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joetommasi
2003-Nov-24, 06:02 PM
I don't get it. The solar system was formed from a lens shaped cloud of gas, dust, rocks, boulders. etc.
The center portion became the sun and the outer parts of it became the planets.
Doesn't it stand to reason that the inner planets should be larger than the outer planets and as we go further and further from the sun the planets should get smaller and smaller?
Like I said, I don't get it. If anyone can explain this anomaly, please do so.

kashi
2003-Nov-24, 08:56 PM
Welcome to the forum jtommasi!

The inner planets aren't capable of having an atmosphere as thick as the outer ones because it will be blasted off into space by solar radiation. According to traditional planetary formation theories, this means that gas giants can only exist further out from the "habitable zone". To my knowledge, most of these planets' mass constitutes their dense atmosphere.

Recently however, many planetary systems have been discovered with gas giants many times the size of jupiter, orbiting closer to their star than Mercury orbits our sun. This no doubt threw a spanner among the works! Perhaps they migrated inwards, or perhaps planetary formation theories need some updating! If they did migrate from distant orbits to closer ones, they may be able to keep their atmosphere once they are sufficiently massive, and if they have a strong electromagnetic field. The migration theory is looking less and less likely however as more and more supermassive planets with small orbits are discovered. Keep in mind however, that our extrasolar planetary detection techniques favour large planets in orbits that only take a few days per cycle!

Hope this helps.

Kashi

Chook
2003-Dec-11, 05:18 AM
WOW! :D

VanderL
2003-Dec-11, 04:10 PM
Hi it's the electrical explanation again.
When a star is viewed as the point of discharge of the interstellar medium, planets are formed when the electrical stress from the surrounding medium exceeds a certain level (depending on mass and current density), a nova event takes place and material from the star is ejected. In this way the current becomes divided over a larger surface, thereby reducing the stress. Planets are naturally formed close to their parent stars, and the size is dependent on how large the surface needs to be to reduce the stress. This process can repeat itself, and if the stress it too high even a new star can be formed, explaining the large number of binary star systems that are found.Rocky planets like our own can very well be former moons of the bigger Jupiter-like planets (just look at Titan and Europa).
for details go to www.holoscience.org and www.electric-cosmos.org
Cheers.

Littlemews
2003-Dec-11, 05:53 PM
I don't know if this is correct or not :P , but most of the planet that close to the sun, they got very strong gravity and high pressure :) therefore, when a star was born, the star was beating by pressure and gravity, so they bcome kinda small(The core), and the jovian planets, they got pressure and gravity too, but not that strong :lol: but they got hydrogen(Liquid Water), When a jovian planet close to the sun, doesn't affect them, because their core already dead... :lol:

So in that case, I think its Gravity and Pressure that makes the inner planet small...

rajasun
2003-Dec-18, 06:33 AM
The reason why massive planets CANNOT have formed in close orbits around a star (especially solar mass stars) is because of the strong stellar wind and heat these stars possess. Look NO further than the instance of HD 209458b, it is fast EVAPORATING! Such "torch" orbit planets will eventually leave behind ONLY their molten cores and become what are termed "Chthonian" planets*.

While I agree that current planetary formation and migration theories are far from being perfect, they do more or less reflect what I believe is actually going on in many of these systems. BTW the "huge" numbers of observed "torch" orbit planets is PRIMARILY due to the method used i.e. radial velocity variation measurements tend to readily identify short orbits massive planets. The migration theories of D. N. C. Lin, J. C. B. Papaloizou, Pavel Artymowicz and others have NOT been proven to be problematic. In fact, migration attributable to circumstances e.g. interaction of planet with residual gas disk, gap opening and planet-planet gravitational perturbation have accounted for most of the known close-in Extrasolar planets.

Traditional planetary formation theory (e.g. the nucleation i.e. accretion of planetesimals and then the acqusition of a gaseous atmosphere) holds that circumstellar planetary disks are at their THICKEST in the middle i.e. corresponding to where the 4 MAJOR planets (i.e. Jupiter, Saturn, Uranus and Neptune) in our solar system are. The accretional mode to planetary formation by and large does a good job in accounting for the location of these 4 planets in their present locations.

