How can a planet lose it's atmosphere?

Question

Under gravity wouldn't anything surrounding or on a planet remain there until a larger object stripped the atmosphere etc. away. I'm thinking specifically of mars! If it had a water bearing atmosphere, it must still have it.

P.s. I know about solar wind etc. but it seems a bit far fetched and where did the solar wind take it if you believe that theory?

just to clarify I believe in the solar wind I'm just not sold on it's ability to strip a planet of atmosphere it's too random, some moons have atmospheres, what protects them?

Answer 1

I quote -

From the knowledge of the planets in the Solar System, we know that planets can only evolve into a habitable world if they have a stable orbit around its host star and if they keep the atmosphere and water inventory during: (i) the period of heavy bombardment by asteroids and comets and (ii) during
the host stars’ active X-ray and extreme ultraviolet (XUV) and stellar wind periods.
Impacts play a minor role for planets with the size and mass like Earth, while high XUV fluxes and strong stellar winds during the active periods of the young host star can destroy the atmospheres and water inventories. We show that XUV produced temperatures in the upper atmospheres of Earth-like planets can lead to hydrodynamic “blow off”, resulting in the total loss of the planets water inventory and atmosphere, even if their orbits lie inside the HZ. Further, our study indicates that Earth-like planets inside the HZ of low mass stars may not develop an atmosphere, because at orbital distances closer than 0.3AU, their atmospheres are highly affected by strong stellar winds and coronal
mass ejections (CME’s). Our study suggests that planetary magnetospheres will not protect the atmosphere of such planets, because the strong stellar wind of the young
star can compress the magnetopause to the atmospheric obstacle. Moreover, planets inside close-in HZ’s are tidally locked, therefore, their magnetic moments are weaker than those of an Earth-like planet at 1AU. Our results indicate that Earth-like planets in orbits of low mass stars may not develop stable biospheres. From this point of view, a HZ, where higher life forms like on Earth may evolve is possibly restricted to higher mass K stars and G stars.

Go to the link for the full article.

Answer 2

Why does the solar wind sound far-fetched to you?

The Sun is emitting a contant stream of particles, and has been doing so for billions of years. With no magnetic field to protect Mars, the solar wind has been blowing across the planet every second of every hour of every day for billions of years. This would eventually carry away the atmosphere into deep space. Earth is protected by the magnetic field, but even then sometimes the solar wind interacts with our atmosphere, providing aurorae for our viewing pleasure.

As far as gravity goes, it can only hold on to atoms and molecules that do not happen to be travelling above escape velocity. At any one time there will always be a proportion of the gas in an atmosphere that is doing just that (and if it hapens to be buffeted by the solar wind particles they might just give it the extra kick needed to escape). On Earth the higher gravity makes that proportion almost vanishingly small, but it is not zero. Earth is constantly losing atmosphere to space.

Answer 3

A planet will lose it's atmosphere if the atoms within it overcome the escape speed needed to escape the planet's gravitational pull. Perhaps the water that is supposed to be on Mars is deuterium (heavy water) which has a heavier mass than normal water therefore may not escape as easily. Maybe there is no water at all. A planet like ours could, if heated enough by the Sun, lose it's atmosphere as the molecules of gas in the air become heated and therefore more energetic giving them enough energy to escape. Or if another large body came near to Earth the atmosphere could be lost to it's gravitational pull.

Remember that the solar wind is not a wind as we know it but it is more a radiation wind i.e. it doesn't blow as the wind on Earth does. Not too sure if it could strip away a planet's atmosphere...I suppose it could but I really don't know.

Answer 4

Two things are needed for a planet to hold on to its atmosphere. Gravity large enough to pull the gasses down, and a magnetic field is also helpful as it deflects solar wind which would otherwise blow our atmosphere into space. In fact this is happening all the time but at a much slower rate than if the earth had no magnetic field.
A planet like Mars has about .25 the gravity of Earth and over billions of years the atmosphere slowly escapes into space, the gravity just isn't strong enough to hold on to it.

Answer 5

Any collection of gas has molecules moving at a range of speeds based on the temperature of the gas. It is quite possible that a fraction of the gas molecules will be moving faster than the escape velocity determined by gravity. So long as there is enough energy being supplied, say by being close enough to the Sun, to keep replacing the energy lost as the faster gas molecules escape the gas will continue to drift off into space until there is either none left or the supply of incoming energy drops.

The solar wind is a stream of plasma blowing off the Sun and into the Solar System at around 500 km/s to as much as 800 km/s. The collision of solar wind ions with gas molecules in planetary atmospheres can provide the gas molecules with enough energy to exceed the escape velocity. Thus the solar wind can erode an atmosphere, blowing the gas off into space.

Answer 6

The lack of a magnetosphere (organised by the planets magnetic field. Marses magnetic field failed when it's core solidified when the planet cooled) surrounding Mars may have allowed the solar wind to erode the atmosphere, the relatively low gravity of Mars helping to accelerate the loss of lighter gases to space. (Wikipedia)

Answer 7

It can lose its atmosphere if it's gravitational pull is insufficient to hold it down and if there are no gases being emitted from the planet's interior to replace the ones which are lost. This may well have been what happened on Mars.

It can also lose it if it's too close to an active star when bursts of activity can literally blow it away. This is believed to have happened to the earth very early on in it's evolution. The gases we now have surrounding us are believed to have been produced by outgassing from the earth's active interior etc.

If the atmosphere consists of reactive gases they might react with rocks or minerals on the planet's surface.

If the planet's temperature gets too hot it can boil the gases off and if it gets too cold they can liquify or freeze.

Answer 8

environment loss is person-friendly, in case you have sufficient time. Mars misplaced its environment... this is in basic terms no longer sufficiently massive (no longer sufficient gravity) to hold onto maximum of it... upload some hundred million years of image voltaic winds blowing it away, and Mars spends maximum of its time as a planet with minimum environment. Earth will lose its environment too, sometime. because of the fact the solar keeps to fuse hydrogen, it gets warmer... extra beneficial image voltaic winds. i've got seen estimates everywhere from a hundred million to 500 million years from now, that life won't have the skill to outlive in the international, because of the fact the oceans will evaporate and the ambience would be stripped away because of the heating, extra beneficial image voltaic winded solar. of direction, the solar is likewise dropping tiny quantities of mass, so Earth will pass to a miles better orbit in that factor physique... in all risk no longer sufficient to outlive. To lose gravitational pull, your planet is going to could desire to lose mass. For it to be substantial, your planet is going to could desire to almost be destroyed interior the technique.

Answer 9

I don't believe the solar wind theory. But I do believe this, because it's true: There was once a layer right above the sky of the Earth that was called the Ozone Layer. I forgot exactly what it's made of, but it would help protect the Earth from harmful sun rays. Once humans started polluting the Earth with cars, factories, and other things, the Ozone Layer faded away. Now harmful sun rays can get to us, that's why they're inventing very protective sunscreen these days, and it's also why so many people have skin cancer.

It's a great example of why us humans are stupid.

Answer 10

Lack of or weak magnetic field.