The most common stars in the Milky-Way galaxy are red dwarfs. They possess about a tenth of the mass of the Sun and extend to about a tenth of the radius of the Sun. As I showed in a recent paper with my brilliant postdoc, Morgan MacLeod, the mean density of such stars is of order 100 grams per cubic centimeter, about 30 times higher than the density of rock on Earth.
In our paper, we argued that a variety of dynamical processes can kick a rocky planet like the Earth to the immediate vicinity of a red dwarf, where the planet would be tidally disrupted and spaghettified into a stream of molten lava. Half of the spaghettified rock will be expelled to interstellar space and break into interstellar meteors, like the IM1 meteor detected by U.S. government satellites in 2014. The other half of the molten rock might end up on the surface of the red dwarf star.
Molten lava or magma erupts onto the Earth’s surface, typically with a temperature in the range of 1,000 to 1,500 degrees Kelvin. It flows almost like syrup, or can be barely flowing at all. The higher is the silica content of the lava, the higher is its viscosity.
Archimedes’ principle, discovered by the ancient Greek mathematician Archimedes, states that any object submerged in a fluid is acted upon by a buoyancy force with a magnitude that is equal to the weight of the fluid displaced by the body. This principle Implies that when molten lava lands on the surface of a dwarf star, it would float like oil in water.
It must be a thrilling experience to float on the surface of a star, as long as one can tolerate the heat. Any lava bubbles would eventually disintegrate because the surface temperature of red dwarfs with a tenth of the solar mass is 2,800 degrees Kelvin, twice that of terrestrial lava.
Nevertheless, the melting temperature of tungsten is 3,695 degrees Kelvin. One could therefore design a ship enclosure made of tungsten with proper heat insulation, that could float and sail on the surface of a red dwarf star. Of course, surviving the space weather, pressure, surface waves and immense heat input would raise major challenges to alien engineers who designed such ships to promote space tourism. I discussed their possible work in a recent 18-minute interview on NPR, available here.
How far do alien tourists need to go in order to practice this extreme form of recreational sport on tungsten ships?
Not very far, since red dwarfs are very abundant. In fact, the nearest star to the Sun is Proxima Centauri, a red dwarf with 12% of the mass of the Sun. It is known to host a rocky planet, Proxima b in its habitable zone. Intelligent residents of Proxima b could have already engaged in ship races on the surface of Proxima Centauri.
Alien tourists have billions of similarly attractive destinations throughout the Milky-Way galaxy. Another advantage of red dwarfs is that they live for trillions of years. As a result, tourism to their surface could be a profitable business for the foreseeable cosmic future.
The sailing perk would be readily available to any resident of a habitable planet around a red dwarf star. But it could be extended by interstellar travel agencies to other red dwarfs. Interstellar sailing trips would be less appealing because of the long duration of the journey. When embarking on an interstellar journey, the travelers would need to stay patient and watch the same movies many times in order not to be bored. Also, Wi-Fi connectivity would be intermittent unless there is already a civilization on a habitable planet near the target red dwarf.
The sailing opportunities on the surfaces of red dwarfs suggest that space tourism could be thrilling. They offer an out-of-this-world experience which is only surpassed by the exhilarating experience of falling into a black hole.
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.
