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ʻOumuamua – Not an Alien Spacecraft

Jülich, 2 July 2019 - Two years ago, astronomers discovered an interstellar object in our solar system for the first time: “ʻOumuamua” had extraordinary characteristics that differed from previously observed asteroids and comets. There were speculations about ʻOumuamua being an alien spacecraft. In a study published in the renowned journal Nature Astronomy yesterday, an international team of scientists showed that ʻOumuamua is of completely natural origin.

When the PanSTARRS1 telescope (Panoramic Survey Telescope and Rapid Response System 1) at the University of Hawaii first recorded data of this rock passing through our solar system, astronomers noticed that the object differed from anything previously observed. ʻOumuamua, which is Hawaiian for “scout”, exhibits properties of both asteroids and comets but it also has characteristics that are different from any celestial body analysed by researchers to date – which led some scientists to speculate that it might be an alien spacecraft.

This is because ‘Oumuamua is the first object to be observed passing through our solar system. “Astronomers have long hoped to see an interstellar object passing through our solar system,” explains Susanne Pfalzner, astrophysicist at the Jülich Supercomputing Centre, who co-published a study on ʻOumuamua several months ago with her colleague Michele Bannister from Queen’s University Belfast in Northern Ireland.

ʻOumuamua is reddish in colour, a property it shares with many bodies in the solar system. “Other than that, it differs greatly: although it can’t be proven conclusively from the recorded data, the asteroid likely has an oblong shape and a conspicuous pattern of movement,” says Pfalzner. “What is particularly baffling is its trajectory through our solar system.” ʻOumuamua appears to accelerate along this trajectory – which is typical of comets. However, the astronomers were unable to detect the gas emissions typical of this.

Fourteen scientists from Europe and the USA worked together to analyse the collected data on ʻOumuamua. Matthew Knight from the University of Maryland put together a strong team of experts in various different areas of work. “This cross-pollination led to the first comprehensive analysis and the best big-picture summary to date of what we know about the object,” says Knight. “We tend to assume that the physical processes we observe here, close to home, are universal. And we haven’t yet seen anything like ʻOumuamua in our solar system. This thing is weird and admittedly hard to explain, but that doesn’t exclude other natural phenomena that could explain it.”

ʻOumuamua continues to present riddles, but Susanne Pfalzner, who uses computer simulations to investigate the origin of objects like ʻOumuamua, does not think that this should lead to speculations about aliens: “It’s completely natural that ʻOumuamua has extraordinary properties. Our analysis suggests that there are natural phenomena that could explain this,” she says. “But, of course, this also means that we still have a lot to learn about space beyond our solar system.”
Susanne Pfalzner and her colleagues have considered a number of mechanisms through which ʻOumuamua may have escaped from its home system. One explanation would be that the celestial body was ejected by a gas giant in a different star system. “According to existing models, the Oort cloud at the outer edge of our solar system may have been created from fragments of Jupiter in the same way,” explains Pfalzner. “Some similar objects could have escaped the gravity of their home star and thus become interstellar travellers.”

The researchers believe that ʻOumuamua is only the first of many visitors from other star systems to be detected. Starting in 2022, the Large Synoptic Survey Telescope (LSST) will record data and scientists hope to discover further interstellar objects. Only then will we be able to say whether ʻOumuamua really is as exceptional as we think today.

Interstellare Objekte wie Oumuamua könnten das Wachstum neuer Planeten beschleunigenʻOumuamua is the first object to be observed passing through our solar system.
Copyright: ESA/Hubble, NASA, ESO, M. Kornmesser, cc by

Further Information:

Original publication: The Natural History of 'Oumuamua, by the ‘Oumuamua ISSI Team: Michele T. Bannister, Asmita Bhandare, Piotr A. Dybczyński, Alan Fitzsimmons, Aurélie Guilbert-Lepoutre, Robert Jedicke, Matthew M. Knight, Karen J. Meech, Andrew McNeill, Susanne Pfalzner, Sean N. Raymond, Colin Snodgrass, David E. Trilling & Quanzhi Ye, Nature Astronomy, published 01 July 2019,
DOI: 10.1038/s41550-019-0816-x

Drifting Interstellar Worlds Like ʻOumuamua Could be the Seeds of New Planets; press release from 8 April 2019

Jülich Supercomputing Centre (JSC)


Prof. Dr. Susanne Pfalzner
Jülich Supercomputing Centre
Tel.: +49 2461 61-85420

Press contact:

Dr. Regine Panknin
Tel.: +49 2461 61-9054