“We haven’t found any way to make that happen, no. His life support alone takes more energy than that.”

“How long until he enters the storm?”

“He’s just entered Mawrth Vallis now. At his current rate of travel, he’ll be at the edge of the storm on Sol 471. That’s twelve days from now.”

“Surely he’ll see something is wrong,” Cathy said. “With such low visibility, it won’t take long for him to realize his solar cells will have a problem. Couldn’t he just turn around at that point?”

“Unfortunately, everything’s working against him,” Venkat said. “The edge of the storm isn’t a magic line. It’s just an area where the dust gets a little more dense. It’ll keep getting more and more dense as he travels onward. It’ll be really subtle; every day will be slightly darker than the last. Too subtle to notice.”

Venkat sighed. “He’ll go hundreds of kilometers, wondering why his solar panel efficiency is going down, before he notices any visibility problems. And the storm is moving west as he moves east. He’ll be too deep in to get out.”

“Are we just watching a tragedy play out?” Cathy asked.

“There’s always hope,” Venkat said. “Maybe he’ll figure it out faster than we think and turn around in time. Maybe the storm will dissipate unexpectedly. Maybe he’ll find a way to keep his life support going on less energy than we thought was possible. Mark Watney is now an expert at surviving on Mars. If anyone can do it, it’s him.”

“Twelve days,” Cathy said to the camera. “All of Earth is watching but powerless to help.”

LOG ENTRY: SOL 462

Another uneventful sol. Tomorrow is an Air Day, so this is kind of my Friday night.

I’m about halfway through Mawrth Vallis now. Just as I’d hoped, the going has been easy. No major elevation changes. Hardly any obstacles. Just smooth sand with rocks smaller than half a meter.

You may be wondering how I navigate. When I went to Pathfinder, I watched Phobos transit the sky to figure out the east-west axis. But Pathfinder was an easy trip compared to this, and I had plenty of landmarks to navigate by.

I can’t get away with that this time. My “map” (such as it is) consists of satellite images far too low-resolution to be of any use. I can only see major landmarks, like craters 50 kilometers across. They just never expected me to be out this far. The only reason I had high-res images of the Pathfinder region is because they were included for landing purposes; in case Martinez had to land way long of our target.

So this time around, I needed a reliable way to fix my position on Mars.

Latitude and longitude. That’s the key. The first is easy. Ancient sailors on Earth figured that one out right away. Earth’s 23.5-degree axis points at Polaris. Mars has a tilt of just over 25 degrees, so it’s pointed at Deneb.

Making a sextant isn’t hard. All you need is a tube to look through, a string, a weight, and something with degree markings. I made mine in under an hour.