A bigger problem is CO₂. The potatoes need to breathe. I know what you’re thinking. “Mark, old chap! You produce carbon dioxide! It’s all part of the majestic circle of nature!”

The problem is: Where will I put it? Sure, I exhale CO₂ with every breath, but I don’t have any way to store it. I could turn off the oxygenator and atmospheric regulator and just fill the Hab with my breath over time. But CO₂ is deadly to me. I need to release a bunch at once and run away.

Remember the MAV fuel plant? It collects CO₂ from the Martian atmosphere. A 10-liter tank of compressed liquid CO₂, vented into the Hab, will be enough CO₂ to do the trick. That’ll take less than a day to create.

So that’s everything. Once I vent the CO₂ into the Hab, I’ll turn off the atmospheric regulator and oxygenator, dump a ton of water on the crops, and head out.

Sirius 4. A huge step forward in my rover research. And I can start tomorrow.

CHAPTER 8

“HELLO, AND thank you for joining us,” Cathy Warner said to the camera. “Today on CNN’s Mark Watney Report: Several EVAs over the past few days… what do they mean? What progress has NASA made on a rescue option? And how will this affect the Ares 4 preparations?

“Joining us today is Dr. Venkat Kapoor, director of Mars operations for NASA. Dr. Kapoor, thank you for coming.”

“A pleasure to be here, Cathy,” Venkat said.

“Dr. Kapoor,” Cathy said, “Mark Watney is the most-watched man in the solar system, wouldn’t you say?”

Venkat nodded. “Certainly the most watched by NASA. We have all twelve of our Martian satellites taking pictures whenever his site’s in view. The European Space Agency has both of theirs doing the same.”

“All told, how often do you get these images?”

“Every few minutes. Sometimes there’s a gap, based on the satellite orbits. But it’s enough that we can track all his EVA activities.”

“Tell us about these latest EVAs.”

“Well,” Venkat said, “it looks like he’s preparing Rover 2 for a long trip. On Sol 64, he took the battery from the other rover and attached it with a homemade sling. The next day, he detached fourteen solar cells and stacked them on the rover’s roof.”

“And then he took a little drive, didn’t he?” Cathy prompted.

“Yes he did. Sort of aimlessly for an hour, then back to the Hab. He was probably testing it. Next time we saw him was two days later, when he drove four kilometers away, then back. Another incremental test, we think. Then, over the past couple of days, he’s been stocking it up with supplies.”

“Hmm,” Cathy said, “most analysts think Mark’s only hope of rescue is to get to the Ares 4 site. Do you think he’s come to the same conclusion?”

“Probably,” Venkat said. “He doesn’t know we’re watching. From his point of view, Ares 4 is his only hope.”