[Titanscape (OP)]

Does the Earth's atmosphere come to a limit determined by the extent of the magnetosphere and the resistance it offers against the strongest solar winds and coronal mass ejections and storms?

Looking at Venus with it's great atmosphere, 100 times the Earth's pressure, same gravity... it has so much gas, maybe a magnetosphere. As an aside does Venus have an iron core, magnetosphere? Venus has a huge atmosphere but also a tail like a comet from the solar wind. Understanding Venus is closer to the sun and it's winds too.

Much further away Mars lost all it's gas, except for a little on the poles being frozen.

Maybe once before long ago, say 2 1/2 billion years ago, the Earth had more air, and water...?

Perhaps Venus will one day be reduced to an atmosphere, closer resembling the Earth's in pressure, and then also have a cooler temperature?

The main question, does the magnetosphere and the extent of our great blue atmosphere match?

[LeeE]

The Earth's magnetosphere extends much further than Earth's atmosphere.  It's generally considered to extend to about 70000km on the side of the Earth facing the Sun and well over 1000000km on the side facing away from the Sun.  The actual size of the magnetosphere varies according to what the Sun is doing.

[einfopedia]

The Earth's magnetosphere extends from Earth's atmosphere.  It's extends a 70000km on the side of earth and1000000km on the side face away from the Sun...

[damocles]

The "extent" of the Earth's atmosphere is very ill-defined. At the Earth's surface the atmosphere is very substantial -- with a pressure around 100 kPa. As you travel upward from the Earth's surface it gets rapidly thinner, with the pressure falling by a factor of about 1000 for each of the first few 50 km increases in altitude.

Perhaps a suitable way to define the limits of the Earth's atmosphere is in terms of the maximum altitude of observations that are primarily due to the presence of material different to (denser than?) the interplanetary medium. This would exclude phenomena that arise solely from interaction between the Earth's magnetic field and the solar wind, for example. It would place the "edge" of the atmosphere somewhere between 100,000 and 200,000 km altitude.

But there is really no sharply defined "edge". At the outer limit, the atmosphere just generally fades into the interplanetary medium.

In the surface atmosphere there are around 2.5 x 10¹⁹ particles per cubic centimetre. At the Earth's distance from the sun, but far from the Earth, the interplanetary medium consists of about 5 particles per cubic centimetre.