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

  • Context: Graduate 
  • Thread starter Thread starter willstaruss22
  • Start date Start date
  • Tags Tags
    Composition Planet
Click For Summary

Discussion Overview

The discussion revolves around the hypothetical composition of an exoplanet located 50 light years away, characterized by a radius twice that of Earth, a mass eight times greater, and a density of 5.52 g cm³. Participants explore various aspects of planetary composition, including the implications of mass and volume on the internal structure and materials of the planet.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants propose that the density and size of the exoplanet suggest it would be composed of lighter elements, potentially including a mix of water and rocky materials.
  • Others argue that the relationship between mass and volume complicates the determination of composition, noting that multiple variables (iron, rock, water, hydrogen/helium) create an underdetermined system.
  • A participant suggests that a planet with a density of 5.52 g cm³ and a radius of 2x Earth might have a significant iron core, a rocky mantle, and a crust, while also being more water-rich than Earth.
  • There is a question about the mean density of Earth, which is stated as 5.52 g cm³, indicating a reference point for comparison.
  • One participant raises a hypothetical scenario about scaling Earth up in size and inquires about the resulting mass, prompting further exploration of the implications of size on planetary composition.

Areas of Agreement / Disagreement

Participants express differing views on the composition of the exoplanet, with no consensus reached. The discussion highlights multiple competing hypotheses regarding the internal structure and materials of the planet.

Contextual Notes

The discussion reflects limitations in determining planetary composition based solely on mass and volume, as the number of unknowns exceeds the available data points. This results in a range of possible compositions that cannot be uniquely identified.

willstaruss22
Messages
108
Reaction score
1
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?
 
Astronomy news on Phys.org
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?
 

Similar threads

Undergrad Exoplanet, HD 137010 b and it's star, HD 137010
  • · Replies 0 ·
Replies
0
Views
1K
High School Exoplanet TOI-4603 b, ~13x Jupiter mass, ~1.04 Jupiter diameter
  • · Replies 22 ·
Replies
22
Views
3K
High School The search for habitable exoplanets in Alpha Centauri
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Early Catalog of Planet-Hosting Multiple Star (≥ 3) Systems
  • · Replies 3 ·
Replies
3
Views
2K
Undergrad Composition of Jupiter: Ices, Cores & Outer Gas Layers
  • · Replies 24 ·
Replies
24
Views
4K
Undergrad The Trouble with TESS: Examining its Limitations in Exoplanet Observations
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad New rocky exoplanet discovered is the closest to Earth
  • · Replies 8 ·
Replies
8
Views
3K
Undergrad New Developments In The Search For Planet X
  • · Replies 2 ·
Replies
2
Views
3K
High School How much in the past do we see these planets?
  • · Replies 2 ·
Replies
2
Views
1K
Undergrad Light fluctuations and finding exoplanets
  • · Replies 3 ·
Replies
3
Views
2K