Dr. Meech’s team has now published the first report of their observations in Nature. The paper describes the interstellar visitor as both reassuringly familiar and utterly alien.
“We don’t see anything like that in our solar system,” Dr. Meech said.
In its color and other imputed properties, Oumuamua resembles the asteroids we already know and fear will one day smash the Earth and human civilization to smithereens.
But asteroid’s shape is weird. It is extremely elongated, at least 10 times as long as it is wide, perhaps 800 yards by 80 yards.
Though the mysterious object is nearly gone, thousands like it probably lurk unsuspected and undetected in our solar system, according to the scientists.
The Pan-STARRS telescope was built to patrol the sky for dangerous asteroids in our own system, not interlopers from beyond. But astronomers got a surprise.
Dr. Meech learned in a phone call one night that her colleagues had found one whose path seemed to originate beyond the solar system altogether. “Wow, this is exciting,” Dr. Meech recalled thinking.
Astronomers had long surmised that interstellar debris might invade the solar system from time to time, in the form of icy chunks spit from the rocky disks forming faraway planets.
Such wanderers would manifest themselves as comets when they got close to our sun, vaporizing and lighting up; however, they have not been seen. Now astronomers know why.
Oumuamua showed no such cometary brightening. It is so dark and faint that it could only have been detected by a powerful telescope with a wide field of view, like Pan-STARRS.
Many more should be visible to the Large Synoptic Survey Telescope, with a diameter of eight meters, being built in Chile. “We have to get ready for these,” Dr. Meech said.
Oumuamua brightens and dims dramatically every 7.3 hours, which suggests that it is rotating about its short axis. That is something the little asteroid could endure without flying apart only if it were made of sterner, stronger stuff than the dirty snow that characterizes most comets.
Spectral measurements have revealed that Oumuamua is dark red, the color of many moons of the outer solar system on which icy organic molecules have been stained by radiation in outer space. Iron can also contribute that color, Dr. Meech said.
How Oumuamua got its shape is a mystery for now. Perhaps, Dr. Meech said, it was shot away from its home star by a supernova explosion. Or perhaps it was formed by a pair of objects that collided and stuck together. Stay tuned.
Where did it come from? Dr. Meech said the astronomers were initially excited when the orbit appeared to point to the brightest star in Lyra, Vega, which is known to have a debris disk. It would have taken the object about 600,000 years to get here from there, astronomers estimated.