A global apocalypse could be closer than you think.
According to astronomers, in five billion years or so, the sun will run out of hydrogen in its core completely and expand, possibly engulfing the earth. Now that's a bright future you don't want. SpaceX CEO Elon Musk recently tweeted that the expansion of the Sun would result in the extinction of all life on the planet, making interplanetary living a necessity. Musk said this in response to a paper warning about mass extinction caused by human activity, arguing for the necessity of working on ways to move off-world. However, while we lack the technology to live on other worlds just yet, we may have a more immediate catastrophe at hand — climate change and global warming.
The emission of greenhouse gases has significantly altered the temperature and climate pattern of our planet. According to six leading international datasets consolidated by the World Meteorological Organisation, 2021 was one of the seven warmest years on record. And these warmest seven years have all occurred since 2015, with 2016, 2019, and 2020 constituting the top three. A strong El Nino event that occurred in 2016 also contributed to recording global average warming. Scientists predict that increased rises in the concentration of greenhouse gases will continue to cause a significant temperature rise, possibly even melting much of the polar ice. And there is also another concern - the amount of energy that reaches the Earth is very slowly increasing over time. This increase will eventually cause severe problems for Earth, causing the planet to one day to become so hot that the Earth's oceans will boil.
Currently, policies in place to prevent global warming revolve around decreasing fossil fuel consumption and investing in greener and cleaner sources of energy. Despite various such pledges to slow down climate change, experts feel that the Paris Agreement will not suffice to prevent the global average temperature from rising to or above 2.7°Fahrenheit (1.5°Celcius).
Now, Sohrab Rahvar, an astronomer and professor of Physics at Sharif University of Technology, Iran, decided to take up the challenges of a heating planet and a more luminous sun. In a preprint paper that hasn't yet been peer-reviewed, Rahvar has made a proposal for a way to decrease the global temperature of our planet. Using gravity assist by asteroids, Rahvar's paper suggests we can increase the orbital distance of the Earth from the Sun, moving the planet to a cooler position.
One thing we have generally thought we could count on is the stability of Earth's orbit. According to an article in Big Think, for the past 4.5 billion years, Earth’s orbital path around the sun has remained practically unchanged, even in the face of giant meteor impacts, the formation of moons, and the continued slowing of our planet’s rotation.
There’s a greater than a 99 percent possibility that Earth’s orbit will continue to remain unchanged. However, this could lead to an eventually unavoidable calamity for the entire planet.
Rahvar's preprint paper proposes an operation that uses the gravity-assist mechanism of the flyby motion of the asteroids close to the earth. To elaborate, Rahvar suggests manipulating the orbit of asteroids in the asteroid belt using solar sails and propulsion engines to guide these towards the orbit of Mars.
The effect of gravitational scattering, where a large object can scatter a smaller one and thereby create an equal and opposite resulting force back onto itself, could be used to increase the orbital distance of the earth which would consequently cool down the Earth's temperature. Now, while this sounds like a grand, exciting idea, propelling the Earth to another orbit has been just one of the myriad solutions proposed to counter climate change. More like a Plan Z, really.
In the preprint, Rahvar calculates the increase in the orbital distance of the earth for each scattering and investigates the feasibility of performing this project. Practical much?
But wait, what is gravity assist and how can it be implemented?
Rahvar suggests moving the asteroids using gravity assist. This was first proposed by spaceflight pioneers Friedrich Zander and Yuri Kondratyuk in their papers published in 1925 and 1938, respectively. The gravity assist maneuver is a technique in which a spacecraft changes its orbital energy and angular momentum by making a close approach with a celestial body, using the body's gravity as a slingshot. It results in a large reduction in fuel usage and flight time. It was first implemented in 1959 by the Soviet probe Luna 3 in its mission to photograph the far side of Earth’s moon. Since then, a number of interplanetary probes, including the Voyagers, Mariner, or Galileo, have applied the technique for this reason.
