So many of you have probably seen the movie “The Martian.” But for those of you who did not, it’s a movie about an astronaut who is stranded on Mars, and his efforts to stay alive until the Earth can send a rescue mission to bring him back to Earth.
Gladly, they do re-establish communication with the character, astronaut Watney, at some point so that he’s not as alone on Mars until he can be rescued. So while you’re watching the movie, or even if you haven’t, when you think about Mars, you’re probably thinking about how far away it is and how distant. And, what might not have occurred to you is, what are the logistics really like of working on another planet — of living on two planets when there are people on the Earth and there are rovers or people on Mars?
So think about when you have friends, families and co-workers in California, on the West Coast or in other parts of the world. When you’re trying to communicate with them, one of the things you probably first think about is: wait, what time is it in California? Will I wake them up? Is it OK to call? So even if you’re interacting with colleagues who are in Europe, you’re immediately thinking about: What does it take to coordinate communication when people are far away? So we don’t have people on Mars right now, but we do have rovers. And actually right now, on. Curiosity, it is 6:10 in the morning.
So, 6:10 in the morning on Mars. We have four rovers on Mars. The United States has put four rovers on Mars since the mid-1990s, and I have been privileged enough to work on three of them. So, I am a spacecraft engineer, a spacecraft operations engineer, at NASA’s Jet Propulsion Laboratory in Los Angeles, California. And these rovers are our robotic emissaries.
So, they are our eyes and our ears, and they see the planet for us until we can send people. So we learn how to operate on other planets through these rovers. So before we send people, we send robots. So the reason there’s a time difference on Mars right now, from the time that we’re at is because the Martian day is longer than the Earth day. Our Earth day is 24 hours, because that’s how long it takes the Earth to rotate, how long it takes to go around once.
So our day is 24 hours. It takes Mars 24 hours and approximately 40 minutes to rotate once. So that means that the Martian day is 40 minutes longer than the Earth day. So teams of people who are operating the rovers on Mars, like this one — this is one of our teams that I’m part of, I usually sit at this table over here — what we are doing is we are living on Earth, but working on Mars. So we have to think as if we are actually on Mars with the rover.
Our job, the job of this team, of which I’m a part of, is to send commands to the rover to tell it what to do the next day. To tell it to drive or drill or tell her whatever she’s supposed to do. So while she’s sleeping — and the rover does sleep at night because she needs to recharge her batteries and she needs to weather the cold Martian night. And so she sleeps. So while she sleeps, we work on her program for the next day.
So I work the Martian night shift. So in order to come to work on the Earth at the same time every day on Mars — like, let’s say I need to be at work at 5:00 pm, this team needs to be at work at 5:00 pm. Mars time every day, then we have to come to work on the Earth 40 minutes later every day, in order to stay in sync with Mars. That’s like moving a time zone every day. So one day you come in at 8:00, the next day 40 minutes later at 8:40, the next day 40 minutes later at 9:20, the next day at 10:00. So you keep moving 40 minutes every day, until soon you’re coming to work in the middle of the night — the middle of the Earth night. Right? So you can imagine how confusing that is.
Hence, the Mars watch. I think they’re going to zoom in. These weights in this watch have been mechanically adjusted so that it runs more slowly. Right? And we didn’t start out — I got this watch in 2004 when Spirit and Opportunity, the rovers back then. We didn’t start out thinking that we were going to need Mars watches.
Right? We thought, OK, we’ll just have the time on our computers and on the mission control screens, and that would be enough. Yeah, not so much. Because we weren’t just working on Mars time, we were actually living on Mars time. And we got just instantaneously confused about what time it was. So you really needed something on your wrist to tell you: What time is it on the Earth? What time is it on Mars? And it wasn’t just the time on Mars that was confusing; we also needed to be able to talk to each other about it.
So a “sol” is a Martian day — again, 24 hours and 40 minutes So when we’re talking about something that’s happening on the Earth, we will say, today. So, for Mars, we say, “tosol.” Yesterday became “yestersol” for Mars. Again, we didn’t start out thinking, “Oh, let’s invent a language.” It was just very confusing. I remember somebody walked up to me and said, “I would like to do this activity on the vehicle tomorrow, on the rover.” And I said, “Tomorrow, tomorrow, or Mars, tomorrow?” We started this terminology because we needed a way to talk to each other. Tomorrow became “nextersol” or “solorrow.” Because people have different preferences for the words they use.