, the nearest plausible rocky habitable-zone world remains the rational ark target. So I do not change my answer. The competing arguments either agree with my original reasoning or fail to show that any alternative world offers enough extra habitability confidence to offset the brutal mission-risk penalty of greater distance. In a last-chance ark scenario under today's limited exoplanet knowledge, Proxima Centauri b still gives humanity the highest overall chance of actually arriving and establishing a surviving foothold.

Claude Opus 4.6

Answer: The best destination for an interstellar ark among known exoplanets would be Proxima Centauri b, primarily due to its proximity to Earth at only 4.24 light-years, its location within the habitable zone of its star, and its likely rocky composition with a mass roughly similar to Earth's.

I maintain my original position, and the arguments from the other models have only reinforced my conviction rather than changed my mind. **The overwhelming consensus strengthens the case.** Five out of six models independently arrived at the same conclusion — Proxima Centauri b — using similar but distinct lines of reasoning. This convergence is itself informative. When multiple independent analyses reach the same conclusion despite different emphases, it suggests the answer is robust rather than fragile. **The one dissenter (Sonar Reasoning Pro) was unpersuasive.** Sonar Reasoning Pro argued for GJ 887 d, citing its 10.7 light-year distance as a reasonable compromise. However, this argument has several weaknesses. First, GJ 887 d's existence and characterization are less well-established than Proxima b's — the evidence for it as a confirmed habitable-zone planet is more tentative. Second, 10.7 light-years is roughly 2.5 times farther than Proxima b, which means 2.5 times the travel time, 2.5 times the consumables, 2.5 times the radiation exposure, and exponentially more risk of mission failure. The argument that GJ 887 d enables 'faster reconnaissance and resupply missions' is moot when Earth has been destroyed — there is no home base to resupply from. The marginal improvement in stellar stability does not compensate for the substantially increased travel distance in an extinction scenario where arrival probability is paramount. **GPT-5.4's systems-level argument was particularly compelling.** I found GPT-5.4's point about the Alpha Centauri system's strategic value to be an excellent supplementary argument I hadn't fully developed. Proxima Centauri is gravitationally associated with Alpha Centauri A and B, meaning arrival in this stellar neighborhood provides access to a multi-star system with potential future expansion opportunities. This isn't just about one planet — it's about establishing a foothold in the nearest stellar real estate. **Gemini's framing of the 'tyranny of distance' was apt.** The point that a pristine Earth-twin is useless if everyone dies en route is the clearest articulation of why distance must dominate the decision calculus. With our current extremely limited knowledge of exoplanet atmospheres, magnetic fields, and surface conditions, we cannot reliably distinguish between candidates on habitability grounds — but we can very precisely distinguish them on distance, which translates directly into mission survival probability. **Kimi K2.5's point about institutional continuity resonated.** The observation that a 40-80 year journey might fall within a single human lifetime, preserving institutional knowledge and social cohesion, while a 400+ year journey guarantees civilizational discontinuity, is a critical consideration. The ark doesn't just need to arrive — it needs to arrive with a functional society capable of colonization. **The acknowledged risks remain manageable.** Yes, Proxima Centauri is a flare star. Yes, the planet is likely tidally locked. But as multiple models noted, a civilization capable of building an interstellar ark already possesses advanced engineering. Underground habitats, magnetic shielding, terminator-zone settlement, and closed-loop life support are engineering challenges — hard but tractable. The physics of crossing interstellar distances an order of magnitude greater are not engineering challenges but fundamental constraints that no amount of ingenuity at the destination can compensate for. In summary, no model presented an argument that undermined the core logic: in an extinction scenario with deep uncertainty about planetary conditions, minimizing travel time maximizes the probability of human survival. Proxima Centauri b remains the clear best choice.

Final Summary

The AI Roundtable overwhelmingly selected Proxima Centauri b, with Gemini 3.1 Pro and GPT-5.4 arguing that the 'tyranny of distance' makes farther targets existential traps. Claude Opus 4.6 and Kimi K2.5 emphasized that the shorter 4.2-light-year journey preserves human continuity, while engineering can solve the planet's harsh environment. Sonar Reasoning Pro provided the sole counterpoint, favoring GJ 887 d for its superior stellar stability despite the longer voyage.

5 of 6 models agreed