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[Jii]

https://www.universe...-as-it-is-today

 

 

In a recent paper, astronomers Konstantin Batygin and Fred C. Adams conducted a detailed study of Jupiter's primordial state. Their results indicate that 3.8 billion after the Solar System after the first solids formed in the Solar System's protoplanetary nebula, Jupiter was 2 to 2.5 times as large as it is today.

 

[russell23]

Here is the preprint version of the paper:

 

https://arxiv.org/abs/2505.12652

 

I do think it is important to keep in mind that this is about the radius of Jupiter, not the mass.  This is a normal aspect of Jupiter's, Saturn's, and Neptune's.   When they are first formed their radius is usually larger than it will be as they age.  There are a number of factors:

 

~ The radius will contract as the planet cools.

~Some mass can be lost from stellar winds and core powered mass loss.

~Tidal interactions with the star can increase the radius (Tidal inflation).

~Strong tidal interactions for really short period planets can lead to significant mass loss from Roche Lobe overflow.

 

In the case of Jupiter, at 5.2 AU the shrinking radius since formation would have been most affected by normal contraction/cooling post formation.

 

  I feel too much emphasis is placed on exoplanet radius measurements that are absent accurate mass measurements.  As an example, I've been compiling a catalog of all discovered exoplanets with equilibrium temperature less than ~600 deg, radius uncertainty <8%, and mass uncertainty <27%.   Within this catalog the mass range for Saturn radius planets is 5.70 Mearth to 320 Mearth. 

 

This is the problem with having a planet's radius but an unknown or large uncertainty mass.  You really have no idea what the planet actually is because nature allows for a large range of masses associated with a given radius.   It gets worse when you start adding in higher equilibrium temperature planets because a low temperature planet with a certain mass-radius combination is going to have a higher H-He fraction than a much higher temperature, short orbital period planet with the same measurements.

 

Or stated another way, if you move a Jupiter like planet (or smaller H-He rich planet) into a short period orbit its radius will be inflated due to stellar heating and tidal inflation.  There was an interesting study done a few years back on the effects of tidal inflation on sub-Saturn radius planets (Millholland).  After accounting for tidal inflation, the actual H-He fractions were quite a bit smaller for close orbiting planets than models that did not account for tidal inflation.

 

So keep in mind Jupiter was not Jumbo in terms of mass, it was just larger radius - which is expected when H-He rich planets first finish forming.

Edited by russell23, 21 May 2025 - 01:50 PM.