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In the Chinese science fiction movie The wandering earth, recently published on Netflix, humanity is attempting to alter the Earth's orbit by using huge thrusters to escape the expanding Sun – and to prevent a collision with Jupiter.
The scenario may one day become reality. In five billion years, the Sun will run out of fuel and will expand, most likely gobbling up the Earth. An apocalypse of global warming is a more immediate threat. Moving the Earth to a wider orbit could be a solution – and it is possible in theory.
But how can we do it and what are the challenges of engineering? For discussion purposes, suppose we aim to move the Earth from its current orbit to an orbit away from the Sun at 50%, similar to that of Mars.
We have developed techniques to move small bodies – asteroids – from their orbits for many years, primarily to protect our planet from impacts.
Some are based on an impulsive and often destructive action: a nuclear explosion near or on the surface of the asteroid, or a "kinetic impact", for example a spaceship colliding with the high-speed asteroid . These are clearly not applicable to the Earth because of their destructive nature.
Other techniques involve rather a very gentle and continuous thrust over a long period, provided by a tug moored to the surface of the asteroid or by a hovering spaceship near it (pushed by gravity or by other methods).
But that would be impossible for Earth because its mass is huge compared to even the largest asteroids.
Electric thrusters
In fact, we have already moved Earth from its orbit. Whenever a probe leaves the Earth for another planet, it sends the Earth a small impulse in the opposite direction, similar to the recoil of a cannon.
Fortunately for us, but unfortunately to move the Earth, this effect is incredibly weak.
The SpaceX Falcon Heavy is today the most capable launcher. We would need 300 billion billion full-capacity launches to achieve orbital change to Mars.
The material constituting all these rockets would be equivalent to 85% of the Earth, leaving only 15% of the Earth in orbit.
An electric thruster is a much more efficient way of accelerating mass – especially ionic drives, which operate by projecting a stream of charged particles that propels the ship forward. We could point and shoot an electric thruster in the direction of flight from the Earth's orbit.
The oversized propeller must be 1,000 kilometers above sea level, beyond the Earth's atmosphere, while remaining firmly attached to the Earth with a rigid beam to transmit the pushing force.
With a beam of ions launched at 40 kilometers per second in the right direction, one would still have to eject the equivalent of 13% of the Earth 's mass in ions to displace the remaining 87%.
Navigate in the light
As light is momentum, but not mass, we may also be able to continuously feed a focused light beam, such as a laser. The required energy would be collected by the Sun and no mass of the Earth would be consumed.
Even using the huge 100 GW laser power plant envisioned by the Breakthrough Starshot project, which aims to propel a spacecraft out of the solar system to explore nearby stars, it would still take three billion years of operation to make the next day. continuous use to achieve the change of orbit.
But light can also be reflected directly from the Sun on the Earth with the help of a solar sail placed near the Earth.
Researchers have shown that a reflective disk 19 times larger than the Earth's diameter would be needed to effect orbit change over a billion years.
Interplanetary billiard
A well known technique allowing two bodies in orbit to exchange speed and change their speed is to use a near passage or gravitational sling. This type of maneuver has been widely used by interplanetary probes.
For example, the Rosetta spacecraft that visited comet 67P in 2014-2016, during its 10-year comet trip, passed close to Earth twice in 2005 and 2007.
As a result, the Earth's gravity field gave Rosetta a substantial acceleration, which would have been unattainable only with thrusters.
As a result, the Earth received an opposite and equal impulse – although this had no measurable effect due to the mass of the Earth.
But what would happen if we could achieve a sling using something much more massive than a spaceship?
Asteroids can certainly be redirected by the Earth and, if the mutual effect on Earth's orbit will be minimal, this action can be repeated several times to result in a considerable change in Earth's orbit.
Some regions of the solar system are dense with small bodies such as asteroids and comets, whose mass is small enough to be moved with realistic technology, but with orders of magnitude greater than what can actually be launched since the Earth.
With a precise trajectory design, it is possible to exploit what is called "leverage Δv" – a small body can be pulled out of its orbit and so switch beyond Earth, giving a much bigger impetus to our planet.
This may seem exciting, but it has been estimated that we would need a million similar passages for asteroids, spaced from each other by a few thousand years, to follow the expansion of the Sun. .
The verdict
Of all the available options, the use of several asteroid fronds seems to be the most feasible at present. But in the future, it might be essential to exploit the light, if we learn to build giant space structures or ultra-powerful laser matrices. These could also be used for space exploration.
But if this is theoretically possible and perhaps a technically feasible day, it might actually be easier to move our species to our neighboring planetary neighbor, Mars, who could survive the destruction of the Sun. After all, we have already landed and swept its surface several times.
After thinking about the challenge of moving Earth, colonizing Mars, making it habitable and moving the Earth's population over time, may not seem so difficult after all.
Matteo Ceriotti, Lecturer in Space Systems Engineering, University of Glasgow.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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