Elon Musk’s vision is to save humanity from a single planet catastrophe by transporting humans from Earth to Mars with the reusable rocket Starship. As I woke up on New Year’s Day, it occurred to me before my morning jog at sunrise that Starship could also save Earth in a completely different way: by slowly moving Earth away from the brightening Sun.
The thought was triggered by an email from one of my followers, Luis Muñoz, an engineer from Spain who asked an excellent question: “Would it be theoretically possible for an advanced civilization to shift their home planet orbit in order to avoid their host star swallowing the planet during the expanded Red Giant phase of that star?”
In response, I explained that our existential risk is not just from engulfment by the Sun, but long before that — from the brightening Sun boiling all liquid water reservoirs on the surface of Earth. Detailed calculations of the future evolution of the Sun imply that the Earth will lose all liquid water on its surface within a billion years as a result of a greenhouse effect triggered by a 10% increase in the Sun’s luminosity. To avoid that fate, the Earth will need to be pushed out by 5% of its current separation from the Sun during the next billion years. As the Sun will continue to brighten, the Earth would need to shift its orbit outward by a factor of 1.3–1.9 within 5.4 billion years before the Sun will leave the Main Sequence of stars. The brightening of the Sun will accelerate 7.6 billion years from now, when the Sun will reach the tip of the Red Giant phase. At that time, the Earth will need to move out by a factor of 50–70 away from the Sun to the Kuiper belt. Given how far they need to relocate, our descendants might choose at that point to leave the Solar system, making our civilizations interstellar — the title of my latest book. A giant exodus of this proportion could have happened long ago for extraterrestrial civilizations in the Milky-Way galaxy.
Given these inevitable existential threats, advanced technological civilizations might have attempted to move their planets in response to the predicted evolution of their host star.
One method to accomplish small orbital shifts for Earth is to engineer gravitational kicks by shifting appropriately the orbits of massive Near-Earth Objects from the Main Asteroid Belt.
An alternative is offered by rocket science. What is the required steady state of launching and receiving Starship rockets in order to kick the Earth’s orbit away from the Sun? The most efficient energy transfers occur if launches are directed opposite to the motion of the Earth around the Sun, and reentries are aligned along this motion, so as to increase the Earth’s orbital angular momentum. In each use-cycle of a single Starship, the Earth will get a net momentum kick in its rest frame of twice the mass of Starship times its speed relative to Earth.
Adopting a Starship mass of 1,600 tons and a launch or reentry speeds of order 15 kilometers per second requires a few launches every second in order to move the Earth significantly away from the Sun. As a result, a hectic schedule of Starship launches could save liquid water in our oceans, rivers and lakes from boiling off in the next 5 billion years.
Luis also asked: “Would it be possible to detect an exo-planet’s orbit shift (either while it happens or after completion) as a techno-signature?”
I explained that a planet which started at the Earth-Sun separation from a sun-like star and grew to twice the initial separation so as to escape engulfment from the subsequent Red Giant, was actually discovered recently through the method of microlensing — as the remnant system magnified light from a background star. This orbit expansion could have resulted naturally from the mass loss of the host star during its evolution. It is difficult to distinguish a natural origin for this orbital shift from an artificial origin, without detecting a signature of a related technological infrastructure.
Finally, Luis asked: “Would that feat make sense energetically compared to fleeing to another habitable planet far away or to a “terraformable” planet nearby?”
I explained that terraforming another planet, like Mars, or migrating from the original planet to an engineered space platform would only help a small fraction of life on Earth to survive, given our current technological abilities. But over the course of millions of years, technological advances might make these solutions practical alternatives to the difficult task of moving Earth away from the Sun.
As of now, we can search for what extraterrestrial civilizations may have accomplished in space. In celebration of the new year, I sent a related message to the research team of the Galileo Project:
“Dear members of the Galileo Project,
Next year promises to bring exciting new data, as we hope to operate three Galileo Observatories with triangulation capabilities by summer 2025. The three locations in Massachusetts, Pennsylvania and Nevada, will sample distinct environments and provide distance, velocity, acceleration, audio and imaging data on several million objects in the sky by the end of 2025. If any particular object would appear to be truly anomalous, we will dedicate a full paper to that object.
We hope to find an anomalous object, as rare as one in a million.
We are deeply grateful to the generosity of our donors who enabled this work.
It is a great pleasure and privilege to work with all of you. Let’s make history. As I told a reporter yesterday: “It is critical to differentiate between doing science and talking about science without doing any science”.
Wishing everyone a successful 2025, full of discoveries!
Avi”
ABOUT THE AUTHOR
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
