Density of Gliese 581 d: What's the Real Number?

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In summary, the density of Gliese 581 d (not c) is estimated to be very close to Earth's, but the numbers listed on Wiki may not be accurate as they lack citations. Further research is needed to determine the exact density of this planet.
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DaveC426913
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I'm trying to find a reasonable estimate of the density of Gliese 581 d (not c).

According to Wiki, d is ~1.96x the radius of Earth and ~7.7x the mass. This makes for a density very near Earth's (2^3=8). Yet they then go on to list its density as 730kg/m^3 or 0.73g/cm^3 - almost as rarefied as Saturn.

Can anyone point me at some more authoritative numbers? I know we're only estimating, but clearly one of those three numbers r,d or m is spurious.
 
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DaveC426913 said:
I'm trying to find a reasonable estimate of the density of Gliese 581 d (not c).

According to Wiki, d is ~1.96x the radius of Earth and ~7.7x the mass. This makes for a density very near Earth's (2^3=8). Yet they then go on to list its density as 730kg/m^3 or 0.73g/cm^3 - almost as rarefied as Saturn.

Can anyone point me at some more authoritative numbers? I know we're only estimating, but clearly one of those three numbers r,d or m is spurious.

They all could be right due to a few things. When you calculate the density via M/V you are basically assuming a constant density throughout the entire planet, but usually that is a decent for a very rough approximation.

I notice the article you mention is lacking citations on both the radius and the density, so it is possible those are flawed as well.
 
  • #3


Thank you for your question. The density of Gliese 581 d is a topic that has been widely debated and there is not a single definitive answer. As you mentioned, the information from Wiki estimates the density to be 730kg/m^3 or 0.73g/cm^3, which is significantly lower than Earth's density. However, this number is based on theoretical models and assumptions, as we do not have direct measurements of the planet's mass, radius, or composition.

In order to have a more accurate estimate of the density of Gliese 581 d, we need more data and observations. One possible way to obtain this information is through transit spectroscopy, which can measure the planet's size and mass by observing how much light is blocked as it passes in front of its star. This method has been used successfully for other exoplanets, but unfortunately, it has not yet been possible for Gliese 581 d due to its orbital position.

Another way to estimate the planet's density is through radial velocity measurements, which can detect the slight wobble of a star caused by the gravitational pull of its orbiting planets. However, these measurements can only provide a minimum mass for the planet, not its actual mass.

Overall, the information we have about Gliese 581 d is not enough to determine its density with certainty. As more advanced telescopes and techniques are developed, we may be able to obtain more accurate measurements and better understand the composition and density of this intriguing exoplanet.
 

What is the density of Gliese 581 d?

The density of Gliese 581 d is estimated to be around 5.6 g/cm3. This is similar to the density of Earth, suggesting that it may have a rocky composition.

How was the density of Gliese 581 d calculated?

The density of Gliese 581 d was calculated using a combination of its mass and radius, which were determined through observations and simulations. The mass was estimated through the planet's gravitational pull on its host star, while the radius was determined through its transit method.

Why is there uncertainty in the density of Gliese 581 d?

There is uncertainty in the density of Gliese 581 d because its mass and radius are not precisely known. These values are determined through indirect methods and can have a margin of error. Additionally, the composition and structure of the planet may also contribute to the uncertainty.

How does the density of Gliese 581 d compare to other exoplanets?

The density of Gliese 581 d is relatively low compared to other exoplanets of similar size. This suggests that it may have a larger proportion of gas and ice in its composition, similar to that of Neptune or Uranus in our own solar system.

Could Gliese 581 d be habitable based on its density?

The density of Gliese 581 d is just one factor in determining its potential habitability. Other factors such as its distance from its host star, atmosphere, and composition also play a crucial role. While the density may suggest a rocky composition, further research and observations are needed to determine its habitability.

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