Author: Jerry Coffey

Scientist know that Saturn is made up of 96% hydrogen and 3% helium with a few other elements thrown in. What they have never been able to confirm beyond a shadow of a doubt is the answer to does Saturn have a solid core.

According to the core accretion theory, the most widely accepted theory of planetary formation, Saturn would have had to form a rocky or icy core with a great deal of mass in order to capture such a high percentage of gasses from the early solar nebula. That core, like those of the other gas giants, would have had to form and become massive more quickly than those of the other planets in order to capture such a comparatively high percentage of primordial gasses. It is possible that atmospheric pressure and temperatures near the core region have allowed or caused some of the core material to be conveyed to the top of the atmosphere and lost into space, greatly reducing the current size of Saturn’s core.

While Saturn most likely formed from a rocky or icy core, it’s low density seems to point to more of a liquid metal and rock mixture at the core. Saturn is the only planet who’s density is lower than that of water. If anything the core region would be more like a ball of thick syrup with a few rocky chunks. There doesn’t seem to be any part of Saturn that is solid as we understand it. That is, there is no place that you could set foot on it and stand.

The metallic hydrogen core of Saturn does generate a magnetic field. A magnetic field created in this way is said to be generated through a metallic hydrogen dynamo. It’s magnetic field is slightly weaker that Earth’s and only extends to the orbit of its largest moon, Titan. Titan contributes ionized particles to Saturn’s magnetosphere which help create aurorae within Saturn’s atmosphere. Voyager 2 measured high solar wind pressure within the magnetosphere. According to measurements taken during the same mission, the magnetic field only extends to 1.1 million km.

The core region of Saturn may never be directly observed. Neither has the Earth’s. Despite that, scientists are fairly certain that, while Saturn has a core, it is not a solid mass of rock or metal, but a liquid metallic mixture similar to all of the gas giants.

Here’s an article about the core accretion theory of planetary formation, and how Saturn and Jupiter might have formed differently.

If you’d like more info on Saturn, check out Hubblesite’s News Releases about Saturn, and here’s some research about how Saturn and Jupiter might have formed around their solid cores.

We have recorded two episodes of Astronomy Cast just about Saturn. The first is Episode 59: Saturn, and the second is Episode 61: Saturn’s Moons.

Sources:
http://abyss.uoregon.edu/~js/ast221/lectures/lec15.html
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Saturn

The rings around Saturn have captured the imagination of humans for hundreds of years. A natural offshoot of that observation has been a desire to know what is Saturn made of. Using various methods of testing, scientists believe that Saturn is composed of 96% hydrogen, 3% helium, and 1% various trace elements that include methane, ammonia, ethane, and hydrogen deuteride. Several of these gases can be found in gas, liquid, and molten states as you descend into the planet.

The state of the gases change with pressure and temperature. At the cloud tops, you would encounter ammonia crystals, but at the bottom of the clouds you would come across ammonium hydrosulfide and/or water. Beneath the clouds, atmospheric pressure increases causing an increase in temperature, so hydrogen moves into a liquid state. Pressure and temperature continue to increase as you close in on the core, causing hydrogen to become metallic. Saturn, much like Jupiter, is thought to have a loose core made up of relatively little rock and some metals.

It is hard to conceive that Saturn is made up of much more than gas based on its low density. Saturn has a density of 0.687 g/cm³. Earth, on the other hand, has a density of 5.513 g/cm³. That means that a planet that has 95 times more mass than Earth has barely 12% of its density. Saturn’s density is so low that it could float on water more easily than most boats.

Modern space based observation has led to many discoveries about the make up of Saturn. The missions began with a flyby of the Pioneer 11 spacecraft in 1979. That mission discovered the F ring. The following year Voyager 1 flew by sending back surface details of several of Saturn’s moons. It also proved that the atmosphere on the moon Titan was impenetrable by visible light. In 1981 Voyager 2 visited Saturn and discovered changes in the atmosphere and the rings as well as confirming the presence of the Maxwell Gap and the Keeler Gap, both first seen by Voyager 1.

