Rocky or Gas giant?

[kikinho]

A planet with 17500 km radius is still a rocky planet, is between a rocky and gas planet or is just a gas giant?

[Michael Kilderry]

I would say that it would still be a rocky planet, but it all depends on density. There are thought to be rocky planets the size of Neptune (25,000 km radius) orbiting close to their stars (Example: 55 Cancri e) so there is no absolute margin between what is too big to be a rocky planet or what is too small to be a gas giant.

This could also be another different type of planet, called a Gas Dwarf. These worlds have a lot of atmosphere like a gas giant, but they also have a core too large for a gas giant, the core's radius typically would probably be half the radius of the whole planet - atmosphere included.

Michael Kilderry

[eburacum45]

I,m not convinced that 55 Cancri e is enrtirely rocky; I expect that when it can be examined in detail, it will have an extensive but hot atmosphere, but this atmosphere would be still evaporating.
In fact there should be detectable traces of this evaporating atmosphere (if it exists)in the vicinity of 55 Cancri.

Of course if 55 Cancri e has lost all its atmosphere already it would be a huge ball of rock with very high gravity, which would also be interesting.

[Michael Kilderry]

Of course 55 Cancri e doesn't have to be entirely rocky - It might be a gas-dwarf! With it's evaporating atmosphere, certain telescopes might even be able to detect a tail coming of 55 Cancri e or even a tail long enough that it forms a ring that follows the orbit of this intriguing world. Who knows, on certain epistellar planets, this ring might get thick enough to cause atmospheric drag on the planet and it might end up falling into it's sun! Although I don't think such a ring could be possible as the tail created by the evaporating atmosphere would probably not follow the orbit so much but point away from the sun - like a comet.

Michael Kilderry

[danielj]

Based in these,how can we know that the Mu Ara planet "e" is really a rocky one.Do someone collected any information about the density of the planet?

[Evil Dr Ganymede]

Depends if we know it's radius. If we know its mass and its radius then we can figure out the density.