Okay.  The solar system is, like, really big, you know?  No, I mean really, really big.  Like, super-massive “epic” big, you know?

Sorry about that.  I couldn’t resist.  Although the wording is annoying, the statement itself is correct.  The solar system is a big place; a lot bigger than some people realize.  Beyond the planets (and poor, demoted Pluto), beyond the Kuiper Belt and the scattered disc, we find the Oort Cloud (rhymes with “fort” and “short”).

NASA/JPL  (Artist’s conception of Kuiper Belt and Oort Cloud)

It’s mind-boggling to think that the tiny little blue rectangle contains the sun, all the planets, and the Kuiper Belt.

Although no confirmed, direct observation of the Oort Cloud has been made, most astronomers believe it to be the source of all long-period comets (like Halley), and of many of the Centaur and Jupiter class comets.  Loosely bound to the solar system, objects in the Oort Cloud are easily influenced by passing stars and the pull of the Milky Way itself.  These shifting gravitational influences will occasionally dislodge an Oort Cloud object and send it shooting into the inner solar system, where we see the objects as comets.

Composed of an inner and outer region, the majority of Oort Cloud objects are believed to be made up of ices such as water, methane, ethane, carbon monoxide, and hydrogen cyanide.  Object 1996 PW is a rocky asteroid believed to originate in the Oort Cloud.

Comet Hale-Bopp; an archetype of Oort Cloud objects:

Image:  Mkfairdpm; English WikiPedia  (some rights reserved) April 1997

Besides long-period comets, only four objects so far are believed to belong to the inner Oort Cloud:  90377 Sedna, 2000 CR105, 2006 SQ372, and 2008 KV42.

While the exact size of the Oort Cloud is unknown, it is believed to extend about 30 trillion km from the sun (18 trillion miles).  That puts its outer boundaries at slightly over three light-years (a light year is exactly 9,460,730,472,580.8 km).  To put some perspective to that distance, after 32 years Voyager I is only 16.596 billion km from the sun.