In about 5 billion years, the Sun will leave the main sequence and become a red giant. It will expand and transform into a luminous sphere, destroying everything around it, including Mercury, Venus, Earth, and Mars. So, can humanity survive after the Sun’s red giant phase? Can we escape to another star system without using spacecraft?
Humans in general, and astronomers specifically, are well aware of the challenges of interstellar travel. Our nearest neighboring solar system is Alpha Centauri. If humanity had to flee from an imminent threat within the Solar System and identify a new home in Alpha Centauri, it would take more than four years traveling at the speed of light to reach it.
Currently, it takes about five years for humans to send an orbiter to Jupiter with our existing technology. There is much debate surrounding generation ships, where humans could live through multiple generations while journeying to a distant habitable planet. Such ships would not require traveling at light speed or anything comparable. Instead, many generations of people would live and die on board during the journey to another star, lasting hundreds or even thousands of years.
Can we escape our doomed “home”?
So, are there other ways that we, or other civilizations, could escape our impending “home”? The author of a new research article in the International Journal of Astrobiology suggests that extraterrestrial civilizations (ETCs) might not need generation ships to escape these threats.
Instead, they could utilize rogue planets as vehicles for travel. Irina Romanovskaya, a Professor of Physics and Astronomy at Houston Community College, argues that extraterrestrial civilizations might use rogue planets to travel between stars to explore and colonize planetary systems. When searching for other civilizations, these efforts might leave behind technosignatures—technical signals (signals from distant planets) or artifacts.
It is possible that rogue planets in the Milky Way or some of the hundreds of billions of other galaxies carry their own life forms within subsurface oceans kept warm by radioactive decay. Then, if they encounter a star and are bound by gravitational pull, that life would effectively use a rogue planet to transport itself in hopes of reaching a more “habitable” location. So why can’t a civilization like ours mimic that?
We might think of rogue planets as dark, cold, and harsh environments. They could indeed be like that unless they have warm subsurface oceans. Despite their harshness, they also offer certain advantages. Rogue planets can provide stable surface gravity, vast amounts of space, and resources. Rogue planets with surface and subsurface oceans could offer water as a depleting resource and protection from cosmic radiation.
ETCs may use rogue planets as vehicles for travel.
An advanced civilization could also design a planet to have even greater advantages by controlling it and developing energy resources. Romanovskaya suggests that while we are on the path to using controlled fusion, advanced civilizations may have already utilized it, which could transform a cold, inhospitable planet into one capable of supporting life.
The author outlines four scenarios in which ETCs could exploit these rogue planets:
– The first scenario involves a rogue planet accidentally passing by the home world of an ETC.
The frequency of this occurrence would be tied to the total number of rogue planets. So far, astronomical studies have not specifically determined how many exist, but they certainly do. In 2021, a group of researchers announced the discovery of between 70 to 170 rogue planets, each the size of Jupiter, in a region of the Milky Way. And in 2020, another study suggested that there could be as many as 50 billion rogue planets in our galaxy. So where do they come from? Most of these planets likely get ejected from their solar systems due to gravitational events, but some may form similarly to stars.
Another source of rogue planets is the Oort Cloud of the Solar System. If another system also has a cloud of similar objects, they could serve as a rich source of rogue planets due to the activities of ejected stars.
Stars with masses ranging from 1 to 7 times that of the Sun undergo post-main sequence evolution, as do supernova progenitors with masses between 7 and 20 times that of the Sun, which can push egg-shaped cloud objects out of their systems, causing them to become unbound from their host stars. But how long might an ETC or Earth civilization expect a rogue planet to come close enough to hitch a ride? A 2015 study indicated that the binary star W0720 (Scholz’s star) passed through our Solar System’s Oort Cloud about 70,000 years ago.
While that was a star and not a planet, it indicates that objects have passed relatively close. If studies predicting billions of rogue planets are accurate, some may have passed near the Oort Cloud long before we had the means to detect them. The Oort Cloud is still far away, but an advanced civilization might be able to see an approaching rogue planet and venture out to meet it.
– The second scenario involves using technology to maneuver a rogue planet closer to a civilization’s home.
With advancements in science and technology, they could select an object from their own Oort Cloud and use a propulsion system to steer it toward a safe orbit near their planet. With enough preparation time, they could adjust the object to their needs, such as by building underground shelters and other infrastructure. Perhaps, with the right technologies, they would change or create a new atmosphere.
– The third scenario is similar to the second, involving an object from the civilization’s outer Solar System.
