New research concludes that the interstellar object that entered our solar system and then rocketed out was a small comet and not a spacecraft, as some had speculated. (JPL/NASA)
In 2017, an unusual small object flew into our solar system from afar, approached the inner solar system and the Sun and then sped back out to interstellar space. In all, it was detected and followed for 11 days.
The object was puzzling because such interstellar visitors had not been observed before, and most mysterious because it accelerated in a most unusual way out of the solar system. This was not the normal behavior of any object in the solar system.
The object, a few hundred meters in length, was first identified as an asteroid because it had not of the sparkle of a comet, and a “dark comet” was proposed, and then something perhaps sent by aliens to explore the solar system. After all, the shape of the object known as ‘Oumuamua — Hawaiian for “Scout”– was described as reddish and sometimes shaped like a pancake and sometimes like a cigar.
‘Oumuamua became an object of great fascination among space scientists and even became the subject a popular book by a Harvard astronomer who argued that it was clearly an alien lightsail. That is, a probe that is propelled by the propulsive radiation of starlight itself.
Now, a paper offers a very different, and apparently quite compelling, explanation.,
In Nature, University of California, Berkeley astrochemist Jennifer Bregner and Cornell University astronomer Darryl propose that the comet’s mysterious deviations from a typical object’s path around the Sun can be explained by a simple physical mechanism likely common among many icy comets: outgassing of hydrogen as the comet warmed up in the sunlight.
What made ‘Oumuamua different from every other well-studied comet in our solar system was its size. It was so small that the gravitational nudge it received around the Sun was slightly altered by the tiny push created when hydrogen gas spurted out of the ice.
And that’s what caused the acceleration, the scientists say.
An artist rendering of ‘Oumuamua, the first known alien object to enter our solar system. It was identified by the Pan-STARRS 1 telescope in Hawaii. It was later followed by observatories around the world and astronomers generally concluded that it had been traveling for millions of years before its chance encounter with our solar system.