After Voyager 2, Cassini–Huygens spacecraft performed a Saturn orbit insertion maneuver to enter orbit around the planet in 2004. The craft had been studying the system for some time before entering orbit. The discoveries made by the craft are numerous and best explained on NASA’s mission page.

Saturn has held the imagination of countless generations. Knowing the answer to ”what is Saturn made of” is a great beginning. Hopefully, you will dive right in and become a Saturnian expert.

Here’s an article about what Saturn’s rings are made of, and information about the planet’s radiation belts.

Here’s an overview of NASA’s Cassini mission to Saturn, and the story of Saturn.

We have recorded two episodes of Astronomy Cast just about Saturn. The first is Episode 59: Saturn, and the second is Episode 61: Saturn’s Moons.

Source: NASA

The iconic images of Jupiter show that it reflects many shades of white, red, orange, brown, and yellow. The color of Jupiter changes with storms and wind in the planet’s atmosphere.

The colors of Jupiter’s atmosphere are created when different chemicals reflect the Sun’s light. Most of Jupiter is hydrogen and helium, but the top of its clouds are composed of ammonia crystals, with trace amounts of water ice and droplets, and possibly ammonium hydrosulfide. Powerful storms on Jupiter are created by the planet’s convection. That allows the storms to bring material, such as phosphorus, sulfur and hydrocarbons, from closer to the planet’s core to the tops of the clouds, causing the white, brown, and red spots that we see dotting the Jovian atmosphere. White spots appear to be cool storms, brown are warm, and red are hot storms.

Jupiter’s Great Red Spot is an extreme example of one of these storms. It has been raging for at least 400 years. It is thought to have first observed by Giovanni Cassini in the late 1600s. It was observed up close by NASA’s Pioneer 10 spacecraft when it made its flyby in 1974. Better and better images were captured by other spacecraft, including the Voyagers, Galileo, Cassini and New Horizons. A century ago, the Red Spot measured 40,000 km across, but now it measures roughly half that, and seems to be shrinking. Astronomers have no idea how long the spot will last nor why it has lasted so long. The storm is so large that it can be seen from Earth by any medium sized or larger telescope.

A more recent storm has developed on Jupiter that has captured the attention of astronomers. Officially dubbed Oval BA , but commonly referred to as Red Jr, this storm is about half the size of the famous Great Red Spot and almost exactly the same color. Oval BA first appeared in 2000 when three smaller spots collided and merged. Scientists theorize that the Great Red Spot may have been created in the same way.

Scientists have been using the color of Jupiter to understand the atmospheric workings of the planet. There are future missions scheduled to bring a more in depth understanding to light. Those missions are also going to study the interaction of the volcanoes on Io with the water ice on Europa. There should be some pretty awesome data coming in the next few years.

Here’s an article from Universe Today about the newly formed Red Spot Jr, and another article about how storms on Jupiter can form in just a single day.

Ask an astronomer for Kids has tackled the same question, and a comparison of Jupiter in true and false color.

We’ve also recorded an entire show just on Jupiter for Astronomy Cast. Listen to it here, Episode 56: Jupiter, and Episode 57: Jupiter’s Moons.

Sources:
http://science.nasa.gov/science-news/science-at-nasa/2006/02mar_redjr/
http://www.nasa.gov/multimedia/imagegallery/image_feature_413.html

No matter how you measure it, Jupiter is a larger than life planet. The size of Jupiter can be measured in four ways: mass, diameter, volume, and surface area. The mass of Jupiter is 1.9 x 10²⁷ kg. It has an equatorial diameter of 143,000 km. The Jovian volume is 1.43 x 10¹⁵km³. The total surface area of Jupiter is 6.22 x 10¹⁰km².

