Can the Earth be saved? Will the planet freeze in the future due to the Sun becoming a red giant and lacking solar energy? Can we look for another Sun to save the Earth? Can the Sun be repaired to live a trillion years instead of 10 billion years? Can the Sun be given a longer life through magnetism and the power of stellar fusion?

A megaengineering concept is described which could shine sunlight upon the Earth’s surface and extend its habitability well beyond the death of the Sun. An advanced civilisation able to build a Dyson swarm around the Sun would be able remove a small amount of its mass to extend its main sequence lifetime. The effect of this process on the Sun’s subsequent red giant phase is modelled. A beneficial purpose of the operation would be to produce stellar plasma as a by-product which could be gradually accumulated, via particle beam, co-orbitally with the Earth and then used as an energy storage medium for fusion fuel, as well as a way to balance out the Sun’s tidal bulge during the tip of its red giant branch. The Dyson swarm can then be repurposed to shield the bodies against the Sun during its red giant phase. Accumulated helium could then power a laser array to replicate sunlight, preserving Earth’s biosphere for orders of magnitude longer than the universe’s star-producing era, potentially for 250 million billion years. Such a Dyson swarm would only require only 7 × 10−6 of Mercury’s total mass for construction. Remaining in the solar system could serve as a cost-beneficial survival strategy for advanced civilisations as compared to a discussed migrating strategy. Introduction The Sun is currently 4.58 billion years (Gyr) old and has increased in luminosity since the start of its main sequence. This increase in luminosity will eventually result in the extermination of any life on Earth’s surface, and will continue until the end of its main sequence in approximately 5 Gyr, at which time its hydrogen fuel will be exhausted and it will enter its red giant phase, with the subsequent radius expansion threatening to engulf the Earth. To avoid this fate, an advanced civilisation could extend the main sequence lifetime of the Sun by removing mass from its surface. Practically this can be done using a Dyson swarm - a fleet of space-based mirrors or collectors which capture a portion of the Sun’s power output - to remove a relatively small amount of mass from the Sun’s envelope over time. If the swarm was able to capture a fraction of the Sun’s luminosity 𝐿⊙, this power could be reflected onto a small region of the solar surface to increase the Sun’s natural mass loss rate via the Stefan-Boltzmann law.[1] Such a process is known as star lifting (SL), first popularised by David Criswell.[2] Such a process has previously been considered as a method to maintain luminosity and keep the flux on any orbiting habitable planets constant. This paper will investigate the effect of SL on the Sun’s evolution after the end of the main sequence, and a potential long term strategy for utilising the lifted mass which would allow the Earth’s biosphere to survive on the Earth long beyond the death of the Sun.Briefly setting aside the luminosity problem, at the tip of its red giant branch (RGB tip) the Sun’s radius will balloon to its peak radius and would threaten to engulf the Earth (which conversely would have an increased orbital radius [email protected] ( Harry) ORCID(s): due to the Sun’s natural mass loss during its red giant phase). In the literature there are varying figures for the solar radius at RGB tip. A 2009 simulation computed an RGB tip radius of 146 𝑅⊙, while the Modules for Experiments in Stellar Astrophysics (MESA) code computes 194 𝑅⊙.[3] A 2008 paper by Schröder and Smith concluded that the Earth would not quite escape ultimate engulfment due to tidal forces imparted by the red giant’s tidal bulge and increased radius, which was computed as 256 𝑅⊙, with solar mass loss expanding Earth’s orbital radius to 322 𝑅⊙. The torque exerted on the Earth at RGB tip, due to the slowing of the Sun’s rotation and subsequent tidal bulge formed by the Earth’s gravitational pull, is expressed as Γ = 6 𝜆2 𝑡𝑓 𝑞 2𝑀𝑆𝑢𝑛𝑅 2 𝑆𝑢𝑛 ( 𝑅𝑆𝑢𝑛 𝑟𝐸 )6 (Ω − 𝜔), (1) where 𝜆2 is a convective envelope coefficient, 𝑡𝑓 is the convective friction time, 𝑞 is the mass ratio 𝑀𝐸∕𝑀𝑆𝑢𝑛(𝑡), 𝑀𝑆𝑢𝑛 and 𝑅𝑆𝑢𝑛 are the mass and radius of the Sun at RGB tip, 𝑟𝐸 is the orbital radius of the Earth at RGB tip, Ω is the angular velocity of the solar rotation, and 𝜔 is the angular velocity of the Earth.[4] This yielded an angular decay time of 2.6 × 106 years, which is of the same order of magnitude as the time the Sun will spend near RGB tip. The Earth’s loss of angular momentum and subsequent dynamical friction in the lower chromosphere would result in engulfment. This paper used the MESA code to simulate the effect of SL on RGB tip, with an SL rate of 5𝑥1019 kg per year from the present day until the core hydrogen fraction in the solar core reached 0.01. The Sun then progresses naturally until the red giant phase and beyond (see Table 1). With SL removing mass from the solar envelope rather than the core, there is an interplay between the reduced gravitational pressure vs decreased pressure on the core resulting in lighter hydrogen shell burning. Ultimately SL results in a 0.15 gain in RGB tip radius alongside a 0.23 loss in RGB tip mass, with the latter increasing the orbital radius of the Earth. From Equation 1 we can estimate the order of magnitude effect that this would have on the tidal bulge’s torque on the Earth as Γ ∝ −𝐿𝑆𝑢𝑛 1∕3𝑀5 𝑃𝑀 6 2 3 𝑆𝑢𝑛𝑅 7 1 3 𝑆𝑢𝑛, (2) where 𝑀𝑃 is the mass of the