Getting the joke of this cartoon probably requires knowing the basic plot of H.G. Wells' novel, The War of the Worlds, in which Martians invading Earth are stymied when they fall prey to ordinary microbes here they don't have at home. I post this today partly to celebrate the successful landing of NASA's latest rover on Mars. It's primary mission--at last!--is to search for signs of life, even microbial life, that may have existed in earlier times when Mars had a decent atmosphere. It will collect soil samples that, it is planned, will be analyzed by many labs using many methods when returned to Earth. Returning anything from a planet has yet to be accomplished.
I had higher hopes for this mission when I thought that returning the samples to Earth was part of it. But it turns out not to be so. The "plans" are vague, and the mission to do so is not yet scheduled. If it happens at all, it likely won't be for another decade. That's disappointing, because the discovery that life has ever existed beyond Earth, let alone that it exists now, would be so wonderful to experience. I hadn't thought about it much recently, but I have come to believe that this discovery, if it is made at all, will be made some time in the next 50 years. This looked like the best opportunity for it in my lifetime. Now it seems less likely.
But if some fossil microbial life is found on Mars, that in itself may not be the only discovery. It is possible that evidence could help answer the question more and more scientists are now asking: did life on Earth originate on Mars? Mars is much older and had a life-supporting environment much sooner. Space rocks etc. are exchanged between the planets all the time, and some microbial life could make the journey intact. Life arose on Earth suspiciously soon after the conditions were right. Could it have been the blossoming of a Martian seed?
And so the question above is asked again in actuality as well as fiction: who are the Martians?