Most asteroids in the solar system move on the same plane as the planets, within 3 degrees of the ecliptic. A large number of asteroids that are closest to us are located in the asteroid belt, present between the orbits of Mars and Jupiter. To have the gravitational interaction of asteroids with the earth, the orbital distance between them and the sun must be reduced. For this, the author suggests the use of solar sails. In the method proposed, the orbital velocity of a number of asteroids in the belt would be lowered using solar sails to provide a braking action - moving the asteroids to lower orbits.
A solar sail spacecraft has enormous reflective sails that capture the momentum of photons of light from the Sun and use that momentum to push the spacecraft forward. The solar sail would be attached to the identified asteroids and used to slow down and decrease the orbital speed of the asteroids. The result would be a spiral motion of asteroids towards the lower orbits.
Rahvar's theory is that when these asteroids pass earth, their gravitational pull would lead to a slight drag on the earth, tugging it out of its existing orbit and placing it onto a new one far away. This would place the Earth at a farther position from the sun, decreasing the Earth's overall surface temperature.
Plans to change the orbit began decades ago
In 2001, a group of astronomers and engineers at NASA's Ames Research Center in California, hinted at the idea that another six billion years could be added to the lifetime of our planet, thereby doubling its working life, by moving the planet to a cooler spot.
Their idea? The same techniques are used by scientists to deflect asteroids or comets heading towards Earth. Dr. Gregory Laughlin, currently the Professor of Astronomy, Director of Undergraduate Studies at Yale University, and his colleagues Don Korycansky and Fred Adams put forward a plan that involves carefully directing a comet or asteroid so that it sweeps close past our planet and transfers some of its gravitational energy to Earth.
In an interview with The Guardian, Laughlin said, "Earth's orbital speed would increase as a result and we would move to a higher orbit away from the Sun."
After passing by Earth, the comet would be directed so that it passed close to Jupiter or Saturn, where the reverse process would occur. The comet would pick up energy from these planets. Its orbit would bring it back to Earth and the process would be repeated. "All you have to do is strap a chemical rocket to an asteroid or comet and fire it at just the right time. It is basic rocket science," Laughlin told The Guardian.
The group, however, acknowledged the plan's shortcomings, which could result in drastic consequences. Directing the asteroid or comet towards earth would require very precise calculations. The slightest miscalculation in orbit could fire it straight into the planet. In their paper in Astrophysics and Space Science, the researchers stated, "The collision of a 100-kilometer diameter object with the Earth at cosmic velocity would sterilize the biosphere most effectively, at least to the level of bacteria. The danger cannot be overemphasized."
Fast-forward to 2019, an article in The Conversation by Matteo Ceriotti, Lecturer in space systems engineering at the University of Glasgow, suggested a similar plan to perform a gravitational slingshot to move Earth to another orbit. With accurate trajectory design, the method suggests that "a small body can be nudged out of its orbit and as a result, swing past the Earth, providing a much larger impulse to our planet. Though the idea seems fascinating, it has been estimated that a million such asteroid close passes are required, to keep up with the sun's expansion."
Another recent article in Big Think suggested using a giant thruster placed at the South Pole.
Launching the Earth into a higher orbit requires a large amount of energy. The article suggests that the same physics that works for launching a rocket into space would also work for launching Earth to a higher orbit. One needs to apply a thrust that changes Earth’s momentum in a positive direction which would eventually boost us farther away from the sun. The thruster would gather energy from the Sun, perhaps using a solar collecting array, then convert the energy to thrust, then apply that thrust to change Earth’s momentum and boost us farther away from the sun.
The thruster should ideally be aimed to push the Earth in the direction it’s already moving. However, that would be very difficult to manage on a rapidly and continuously rotating planet. The article suggests instead that the thruster should be fired continuously, "under the assumption that one could gather, control, transport, and convert that energy into usable work."
The result is that the Earth would begin to accelerate and be boosted to a higher orbit. As the kinetic energy is increased through continued thrusting, "it will help dig us out of the Sun’s gravitational potential well. That would take us to a greater orbital distance and enable us to slowly decrease the flux of the solar radiation that strikes our planet", according to the article.
