Visions of the Cosmos

Planetary Science

The Solar System

 Jupiter

Jupiter and Earth compared.  Courtesy NASA/JPL

Jupiter has been known since ancient times and during the nineteenth and twentieth centuries was studied by astronomers all over the world by telescopes.  It was only towards the last quarter of the twentieth century that it was observed by very powerful telescopes including the Hubble Space Telescope and was visited by a number of spacecraft.

Jupiter was first visited by Pioneer 10  in 1973 and later by Pioneer 11,Voyager 1, Voyager 2 and Ulysses. The most significant mission was the Galileo Mission which lasted for eight years and studied the planet and its moons extensively.  This mission is dealt with in the section of this web-site entitled 'The Moons of Jupiter'.

At perihelion or in simple language, the nearest distance of Jupiter to the Sun is  740,742,598 kilometers (4.951 astronomical units).   At aphelion or in simple language the furthest distance from the Sun is 816,081,455 kilometers ( 5.455 astronomical units)

This true-colour simulated view of Jupiter taken by NASA's Cassini spacecraft on 7 December 2000. The resolution of the high resolution image is about 144 kilometres per pixel. Jupiter's moon Europa is casting the shadow on the planet. NASA/ JPL /University of Arizona.  From ESA micromedia library.

Jupiter is by far the most massive planet in the Solar System and is an example of a Gas Giant. The mass of Jupiter is 318 times that of Earth and it is more than twice the mass of all the other planets put together

It is by no means a perfect sphere and squashed at the poles.  It's equatorial diameter is  142,984 kilometres - its polar diameter is 133,709 kilometers.  Its 'surface area is 6.14 X 10 which is 120 times that of the EarthJupiter is just about as large in diameter as a gas planet can be. If more material were to be added, it would be compressed by gravity such that the overall radius would increase only slightly. A star can be larger only because of its internal (nuclear) heat source. (But Jupiter would have to be at least 80 times more massive to become a star.)

Extra solar planets have been discovered with much greater masses than Jupiter. There is no clear-cut definition of what distinguishes a large planet such as Jupiter from a brown dwarf 'star'.  Currently, if an object  is 13 Jupiter masses or above, large enough to burn deuterium, it is considered a brown dwarf; below that mass (and orbiting a star or stellar remnant), it is a planet.  Jupiter is thought to have about as large a diameter as a planet of its composition can; adding extra mass would actually cause the planet to shrink due to increased gravitational compression. The process of further shrinkage with increasing mass would continue until thermonuclear reactions began and first deuterium burning with more mass lithium burning giving us a brown dwarf and still more hydrogen burning giving us a low mass red dwarf star.   This whole question will be discussed in the next main chapter of the web-site on STARS.  This has led some astronomers to term Jupiter a "failed star". Although Jupiter would need to be about seventy-five times as massive to become a true star, the smallest red dwarf  is only about 30% larger in radius than Jupiter.

Jupiter does not have a solid surface and  the gaseous material simply gets denser with depth (the radii and diameters quoted for Jupiter are for a levels corresponding to a pressure of 1 atmosphere) What we see when looking at these planets is the tops of clouds high in their atmospheres (slightly above the 1 atmosphere level).

Jupiter overall composition is about 90% hydrogen and 10% helium with traces of methane, water, ammonia and "rock". This is very close to the composition of the primordial Solar Nebula from which the entire solar system was formed. Saturn is the other Gas Giant in the Solar System and has a similar composition.  Uranus and Neptune are sometimes referred to wrongly as Gas Giants - however they are better referred to Ice Giants.

Our knowledge of the interior of Jupiter and Saturn is highly indirect and is likely to remain so for some time. (The data from Galileo's atmospheric probe only went  down only about 150 km below the cloud tops.)

Jupiter probably has a core of rocky material amounting to something like 10 to 15 Earth-masses.

