In the movie - when Watney is recovering after being left behind and drilled by the antenna - he's laying in his bunk moping. Or thinking. Or both. And you can see every couple of seconds the exterior searchlight flashing through the hab windows as it sweeps by. Even when he wasn't the only human on the planet, when his crewmates were there with him ... what was the purpose of the 24/7 searchlight?

No crew was going to go wandering around on the surface during the night (unsafe! NASA wouldn't permit it!) and meanwhile the light constantly flashing in the windows would disturb the sleep of the crew (leads to unfit crew! therefore to unsafe conditions! NASA shouldn't've permitted it!)

(Or am I overthinking this and this is just one of those movie things. For visualization purposes.)

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    If for some reason you need to go outside the hab at night, you really want to have that light on so you can find your way back. Getting lost means death by asphyxiation. People have walked off hiking trails right here on Earth and starved to death because they got turned around and couldn't find their way back. You'll die much faster on Mars. You don't want any chance of someone switching that light off while you're out there, so there's probably no way to turn it off.
    – Kyle Jones
    Commented Dec 7, 2016 at 5:44

2 Answers 2


There is no mention of the HAB light in the source novel; there, the HAB transmits a homing signal that can be picked up by a suit or a rover. Watney uses this signal when returning with Pathfinder.

The only reason I can think comes from Kyle Jones' comment. It could be possible that the signal transmitted by HAB might not be "visible" during a storm, while a light would. This is not very likely though, as the HAB's signal was capable of transmitting as far as 100 km (at very best), or 40 km (normal range).

Your last line is basically correct - there is no reason whatsoever for the HAB to have this searchlight. Other than Ridley Scott's genius, I suppose.


I for one, if found to be on a planet that could be monitored by satellite, would turn on what would be the equivalent of a help sign on the beach. Now this of course would only work at night.

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