A change in orbit has even been proposed by politicians - albeit ones without much scientific knowledge or understanding. At a congressional hearing in June 2021, Republican Representative Louie Gohmert of Texas, who is a climate skeptic who once argued global warming was a good thing as it would allow people to "grow more plants", has also asked a U.S. Forest Service official if their organization or the Bureau of Land Management could change the orbit of the moon or Earth to reverse the effects of human-caused climate change.
Scientific American took a look at the matter. In their article, Britt Scharringhausen, the planetary astronomer at Beloit College suggested, "Radiative equilibrium, the balance between incoming energy from the sun’s rays and energy emitted from Earth, is key to our understanding of our planet’s changing temperature." Scharringhausen also devised an equation to describe the connection between Earth's temperature, the Sun's temperature, the radius of the Sun, distance to the Sun, and Earth's albedo, which measures how well our planet reflects solar energy. In order to make Earth cooler, a variable such as the sun’s temperature or radius, Earth's albedo, or the distance to the sun would need to be changed. He suggests that if you discount reducing the Earth's albedo by tackling emissions, then we are left with moving the planet.
The problem is that this will take a lot of energy, by Scharringhausen’s calculations, decreasing the temperature by 37.4°Fahrenheit (3°Celcius) would require us to move the planet an additional three million kilometers from the sun. This would take around 5 x 1031 joules of energy. Easy, right? Well, no - because he also calculates that the Earth's current annual global electricity production is around 1019 — just 0.0000000000002 percent of what we’d need.
So, Scharringhausen proposed another method - detonating a nuclear bomb near it. “It will basically vaporize part of the asteroid, and that escaping rock vapor acts like rocket exhaust and will push the asteroid along,” she told Scientific American.
Though the scaled-up experiment could shift a planet's orbit, it would take a billion times more nuclear explosions than we have ever set off to move Earth the required distance, or the equivalent of dropping an atomic bomb every second for 500 years, according to Geza Gyuk, director of astronomy at the Adler Planetarium in Chicago.
Another option mentioned in the Scientific American article is very similar to Rahvar's — siphoning off the energy of other celestial objects, such as passing asteroids or comets, by engineering close planetary flybys. For moving our planet, the issue with the method is scale. Ethan Siegel, a theoretical astrophysicist and science writer, said, "The total mass of the asteroid belt is only four to five percent of that of the moon or 0.05 to 0.06 percent of that of Earth. Using the mass of the entire asteroid belt in flybys would migrate Earth away from the sun by less than 748,000 kilometers, or a quarter of the distance we’d need. A single off-course collision with our planet would spark immediate destruction resulting in global mass extinction."
Despite these possibilities, it looks like a working prototype is a long way off.
Is this project feasible?
In an interview with The Sun, Rahvar said, "We need a series of asteroids to [pass close to] Earth to have effective temperature loss. For instance, in order to decrease the Earth's temperature to one degree, we need to move it away from the sun in the order of 150,000 miles. The result would be a fainter sun in the sky and a decrease in the Earth's temperature."
Rahvar admits that the process would take decades. As per the preprint, the time scale to lower the orbit is about 70 years for a 1,010 kg asteroid.
But, the proposal has already triggered controversy among scientists.
Jonathan McDowell, a researcher at the Harvard–Smithsonian Center for Astrophysics, told The Sun that the proposal risked flinging a space rock straight into Earth. "I haven't worked through the maths in detail but some of it looks dodgy. He also completely fails to follow through with discussing the implications of his results," he said.
"Even if you assume his results are right, they imply that to fix global warming this way you would need to put hundred-square-kilometer sails on each of about a hundred million asteroids and wait a century, with a significant risk of putting one or more of these asteroids accidentally on a collision course with Earth – if not on the first pass, then on subsequent orbits," he added.
Professor Brad Gibson, an astrophysicist at the University of Hull, resonated with his comments and described the plan as "not feasible today in the slightest".
Rahvar, however, said, "Advanced future civilizations on the earth will definitely have the capacity to carry out the project that I propose here."