Above the core lies the main bulk of the planet which consists of metallic hydrogen. This exotic form of the most common  element is possible only at pressures exceeding 4 million bars, as is the case in the interior of Jupiter (and Saturn). Liquid metallic hydrogen consists of ionized protons and electrons (like the interior of the Sun but at a far lower temperature). At the temperature and pressure of Jupiter's interior hydrogen is a liquid, not a gas. It is an electrical conductor and the source of Jupiter's magnetic field. The outermost layer is composed primarily of ordinary molecular hydrogen and helium which is liquid in the interior and gaseous further out. The atmosphere we see is just the very top of this deep layer. Water, carbon dioxide, methane and other simple molecules are also present in tiny amounts.

 Three distinct layers of clouds are believed to exist consisting of ammonia ice, ammonium hydrosulfide and a mixture of ice and water. However, the preliminary results from the Galileo probe show only faint indications of clouds (one instrument seems to have detected the topmost layer while another may have seen the second). But the probe's entry point (left) was unusual -- Earth-based telescopic observations and more recent observations by the Galileo orbiter suggest that the probe entry site may well have been one of the warmest, driest (low water vapour content) and least cloudy areas on Jupiter at that time.

The approximate accepted composition of the upper cloud levels are:-

 86%            Hydrogen  

 ~14%           Helium                                                                                                     
0.1%            Methane
0.1%            Water Vapour
0.02%          Ammonia
0.0002%      Ethane
0.0001%      Phosphine
<0.00010%  Hydrogen Sulphide

Data from the Galileo atmospheric probe also indicate that there is much less water than expected. The expectation was that Jupiter's atmosphere would contain about twice the amount of oxygen (combined with the abundant hydrogen to make water) as the Sun. But it now appears that the actual concentration much less than the Sun's. Also surprising was the high temperature and density of the uppermost parts of the atmosphere

Jupiter and the other gas planets have high velocity winds which are confined in wide bands of latitude. The winds blow in opposite directions in adjacent bands. Slight chemical and temperature differences between these bands are responsible for the coloured bands that dominate the planet's appearance. The light colored bands are called zones; the dark ones belts. The bands have been known for some time on Jupiter, but the complex vortices in the boundary regions between the bands were first seen by Voyager. The data from the Galileo probe indicate that the winds are even faster than expected (more than 640kph/400 mph) and extend down into as far as the probe was able to observe; they may extend down thousands of kilometers into the interior. Jupiter's atmosphere was also found to be quite turbulent. This indicates that Jupiter's winds are driven in large part by its internal heat rather than from solar input as on Earth.

The vivid colours seen in Jupiter's clouds are probably the result of subtle chemical reactions of the trace elements in Jupiter's atmosphere, perhaps involving sulphur and phosphorus whose compounds and elemental allotropic forms take on a wide variety of colours, but the details are unknown.

Picture Courtesyc NASA/JPL

The Great Red Spot (GRS) has been seen by Earthly observers for more than 300 years (its discovery is usually attributed to Cassini, or Robert Hooke in the 17th century). The GRS is an oval about 12,000 by 25,000 km, big enough to hold two Earths. Other smaller but similar spots have been known for decades. Infrared observations and the direction of its rotation indicate that the GRS is a high-pressure region whose cloud tops are significantly higher and colder than the surrounding regions. Similar structures have been seen on Saturn and Neptune. It is not known how such structures can persist for so long.

Jupiter radiates more energy into space than it receives from the Sun. The interior of Jupiter is hot: the core is probably about 20,000 K. The heat is generated by the Kelvin-Helmholtz mechanism, the slow gravitational compression of the planet. (Jupiter does NOT produce energy by nuclear fusion as in the Sun; it is much too small and hence its interior is too cool to ignite nuclear reactions.) This interior heat probably causes convection deep within Jupiter's liquid layers and is probably responsible for the complex motions we see in the cloud tops. Saturn and Neptune are similar to Jupiter in this respect, but oddly, Uranus is not.

Jupiter is just about as large in diameter as a gas planet can be. If more material were to be added, it would be compressed by gravity such that the overall radius would increase only slightly. A star can be larger only because of its internal (nuclear) heat source. (But Jupiter would have to be at least 80 times more massive to become a star.)

