Outer space is very cold, with temperatures approaching absolute zero. The reason space is so cold is because it is mostly empty, containing very little matter to provide heat. There are several factors that contribute to the freezing temperatures in outer space.
What is Outer Space?
Outer space refers to the vast expanses of the universe outside of the atmospheres of celestial bodies such as planets and stars. There is no exact boundary where outer space begins, but it is commonly defined to begin about 100 km above the surface of the Earth.
Outer space consists mostly of empty space, with only tiny amounts of gas, dust, and cosmic radiation. Since it contains very little matter to transfer energy, the temperature approaches absolute zero (0 Kelvin or -273.15 Celsius).
Factors Contributing to the Cold Temperatures
Lack of Atmosphere
Planets and stars have atmospheres which trap heat. Earth’s atmosphere acts like a blanket, absorbing heat radiated from the planet’s surface and greenhouse gases. This warms the lower atmosphere to livable temperatures around 15°C on average.
In space, there is no atmosphere and therefore no greenhouse effect or blanket to keep heat near the surface. Any heat radiated by objects in space is lost into the vast expanse.
Lack of Convection
On Earth, heat transfer occurs through convection in the atmosphere and oceans, helping redistribute warmth across the globe. Hot air and water rises while cool air and water falls, circulating heat vertically and horizontally.
Without air or water in space, convection cannot occur. Heat cannot be transferred or carried between areas in space.
Thermal Radiation
All objects with temperature above absolute zero emit thermal radiation. On Earth, we gain heat from solar radiation during the day, but at night thermal radiation from the surface causes cooling. In space, there is no solar radiation and any object will radiate heat outwards until reaching extreme cold temperatures near absolute zero.
Expansion of Gases
As gases expand, they cool. With essentially no pressure in space, any gas atoms will expand tremendously, decreasing in temperature. For example, if a pressurized gas canister was opened in space, the released gas would rapidly expand and cool.
Exact Temperature of Outer Space
So exactly how cold is outer space? There is no single temperature that applies everywhere. The exact temperature depends on whether any sources of heat are present nearby. Let’s look at some general temperature ranges:
| Location | Temperature |
|---|---|
| Near Earth (thermosphere) | 1000°C – 2000°C |
| Between planets and stars | ~3°K (-270°C) |
| Near the Sun | 5000°C – 6000°C |
As you can see, outer space ranges from extremely hot to cold depending on proximity to heat sources. Let’s look at the extremes in more detail:
Near Stars
The maximum temperature occurs near stars which produce tremendous heat and energy. For example, near our Sun the average temperature is 5800°C. At this proximity the solar radiation is intense.
Interstellar Space
In interstellar space, far from any stars or planets, the average temperature dips down to around 3°K (-270°C). This is just barely above absolute zero. Without any significant heat sources, space is dark and frigid.
Near Earth
Surprisingly, the upper atmosphere 100+ km above Earth’s surface can reach over 1000°C. Extreme ultraviolet radiation from the Sun is absorbed at these altitudes, creating very high temperatures.
However, in low Earth orbit where the ISS resides, and where the atmosphere is thin, temperatures vary from -150°C to 120°C depending on sun exposure. In shade, temperatures drop dramatically.
Effects on the Human Body
The extreme cold of outer space presents major hazards for unprotected humans.
Decompression
One of the greatest risks is decompression and ebullism. The near vacuum of space causes gases to rapidly leave the body. Without a pressurized space suit, fluids in the throat and lungs may boil and the cardiovascular system can be damaged.
Heat Loss
In the freezing temperatures of space, heat would be rapidly lost from any exposed skin or tissue. Heat loss occurs through radiation, evaporation, convection, and conduction. After about one minute, the loss of heat would be fatal as the body freezes.
Lack of Oxygen
The lack of atmospheric oxygen will also lead to asphyxiation within minutes if no supplemental oxygen is available.
Cell Damage
Cosmic radiation can damage DNA and cells. Without Earth’s magnetic field and atmosphere providing shielding, charged particles from the solar wind and cosmic rays can penetrate exposed tissues.
Conclusion
In summary, the exact temperature of outer space varies greatly depending on location, ranging from scorching hot near the Sun to just barely above absolute zero in interstellar space. The lack of atmosphere, convection, and air pressure, along with intense radiation from the Sun and other stars, all contribute to the extreme temperature extremes. Any humans without protection would quickly die from decompression, freezing, asphyxiation, and cell damage.