At the opening of his legendary 1960s TV anthology “The Twilight Zone,” writer Rod Serling spoke of an eerie place between “light and shadow.” The dim outer periphery of our solar system is a gravitational twilight zone when drifters from other stars mingle with lost solar system debris, according to a recent study.
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At a distance of roughly six trillion miles from the sun an unknown number of ancient comet nuclei — each just a few miles across — drift at temperatures near absolute zero. When gravitationally perturbed they fall toward the inner solar system like apples shaken from a tree. At least we think they are there, based on the random direction and frequency at which comets dive-bomb the inner solar system.
This hypothetical region is named the Oort cloud after mid-20th century Dutch astronomer Jan Oort, who first proposed such a twilight region to explain what seemed to be a hidden reservoir of comets.
But a sexier name would be the “Alien Comet Zone.” Did I say alien? Yes, because this primeval deep freezer may contain comets that were gravitationally snatched from other stars.
Hal Levinson of the Southwest Research Institute (SWRI) in Boulder, Colorado reports that computer simulations show that the early sun could have stolen comets from neighboring newborn stars 4.5 billion years ago. Given the close proximity of young stars — as we see in the nearby Orion Nebula — “It’s hard to imagine it not happening,” says Levison.
Conventional wisdom has been that comets accompanied our own solar system’s planetary formation and then got gravitationally booted out to huge distances, like storing junk in the attic. But this kind of mayhem was happing around neighboring star systems too. Therefore, interstellar space got cluttered with a snowstorm of comets orphaned from their birthing star.
Levinson’s model estimates that there should be 400 billion comets out there that are loosely bound to the sun. But in those simulations where the comets only originate in the newborn solar system, the predicted population is a paltry 6 billion — one for nearly every person now living on Earth.
Levinson and his team say that the “alien comet” idea is bolstered by observations that find comets with very long orbital periods. These should have come from another star Levison maintains.
If this idea is correct, that comets could give us not just domestic chemistry of the primeval solar system, but imported chemical samples of the environment around those stars that where born along with the sun.
Rather than devising interstellar probes to collect such samples, all we have to do is sit back and wait for the samples to come to us.