Jupiter’s mass is 318 times that of Earth’s and around 2.5 times that of the rest of the Solar System combined. Jupiter may be the most massive planet in our Solar System, but it would need another 50-80 times its current mass in order to begin fusing its hydrogen into helium and become a star. The planet’s diameter is 11.2 times larger than Earth’s. Jupiter’s volume is 1321 times larger than Earth’s and it’s surface area is 122 times that of Earth’s.

While the size of Jupiter makes it seem like the largest possible planet, it is not. TrES-4 is estimated to be 70% larger than Jupiter, but it is less massive and has a lower density. That means that it is, well…fluffy. It’s density is so low that it would float on water. The planet is located about 1,400 light-years away, and orbits its host star every 3.5 days. It orbits 7.2 million km from its star, reaching a temperature of 1,600 Kelvin. The discovery of TrES-4 was made by astronomers working with the Trans-atlantic Exoplanet Survey. To capture transiting planets, the network of telescopes take wide-field timed exposures of clear skies on as many nights as possible. Astronomers then measure the amount of light coming from every single star in the field to detect if any have changed in brightness. In the case of TrES-4, it dims the amount of light received by the star by about 1%. Scientists are trying to figure out how a planet with so little mass could get so large. ”TrES-4 appears to be something of a theoretical problem,” said Edward Dunham, Lowell Observatory Instrument Scientist. ”It is larger relative to its mass than current models of superheated giant planets can presently explain. Problems are good, though, since we learn new things by solving them.”

Jupiter’s size is amazing, but as we expand our knowledge of the Universe, we are finding that it is not nearly the largest possible planet. As TrES-4 has demonstrated, there are planets out there that defy our current understanding.

Here’s an article from Universe Today about how big planets can get, and another about a star that’s the size of Jupiter.

Here’s all the information you could want about Jupiter from Wikipedia, and more general Jupiter information from Nine Planets.

We’ve also recorded an entire show just on Jupiter for Astronomy Cast. Listen to it here, Episode 56: Jupiter, and Episode 57: Jupiter’s Moons.

Sources:
NASA
http://www.lowell.edu/

One of the first things that many people ask about a planet is whether there is water or not. So, naturally, the question ”is there water on Jupiter?” has been asked many times. The answer is yes, there is a small amount of water, but it is not ”on” Jupiter. It is in the form of water vapor in the cloud tops.

Scientists were surprised to find only trace amounts of water on Jupiter. After all, they had reasoned that Jupiter should have more oxygen than the Sun. The oxygen would have combined with the more than abundant hydrogen in the Jovian atmosphere, thus making water a significant component. The trouble is that the Galileo space craft found that Jupiter’s atmosphere contains less oxygen than the Sun; therefore, water is a minor trace element in the atmosphere.

That does not mean that there is not significant amounts of water elsewhere in the Jovian system. A few of Jupiter’s moons have been found to have water or water ice in their atmosphere or on their surface. Europa is the most important source of water in the system. Europa is thought to have an iron core, a rocky mantle and a surface ocean of salty water. Unlike oceans on Earth, this ocean is deep enough to cover the whole surface of Europa, and being far from the sun, the ocean surface is globally frozen over. Europa’s orbit is eccentric, so when it is close to Jupiter the tide is much higher than when it is at aphelion. Tidal forces raise and lower the sea beneath the ice, most likely causing the cracks seen in images of Europa’s surface. The tidal forces cause Europa to be warmer than it would otherwise be. The warmth of Europa’s liquid ocean could prove critical to the survival of simple organisms within the ocean, if they exist.

