Blood would boil on Mars primarily due to the extremely low atmospheric pressure, which causes bodily fluids to vaporize at normal body temperature.
The Peril of Low Pressure
Mars possesses an incredibly thin atmosphere, with a surface pressure less than one percent of Earth's. For comparison, Mars's atmospheric pressure is roughly equivalent to being at an altitude of about 30,000 meters (100,000 feet) above Earth's surface. On Earth, water boils at 100°C (212°F) at sea level, but as altitude increases and atmospheric pressure drops, the boiling point decreases significantly. On Mars, with its near-vacuum conditions, water—and thus the water in human blood and other body fluids—would boil at a temperature far below normal human body temperature.
Ebullism: Boiling Body Fluids
The phenomenon of bodily fluids boiling due to extremely low ambient pressure is known as ebullism. This occurs when the external pressure drops below the vapor pressure of the body's liquids, causing them to convert into gas. This critical pressure threshold is often referred to as the Armstrong Limit, which is approximately 0.06 atmospheres (6.3 kilopascals) or about 1/16th of Earth's standard atmospheric pressure at sea level.
If an unprotected human were exposed to the Martian surface, their internal body temperature (around 37°C or 98.6°F) would be far above the boiling point of their blood and other bodily fluids in such low pressure. This rapid depressurization would cause the liquids in the blood and tissues to vaporize, effectively boiling the blood. This fatal process would occur almost simultaneously with suffocation, as there is insufficient air to breathe.
Here's a comparison of relevant atmospheric conditions:
| Feature | Earth (Sea Level) | Mars (Surface Average) | Impact on Boiling Point |
|---|---|---|---|
| Atmospheric Pressure | ~101.3 kPa (1 atm) | ~0.6 kPa (0.006 atm) | Significantly lower |
| Boiling Point of Water | 100°C (212°F) | ~10°C (50°F) or lower, depending on precise pressure and conditions | Drastically reduced |
| Human Body Temperature | 37°C (98.6°F) | 37°C (98.6°F) | Constant |
As the table illustrates, a human's normal body temperature of 37°C is well above water's boiling point on Mars, leading to ebullism.
Beyond Boiling: Other Dangers
While ebullism is an immediate and catastrophic effect, unprotected exposure to the Martian environment presents other fatal dangers:
- Asphyxiation (Suffocation): The atmosphere on Mars is over 95% carbon dioxide, with very little oxygen. This makes it utterly unbreathable, leading to rapid suffocation.
- Extreme Cold: Martian temperatures can plummet to -125°C (-195°F) in winter near the poles, though average temperatures are around -63°C (-81°F). While freezing would occur, the boiling of fluids due to pressure would be the more immediate threat to an unprotected body.
- Radiation: Mars lacks a global magnetic field and has a very thin atmosphere, offering minimal protection from harmful solar and cosmic radiation.
Protecting Human Life
To survive on Mars, humans require robust protection to simulate Earth-like conditions. This includes:
- Pressurized Suits: Astronauts venturing onto the Martian surface would need highly specialized spacesuits that maintain a stable internal pressure equivalent to Earth's atmosphere. These suits are essentially personal spacecraft, providing breathable air, temperature control, and radiation shielding.
- Pressurized Habitats: Any long-term human presence would necessitate pressurized modules or underground habitats that offer a stable, breathable environment for living and working.
These protective measures are crucial to prevent the lethal effects of the Martian environment, including the dangerous phenomenon of blood boiling.
