Damaged Interstellar Spacecraft
Humanity’s first interstellar spacecraft, Voyager 1, will reach a distance of 1 light day from Earth on Wednesday, November 18, 2026, after 49 years of travel. It will exit the outer edge of the Oort cloud at a distance of ~3 light years within ~50,000 years.
Over a billion years, Voyager 1 will traverse 56,000 light years, roughly twice the distance of the Sun from the Galactic center. One may wonder: How much interstellar gas and dust will be swept by its frontal surface during that time?
A simple calculation implies that merely 0.1 grams per square centimeters of gas (and a hundred times less of dust) will be swept up over a billion years, corresponding to a film thickness of only 1 millimeter at solid density. However, the interstellar gas will not stick. Hydrogen atoms arriving at a speed of several tens of kilometers per second would deposit their initial energy at a depth of a few nanometers into the surface and diffuse back out. The net inventory of implanted gas is a fraction of a monolayer, and it’s steady-state, not cumulative. Dust would sputter the surface and vaporize, with each impact removing more spacecraft material than it adds. Dust impacts, plus sputtering by the gas atoms themselves, would erode Voyager 1’s surface by a few tens of micrometers per billion years, enough to dull the gold plating on the Golden Record’s cover, designed by Carl Sagan and Ann Druyan. Cosmic rays do the deeper damage, breaking down polymers and embrittling metals. If Voyager 1 happens to plow through a dense molecular cloud (with such clouds occupying about a percent of the disk’s volume), the intercepted mass in that stretch could exceed the entire billion-year average.
What is the probability that Voyager 1 will collide with a star?
Taking account of the local number of stars per unit volume as well as their gravitational focusing effect on the spacecraft, one gets a collision probability of roughly three parts in a billion over a billion years. The probability is ~10,000 smaller for a collision with a planet.
What is the probability that Voyager 1 will pass within the planetary orbits of a Solar system analog without colliding with any planet?
Voyager 1 will come within 3 light years of a star several thousand times per billion years. Its first such close encounter will be with the Gliese 445 in ~40,000 years away when Gliese 445 will arrive at a distance of about 1.6 light-years from the Sun. A pass within a few hundred AU, close enough for a star’s gravity to deflect Voyager 1’s course noticeably, happens once per 300 million years. A passage within 10 AU from another star, will occur when the Universe will age by a factor of ~3.
Capture into a bound orbit around another star is possible only through a rare three-body encounter and is highly improbable. Over very long times a gentle capture by a passing star’s gravity is more likely than any impact.
Statistically, Voyager’s fate is to keep going and slowly erode by gas, dust and cosmic-ray damage, which will turn it into a bruised lump of matter. Whether any interstellar archaeologist will care to study its scarred Golden Record remains to be seen.
Our future interstellar spacecraft will likely use propulsion to speeds that exceed the 1970s rocket speed achieved by Voyager1. Despite the delay in their launch dates, future interstellar vehicles sent out by humanity will eventually run ahead of Voyager 1 and be the first to be noticed by interstellar archaeologists. This is good news because our future avatars will carry technological fingerprints of advanced robots and superintelligence (SI) that flag the more sophisticated future ahead of us. As of now, there is a lot of room for improvement.
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SI-guided spacecraft are likely to actively navigate towards the habitable environments of stars where they can power their batteries and find raw-materials to create self-replicating products. Given the above-mentioned probabilities, we are much more likely to encounter guided visitors, as long as they exist, than defunct space remnants like a bruised Voyager 1 in the inner solar system.
Alien AI-guided craft might represent our technological future. Rather than speculate about the probabilities for encountering them, we should use our most advanced telescopes to search for them. This is what the Galileo Project under my leadership is attempting to do. For our latest results, click here and here.
During 27 years of marriage to my wife, I had never been approached by a woman who explicitly attempted to have an affair with me. This is my perception of the situation. However, it is also possible that many women attempted to flirt with me but I did not recognize their signals because I was not tuned to the possibility that they are out there.
When Elon Musk tweeted today here: “It troubles me greatly that we do not yet see any sign of aliens,” echoing Enrico Fermi’s question: “Where is everybody?”, I could not help myself but wonder whether we did not recognize signals from alien technologies because we were not tuned to the possibility that they are out there.
ABOUT THE AUTHOR
Avi Loeb is chair of the UAP Science Advisory Council to the White House, Pentagon, FBI and intelligence agencies, director of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative (2016–2021), former director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics (2005–2026), 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 (2018–2019) and a former chair of the Board on Physics and Astronomy of the National Academies (2018–2021). 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.
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