ASTC25 SMP Atmospheres of Giant Planets

Analysing and Classifying the Atmospheres of

Different Giant Solar Planets

Demin Xu

Eric Yeung

Ricky Han

Abstract. The giant planets in the solar system, also known as Jovian planets, have

different atmospheres than terrestrial ones. The purpose of this paper is to classify and

provide some information for their atmospheres. Specifically, Jupiter, Saturn, Uranus,

and Neptune were looked at; atmospheric dynamics were also explored.

Jovian Planet Atmospheres 2

Atmospheres of Jovian Planets

Atmospheres of planets usually serve the purpose of dealing with cosmic radiation

and regulating the temperature of the planet. The giant planets, sometimes called

Jovian planets, consist of Jupiter, Saturn, Uranus, and Neptune with Jupiter and

Saturn being gas giants. As the Jovian planets formed further away from the sun,

their atmospheres receive less radiation via an inverse square distance relation. The

corresponding temperatures of the Jovian planets from ascending order of distance from

the sun at an altitude in which the pressure is the same as Earths sea level pressure

are 290K, 170K, 150K, 78K, and 69K. There is a method to measure the compositions

of Jovian planets atmospheres. Spectrometers on Earths surface, and even on space

probes, absorb light with only specific wavelengths along the line of sight. This gives

us the spectral lines; there are 2 types of spectral lines: emission lines, and absorption

lines. We are interested in only the absorption lines as those give us the atmospheres

chemical composition.


Table 1. Compositions of Jovian Planet Atmospheres Below the Clouds[1]

Molecule Jupiter Saturn Uranus NeptuneH2 86.4 97 83 79

He 13.6 3 15 18

H2O 0.1

CH4 0.21 0.2 2 3

NH3 0.07 0.03

H2S 0.008

The values are in percentages. The dashes represent unobserved quantities.

After measurements, it is found that hydrogen gas and helium dominate the

atmospheres of all the Jovian planets with little traces of hydrogen compounds. This

mixture of hydrogen and helium resembles the composition in the sun. Methane is the

next most abundant; water, ammonia, and hydrogen sulfide are often unobservable in

almost all the Jovian planets. For contrast, Earths atmosphere is made of predominantly

nitrogen and oxygen.

From this relationship of distance and temperature, it is clear that the clouds on

the Jovian planets are condensed at different altitudes in the atmosphere on different

planets since gas condensation depends on both pressure and temperature.

Figure 1. Composition of atmospheres. Cloud Altitudes in Jovian Planet

Atmospheres by Portia Wolf.


Atmosphere of Jupiter

Jupiter is the largest and most massive planet in our solar system and is one of the

gas giants. The atmosphere of Jupiter is only a small surface layer, compared to the

whole interior of the Jupiter. The atmospheric structure of Jupiter is similar to Earths

atmosphere, 90% hydrogen and 9.99% helium. The composition contains a troposphere,

stratosphere, mesosphere, and thermosphere. The troposphere is the area where we

can find the visible clouds. The stratosphere is a region that the atmosphere is warm;

however, it is not like how the earth is warmed by the presence of ozone, the source of

warming the Jupiters stratosphere is the hazes of methane. The mesosphere of Jupiter

is like on other planets, its a static region which balances the incoming and outgoing

energy. For the thermosphere, its another place to heat the atmosphere. This region is

warmed from the suns radiation, also the incoming from the magnetosphere helps raise

the temperature of thermosphere. As the depth of atmosphere increases, pressure and

temperature would raise. It makes the hydrogen gas change into a liquid; consequently,

Jupiter has the largest ocean in the solar system. [Fig. 2] shows the temperature of

the whole atmosphere. The temperature of the mesosphere is about 170 K, and rises

to 850 K for the thermosphere. The pressure is a relative way to measure the altitude

where the temperature changes in the mesosphere. The surface of Jupiter is defined as

the place where the pressure of the atmosphere is 100 kPa, which is the atmospheric

pressure at earths surface. It is relative because humans have not landed on the surface

of Jupiter. If a spacecraft were to descend from the visible clouds made of ammonia

ice, it would reach the core after clouds and water vapour. But the core is theorised

to contain liquid metallic hydrogen with some helium. The temperature of the core is

36,000 Kelvin, and there is no way to find a place to land the spaceship. Another way

is to land below the surface of Jupiter. However the atmosphere is covered with clouds


Figure 2. The temperature profile of Jupiters entire atmosphere by Arizona Press.

composed of ammonia crystals and some may contain ammonium hydrosulfide, these

clouds have two different colours: light-hued and dark. It causes horrifically strong

storms, wind speeds usually are larger than 360 km/h. The Great Red Spot of Jupiter,

abbreviated as GRS henceforth, is considered as a hurricane which lasted for at least

400 years. Combined with lightning and extremely large pressure, the spacecraft would

be crushed.

