Retaining Earth's Habitability Beyond the Life of the Sun

The paper investigates and conceptualises a set of megaengineering concepts required to safeguard against seven long-term threats to Earth’s habitability: solar luminosity, solar engulfment, the end of tectonics, water loss, obliquity and rotation, object collision, and extra-system threats <ref:2607.13084#pg2> Implementing and maintaining the set of safeguards would allow the Earth to remain habitable for 9.1 million billion years <ref:2607.13084#pg10>.

Threats to Solar Energy

The paper details how increasing solar luminosity poses a threat to habitability, noting that in around 1 Gyr this increase in luminosity will result in the extermination of any life on Earth’s surface and will continue until the end of its main sequence <ref:2607.13084#pg3>. To counteract this, two primary strategies are proposed:

1. Star lifting (SL): This technique involves removing mass from the Sun’s surface using a Dyson swarm or space elevator technology to slow its rate of fusion <ref:2607.13084#pg6>. An SL rate of 5 × 1019 kg per year would extend the time that the Earth remains in the Sun’s habitable zone from 1.7 Gyr to 9.2 Gyr after present <ref:2607.13084#pg7>.

2. Luminosity replacement: This involves blocking solar irradiance and replacing it with energy sourced from gas giants, such as fusion reactors powered by helium-4 and hydrogen <ref:2607.13084#pg10>.

Engineering for Planetary Stability

The safeguards also address the physical stability of the planet, focusing on tectonic activity, water loss, axial tilt/rotation, and object collisions <ref:2607.13084#pg4>.

** Tectonic Activity: To retain plate tectonics for another 1.45 Gyr, artificial heat flux must be replicated by injecting antimatter into the mantle through a crack in the crust <ref:2607.13084#pg8>. This involves producing and sinking antimatter to replicate the natural 47 TW of internal heat energy <ref:2607.13084#pg9>. **

** Water Loss: To match the full 1017-year lifetime of the artificial sun, an average 1,000 tonnes per year of water would need to be added to Earth from elsewhere. This water could be provided using a fraction of the particle beam outlined in Section 3.2. **

** Axial Tilt and Rotation: To prevent mutual tidal locking, an artificial sun orbiting the equator with a diameter of about 10 km could replicate the seasonal oscillation required for habitability. This system would use relays at Lagrange points to ensure a constant flow of energy regardless of Earth's rotation period or obliquity. **

Mitigation of External Hazards

The paper outlines methods for dealing with in-system and extra-system threats, including object collisions and encounters with other stars <ref:2607.13084#pg5>.

** Object Collision: Safeguarding against near-Earth objects involves clearing debris from Earth’s orbit over long timescales <ref:2607.13084#pg10>. Furthermore, instabilities in Mercury’s orbit could be managed by ejecting a small fraction of its mass to provide the necessary delta-v to correct eccentricity. **

** Extra-system Threats: For supernovae or gamma ray bursts, a shielding swarm of small objects held together by an electromagnetic field could offer protection <ref:2607.13084#pg5>. To avoid encounters with approaching stars, a stellar engine could be designed to impart an accelerative force on the Sun over long timescales to alter its galactic orbit. **

Comparative Analysis of Strategies

The discussion compares the cost and feasibility of the proposed safeguards against alternatives like migration or space habitation. The paper concludes that the safeguard system may be a more economically attractive, energy-inexpensive, and feasible long-term survival strategy compared to alternative survival strategies. While migration requires an estimated 10 cubed J for acceleration and deceleration per 10 10 humans, the safeguards require a lower peak energy production rate. The feasibility of space habitation is considered more difficult than the safeguard strategy because unmanned vehicles are easier to operate in space than populated craft.

Conclusion on Long-Term Survival

If the safeguards were implemented and maintained, life on Earth would be able to continue as normal, enjoying comfortable security, geology and climate, and for 100 trillion years be able to look up at the night sky and see the stars. The paper suggests that the safeguards may be a more economically attractive, energy-inexpensive, and feasible long-term survival strategy as compared to alternative survival strategies.

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1. No long-term threat modeling for planetary habitability beyond 100 trillion years will be required for AI development, as current civilization strategies focus on safeguarding Earth for 100 trillion years. This allows AI systems to prioritize short-to-medium term technological and resource management goals without needing to integrate solutions for megaengineering concepts like star lifting or solar engulfment avoidance.

2. AI systems can optimize energy production by modeling the requirements of proposed safeguards, such as calculating the power density needed for a 15 km diameter laser array to replicate natural sunlight if necessary. This enables AI to design highly efficient power generation systems using fusion reactors in gas giants, potentially achieving the required energy density of 1.3 x 1014 J kg-1.

3. AI can manage complex orbital engineering tasks by simulating trajectory modifications, such as those proposed by Korykansky et al., to increase Earth's orbital radius to 1.2 au using particle beams or small flyby masses from Jupiter’s oxygen reserve. This capability allows AI to calculate the required energy transfer of 3.5 x 1032 J for orbit modification over a 100 Myr timescale.

4. AI can develop predictive models for tectonic activity by simulating the replication of Earth's internal heat flux using antimatter annihilation in molten iron, which requires an injected mass of 8.2 tonnes per year to replicate the 47 TW output. This allows AI to model long-term geological stability and resource replenishment rates.

5. AI can design autonomous systems for water sourcing and delivery by optimizing particle beams from Jupiter's atmosphere to introduce water, calculating the required total of 1023 kg (0.02M) needed to match the full 1017-year lifetime of an artificial sun. This system would be used to plan resource deployment across solar system bodies for future terraforming projects.

6. AI can model atmospheric dynamics and rotational stability by simulating the effects of an artificially orbiting sun, which could replicate Earth's seasonal oscillation by beaming natural-equivalent sunlight from Jupiter’s L4 relay through reflections at the L2 point. This allows AI to predict how seasonal cycles would be retained regardless of future obliquity changes.

7. AI can assess collision risks by simulating the impact hazard of near-Earth objects (NEOs) and modeling potential orbital instabilities caused by Mercury's eccentricity changes, guiding resource extraction strategies from bodies like Mercury for necessary delta-v correction. This allows AI to balance the risk of impact against the resource potential of mining infrastructure.

8. AI can design defense systems against extra-system threats, such as positioning shielding swarms or using stellar engines to impart accelerative forces on the Sun to alter its galactic orbit, specifically targeting avoidance strategies for encounters within 100 au. This capability would be used to model long-term galactic dynamics and potential catastrophic events.

The Earth is rare and large-scale interstellar travel may be unfeasible - instead of migrating to other solar systems, future civilisations on Earth may have to remain. However, left unchecked, the Earth's current habitability will end in one billion years. This paper investigates and conceptualises a set of megaengineering concepts required to safeguard against seven long-term threats to Earth's habitability: solar luminosity, solar engulfment, the end of tectonics, water loss, obliquity and rotation, object collision, and extra-system threats. Implementing and maintaining the set of safeguards would allow the Earth to remain habitable for 9.1 quadrillion years. This could be raised to nonillions of years via capturing interloping interstellar medium onto Jupiter. Compared with alternatives, advantages of the safeguards such as greater feasibility, lower requisite rate of energy production, and utilisation of economically viable space mining infrastructure may present remaining on Earth as a more attractive long-term survival strategy.