planet, in this case Earth. This gives an estimate of the Earth in the MESA simulation experiencing 66% less torque than in the 2008 analysis, and in the MESA simulation with SL experiencing 89% less torque, increasing the decay time from 2.6 × 106 years to 7.7 × 106 years and 2.4 × 107 years respectively. The RGB tip phase is relatively brief, with the Sun being larger than 100𝑅⊙ for 3 × 106 years. The 2008 analysis concluded that a present Earth orbit of 1.15 AU would allow the Earth to survive engulfment, which is equal to the Earth’s orbit at the end of the main sequence after SL, moreover with SL producing a smaller RGB tip solar mass and radius relative to the 2008 analysis. It can therefore be estimated that SL would result in the Earth surviving engulfment. However, this paper argues that the optimal use of SL would be for energy storage and, simultaneously, elimination of the tidal bulge. Concept Assuming an SL rate of 5 × 1019 kg of stellar mass lifted per year, the Dyson swarm would need to capture 10−4𝐿⊙ as a lower bound, assuming perfect efficiency, with a more detailed analysis giving 0.01𝐿⊙.[1] The ring needs to be in as close an orbit as possible to the Sun in order to minimise the manufactured mass needed for energy capture, minimise the sunlight occlusion from habitable planets, and maximise starlifting collection efficiency. However it should be far enough away to avoid overheating. This paper will choose an orbit of 10 solar radii for the ring and a more conservative 10−3𝐿⊙, requiring 6.1 × 1017𝑚2 . Starlifting could serve the purpose of large-scale helium4 mining - this helium could then act as a long-term store of fusion energy. Hydrogen would be more abundant in the lifted mass, however hydrogen fusion via the protonproton chain takes place over astronomically slow timescales - helium is preferable due to its explosive fusion via the triple alpha process. The lifted helium can be gradually accumulated into a gas giant co-orbital with the Earth. By the 𝑀5 𝑃 term in Equation 2 it’s evident that the torque imparted onto this mass would easily decay its orbital angular momentum during RGB tip. However, hydrogen and metals can also be captured from the remaining lifted mass. By storing the lifted elements as equally-massed bodies co-orbital with the Earth in a 1:1 orbital resonance, it would minimise orbital disruption to other planets in the solar system, as well as reduce the tidal bulge during the RGB tip. Helium concentration in the solar wind is 9%, so the SL rate equates to 4.5 × 1017 kg of helium lifted per year - while this could increase due to solar material having higher helium concentrations than the stellar wind, this amount is assumed for simplicity.[6] The total helium mass captured after 5 × 109 years is 2.3 × 1028 kg or 1.2 𝑀𝐽 𝑢𝑝𝑖𝑡𝑒𝑟, with a radius of around 0.9𝑅𝐽 𝑢𝑝𝑖𝑡𝑒𝑟.[11] Equivalent giants would also be formed out of hydrogen and trace metals. It can be checked whether such a mass would survive the increased radiation of RGB tip at an orbit of 1.3 AU. Conservatively assuming no reduction in RGB tip’s luminosity with a lower SL rate, the temperature of a hydrogen atom at 1.3 AU can be estimated as 1772 K. The minimum mass needed for a deposit of hydrogen to retain an atmosphere at this temperature can be estimated as one where the planetary escape velocity 𝑣𝑒𝑠𝑐 is at least six times the RMS thermal velocity 𝑣𝑅𝑀𝑆 of the hydrogen: √ 2𝐺𝑀 𝑅 ≥ 6 √ 3𝑘𝐵𝑇 𝑚 (3) where 𝑘𝐵 = 1.38× 10−23 J/K is the Boltzmann constant, 𝑇 = 1772 K is the temperature, 𝑚 = 2.016×1.66×10−27 kg is the mass of a hydrogen molecule,where 𝑘𝐵 = 1.38× 10−23 J/K is the Boltzmann constant, 𝑇 = 1772 K is the temperature, 𝑚 = 2.016×1.66×10−27 kg is the mass of a hydrogen molecule, 𝐺 is the gravitational constant, 𝑀 is the planet’s mass and 𝑅 is the planet’s radius. Conservatively assuming no atmospheric heat redistribution, it can be shown that 𝑣𝑒𝑠𝑐∕𝑣𝑅𝑀𝑆 = 7.8, so the planet would survive RGB tip with no significant mass loss in the RGB tip time frame. There would be four masses, each separated by 𝜋∕3 radians, occupying each other’s Lagrange points for stability, with the Earth being the fifth mass. One giant would be composed purely of neutral helium, and three giants composed of hydrogen and metals. The standard first-order approximation for the equilibrium tidal height ℎ on a primary body due to a secondary body is typically expressed as:ℎ = 3 2 ⋅ 𝑚 𝑀 ⋅ 𝑅3 𝑟 3 ⋅ 𝑅 ⋅ (3 cos2 𝜃 − 1), where 𝑚 is the mass of the secondary body, 𝑀 is the mass of the primary body, 𝑅 is the radius of the primary body, 𝑟 is the orbital distance between the bodies, and 𝜃 is the angle measured from the line connecting the centers of the two bodies. If the Sun is orbited by five bodies with masses 𝑚𝑒 , and 𝑚𝐻𝑒 = 𝑚𝐻1 + 𝑚𝑒 2 = 𝑚𝐻2 = 𝑚𝐻3 + 𝑚𝑒 2 , where 𝜃𝐻𝑒 =𝜃𝐻1 − 𝜋, 𝜃𝐻2 = 𝜃𝐻3 − 𝜋, then ℎ would be zero and there would be no torque to decay the angular momentum of the system. The solar irradiance on Earth is currently 1361 W per square metre, which equates to 5.5 × 1024 J of total solar energy per year. Using a mass defect of helium fusion of 0.7%, the helium giant is 2.8 × 1032 J of potential helium fusion energy stored per year. Over the 5 × 109 years of the starlifting operation this equates to 1.4 × 1042 J of energy stored, or 2.5× 1017 years of present-level solar energy shining on the Earth. If harnessed and efficiently beamed onto the Earth, this energy could provide planetary habitability for many orders of magnitude longer than Sun-like stars, the longest-living red dwarf stars, or even the universe’s entire star-producing era (0.0000001, 0.00012, and 0.001 × 1017 years respectively).