Atmosphere of Saturn

As with the other gas giant in the solar system Jupiter, Saturns atmosphere is composed

of a majority of hydrogen and helium. The structure of Saturns atmosphere consists of,

from descending altitude: stratosphere, tropopause, and the troposphere. In the region

of the tropopause, the boundary between the stratosphere and the troposphere, there

is high haze. The troposphere has 3 regions that condense different gases: ammonia

ice clouds, ammonium hydrosulfide ice clouds, and water ice clouds. The tropospheres

temperature ranges from 143.2 K to 353.2 K. The highest region of the troposphere,

ammonia ice clouds, is found to be at an altitude corresponding to 100 kPa or 100


km below the tropopause. The temperature in this region is 23.15 K. The ammonium

hydrosulfide ice clouds region of the tropopause, 100 km from the tropopause, has a

temperature of 203.2 K. Lastly, the water ice clouds region, 130 km below the tropopause

at a pressure > 1000 kPa, has a temperature of 273.2 K. Although Saturn does not have

a distinct landmark like Jupiters GRS, the encounters with Saturn from the Voyager

1 space probe prove that Saturn is home to very violent winds. These winds reach up

to 1800 km/hr at the equator [2]. These winds help redistribute heat away from the

subsolar zone of the planet. Similar to Jupiter, Saturn has occasional violent white

storms; the size of each storm is bigger than the Earth, but the last one observed was

in 1994 by the Hubble Space Telescope. In addition, the space probe also discovered

that the atmosphere was made up of 25% helium and roughly 75% hydrogen gas. The

lower helium composition in the atmosphere, while Saturn retains the same abundance

of helium as Jupiter, suggests that heavier helium isotopes may be sinking through the

hydrogen. At low enough temperatures, the helium condenses into helium raindrops

that fall toward the core. Saturn also has a distinct aurora

Atmosphere of Uranus

Uranus is primarily hydrogen and helium. The mole fraction of its helium, as per mole,

is 0.15 0.03 mm; quality in the upper troposphere, the equivalent of 0.26 0.05

percentage points. This value is very close to 0.275 0.01 in the original star quality

percentage. Displayed in the star of the gas, helium is unstable in the planet. In the

atmosphere of Uranus, the third most abundant molecule is methane. Methane in the

visible and near infrared absorption band for Uranus is made clear blue green or dark

blue colour. At the top of the methane clouds, the atmospheric pressure is 1.3 mPa,

the mole fraction of methane in the atmosphere is 2.3%, the amount is about 20 to


30 times that of the sun. In Uranus, the atmosphere is warming the outermost layers

and the halo, uniform temperature, around 800 K to 850 K. People still do not know

what kind of high temperature heat source exists to support this, although the low

efficiency of cooling and upper stratospheric hydrocarbons can contribute some energy.

But even the far ultraviolet and super ultraviolet radiation of the sun, or the aurora

activity is not enough to provide the needed energy. In addition, hydrogen molecules

and subsurface temperature and halo with large proportion of free hydrogen atoms, their

low molecular weight and high temperature may explain why the halo can be expanded

to 50000 km from the planet; that is twice the radius of Uranus. The extended halo

is a unique feature of Uranus. Its role includes the damping around Uranus small

particles, causing some of the dust particles in the Uranus ring wear. Uranus in the

subsurface temperature and corresponds to the upper layer in the stratosphere Uranus

ionosphere. Observation shows that the ionosphere to occupy the height of 2000 km to

10000 km. Ionospheric density than Saturn Uranus or Neptune is high, it may cause

the concentration of hydrocarbons in the lower stratosphere. The ionosphere is a major

area under the suns ultraviolet radiation, its density is changed according to the solar

activity. The aurora activity is not obvious and significant as Jupiter and Saturn.

