In 7.6 billion years the Sun will expand as a red giant star and engulf the Earth. Friction on the solar envelope will drag the Earth inwards towards the core of the Sun where it will evaporate and disperse into hot gas at a temperature of thousands to millions of degrees.
This inevitable future is macabre. All human creations on Earth will be gone, including buildings, statues, books and digital content, as well as mansions, bank accounts and yachts of the most privileged individuals. Our artificial satellites will be lost and the Moon would quickly crash on Earth even before the Earth will disperse. The information that defines our civilization in our computers will disappear in a hot soup of free nuclei and electrons. Extraterrestrials will be unable to recover our culture once the Universe will grow older by 55% of its current age.
Thinking about the inevitable death of Earth should give us a pause. The territories over which people sacrifice their life in Ukraine and the Middle-East today will not exist in the future. Given this gruesome fate, are terrestrial disputes really worth it? Instead of killing each other, the intelligent thing for us to do is to cooperate and use our resources to develop the technologies that would allow us to escape global existential catastrophes. Science is better than politics. This is the sentiment that I conveyed in a fascinating podcast that I had yesterday with the visionary Nevsah Karamehmet, who promotes the future well-being of humanity.
Within the Milky Way galaxy, there were billions of solar-mass stars which formed more than 7.6 billion years before the Sun. They had already gone through this red giant phase and consumed their inner planets. Any intelligence on these planets disappeared in the fiery catastrophe that accompanied a dying star.
My postdoc, Morgan MacLeod, was involved in the recent discovery and interpretation of a flash of heat emitted by a star engulfing a planet. The optical flare is only a hundred times brighter than the Sun over a few months. The first hints for this event were revealed in optical images from the Zwicky Transient Facility by Kishalay De at MIT. Archival infrared coverage from NASA’s Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE), confirmed the engulfment event, named ZTF SLRN-2020. Morgan’s calculations indicated that the star likely consumed a gas giant planet, about the size of Jupiter. The consumption of an Earth-mass planet would have been accompanied by a much fainter flare.
Such events are estimated to occur roughly once a year in the Milky Way, implying that about ten billion of them occurred during the history of our galaxy. We can name one such engulfment event per living human on Earth. When considering the Universe at large, there should be a trillion times more planets that were swallowed by their host star throughout cosmic history.
The engulfment of planets by their host star occurs also during the early formation phase of planetary systems. Planets migrate into their star as a result of friction on the gaseous disk in which they are embedded during the first million years after their formation, or as a result of gravitational scattering on other planets. These interactions drive some planets out of the planetary system and others into the star.
After its red giant phase, the core of the Sun containing about 60% of its mass will cool and become a white dwarf. Surprisingly, most white dwarfs show fresh heavy elements in their atmospheres, indicating recent accretion episodes of rocky material, whereas others are occulted by rocks on tight orbits. Surprisingly, some white dwarfs host giant planets within the region that was supposed to be engulfed by their red giant progenitor.
Recent computer simulations studied engulfed planets of various masses and demonstrated that Jupiter-mass planets can survive engulfment by a red giant, as they eject material from the stellar envelope. Small planets like the Earth cannot survive.
For now, the Sun is our source of life on Earth. In a recent correspondence with the brilliant entrepreneur Guy Spier and the Director of Partnerships at the WORLD.MINDS organization, Mor Eini, I was asked early this morning why I enjoy jogging at sunrise. I explained: “Jogging at sunrise offers me the company of bunnies, wild turkeys, ducks and birds. I saw all of them this morning. But the most important benefit of jogging early is that there are no people around. I love nature left to its own devices, and consider what lies beyond Earth as an extension of this sentiment.”
Eventually, the spectacle I witness every morning will go away. Both the Sun and the Earth will be gone. Here’s hoping that future generations will get their act together and preserve what we cherish on space platforms that will escape the devastating death of Earth. For now, we must keep in mind those past civilizations which perished on their home planet. I am actively searching for any technological packages that they have launched to interstellar space. Finding them would inspire Earthlings to do better.
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. His new book, titled “Interstellar”, was published in August 2023.
