Isn’t that a poetic title?

Deep in the outer Solar System (about 1/4 the way to Proxima Centauri), lies the hypothesized home of long-period comets; the Oort Cloud (rhythms with “fort”, “short” and “snort”).  Possibly a remnant of our Solar System’s original protoplanetary disc, the Oort Cloud was hypothesized by astronomer Jan Oort in 1950 to resolve a paradox concerning comets (basically, there shouldn’t be any comets left in the Solar System, so where are they coming from?).

Oort Cloud comparison - NASA/CalTech/R.Hurt

Believed to occupy a space from about 5,000 AU to about 50,000 AU, the Oort Cloud is thought to contain several trillion objects.  These objects would be small (some tiny), and the Oort Cloud is believed to have a total mass of only about 5X the Earth.  While there have been no confirmed, direct observations of the Oort Cloud, four Trans-Neptunian objects are considered part of the structure:  90377 Sedna, 2000 CR (105), 2006 SQ(372), and 2008 KV (42).

Voyager 1 conception - American Museum of Natural History

Admittedly, not much is yet known about the Oort Cloud.  It’s too far away and its objects are too small to allow easy study.  Hopefully, once Voyager 1 gets a bit further out, we’ll have more information.  Voyager 1, by the way, is currently in the heliosheath, and should enter heliopause in 2015.  That puts it about 10.6 billion miles away.  It has a long way to go before it will enter the Oort Cloud, if ever.  Also, New Horizons will blow past Pluto in July, 2015, and continue on toward the Kuiper Belt and the Oort Cloud.

Illustrated as roughly spherical, the Oort Cloud is very tenuously bound to the Sun’s gravity.  It is also influenced by the gravity of nearby stars, like Proxima Centauri.  It’s thought that gravity perturbations from nearby stars and planets are what sends objects from the Oort Cloud rocketing into the Inner Solar System, giving us comets.

Oort Cloud - NASA - It's big, for certain

While distant and mysterious, the Oort Cloud serves as a reminder that we really know very little about the Solar System (much less the Universe) in which we live.