The reason why these 4 massive planets can acquire their "thick" gaseous covers can be pinned down to their location beyond the "snow-line" radius i.e. distance from primary star (in the case of the Solar System - the Sun) where temperatures are cold enough for the formation of "ices". As proto Jupiter, proto Saturn, proto Uranus and proto Neptune (i.e. Jupiter, saturn, Uranus and Neptune in the process of forming) grow in size (in the middle of the Solar Nebula), once a critical mass (estimated to be ~10 Earth masses), they start to attract nearby (within the Feeding Zones of the respective proto planets) "ices" and other volatiles e.g. hydrogen and helium and consequently so explains the presence of hydrogen/helium/"ices" rich atmosphers on Jupiter, Saturn, Uranus and Neptune.

Source:
*
http://arxiv.org/pdf/astro-ph/0312384

Title: Evaporation rate of hot Jupiters and formation of Chthonian planets
Authors: G. Hébrard, A. Lecavelier des Étangs, A. Vidal-Madjar, J.-M. Désert, R. Ferlet (IAP)
Comments: To be published in the proceedings of the XIXth IAP Colloquium "Extrasolar Planets, Today And Tomorrow", 2 pages

Among the hundred of known extrasolar planets, about 15% are closer than 0.1 AU from their parent stars. But there are extremely few detections of planets orbiting in less than 3 days. At this limit the planet HD209458b has been found to have an extended upper atmosphere of escaping hydrogen. This suggests that the so-called hot Jupiters which are close to their parent stars could evaporate.
Here we estimate the evaporation rate of hydrogen from extrasolar planets in the star vicinity. With high exospheric temperatures, and owing to the tidal forces, planets evaporate through a geometrical blow-off. This may explain the absence of Jupiter mass planets below a critical distance from the stars. Below this critical distance, we infer the existence of a new class of planets made of the residual central core of former hot Jupiters, which we propose to call the ``Chthonian'' planets.

Hope this helps!

;)

The_Radiation_Specialist
2006-Jan-06, 05:14 PM
hmm...

William_Thompson
2006-Jan-09, 02:00 AM
Welcome to the forum jtommasi!

The inner planets aren't capable of having an atmosphere as thick as the outer ones because it will be blasted off into space by solar radiation. ...Kashi

I think that this is wrong. Venus Earth and Mars have atmospheres. And gravity and mass has a lot to do with keeping a thick atmosphere

William_Thompson
2006-Jan-09, 02:08 AM
The reason why massive planets CANNOT have formed in close orbits around a star (especially solar mass stars) is because of the strong stellar wind and heat these stars possess. Look NO further than the instance of HD 209458b, it is fast EVAPORATING! Such "torch" orbit planets will eventually leave behind ONLY their molten cores and become what are termed "Chthonian" planets*.


I think parts of the equation are omitted here. What about the very thing that keeps us alive and healthy? Our planet has a thick metalic core which produces a magnetic field to fend off radiation.

Large planets with the right composition that are close to their star might have the same luxury and fend of the thing that would strip away their atmosphere.

Ken G
2006-Jan-09, 02:23 AM
It is not "radiation" of the type that magnetic fields deflect that boils off gaseous hydrogen from inner planets. It is light radiation-- sunlight. We get all of that, but our N2 and O2 atmosphere comprises of heavy molecules that do not approach escape speed even in direct sunlight. However, if we had an envelope of gaseous hydrogen, crucial for "gas giant" planets, the smaller and lighter hydrogen would achieve speeds in direct sunlight that would cause the gas to rapidly boil off into space. At larger distances (read, Jupiter), the temperatures are colder and this does not happen to Jupiter's gaseous hydrogen, even before Jupiter piled up so much hydrogen that its mass got huge and escape became even more difficult. So you have to get past an initial period of hydrogen escape to pile up a truly huge hydrogen envelope, and this means you have to be farther from the Sun than the four rocks. It all makes perfect sense in our solar system, and will in other solar systems as well, as soon as we can detect "normal" planets.