# What is the Composition of an Exoplanet 50 Light Years Away?

• willstaruss22
In summary, the conversation discusses the composition of an exoplanet 50 light years away, which has a radius 2 times that of Earth, 8 times the mass, and a density of 5.52 g cm/3. It is mentioned that the composition of this planet cannot be determined simply based on its mass and volume, as there are multiple variables such as the amount of iron, rock, water, and hydrogen/helium. The example of Uranus, which has a similar escape speed, is also mentioned. The conversation then goes on to discuss the possibility of a planet with a large iron core and a water-rich mantle and crust, similar to Mars. Lastly, it is questioned what would happen if Earth's radius
willstaruss22
Lets say there is an exoplanet 50 light years away. The radius of this planet is 2x Earths with 8x Earths mass and a density of 5.52 g cm/3. What is the composition of this planet?

willstaruss22 said:
Lets say there is an exoplanet 50 light years away. The radius of this planet is 2x Earths with 8x Earths mass and a density of 5.52 g cm/3. What is the composition of this planet?

Stuff.

It's a lot simpler than that. Compare the volume of the exoplanet with the volume of the earth. Anything jump out at you?

I know it would be made of lighter elements but would the lighter elements be water/rocky mix or a smaller iron core with a silicate mantle and crust making up most of the mass?

What is the mean density of the Earth?

5.52 g cm/3

That´s precisely why the composition of an exoplanet is unknowable.

There are 2 observables - the total mass and volume. There are 4 major variables of internal composition: the amount of iron, the amount of rock, the amount of water and the amount of hydrogen/helium. Remember that 2x Earth radius and 8x Earth mass means twice Earth escape speed, and that is in the region of what Uranus has.

If a body consisted of only 2 variable substances, like iron and rock, or rock and water, or water and hydrogen, then you could solve for an unique composition that fits the observed mass and diametre. If you have 3 unknowns then you cannot solve, because it is underdetermined equation system, and you have degenerate solutions. A body with tiny iron core and mainly rock, like Moon, can have the same density as a body with a big iron core but also a large amount of water on top. And as stated, you have 4 unknowns, not even just 3.

Lets remember that Uranus has a density of only 1.32 a radius of 4x Earth and has a small rocky core, water/ice mantle and hydrogen rick atmosphere. I would think that a planet with a density of 5.52 with 2x Earth radius would have most of its mass made into a iron core, rocky mantle and crust while being much more water rich than Earth. I mean take Mars for example it is made of less dense materials on average.

What would happen if you took the Earth (with the same composition of minerals, water, air, etc.) and scaled it up so that its radius doubled? What would be the mass of the larger planet?

## 1. What is the composition of the Earth's crust?

The Earth's crust is primarily made up of oxygen (46.6%), silicon (27.7%), and aluminum (8.1%). Other elements present in smaller amounts include iron, calcium, sodium, and potassium.

## 2. How does the composition of the Earth's atmosphere compare to other planets?

The Earth's atmosphere is primarily composed of nitrogen (78%) and oxygen (21%), with trace amounts of other gases such as carbon dioxide, water vapor, and argon. This composition is unique compared to other planets in our solar system, as most have much thicker atmospheres dominated by gases like hydrogen and helium.

## 3. What elements make up the majority of the Earth's core?

The Earth's core is mainly made of iron (85%) and nickel (10%), with smaller amounts of sulfur, oxygen, and other elements. This composition is similar to that of other rocky planets in our solar system.

## 4. How has the composition of the Earth changed over time?

The composition of the Earth has changed significantly over its 4.5 billion year history. In the early stages, the Earth's atmosphere was mostly composed of carbon dioxide and water vapor. As the Earth cooled, the formation of oceans and the emergence of life led to the decrease of carbon dioxide and increase in oxygen in the atmosphere.

## 5. What is the role of plate tectonics in shaping the composition of the Earth?

Plate tectonics plays a crucial role in the composition of the Earth. Through the movement and collision of tectonic plates, new rocks are formed and old rocks are recycled, leading to changes in the Earth's crust and mantle. This process also affects the distribution of elements and minerals on the Earth's surface.

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