Photo Jupiter's Magnetosphere Credits: NASA/JPL/Johns Hopkins University Applied Physics Laboratory

The vast magnetosphere of charged particles whirling around Jupiter, normally invisible, can be imaged by a new type of instrument aboard the Cassini spacecraft and is seen here. Three features are sketched in for context: a black circle showing the size of Jupiter, lines of Jupiter's magnetic field, and a cross-section of the Io torus, a doughnut-shaped ring of charged particles that originate from volcanic eruptions on Jupiter's moon Io and circle Jupiter at about the orbit of Io. Jupiter's magnetosphere is the largest object in the solar system. If it glowed in wavelengths visible to the eye, it would appear two to three times the size of the Sun or Moon to viewers on Earth. Cassini's ion and neutral camera detects neutral atoms expelled from the magnetosphere, deriving information about their source. This image was taken shortly after Cassini's closest approach to Jupiter, about 10 million kilometres from the planet on 30 December 2000.

Jupiter has a huge magnetic field, much stronger than Earth's. Its magnetosphere extends more than 650 million km (past the orbit of Saturn!). (Note that Jupiter's magnetosphere is far from spherical -- it extends "only" a few million kilometers in the direction toward the Sun.) Jupiter's moons therefore lie within its magnetosphere, a fact which may partially explain some of the activity on Io. Unfortunately for future space travellers and of real concern to the designers of the Voyager and Galileo spacecraft, the environment near Jupiter contains high levels of energetic particles trapped by Jupiter's magnetic field. This "radiation" is similar to, but much more intense than, that found within Earth's Van Allen belts. It would be immediately fatal to an unprotected human being.
 

Jupiter has rings like Saturn's, but much fainter and smaller (right). They were totally unexpected and were only discovered when two of the Voyager 1 scientists insisted that after travelling 1 billion km it was at least worth a quick look to see if any rings might be present. Everyone else thought that the chance of finding anything was nil, but there they were. It was a major coup. They have since been imaged in the infra-red from ground-based observatories and from the Galileo spacecrft

Unlike Saturn's, Jupiter's rings are dark.. They're probably composed of very small grains of rocky material. Unlike Saturn's rings, they seem to contain no ice.

 

In July 1994, Comet Shoemaker-Levy 9 collided with Jupiter with spectacular results (left). The effects were clearly visible even with amateur telescopes. The debris from the collision was visible for nearly a year afterward with HST.

 

 

Jupiter radiates more energy into space than it receives from the Sun. The interior of Jupiter is hot: the core is probably about 20,000 K. The heat is generated by the Kelvin-Helmholtz mechanism, the slow gravitational compression of the planet. (Jupiter does NOT produce energy by nuclear fusion as in the Sun; it is much too small and hence its interior is too cool to ignite nuclear reactions.) This interior heat probably causes convection deep within Jupiter's liquid layers and is probably responsible for the complex motions we see in the cloud tops. Saturn and Neptune are similar to Jupiter in this respect, but oddly, Uranus is not.

Jupiter is just about as large in diameter as a gas planet can be. If more material were to be added, it would be compressed by gravity such that the overall radius would increase only slightly. A star can be larger only because of its internal (nuclear) heat source. (But Jupiter would have to be at least 80 times more massive to become a star.)

The Galileo Probe

No web-site on  Jupiter would be complete without a discussion of the Galileo Space Probe. 

The Jupiter Probe Astronomical Picture of the Day 7 December 1995 Courtesy NASA
 
The Galileo Probe and Orbiter separated on July 13, 1995 and both arrived at Jupiter on slightly different trajectories. The Galileo Orbiter successfully became the first spacecraft to enter an orbit about Jupiter a few hours after the Probe's successful descent into the atmosphere. The Orbiter and the Galileo Mission as a whole and the spectacular investigation of the four large moons of Jupiter is discussed in the part of this web-site entitled the 'Moons of Jupiter'.  After a six year journey through the Solar System and after being accelerated to a speed of 170,700 km/hour (106,000 mph) by Jupiter's tremendous gravitational pull, the Galileo Probe successfully entered Jupiter's atmosphere at 22:04 UT ( 2:04 P.M. PST) on December 7, 1995. During the first two minutes of this most difficult atmospheric entry ever attempted, temperatures twice as hot as the Sun's surface temperature and deceleration forces as great as 230 g's (230 times the acceleration of gravity at Earth's surface) were produced as the spacecraft was slowed down by Jupiter's atmosphere.

