Asteroids passing us by, and even potentially sending us to our deaths, is not news even for astronomers. But one that comes from outside our solar system definitely is. That is exactly why the asteroid named `Oumuamua has astronomers all over the world scampering when it passed by almost undetected. In addition to the asteroid’s unusual shape, `Oumuamua has been estimated to have been traveling hundreds of millions of years before its chance, and probably only, encounter with our solar system.
Most of the asteroids and comets we see or hear about come from our own ‘hood. They orbit the sun just as we and our planetary neighbors do, though in more erratic shapes and longer times. But our galaxy is made up of more than just those and, sometimes, some objects outside our neighborhood do come by for a very short and once in a lifetime visit.
When `Oumuamua was detected by the Hawaiian Pan-STARRS 1 telescope, it was almost mistaken for just another asteroid. While that might be true in terms of the object’s composition, calculations of its orbit revealed that it could not have come from our own solar system. In other words, this was an interstellar asteroid.
This sent scientists scampering to gather more data before the asteroid exited our solar system. It had already passed its nearest point to the sun in September, so it was a race against time. Thanks to the European Southern Observatory’s Very Large Telescope or VLT, they were able to gather just enough to determine the possible composition, not to mention the shape of the asteroid.
`Oumuamua was observed to vary dramatically in brightness every 7.3 hours when it spins on its axis. These lead scientists to theorize that, unlike most asteroids, it was very elongated with a convoluted shape. It had a dark red color with no dust around it, which meant it was dense and made up of rock or high metal content, with no traces of water or ice.
But perhaps the most intriguing part of the puzzle is `Oumuamua’s origin point, which is calculated to be from the direction of Vega in the constellation of Lyra. However, `Oumuamua took so long to pass our solar system, even at 95,000 km/h, that Vega might not have been in that position in space hundreds of thousands of years ago.
In truth, an interstellar asteroid might pass the solar system at least once a year. Most, however, have been under the radar. This very brief, almost missed blush of the first recorded interstellar visitor might give scientists more motivation to be on the lookout for more curious objects, especially now that we have equipment powerful enough to detect them.