Some scientists at NASA believe that the ocean under Europa’s surface does not consist of water, but say light reflected from the moon’s icy surface bears the spectral fingerprints of hydrogen peroxide and strong acids, perhaps close to pH 0. They are not sure whether this is just a thin surface dusting or whether the chemicals come from the ocean below. The hydrogen peroxide certainly seems to be confined to the surface, as it is formed when charged particles trapped in Jupiter’s magnetosphere strike water molecules on Europa. On the other hand, parts of the surface are rich in water ice containing what appears to be an acidic compound. Robert Carlson of NASA’s Jet Propulsion Laboratory thinks this is sulfuric acid. He believes that up to 80 per cent of the surface ice on Europa may be concentrated sulfuric acid. He goes on to suggest that this may be confined to a layer formed by surface bombardment with sulfur atoms emitted by volcanoes on Io. Tom McCord of the Planetary Science Institute in Winthrop, Washington and Jeff Kargel of the US Geological Survey in Flagstaff, Arizona point out that the greatest concentrations of acid seem to be in areas where the surface has been broken by tidal forces. They believe that ocean liquid has gushed up through those cracks and the ocean is actually the source of all of the acid. This theory holds that the acid on the surface began as salts(mainly magnesium and sodium sulphates), but the intense surface radiation caused chemical reactions which left an icy crust containing a high concentration of sulfuric acid as well as other sulfur compounds. That means that the ocean is an acidic brine that would be destructive to life as we know it.

Giving the answer to ”is there water on Jupiter” is probably the simplest piece of information about the planet. Nearly everything else is open a lot of interpretation until more space craft are sent for additional exploration.

Here’s an article about how the water on Europa might actually be corrosive to life, and the discovery of an extrasolar planet that does have evidence of water.

The Nine Planets site has a great description of Jupiter, including its lack of water, and an old article about Galileo’s search for water on Jupiter.

We’ve also recorded an entire show just on Jupiter for Astronomy Cast. Listen to it here, Episode 56: Jupiter, and Episode 57: Jupiter’s Moons.

Sources:
NASA: Jupiter
NASA: Europa

No one can definitively say when the discovery of Jupiter took place nor who discovered it. Why is it so hard? It is one of the five planets that can be seen in the night sky. Only Venus and the Moon are brighter. Frankly, it is nearly impossible to miss. NASA lists the planet as having been discovered by the Ancients. The planet is called Marduk in ancient Babylonian texts, Zeus in early Greek manuscripts, and Jupiter in Roman antiquity.

What is known are some of the firsts in the exploration of Jupiter. In 1610, Galileo Galilei turned his rudimentary telescope on Jupiter, and realized that it had 4 large moons orbiting it: Io, Europa, Ganymede and Callisto. This was an important discovery, because it demonstrated that Earth was not the center of the Universe as proponents of the geocentric view believed.

In the1660s, Giovanni Cassini used his telescope to discover spots and bands across the surface of Jupiter, and was able to estimate the planet’s rotational period. He is thought to be the first to observe the planet’s Great Red Spot, a giant storm that is still raging. Imagine a single storm that rages for over 450 years and is larger than the Earth.

The first spacecraft to visit Jupiter up close was NASA’s Pioneer 10 in 1973. That mission was closely followed by Pioneer 11 in 1974. Both of NASA’s Voyager spacecraft flew past in 1979, sending back many of the famous pictures we’re all familiar with. Since then, the Ulysses solar probe, NASA’s Cassini spacecraft and New Horizons have all made flybys of the planet.

The only spacecraft to actually orbit Jupiter was NASA’s Galileo mission, which went into orbit in 1995. NASA scientists were not satisfied with a few orbits of Jupiter. They wanted to see a bit more of the Jovian system, so Galileo was sent to observe a few moons. Galileo is credited as being the first spacecraft to observe a comet hitting a planet(Jupiter), first to flyby an asteroid, first to discover an asteroid with a moon, and it was the first to measure the crushing atmospheric pressure of Jupiter with a descent probe. The mission discovered evidence of subsurface saltwater on Europa, Ganymede and Callisto and revealed the intensity of the volcanic activity on Io.

We may not know the exact date of the discovery of Jupiter, but we know many first about the planet. Even now, scientists are planning the next mission and hoping to be the first to discover something about the Jovian system.

