Crabs with Metallic Blood

The short story "Uncommon Sense," by Hal Clement may be the best example ever of what makes hard science fiction so appealing.

Hard SF is essentially speculative fiction in which the author makes sure he gets the science right. In the past, I've talked about Poul Anderson and Robert Heinlein, who wrote superb hard SF, combining accurate science with strong plots and great characters.

But as Poul Anderson once wrote, Hal Clement set the standard for hard SF. His best-known work is Mission of Gravity (1954), set on a high-gravity world. And now that I've written that sentence, I now feel obligated to read the novel again--so I'll probably do a post about it soon. But for today, we'll talk about "Uncommon Sense," published in the September 1945 issue of Astounding Science Fiction magazine.

The protagonist is Laird Cunningham, a rich guy who travels from planet to planet looking for unusual animal species pretty much because he enjoys doing so. But now he's in trouble. He's learned his two assistants are planning on hijacking his small ship. He crash lands on a small planet and makes a break for it, wearing a space suit with several days supply of food and air.

The planet is only slightly larger than the Moon, so it has a low gravity. But it's very near a hot star and during the daytime Cunningham must stay in a cave to hide from the heat and radiation. The planet is also has a near-vacuum level atmosphere.

In the meantime, the two hijackers--with access to better protected suits--are repairing cracks in the hull of the ship.  During the day, Cunningham can't get to the open airlock without being spotted. During the night, the airlock is closed when the bad guys go back inside.

Cunningham passes the time by watching the local fauna. There are small crab-like things that feed on the plants, slightly larger crab-like things that feed on the little guys and 40-foot-long centipedes that feed on everything. Cunningham uses a sharp rock to dissect one of the little guys and discovers that it has liquid metal for blood. That makes sense--since the daylight temperature is hot enough to melt lead.

But isn't this useless information? In a day or two, the ship will be repaired and he'll be stranded here to die.

Well, it turns out no information is ever useless. With what he's learned of the anatomy of the little crabs--and what he's deduced about how the fauna on this world "sees"--AND what he knows about the temperature extremes between night and day--he just might come up with a plan for distracted the bad guys long enough for him to sprint into the space ship airlock and lock the villains out.

It's a fun story because in the end, it all makes sense. Clement does a fantastic job of world-building--coming up with an ecosystem that might logically exist on an airless world with vast diurnal temperature extremes. Then he comes up with a clever way for the protagonist to use this information to outwit his enemies. It's a tight, well-plotted story that could be used as a model for anyone learning how to write good science fiction.