Ka has many meanings.
Ka is said to be the name the legendary little red people give to themselves. The Ka, the original Martians, chose to be invisible to the human colonists and instead observe them and see how they would do. It is said that John Boone was the only person that they talked to, so John spoke of areoformation and was able to gather many people around him. But the humans took John away, and the Ka spoke no more. The only other person they spoke to was Nirgal; thanks to the Ka, Nirgal really did feel Mars and brought all Martians together to make a system that was just, for both Martians and humans.
Suitably enough, the sound "ka" is found in many Mars-related words of many languages. The Japanese name for Mars is Kasei, meaning "fire star" (ka is "star"). The Arabic, Indonesian and Malay name for Mars is Al Qahira (also Arabic for Cairo, "the victorious").
The Ka legend gave its name to the political movement the Ka, that was represented in the Pavonis Mons Congress.
Also, "Ka" is a versatile word in Martian speech. It can be a simple and popular greeting among fellow Martians, or an exclamation, or a sign of agreement.