Telescope will reveal intruders
The Vera C. Rubin Observatory is under construction on a mountain peak in Chile. From 2022, once the telescope has been completed, it will capture a section of the sky every 18 seconds with the world’s biggest camera. The telescope will automatically sound the alarm if an unknown object appears.
Canadian astronomer Robert Weryk is busy at work at the Pan-STARRS telescope in Hawaii. Going over the telescope images on his computer, he spots a tiny bright spot. Initially he thinks it is just a common asteroid. But there is something odd about the way the object moves. It is speeding unusually fast across the sky – and doesn’t follow the usual elliptical path of other objects in the Solar System.
Robert Weryk was looking at just the right section of the sky at just the right time – the night of 19 October 2017 – to became the first person ever to observe an object that is orbiting neither the Sun nor any other star. The speed and the path reveal that the alien object has been travelling thousands of billions of kilometres through interstellar space after being flung from an alien planetary system.
The object that Robert Weryk discovered was given the Hawaiian name of Oumuamua – or, more prosaically, 1I/2017 U1. ‘1I’ indicates that it is the first interstellar object ever observed, but astronomers suspect it is not alone. Numerous objects must have left their original orbits around another star and ended up in interstellar space. But given the vast distances between stars, it is rare for one of them to visit our neighbourhood.
Such a heavenly body might provide us with unique insight into how planets form around other stars, perhaps also a better understanding of our own solar system’s history. The problem is the time required to plan a mission to get up close, or to snatch a sample like the one returned to Earth by the Japanese spacecraft Hayabusa2 last December, landing spectacularly in South Australia. The asteroid visited by Hayabusa2 was 162173 Ryugu, which orbits the Sun predictably every 16 months. But interstellar objects like Oumuamua are only passing through, travelling too fast for us to build and launch a probe to reach them in time.
Nevertheless, that is what scientists hope to do. A European space mission with Japanese participation aims to launch a space probe that will lie in wait in space ready for the next interstellar object to appear. And in the UK, engineers have not given up the idea of catching Oumuamua, although the asteroid is already heading out of our Solar System at around 38 kilometres per second relative to our Sun. Catching up would require an extremely speedy probe.
Amateur discoveries
Searching for small objects entering our Solar System isn’t easy. It requires a special telescope with a broad view and very sensitive digital cameras able to register the tiniest bright spots in the sky. Survey telescopes such as the Pan-STARRS telescope that first captured the faintly reflected sunlight from Oumuamua take pictures of the sky and compare them to older images automatically. Astronomers can thereby be alerted quickly when a new object appears in the sky.
Pan-STARR’s primary task is to spot objects that come so close to Earth they could constitute a danger to us. But a side effect of this is the spotting of thousands of unknown asteroids and comets. If an interstellar object appears in the sky above Hawaii, the telescope captures it, just as with Oumuamua in 2017.
But with a little luck, less sophisticated equipment could also do the job. On 30 August 2019, a second interstellar object was discovered by amateur astronomer Gennadiy Borisov using only his homemade telescope located in the Crimea peninsula.