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Just over a month ago, scientists working on the Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) observatory at Haleakala, Hawaii caught a glimpse of something truly extraordinary: the first known interstellar object to pass through the solar system. Over the past month, we’ve refined observations and detailed what we could make of the object. Now known as 1I/2017 U1 ‘Oumuamua, it’s the first object of its kind. The “I” denotes its interstellar origin (ISO).

‘Oumuamua plunged into the solar system as if dropped into it from above, closing to within 0.25 AU from the sun. That puts it between the orbit of the sun and Mercury, but there was no hint of a “tail” as ‘Oumuamua approached. On its initial approach from “above” the solar system, the asteroid was moving at a solid 15.8 miles per second (25.5km/s). It bottomed out “under” the solar system after the sun’s gravity pulled it into a different orbit, and is now on its way back out of the solar system on a different trajectory and an even higher speed (44km/s).

`Oumuamua is rapidly fading as it heads out of the Solar System and recedes from both the Sun and the Earth, so getting new observations as fast as possible was crucial. “The IfA team — including those who discovered 1I — was already prepared to rapidly follow up solar system discoveries from Pan-STARRS, which is operated by the IfA and funded by NASA,” said Karen Meech, the astronomer who led the investigative team. “We were able to rapidly develop a follow-up strategy on a very short timescale. It is exciting to think that the brief visit by `Oumuamua gave us the opportunity to do the first characterization of a sample from another solar system.”

Based on its observed characteristics, ‘Oumuamua is roughly cigar shaped, with two of its axes about 80 meters across and the third 800 meters long. Its trajectory and speed suggest it’s not an ejected fragment of our own solar system at any previous stage in its development. While this possibility cannot be completely ruled out, the research team seems to think it’s a distant possibility. In fact, they theorize that its encounter with our own sun may have been the first time ‘Oumuamua encountered another star at all.

The entire encounter, brief as it has been, reminds us of Arthur C. Clarke’s classic sci-fi book, Rendezvous with Rama, in which a massive cylindrical spacecraft on a fast approach inside our own solar system is explored by humans before it continues on its journey towards the Large Magellanic Cloud. We won’t see ‘Oumuamua again, but its brief visit to our solar system expanded our understanding of the cosmos, just a bit.

Feature image by ESO/M. Kornmesser .