At a speed of 3,000 km/hour (1,900 mph), the Probe's parachutes were deployed when the probes speed was 3,000 kilometers per hour (1,900 mph) and the heat shields fell away for the start of the direct measurements of the conditions of the atmosphere. and the transmission of The data was transmitted via a radio link to the Galileo Orbiter which was 215,000 km above the probe.

The Descent of the Probe Artists Impression Courtesy NASA

The data from the Probe  was stored  in the computer memory on board the orbiter and on its tape recorder for later playback to Earth, The collection of data by the probe continued for 57.6 minutes.  At about at depth of 600 km (373 miles) after entering the tenuous upper reaches of Jupiter's atmosphere lasted  .  It failed only after the communication system on the Probe succumbed to the extreme environmental conditions deeper in the atmosphere of Jupiter (the jovian atmosphere).

Several key elements and compounds were found to be less abundant than expected in the sample taken by the probe.The Neutral Mass Spectrometer (NMS) experiment's objective was to accurately determine the composition of the atmosphere. Initial results indicate the atmosphere has less water than expected. The atmosphere also appears to have less methane gas. less hydrogen sulphide, less neon and less helium than expected.   The abundance of Helium was found to be significantly less than that in the Sun. These results suggest our ideas about the formation and evolution of Jupiter may have to be revised. In particular, fractionation or "raining out" of Helium appears to have occurred in the atmosphere. 

        The Probe apparently entered a rather special location in the atmosphere of the planet.  

This may account for the many apparent surprises found by the Probe during its descent.  After all if a probe was sent through the atmosphere of Earth over the Sahara Desert the results of the measuement of the humidity woul

sd be very low and quite misleading for the planet as  a whole.

The Galileo Probe Project was managed by NASA's Ames Research Center, Mountain View, California.  Hughes Space and Communications built the Galileo Probe spacecraft. NASA's Jet Propulsion Laboratory, Pasadena, CA built the  spacecraft and manages the overall mission.

 
 

The Schoemaker-Levy Comet

The Schoemaker -Levy Comet  was observed long before it reached the giant planet.  It was named after the three people who discovered it and observed it Eugene and Caroline Shoemaker and David Levy.

Comet Shoemaker-Levy 9 in a V-band image obtained 19 June 1993 with the Lowell Observatory 1.1-meter telescope. Seen about 13 months before Jupiter impact, the faint overall dust fans are still visible as well as material around each nucleus. Credit University of Alabama

On 24 July 1994 comet slammed into Jupiter.  As it approached the giant planet it broke into nine fragments

 

 

As the fragments of the comet crashed into Jupiter brusess would appear on the face of the planets atmosphere as shown in the photograph.

Caption:

Jupiter G impact evolution
Credits:
R. Evans, J. Trauger, H. Hammel and the HST Comet Science Team
ID number:
ESAUCBUTYWC

Credit ot European Space Agency Micromedia

This mosaic of WFPC-2 images shows the evolution of the G impact site on Jupiter. The images from lower right to upper left show: the impact plume at 07/18/94 07:38 UT (about 5 minutes after the impact); the fresh impact site at 07/18/94 at 09:19 UT (1.5 hours after impact); the impact site after evolution by the winds of Jupiter (left), along with the L impact (right), taken on 07/21/94 at 06:22 UT (3 days after the G impact and 1.3 days after the L impact); and further evolution of the G and L sites due to winds and an additional impact (S) in the G vicinity, taken on 07/23/94 at 08:08 UT (5 days after the G impact).

 

Solar System