Life on Mars?
Hmmmm well if you believe Gerry Anderson there is either; Gigantic fire spitting Martian Rock Snakes (Thunderbirds are Go, movie). Evil Mysterons who will wage a terrible war on Earth and kill people (Captain Scarlet), Androids from the planet Guk lead by their evil Queen Zelda (Terrahawks) Or all three.
Hardly room for exploatory probes in that case.