I calculated how long we've had continuous presence around the various planets, etc.

[CaptRobau]

This all started with me wanting to know how long mankind has had a continuous probe presence in/around the planet Mars. After I looked that up I decided to do it for the rest as well. I've limited myself to probes that were active, so no derelicts (because that would make it continuous after the first orbiter).

Sun

On December 16, 1965 the US launched Pioneer 6 into a heliocentric orbit. The long life of the Pioneer solar probe bridged the gap to more recent solar observatories. At the moment there are about half a dozen probes in an orbit around the Sun (and a few probes en route to planets).

Mercury

Since MESSENGER's orbital insertion around Mercury on March 18, 2011 we've had something around Mercury continuously. Namely MESSENGER. We haven't sent much to Mercury .

Venus

On April 11, 2006 the Venus Express has been in orbit around Venus.

Earth (unmanned)

Since Sputnik 2 was launched on November 3, 1957 we've had at least one operational probe in Earth orbit. The Starfish Prime high-altitude nuclear test nearly broke the chain, but enough satellites survived to bridge the gap where (commercial) communications satellites began being sent up.

Earth (manned)

ISS Expedition 1 went up on November 2, 2000 and we've had a person up there ever since. If not for the gap between Mir and ISS this date would lie somewhere in the late 80s.

Moon

We've sent a lot of probes to the Moon, but there were a few gaps meaning that we've only had a continuous presence since June 23, 2009 with the Lunar Reconnaissance Orbiter.

Mars

The Mars Global Surveyor inserted itself into Mars orbit on November 9, 1997 and has passed the baton to orbiters and rovers that are still operational.

Saturn

Since July 1, 2004 Cassini has been sending us data on our favorite ringed planet.

[Sirrobert]

Now we just need some forcefields and we can have manned solar presence