Mars Odyssey is a robotic spacecraft that gathers information, including images and sends it back to Earth. Jet Propulsion Laboratory (JPL) listens to Odyssey talk and talks back to her. She also relays what the Mars Rovers say to JPL.  In a way, for Mars, Odyssey is gossip central.

Mars Odyssey Orbiter was launched on April 7, 2001.

Odyssey reached an orbit around Mars on October 24, 2001. JPL had to adjust her orbit until she was where it needed to be.
This is a basic diagram of what instruments are on board.

There is a very complicated explanation of all this, but I’m not the one to give it. I am easily confused.

This is a picture of Odyssey over Mars as drawn by an artist.

Odyssey had some parts wearing out. JPL put Odyssey on safe mode so that they could switch over to the back up system. The back up system hadn’t been booted since 2001, before she was launched.
During the switch over, Mars Reconnaissance took over the duties for Odyssey. Mars Reconnaissance is a newer robotic spacecraft orbiting Mars.
A picture of Mars Reconnaissance.

JPL rebooted the back up system on Odyssey and she was up and running. The first bit of data they received was from the Mars Exploration Rover, Opportunity.

A picture of Opportunity.

The other rover has more than one way to talk to JPL, but she uses Odyssey as well.

The last picture is of the Mars Science Laboratory, Curiosity.