An international team of asteroid and comet experts, including two from the University of Hawaii, 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 Hawaii’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 ‘Oumuamua 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 ‘Oumuamua, a name chosen in consultation with Hawaiian language experts Ka’iu 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 ‘Oumuamua’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 ‘Oumuamua 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 ‘Oumuamua 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 ‘Oumuamua and will meet again late this year. Their first priority was to determine whether there is any evidence to support the hypothesis that ‘Oumuamua is a spacecraft built by an alien civilization.
“We put together a strong team of experts in various different areas of work on ‘Oumuamua. 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 ‘Oumuamua 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 ‘Oumuamua’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, ‘Oumuamua’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 ‘Oumuamua’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 ‘Oumuamua’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 ‘Oumuamua 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 ‘Oumuamua 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 ‘Oumuamua 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 ‘Oumuamua 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 ‘Oumuamua’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 ‘Oumuamua 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 ‘Oumuamua 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 ‘Oumuamua was a unique and extremely interesting but completely natural object.