Could we live on the outer planets?

Science in dialogue

Are there other planets other than Earth that have oxygen?

Yes, oxygen can also be found on other planets, but mostly in connection with other elements - but not in free form in the atmosphere.

According to the latest definition of planets by the IAU (International Astronomical Union), our solar system includes eight planets. Four of them - Mercury, Venus, Earth, and Mars - are also known as Earth-like planets. They consist of solid rock coats and a liquid iron core. A solid inner core can be located in the center of the iron core. The rock mantles contain oxygen in combination with silicon and other substances - the so-called silicates. The iron core can also contain oxygen. Oxygen is also found in the atmospheres of Venus and Mars, but mainly in bound form as carbon dioxide.

In contrast, the planets Jupiter and Saturn, which belong to the outer planetary system, are gaseous and essentially consist of hydrogen and helium, plus water, ammonia and methane. In the deep interior the pressure is so high that the gas has fluid properties. At the center of these planets are cores made of heavier materials such as silicates and iron. Uranus and Neptune, the other two planets in the outer planetary system, have a similar structure to Jupiter and Saturn, but contain significantly less hydrogen and helium.

Oxygen only occurs in its pure form in the earth's atmosphere. This is one of the reasons why the earth has a special position in our planetary system. Free oxygen allows life forms as we know them from our earth today. However, primitive life also existed on early Earth, when the atmosphere was similar to that of Mars and Venus. In addition, unlike the other earth-like planets, the earth does not have a rigid (very old) surface, but rather has very dynamic tectonics: the surface is constantly being circulated and is changing in the process. For example, while the surface of Mars is around three to four and a half billion years old, the earth's continents are two billion years old, and the ocean floors are only 60 million years old on average.

Whether there are extrasolar planets, the planets that were discovered outside of our solar system, with earth-like oxygen atmospheres, cannot be said at the moment. So far only statements about the composition of the atmospheres of very large gas planets are possible here. These can also be explored by examining the light spectrum emitted by the planets from the earth or from near-earth space. In order to research the composition of a planet's interior, a spaceship would have to be brought close to the planets. However, the detection of oxygen (and carbon) in the atmosphere of a planet outside the solar system (HD 209458b in the constellation Pegasus) has already been successful.

The question was answered by Professor Dr. Tilman Spohn, Institute for Planetary Research, German Aerospace Center