The cigar-shaped object known as ‘Oumuamua may be the first interstellar interloper to be discovered, but it’s not likely to be the last. Statistics suggest that there are lots more space rocks like it out there.
How many? About 100 septillion in our Milky Way galaxy, according to Yale astronomer Gregory Laughlin, who has analyzed the light curve and weird orbit of ‘Oumuamua — a Hawaiian word that basically means “first messenger from afar.”
That number is a 1 followed by 26 zeroes.
Laughlin arrived at that estimate by extrapolating from the observational capabilities of the Pan-STARRS Telescope in Hawaii, the instrument that first detected the object back in October 2017.
“The fact that Pan-STARRS was able to observe ‘Oumuamua means that there are on the order of 1026 such objects in our own galaxy, floating freely,” Laughlin told an overflow crowd today at the American Astronomical Society’s winter meeting in Seattle.
The mass of all those objects would add up to roughly 100 billion Earth masses, or the equivalent of one Earth for each star in the galaxy, he said.
Based on variations in ‘Oumuamua’s light curve, astronomers deduced that the object was extremely elongated — potentially with a 10-to-1 ratio of length to width. It was also accelerating more than expected on its way out of the solar system, which led some astronomers to speculate over whether it could have been an alien light sail.
‘Oumuamua’s weird shape and behavior added to its interstellar appeal, but Laughlin said subsequent research has shown that the patterns in its light curve are “perfectly consistent” with a moderate amount of comet-like outgassing in a specific direction.
“Over time, one gets a rotation spectrum that looks very similar to what was observed. … We think that the acceleration, the rotation and the chaotic light curve are all reasonably in match,” he said. “There’s lots of mysteries with ‘Oumuamua, but it doesn’t appear that there’s anything completely crazy.”
Laughlin said the details will be laid out in a research paper that he and his colleagues are preparing for publication.
As more next-generation telescopes swing into operation, it’s possible that more objects like ‘Oumuamua will show up. But Laughlin noted that ‘Oumuamua itself is fading from view forever as it makes its solar system exit.
“The odds of it coming close to another star are roughly 1 in every 1014, 1015 years,” he said. “So those brief, exciting moments in September and October were wonderful for us, but they were really the time of ‘Oumuamua’s life.”