The first known asteroid from interstellar space has been observed and measured, and the object is exceptionally weird, according to the European Southern Observatory.
The unique rock was first spotted when the Pan-STARRS 1 telescope in Hawaii picked up a faint point of light moving across the night sky. Measurements of the object's trajectory quickly made it obvious that it couldn't possibly be from our solar system; this was an interstellar asteroid, a momentary visitor to our neighborhood that had likely been wandering around alone in space for billions of years.
Not only is this asteroid the first-known interstellar object discovered to pass through our solar system, but its shape and appearance seems to defy all expectations. It's dark reddish in color and appears highly elongated, even cigar-shaped. In fact, its shape harkens back to the movie "Star Trek IV: The Voyage Home," in which Capt. Kirk and crew head back to Earth only to discover that a nefarious cigar-shaped object has entered the solar system, broadcasting the sounds of humpback whales, and is threatening to destroy the planet.
Thankfully, this object isn't quite so talkative and hostile, and already looks to be rapidly departing the solar system. Scientists have named it 'Oumuamua. ("Ou" means "reach out for," and "mua," with the emphasis on the second "mua," means 'first, in advance of' — reflecting the nature of the object as a "scout" or "messenger" from the past.)
"We had to act quickly," explained team member Olivier Hainaut from European Southern Observatory in Garching, Germany, about discovering the object's rapid escape trajectory. "'Oumuamua had already passed its closest point to the Sun and was heading back into interstellar space."
Researchers surmised that 'Oumuamua's dark, red color is indicative of a high metal content that has been irradiated from cosmic rays over the course of millions of years. Since the object has probably been wandering the Milky Way unattached to any solar system for so long, its origin is extremely difficult — perhaps impossible — to pinpoint.
An asteroid or a comet?
Some scientists initially thought the object might be a comet. Comets differ from asteroids because they are comprised of ice, dust and rock while asteroids have metal instead of ice. Researchers from Queen's University in Belfast (QUB), Ireland, noticed 'Oumuamua reflected sunlight and is similar to icy objects in space that have a dry crust, meaning there may be the presence of water.
"This is because 'Oumuamua has been exposed to cosmic rays for millions, or even billions, of years, creating an insulating organic-rich layer on its surface," Professor Alan Fitzsimmons said in a statement. "We have also found that a half-meter thick coating of organic-rich material could have protected a water-ice-rich comet-like interior from vaporizing when the object was heated by the sun, even though it was heated to over 300 degrees centigrade."
Since then, however, it has been determined that 'Oumuamua is an asteroid, not a comet — which only seems to deepen the mystery, according to NASA. "While it is a historic discovery, the existence of interstellar objects is not a surprise," the space agency explains. "What is a surprise, however, is the fact that the first detected interstellar object is an asteroid — not a comet as most scientists had expected. Even more surprising is the strange, highly-elongated shape of 1I/2017 U1. None of the known asteroids or comets in our own solar system have such an elongated shape."
'Oumuamua's tumbling motion is unusual, too, as a team of QUB researchers reported in February 2018. Its chaotic movements point to a "violent past," they noted, possibly due to an ancient collision with another asteroid before it was thrown out of its own solar system.
"Our modeling of this body suggests the tumbling will last for many billions of years to hundreds of billions of years before internal stresses cause it to rotate normally again," QUB astrophysicist Wes Fraser said in a statement. "While we don't know the cause of the tumbling, we predict that it was most likely sent tumbling by an impact with another planetesimal in its system, before it was ejected into interstellar space."
Scientists are racing to learn as much as they can about 'Oumuamua before it leaves us forever. The asteroid is expected to pass above Jupiter's orbit in May 2018, followed by Saturn in January 2019 and then Neptune in 2022. Still, its brief visit might leave us with more questions than answers.
Although it's the first interstellar space rock ever observed, astronomers estimate that we have at least one such alien visitor per year. So after 'Oumuamua leaves us, we'll just have to keep looking for more.
"We are continuing to observe this unique object," said Hainaut, "and we hope to more accurately pin down where it came from and where it is going next on its tour of the galaxy. And now that we have found the first interstellar rock, we are getting ready for the next ones!"
Check out this video, compiled by ESO, for more info about this wild object:
Editor's note: This file has been updated with new information since it was originally published in November 2017.