We’ve already discussed that, for example, it won’t be very good on Mars without a spacesuit. On “hospitable” Venus, too. Remember how Arnie looked when he found himself in a vacuum on the red planet for a couple of minutes in Total Recall? He definitely didn’t like it, and despite the fact that it’s a movie and everything is made of rubber (yes, back then it still had no special effects, which makes it doubly interesting to watch), the situation is shown quite realistically .
Finding yourself on the surface of Mars without a spacesuit is a sure and quick path to death. The rarefied atmosphere, consisting mainly of carbon dioxide, is unsuitable for breathing. The pressure 170 times lower than on Earth will lead to instant decompression: boiling of fluids in the body, rupture of the lungs and severe cerebral edema. Low temperatures (on average -60°C) will cause frostbite and general hypothermia. The absence of the ozone layer will make a person defenseless against harmful ultraviolet radiation, causing burns and DNA damage. As a result, death will occur within a few minutes, if not seconds. This is typical for many planets. But what will things be like on the Moon?
On the moon, without a spacesuit, you will probably even remain conscious for at least 10 seconds. The sun will be very bright, your skin, already uncomfortable due to the lack of pressure, will quickly begin to get sunburned. However, all the moisture in your body will evaporate/boil almost instantly, taking the heat with it. This will be very noticeable to your eyes, mouth and nose, which will dry out quickly. This will also probably be the last thing you are aware of before you lose consciousness.
You will lose consciousness between 20 and 30 seconds after exposure to the vacuum. You will be able to breathe, but nothing will come in when you inhale, and you will exhale all the gases from your lungs when you exhale. This will deplete your body of all the gas, which will be directed to your brain and cause rapid unconsciousness.
The best part is that it’s all very peaceful against the backdrop of Mars. You don’t explode, you don’t freeze, you don’t have any trouble breathing. You just keep breathing, mostly unaware that anything is wrong, a slight tingling sensation, sounds become muffled, a strange sensation like saliva is bubbling on your tongue, and you lose consciousness.
The exact time it takes to lose consciousness will depend on how fast your blood is moving and how quickly you are exposed to the full vacuum. Each heartbeat will pull the degassed blood closer to your brain, and when your brain has received the full dose, you will lose consciousness.
Another interesting thing. In case of sudden depressurization on the Moon, there is a chance to change into a spacesuit in time. But it is extremely small if it is not in the immediate vicinity. A person must act instantly and accurately, relying on his training. Every second counts. If the spacesuit is a few steps away, it is theoretically possible to put it on in time, but this will require incredible reaction speed and luck. In most cases, especially in case of sudden depressurization, there will unfortunately not be enough time. But on Mars, one could not even dream of such a trick.