Asteroid ‘Oumuamua was a cigar-shaped asteroid so unusual that some astronomers suggested it was built by an alien civilisation. Now an international group of scientists have released the results of a new investigation of the strange object, which is zooming out of the solar system at 114,000 kilometres per hour. It is the first space rock discovered in our solar system that appears to have originated from another part of the galaxy. ‘Ouamuamua was spotted last year and later scanned for radio signals to make sure it was not an extraterrestrial probe. Although the results of this probe proved it was natural in origin, astronomers have argued about whether it was an asteroid or a comet ever since. Telescopes first spotted the mysterious red-tinged object last October as it zipped through the inner solar system. Neither a coma nor tail was spotted behind our first confirmed interstellar guest, which are the hallmarks of an icy comet. Now the Hubble Space Telescope has been used to examine the object in great detail. Italian astronomer Marco Micheli said new observations show ‘Oumuamua being propelled through space by gasses shooting out from behind it, which is a process called ‘outgassing’ that’s common in comets. The release of what’s believed to be gaseous carbon monoxide, carbon dioxide and water applied only a tiny force on the object (about 1,000 times smaller than the effect of the sun’s gravity), the researchers said. The team’s measurements ‘were so precise that we could see the change in position caused by the outgassing,’ said co-author Paul Chodas, manager of NASA’s Center for Near-Earth Object Studies at Jet Propulsion Laboratory in Pasadena, California.
‘It’s an exciting discovery,’ said Micheli of the European Space Agency. Micheli said computer models suggest objects typically are ejected during the formation of planetary systems, and that most of these castaways should be comets given their location on the frigid outskirts of their systems. Only a tiny fraction should be asteroids, by scientists’ best calculations. Had it been an asteroid, it would have been ‘extremely lucky to beat these odds’ – or it would have underscored scientists’ misunderstanding of the early solar system, Micheli said. Discovered by a telescope in Hawaii, Oumuamua is a Hawaiian word which means messenger from afar, or scout. Now it’s long gone, and our chances of knowing exactly what it was have disappeared with it.
The University of Toronto’s Alan Jackson, who reported in March that Oumuamua likely came from a two-star system, remains unconvinced of its true identity. ‘But this is certainly an interesting new piece of information for us to chew on,’ he said in an email. Astronomers from the University of Hawaii spotted ‘Oumuamua – named after the Hawaiian term for ‘scout’ or ‘messenger’ – in October passing the Earth at about 85 times the distance to the moon. It is the first object discovered in the solar system that appears to have originated from another part of the galaxy. Although thought to be an asteroid, ‘Oumuamua’s elongated cigar shape hundreds of metres in length but only one-tenth as wide is highly unusual for a typical space rock. ‘We think this is a tiny, weird comet,” said Marco Micheli from the European Space Agency. ‘We can see in the data that its boost is getting smaller the farther away it travels from the Sun, which is typical for comets.’
Credit: Jasper Hamill for Metro, 28 June 2018.