Atmosphere of Neptune

Neptune orbits the sun as the eighth planet and also the suns fourth largest objects.

With regards to diameter and volume, Neptune is smaller than Uranus, but Neptunes

mass is greater than Uranus, about 17 times of the earth. Neptunes atmosphere is given

priority to hydrogen and helium with traces of methane in the atmosphere; the methane

in the atmosphere is part of the blue planet. At high altitudes, Neptunes atmosphere

is 80% hydrogen and 19% helium, there are traces of methane. The main absorption


band appeared in more than 600 nm wave and infrared spectrum. Compared with

Uranus, it is the absorption of atmospheric methane partial, Neptune brings blue tones,

while Neptune lively nattier blue differs from Uranus soft cyan, atmospheric levels of

methane because Neptune is similar to Uranus, some unknown atmospheric composition

is thought to help the colour of Neptune. Neptunes atmosphere can be subdivided into

two major areas: the lower troposphere, its temperature decrease with height; And

the stratosphere, where temperature increases with height. The boundary between the

two layers, appear in the troposphere air pressure of 10 kPa, approximately equal to

the earth a standard atmospheric pressure. The stratosphere in the air pressure is

lower than the 10 to 10 barye (1-10 Pa) become hot in layers, the thermal stratification

gradually transition to the mesosphere. The reason is still unclear for the planets

thermal stratification with abnormal high temperature of about 750 K. To get that

heat from ultraviolet radiation from the sun is improbable since the distance from the

sun is too great. One candidate for this heating is the planets magnetic field and

ion interaction; another candidate is from internal gravity waves in the atmosphere.

Thermal stratification can detect carbon dioxide and water; the source may come from

outside, such as meteoroids and dust.

Atmospheric Dynamics

Atmospheric movement form is varied, the different forms of exercise have different

characteristics, the difference of them, mainly by pushing air force caused by different.

This will naturally affect the level of atmospheric movement. Atmospheric motion of

different spatial scales, describes all kinds of sports have different forms of dynamic

equations of a simplified form. But generally speaking, the movement is decided by

its main factors. Therefore, the task of atmospheric dynamics, the first is the main


factor to distinguish between different types of atmospheric motion and the secondary

factors, and then according to different conditions, the atmospheric dynamic equations, a

practical simplification, the solution of equations. These solutions to reflect the specific

state of atmospheric movement, but also clearly reflects the physical process in the

evolution of the motion state. Atmosphere is the fundamental forces, gravity, Coriolis

force, the pressure gradient force and viscous force (friction force). In different scales

of atmospheric motion, the force is different, the inertial acceleration is also different.

Generally, the ratio between the inertial force of horizontal motion and the Coriolis

force, is defined as the Rossby number; it can be used as the scale for types atmospheric

motion characteristics, u is the scale scale for the horizontal wind speed characteristics,

f = 2 sin (with the earths rotation angular velocity , for latitude) for the Coriolis

parameter.The greater the Ro is, the larger the effect of Coriolis force. A smaller Rossby

number would indicate a system that is affected more by centrifugal and other inertial

forces. The middle latitude area of atmospheric movement, u 10 m/s, f 10.14

seconds. In the case of the large scale motion, Ro is about 1/10, this suggests that the

inertia force is smaller than the Coriolis force, under the rough approximation can be

left out. In this way, the pressure gradient force and Coriolis force balance, forming

geostrophic wind.As for the mesoscale movement, Ro 1. The Rossby number is an

important parameter describing atmospheric horizontal motion characteristics. On the

other hand, the inertia force of vertical direction and the ratio of the Archimedes is

defined as the Froude number, i.e., where is the characteristics of the vertical velocity

scale atmospheric movement. When the Froude number Fr 1, the motion is quasi

static. If Fr 1, which means is larger, the movement will be static. Large scale

exercise is quasi static commonly.


References

[1] J. Kelly, C. C. Petersen, A. Chaikin, The New Solar System, 4th Ed. (Cambridge, MA), pp.

201-221

[2] Saturns Atmosphere. WWW Document. (http://www.esa.int/)

[3] J. Saur, D. F. Strobel, Atmospheres and Plasma Interactions at Saturns Largest Inner Icy

Satellites, The astrophysical journal 620 (2005)

ASTC25 SMP Atmospheres of Giant Planets

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