One million alien visitors from another star system could already be lurking in the solar system. We aren’t talking about “little green men” here, however — more “little (and not so little) gray rocks,” asteroids from the triple star system Alpha Centauri.
Alpha Centauri is the closest star system to our own, lying around 4.3 light-years away. New research has indicated that, if Alpha Centauri ejects as much material as the solar system, then as many as one million space rocks larger than 328 feet (100 meters) wide could be lurking in the Oort Cloud, a band of icy material at the edge of our solar system. Some of these alien visitors could even make their way into the inner solar system.
The scientists behind the new finding suggest that the amount of material entering the solar system from Alpha Centauri will increase over the next 28,000 years as the neighboring star system makes its closest approach to our own.
“We were a little surprised to find that the amount of material from Alpha Centauri was not completely negligible,” team member and University of Western Ontario researcher Paul Wiegert told Space.com.
“Space is ‘big,’ and so it would not have been a surprise to find that perhaps no material from Alpha Centauri could reach us at all. The fact that it could be present at levels that we could detect is a pleasant surprise,” he added. “These objects really could be anywhere in the solar system at any given time.”
Related: Alpha Centauri: Facts about the stars next door
Alpha Centauri pelts the solar system like a wet dog
Wiegert and his colleague, University of Western Ontario Ph.D. student Cole Gregg, were inspired to conduct a study of these alien invaders by the first known interstellar visitors.
These were the cigar-shaped ‘Oumuamua, which caused a stir when it zipped through the inner solar system in 2017, and the more conventionally shaped comet/asteroid hybrid 2I/Borisov, which was discovered in 2019.
“We will certainly discover more than the two currently known interstellar visitors, ‘Oumuamua and comet Borisov,” Wiegert said. “This is an attempt to understand where the interstellar visitors we will discover in the future are likely to arrive from.”
Alpha Centauri is home to three stars, including the closest star to Earth other than the sun, Proxima Centauri, and an unknown number of planets.
As these stars and planets whirl around each other, their gravitational interactions perturb the orbits of other smaller objects in Alpha Centauri, ranging from asteroids and comets — planetesimals left over from the formation of our neighboring system — to particles of dust.
Think of Alpha Centauri as a wet dog after a long muddy walk, shaking off a damp spray of dirt, mud, water, and even tiny pebbles. And just as that dog’s owner gets pelted with this material if they stand too close, the solar system is pelted with matter from Alpha Centauri, with the Oort Cloud serving as our unfortunate jacket, catching much of the detritus.
The duo conducted a simulation of the solar system and Alpha Centauri that lasted for over 100 million years. It showed that a significant number of objects can reach the solar system from Alpha Centauri.
“Objects from Alpha Centauri might enter the extreme outer boundaries of our solar system, defined to be the outer edge of the Oort Cloud, at a rate of perhaps 50 per year,” Wiegart said. “But only a very small fraction of these would get close enough to the sun to be visible. We estimated there is only a one-in-a-million chance that an asteroid from Alpha Centauri is currently within the orbit of Saturn.”
The researcher added that, because of the high speed at which they enter the solar system, many of these interstellar visitors are unlikely to hang around our cosmic backyard, making fly-through visits just like ‘Oumuamua and 2l/Borisov.
“Because they have rather high speeds, they do not get gravitationally captured by our sun but instead simply pass through our system,” Wiegart added.
The duo’s findings could be useful in the future because the research suggests clues that could be used to indicate interstellar visitors that originate from Alpha Centauri.
“Our study does show that asteroids from Alpha Centauri do have rather specific directions and speeds, and if a new asteroid were discovered traveling in that manner, it would be a strong indicator that it might have Alpha Centauri as its origin,” Wiegart said.
“The possibility of studying material from Alpha Centauri is incredibly exciting,” Wiegart said. “Finding an asteroid from there in our solar system would be like getting a sample return mission from another star system, but for free.”
The research added that the next step is to examine other nearby star systems to see how efficiently material might be transported naturally from them to our solar system.
“Presumably some are more efficient sources of such material than others, and we are interested to know which ones to expect to see material from, and which we don’t,” Wiegart concluded. “Being able to compare materials from a different star system with those of our own for the first time… who knows what we might discover?”
The duo’s research appears as a pre-peer reviewed paper on the paper repository site arXiv.