Romanovskaya uses the dwarf planet Sedna in our Solar System as an example. Sedna has a highly eccentric orbit, taking it from 76 AU from the Sun to 937 AU over approximately 11,000 years. With sufficient technology and lead time, an object like Sedna could be transformed into a vessel for escape. The study’s author notes that civilizations capable of doing such things would be advanced civilizations that have explored their planetary systems at least 60 AU from their host stars.
There are many potential issues here, such as bringing a dwarf planet from the far reaches of the Solar System inward could disrupt the orbits of other planets, leading to all sorts of lurking dangers. But these dangers would be minimized if a civilization around a post-main sequence star had already migrated with its habitable zone changing. Discussions about the energy required and the time needed for migration have also been conducted.
– The fourth scenario also involves objects similar to Sedna.
When a star leaves the main sequence and expands, there will be a critical distance at which objects will be ejected from the system rather than remaining bound by the gravitational pull of the dying star. If an ETC could accurately determine when these objects would be ejected from the rogue planet, they could prepare in advance and extract it from the dying Solar System. However, this could be extremely dangerous, as the intense mass loss from the star would pose a significant risk.
It can be seen in all the scenarios mentioned above that wandering planets or other celestial bodies will not be a permanent home but rather a lifeboat. These planets do not serve as a means of escape from existing threats. These drifting planets are isolated and have fewer resources than planets within the solar system. For instance, there are no asteroids to mine, no free solar energy, no day-night cycles or seasons, no ecosystems, and even no bacteria. They are simply a means to an end. Therefore, researchers indicate that instead of turning freely drifting planets into long-term homes, extraterrestrial civilizations will use freely drifting planets as vehicles to travel between stars to reach and colonize other planetary systems.
Wandering planets or other objects could be “lifeboats” for humanity.
Professor Romanovskaya also speculates that if a civilization does this repeatedly, it is not merely to escape a dying star but to spread throughout the galaxy and colonize it. In this way, the parent civilization could create unique and autonomous offspring civilizations living on different planets, moons, or regions of space. A civilization of “hitchhikers” in the universe would act as a “parent civilization” aimed at spreading the seeds of its offspring civilizations in the form of colonies in various planetary systems.
Humanity is only at the early stage of protecting itself from the catastrophic impacts of asteroids, and we are still unable to manage our planetary climate with any level of stability. Therefore, thinking about using drifting asteroids to ensure humanity’s survival seems quite far-fetched, but the aforementioned studies seem less about us and more about discoveries of other civilizations.
All this activity could generate signaling techniques as well as artifacts indicating the presence of extraterrestrial civilizations (ETC). The wandering planets used as rescue vessels could produce technical features such as electromagnetic emissions or other phenomena. An ETC could use solar sails to maneuver a freely drifting planet or utilize them on a spacecraft launched from one of those drifting planets once they have reached their destination. In both cases, the solar sails create a technical feature: cyclotron radiation.
Controlling a spacecraft or a drifting planet with solar sails would produce cyclotron radiation due to the interaction of the interstellar environment with the magnetic sails. Infrared emissions could be another technological characteristic emitted as waste heat by ETC on a planet. Anomalous infrared emissions or unnatural changes in infrared levels could be detected as a signaling technique. Infrared could be emitted unevenly across the planet’s surface, indicating the underlying technique or technology. An unusual mix of different wavelengths of electromagnetic energy could also be a signaling technique. The atmosphere itself, if it exists, could also contain these characteristics, depending on what is observed, as it might hold evidence of terrain.
A more advanced civilization than ours may have faced an existing threat from their dying star.
Currently, astronomers do not know how many wandering planets there are or whether they are concentrated in certain areas of the galaxy. We are at the starting line of uncovering these facts; however, better ideas may soon emerge.
The Vera Rubin Observatory will see its first light in 2023. This powerful observatory will image the entire sky several nights a month in detail. It houses the largest digital camera ever produced. Vera Rubin is particularly adept at detecting anything that changes position or brightness within a few days. It will have a good chance of spotting any intruders, such as rogue planets, that may approach our solar system.
There is also a very high likelihood that some of those wandering planets will exhibit unusual and perplexing characteristics; these queries may be answered by science, just as was done with ‘Oumuamua. It is speculated that a more advanced civilization than ours may have faced an existing threat from their dying star. And they may have made a Herculean effort to capture a wandering planet to tailor it to their needs. They may have boarded it and launched it towards some distant, stable star to ensure long-term survival. They might also be wondering whether there is life at their destination and how they might be received after their long journey.
