It just occurred to me that while Mars is cold from a human's perspective, from a radio engineer's perspective it's still kind-of hot.
When even the largest DSN antennas are pointed at Mars to receive signals from spacecraft in orbit around Mars, or even potentially on the surface, they can't really resolve or separate thermal radio noise from the planet from radio transmissions of the same frequency by a spacecraft.
Using 32 GHz (9 mm wavelength, from here) and 70 meters, I get a beam width much larger than the planet even at closest approach.
Even on a per-Hz basis, wouldn't the thermal radiation from the whole planet be much stronger than radio transmissions from spacecraft there?
note: I've just found out that the first 70m dish was built specifically to "talk to Mars' or actually Mariners 3 and 4, who's missions flew past Mars. While Mariner 3 didn't make it, Mariner 4 did. Why does the word “Mars” shows up in google maps when viewing the Goldstone DSN complex?