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ʻOumuamua is Not an Alien Spacecraft

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01 July 2019, 5:00AM HST

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Dr. Karen Meech
UH Institute for Astronomy
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Dr. Robert Jedicke
UH Institute for Astronomy
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Artist's impression of insterstellar object
ʻOumuamua artist's impression and actual image

This artist's impression shows the first interstellar object discovered in the Solar System, ʻOumuamua. Observations made with the NASA/ESA Hubble Space Telescope, CFHT, and others, show that the object is moving faster than predicted while leaving the Solar System.

The inset shows a color composite produced by combining 192 images obtained through three visible and two near-infrared filters totaling 1.6 hours of integration on October 27, 2017, at the Gemini South telescope.


Credit: ESA/Hubble, NASA, ESO/M. Kornmesser, Gemini Observatory/AURA/NSF
High Res JPG

An international team of asteroid and comet experts, including two from the University of Hawaiʻi, agrees on a natural origin for our first interstellar visitor.

On October 19, 2017, the Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS1) telescope, located at the University of Hawaiʻi's Haleakala Observatory, discovered the first known interstellar object to pass through our solar system. Researchers from around the world raced to collect as much data as possible before ʻOumuamua traveled beyond the reach of Earth's telescopes. In all, they had only a few weeks to observe the strange visitor.

The object is now usually known as ʻOumuamua, a name chosen in consultation with Hawaiian language experts Kaʻiu Kimura and Larry Kimura, which reflects the way this object can be considered a scout or messenger sent from the distant past to reach out to us (`ou means "reach out for", and mua, with the second mua placing emphasis, means "first, in advance of").

Early reports of ʻOumuamua's characteristics led some to speculate that the object could be an alien spacecraft sent from a distant civilization to examine our star system. But a review of all the available evidence by an international team of 14 experts strongly suggests that ʻOumuamua has a purely natural origin. The research team reported their findings in the July 1, 2019, issue of the journal Nature Astronomy.

"We have never seen anything like ʻOumuamua in our solar system," said Dr. Matthew Knight, the team leader from the University of Maryland "but our preference is to stick with analogs we know, unless or until we find something unique. The alien spacecraft hypothesis is a fun idea, but our analysis suggests there is a whole host of natural phenomena that could explain it."

The team of 14 astronomers hailing from the U.S. and Europe met late last year at the International Space Science Institute (ISSI) in Bern, Switzerland, to critically assess all the available research and observations on ʻOumuamua and will meet again late this year. Their first priority was to determine whether there is any evidence to support the hypothesis that ʻOumuamua is a spacecraft built by an alien civilization.

"We put together a strong team of experts in various different areas of work on ʻOumuamua. This cross-pollination led to the first comprehensive analysis and the best big-picture summary to date of what we know about the object," Knight explained. "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."

"While ʻOumuamua's interstellar origin makes it unique, many of its other properties are perfectly consistent with objects in our own solar system" said Dr. Robert Jedicke of the University of Hawai'i's Institute for Astronomy (IfA). In fact, ʻOumuamua's orbit, its path through our solar system, matches a prediction published in a scientific journal by Jedicke and his colleagues half a year before ʻOumuamua's discovery.

The ISSI team considered all the available information in peer-reviewed scientific journals and paid special attention to the research published by IfA researchers. In particular, Dr. Karen Meech's research paper in the journal Nature that first reported on ʻOumuamua's discovery and characteristics in December 2017, just two months after the unusual object was identified by Pan-STARRS1. "It was exciting and exhausting to coordinate all the ʻOumuamua observations with my co-authors from all around the world. It really was a 24 hour a day effort for the better part of two months. In that paper we established that ʻOumuamua rotates once in about seven hours and that is had a red color similar to many objects locked within our own solar system." said Meech. That work also showed that ʻOumuamua must have an extremely elongated shape, like a cigar or maybe a frisbee, unlike any known object in our solar system based on changes in its apparent brightness while it rotated.

Meech and other UH researchers were critical to another paper published in Nature a year ago that indicated ʻOumuamua is accelerating along its trajectory as it leaves our solar system. This behavior is typical of comets but astronomers have found no other visual evidence of the gas or dust emissions that create this acceleration. Meech explained that "while it is disappointing that we could not confirm the cometary activity with telescopic observations it is consistent with the fact that ʻOumuamua's acceleration is very small and must therefore be due to the ejection of just a small amount of gas and dust."

The ISSI team considered a number of mechanisms by which ʻOumuamua could have escaped from its home system. For example, the object could have been ejected by a gas giant planet orbiting another star. According to this theory, Jupiter created our own solar system's Oort cloud, a population of small objects only loosely gravitationally bound to our Sun in a gigantic shell extending to about a third of the distance to the nearest star. Some of the objects in our Oort cloud eventually make it back into our solar system as long period comets while others may have slipped past the influence of the Sun's gravity to become interstellar travelers themselves.

The research team expects that ʻOumuamua will be the first of many interstellar visitors discovered passing through our solar system and they are collectively looking forward to data from the Large Synoptic Survey Telescope (LSST) which is scheduled to be operational in 2022. The LSST, located in Chile, may detect one interstellar object every year and allow astronomers to study the properties of objects from many other solar systems.

While the ISSI team hopes that LSST will detect more interstellar objects they think it is unlikely that astronomers will ever detect an alien spacecraft passing through our solar system and they are convinced that ʻOumuamua was a unique and extremely interesting but completely natural object.

The research paper, "The Natural History of ʻOumuamua," the ʻOumuamua ISSI Team (Michele Bannister, Asmita Bhandare, Piotr Dybczyński, Alan Fitzsimmons, Aurélie Guilbert-Lepoutre, Robert Jedicke, Matthew Knight, Karen Meech, Andrew McNeill, Susanne Pfalzner, Sean Raymond, Colin Snodgrass, David Trilling and Quanzhi Ye), was published in the journal Nature Astronomy on July 1, 2019.


This work was supported by the UK Science and Technology Facilities Council (Award Nos. ST/P0003094/1 and ST/L004569/1), the National Science Foundation (Award Nos. AST1617015 and 1545949), NASA (Award Nos. GO/DD-15405, GO/DD-15447, NAS 5-26555, NNX17AK15G and 80NSSC18K0829), the National Science Centre in Poland (Award No. 2015/17/B/ST9/01790) and the European Research Council (Award No. 802699). The content of this article does not necessarily reflect the views of these organizations.

More information about The PanSTARRS project can be found at the PanSTARRS project website http://panstarrs.ifa.hawaii.edu

The Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) is a wide-field survey observatory operated by the University of Hawaiʻi Institute for Astronomy. The Minor Planet Center is hosted by the Harvard-Smithsonian Center for Astrophysics and is a sub-node of the Planetary Data System Small Bodies Node at the University of Maryland (http://www.minorplanetcenter.net ). JPL hosts the Center for Near-Earth Object Studies (CNEOS). All are projects of NASA's Near-Earth Object Observations Program, and elements of the agency's Planetary Defense Coordination Office within NASA's Science Mission Directorate.

Founded in 1967, the Institute for Astronomy at the University of Hawaii at Manoa conducts research into galaxies, cosmology, stars, planets, and the sun. Its faculty and staff are also involved in astronomy education, deep space missions, and in the development and management of the observatories on Haleakalā and Maunakea. The Institute operates facilities on the islands of Oahu, Maui, and Hawaii.