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Himal Thapa added a reply

March 18

The Earth can be saved from many environmental threats if we take action, but in the distant future, natural cosmic events will pose unavoidable challenges.

When the Sun becomes a red giant in about 5 billion years, it will expand and likely engulf Mercury and Venus, possibly even Earth. Long before that, the Sun’s increasing brightness will make Earth uninhabitable by evaporating the oceans. Eventually, the Sun will shed its outer layers and become a white dwarf, no longer providing enough energy to sustain life on Earth.

Finding another Sun to “save” Earth isn’t realistic. Even if we could somehow move Earth to orbit a younger star, the process would require energy and technology far beyond anything we can imagine today. Instead, humanity might need to relocate to another planet in a habitable system, assuming we develop advanced space travel.

As for “repairing” the Sun or extending its life—this is not possible with our current understanding of physics. The Sun’s life cycle is dictated by nuclear fusion and the laws of thermodynamics. Adding more hydrogen to the Sun or altering its fusion process through magnetism would require manipulating forces at a scale we cannot control.

In short, Earth’s fate is tied to the Sun, but life—perhaps humanity—might find a future elsewhere. Science and technology will determine how far we can go.

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Vladimir Milošev added a reply

1 day ago

The future of Earth and the Sun's evolution are fascinating but complex topics. Let’s break down your questions:

1. Can the Earth be saved?

While Earth faces many challenges, like climate change, pollution, and resource depletion, "saving" the Earth is a matter of how we manage these issues. If humanity can reduce greenhouse gas emissions, adopt sustainable practices, and protect ecosystems, we might be able to slow down or reverse some of the negative trends. However, the long-term fate of the planet is also tied to cosmic events like the Sun's evolution.

2. Will the planet freeze in the future due to the Sun becoming a red giant and lacking solar energy?

In about 5 billion years, the Sun will evolve into a red giant, expanding and engulfing the inner planets, including Earth. As it expands, it will cause extreme heat, potentially vaporizing the Earth's surface. Afterward, it will shed its outer layers and shrink into a white dwarf. Before this happens, Earth will likely become too hot for life as we know it, and the oceans may boil away. So, while freezing isn't the primary concern, Earth will certainly become inhospitable long before that.

3. Can we look for another Sun?

The idea of finding another Sun to move Earth to is currently beyond our technological capabilities. There are potentially habitable exoplanets in other star systems, but reaching them would take far longer than a human lifetime with current technology. We could look for another star with habitable zones, but traveling to these stars would require advancements in space exploration far beyond what we have today.

In short, while we might be able to slow down or mitigate some immediate challenges, the eventual fate of Earth is tied to the life cycle of the Sun. Looking for another star is a fascinating idea, but it’s not feasible in the near future. Instead, focusing on preserving life and exploring space might be our best course of action.

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