The Oort Cloud

The astronomy world was buzzing with the news that NASA had announced that Voyager I, the space probe launched in 1977, had reached interstellar space. After passing by the outer planets and their moons, and sending back spectacular images, it's now on its way to boldly go where no hardware has gone before.

But it's not that simple. Voyager, if the data is correct, has reached interstellar space, but has not left the solar system, and that's because the definition of the solar system is complex.

It is true that Voyager has left left the heliosphere, that area of the solar system that is influenced by the solar wind. So, in a sense, it has left the nest of the mother Helios. But there is more to the solar system that that. There is a considerable stretch of space between the heliosphere and the edge of the Oort Cloud, which will take Voyager another 300 years to cross.

What is the Oort Cloud? For one thing, it's got a great name, as if Douglas Adams or Kurt Vonnegut had named it. It's named after a Dutch astronomer who discovered it. Basically, it's a ring of particles, or icy planetisimals, that circle around the solar system. It's thought to be a source of many comets that have made their way through our solar system, but there's still a lot that is not known about it.

But what fascinates me is that it is an example of just how vast space is. Voyager, the farthest a man-made object has ever traveled, is 125 AU from the sun. It has taken 36 years to reach that considerable distance. But it will take another 300 years for the probe to reach the inner edge of the Oort Cloud. It will take another 30,000 years for it to make through the cloud in its entirety. Put another way, the Kuiper Belt, which is a band of objects that are classified as trans-Neptunian, and includes the decommissioned planet Pluto, is 1/1,000 of the distance from the sun as to the outer edge of the Oort Cloud, which is 50,000 AU, or approximately one light year, away from the sun.

It's just a further reminder of how the notion of interstellar travel is one of science fiction, not science fact. The Oort Cloud is one quarter of the way to Proxima Centauri, the star closest to the sun. So, even traveling at light speed, which Einstein posited is physically impossible, it would take four years for anyone to make it from there to here. Unless there's something going on that we can't account for, like wormholes or the bending of the time/space continuum, it would be a major effort to get here, with technology that is far advanced our own. The universe is only so old--has there been time for any civilization to reach such heights?

Voyager's first contact with another star, if it is still going, would be Gliese 445, in 40,000 years. The probe includes phonograph records of various sounds of Earth, including music by Beethoven, Mozart, and Chuck Berry. Surely the Chuck Berry would inspire interest in civilizations out there to come visit. Of course, the ironic thing is that the phonographs are obsolete technology here on Earth.