‘A messenger from afar, arriving first’: First observed interstellar object actually a comet

Researchers studying the first observed interstellar object that entered our solar system in October 2017 say the object is a comet, after previously being labeled an asteroid.

‘Oumuamua, a name that bears the Hawaiian meaning of “a messenger from afar, arriving first,” was discovered through observations taken at the Pan-STARRS survey in Hawaii, with follow up observations taken by the European Space Agency’s (ESA) Optical Ground Station (OGS) telescope in Tenerife – with multiple telescopes training sights on the object around the world.

According to recent observations made June 1 by ESA, ‘Oumuamua is moving fast enough to escape the Sun’s gravitational pull. Data from the Hubble Space Telescope and various international partners showed the object was moving faster than predicted – leading to the understanding it was indeed a comet by shedding weight through ices turning to gases while also shedding dust – along with observed variations to its trajectory.

Initial observations didn’t show any emission of gases or dust commonly associated with comets.

Researchers led by ESA astronomer Marco Micheli and University of Hawaii Astronomer Dr. Karen Meech found ‘Oumuamua was slightly off from the path anticipated if it were only influenced by the Sun – with their results being published in Nature.

Micheli was part of the Pan-STARRS team that discovered ‘Oumuamua, and with University of Hawaii Astronomer Rob Weryk was the first to notice the object was interstellar by combining Pan-STARRS’ data to observations made with ESA’s OGS telescope.

“Apart for the intrinsic interest in knowing the object better, it also confirms what most theoretical models were predicting on the origin of these objects,” Micheli said. “It is thought that interstellar objects like ‘Oumuamua are produced and ejected into interstellar space during the initial phases of planetary formation. However, these models predicted that the vast majority of the ejected bodies will be cometary, because they would have formed in the outside parts of the planetary system, where more ices are present. Seeing that ‘Oumuamua, our first discovered interstellar object, is indeed cometary brings further support to these theoretical models.”

All of the observations were made on short notice through an international effort, he added. Meech wrote all the observing proposals, organized all efforts to observe ‘Oumuamua and helped orchestrate the paper published in Nature last November.

“’Oumuamua remained observable for just a bit more than two months, but despite the short time our team, and many other groups worldwide, were able to point dozens of telescopes, including almost all the most powerful ones, to this interesting objects, obtaining observations and data with different techniques,” Micheli said.

Meech said ‘Oumuamua is an unusual comet.

“Still some observers tried to see one of the minor gas species that is usually dragged out with water – cyanide – and this was not seen,” Meech said. “This means the comet can’t have the same chemistry as comets in our solar system.  We felt we should have seen dust too – usually small dust is very easy to see – but it came be that the small dust gets eroded from the surface when it travels through interstellar space.”

Micheli said the objects is now too faint to observe “with even the most powerful telescopes” and that its origins aren’t clear since existence of the non-gravitational force makes it harder to determine where ‘Oumuamua came from. But the object could be well-traveled, but its age is also unknown.

“The experience gathered during its passage will definitely be extremely valuable when the next one is discovered, and we hope to be able to get even more observations when that time comes,” Micheli said.

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