An average of seven interstellar objects pass by the sun every year, potentially close enough for us to observe and even visit, according to a new analysis. Some of these could even be from another galaxy.
To date, two objects from other planetary systems have been found in our solar system: 鈥極umuamua in聽2017 and the comet Borisov in 2019. We know these objects are interstellar in origin because they are moving faster than the escape velocity of our solar system.
Stars like our sun are expected to聽eject trillions of such objects from their star system in their lifetimes, so astronomer Marshall Eubanks at聽the company Space Initiatives and his colleagues used data on the motion and velocity of nearby stars from the European Space Agency (ESA)鈥檚 Gaia telescope to estimate how many of them might end up in聽our neighbourhood.
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They found that an average of 6.9 interstellar objects around the size of 鈥極umuamua 鈥� at least 100 metres across 鈥� should pass within 1 astronomical unit (the Earth-sun distance) of the sun every year.
The researchers estimated this by calculating the expected velocities of interstellar visitors and working out how long they should remain in our solar system. They found that the large majority should travel up to 100 kilometres per second, indicating they originate from the聽main plane of the Milky Way.
But a small portion 鈥� 0.03 per cent, or three objects per century 鈥� could have velocities of more than 530 kilometres per second, meaning they originated from outside our galaxy鈥檚 disc, perhaps even from another galaxy.
Some of these interstellar objects could be potential targets for remote observations or even visits by future spacecraft, like ESA鈥檚 Comet Interceptor mission. 鈥淲e will never in our children鈥檚, children鈥檚, children鈥檚 lifetimes send a probe to another galaxy,鈥� says Eubanks. 鈥淚n this case, it might just fall into our lap.鈥�
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