I Why is Mars not considered a "full-fledged" planet?

[swampwiz]

https://www.space.com/ancient-earth-had-thick-toxic-atmosphere-like-venus

There may have been many planetary embryos in the early Solar System, but the only one that still survives is Mars, which is not a fully fledged planet like Earth or Venus.

 

[DennisN]

Hi, @swampwiz!
Mars is definitely considered to be a planet (and so are Mercury, Jupiter etc.)
But Mars has a comparatively thin atmosphere, and maybe that's why the author wrote like he/she did, I don't know.

 

[DrSteve]

It is a full fledged plant like any of the other 7

 

[sysprog]

Fledge relates etymologically to 'fliegen', flight, metonymically to birds' maturation of feathers sufficient for flying $-$ perhaps that is what the writer of the paper had in mind when he thought of saying that Mars is not full-fledged $-$ although it is properly the birds that are or are not full-fledged, and not the planet or its atmosphere, it seems clear that the atmosphere of Mars is not dense enough to allow Martian birds to fly $-$ ergo, if there are birds on Mars, they are flightless, like the Dodo.

 

[Vanadium 50]

You start with de-planeting Pluto, and see where it leads to?

 

[lomidrevo]

Why is Mars not considered a "fully fledged" planet?

Read just the next sentence following the part you have qouted:

There may have been many planetary embryos in the early Solar System, but the only one that still survives is Mars, which is not a fully fledged planet like Earth or Venus.
The late stages of accretion involve giant impacts that release enormous amounts of energy. We think the last impact in Earth’s accretion involved a Mars-sized embryo hitting the growing Earth...

As it is believed that Mars didn't experience such a big impact, from this point of view it didn't go through the last stage of planetary formation. I am not sure how much is this hypothesis respected, but other sources mention it too, see below quotes and links.

https://arxiv.org/abs/1704.00184

With approximately one ninth of Earth's mass, Mars is widely considered to be a stranded planetary embryo that never became a fully-grown planet.

https://Earth'sky.org/space/mars-is-a-planetary-embryo-study-shows

According to planet formation theory, there was a process of building that went on in the early solar system – smaller planetesimals to larger planetary embryos to actual planets. The idea here is that – while Earth formed slowly from planetary embryos colliding – Mars is itself a solitary planetary embryo that formed very early in the history of our solar system.

https://www.bbc.com/news/science-environment-13567381

By modelling this process, astro-physicists can determine the size of planets they expect to form at a given distance from the Sun. Mars is an outlier; it should have grown to around the size of the Earth, but remains about one-tenth its size.

Because of Mars' small size, many scientists have long suspected that the Red Planet avoided the collisions that allowed other neighbouring planets to increase their girth

 

[mathman]

It all sounds like a play on words!

 

[hutchphd]

Perhaps the designation has to do with lack of internal dynamics sufficient to create a Magnetic field. As I understand it this may be responsible for the "ablation" of the Martian atmosphere by solar wind, (but I don't understand much).

 

[stefan r]

Perhaps the designation has to do with lack of internal dynamics sufficient to create a Magnetic field. As I understand it this may be responsible for the "ablation" of the Martian atmosphere by solar wind, (but I don't understand much).

Venus does not have much magnetic field either.

 

[SpaceJacob]

The first my thought was, "It's just a play on words," but @lomidrevo post made me think a little more deeply about it. I seem to have a good knowledge of astronomy, but I completely forgot about the different stages of planet formation. However, it's just a theory. Now, Mars is considered to be a planet, and scientists ain't going to downgrade the status of Mars. However, anything is possible in this world.