Here are some images of the Jupiter flyby from NASA’s New Horizons spacecraft, and an article about Cassini’s flyby of Jupiter.

Here’s the archived page for NASA’s Galileo mission to Jupiter, and information about the Voyager mission’s images of Jupiter.

We’ve also recorded an entire show just on Jupiter for Astronomy Cast. Listen to it here, Episode 56: Jupiter, and Episode 57: Jupiter’s Moons.

Sources:
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Jupiter&Display=Facts
http://solarsystem.nasa.gov/galileo/

The mass of Jupiter is 1.9 x 10²⁷ kg. It is hard to fully understand a number that large, so here are a few comparisons to help. It would take 318 times Earth’s mass to equal Jupiter’s. Jupiter is 2.5 times more massive than all of the other planets in our Solar System combined. Jupiter is actually so massive that if it gained much more mass it would shrink.

How can additional mass cause a planet to shrink? Gravitational compression. Given that there is no more hydrogen or helium gas floating around for Jupiter to collect, it would gain mass through the accretion of rocky bodies like asteroids. Jupiter’s intense gravity would pull additional rock tightly together shrinking the diameter of the planet and increasing its density. As the density increased so would the gravity, further compressing the planet. Scientists estimate that Jupiter would have to accumulate 3-4 times its current mass in order to begin compressing. Since there isn’t that much material in our Solar System, it is a pretty good bet that Jupiter will never shrink.

But what if it did? There have been rumors floating around for decades that Jupiter could ignite fusion and become a star at any time. They are all false science and garbage at best. The mass of Jupiter is no where near enough for sustained nuclear fusion. Fusion requires high temperatures, intense gravitational compression, and fuel. Jupiter has the right fuels in abundance. There is plenty of hydrogen to be had, but the planet is too cold and lacks the density for a sustained reaction process. Scientists estimate that Jupiter needs 50-80 times its current mass to ignite fusion. As stated in the paragraph above, there isn’t enough material to be had, so Jupiter can not become a star.

At one time, scientists thought that Jupiter was the largest that a planet could become without igniting fusion and becoming a star. They discovered the fallacy of that belief once technology expanded their view of the universe. According to Dr. Sean Raymond, a post doctoral researcher at the Center for Astrophysics and Space Astronomy (CASA) at the University of Colorado, ”In terms of gaseous planets, once they reach 15 Jupiter masses or so there is enough pressure in the core to ignite deuterium fusion, so those are considered ‘brown dwarfs’ rather than planets.”

As you can see, the mass of Jupiter may seem awesome in comparison to Earth, it is a tiny fish in a world of sharks. Scientists have found a few hundred gas giants larger than Jupiter as they have surveyed the night sky. Who knows what is in store as telescope technology improves in the coming years.

Here’s an article from Universe Today explaining just how big planets can get, and an article about how Jupiter and the other gas giants might have gobbled up their moons while they were forming.

This site has more detailed information about the mass of Jupiter, and a page from NASA that helps you calculate the density of the planets.

We’ve also recorded an entire show just on Jupiter for Astronomy Cast. Listen to it here, Episode 56: Jupiter, and Episode 57: Jupiter’s Moons.

Sources:
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Jupiter
http://planetquest.jpl.nasa.gov/news/tres4.cfm

As an avid reader, I have come across many books that proposed the idea of life on Jupiter. Some even proposed that Jupiter is lifeless, but its moons harbor advanced life forms. Is there life on Jupiter? While there have been no samples taken that could test for microscopic life on the planet, there is quite a bit of compelling evidence that shows there is no possible way for life as we know it to exist anywhere on the planet. Try this link for one scientist’s take on finding life in the cosmos.

First, let’s look at the conditions on Jupiter that preclude the existence of life. The planet is a gas giant composed mainly of hydrogen and helium. There is virtually no water to support known life forms. The planet does not have a solid surface for life to develop anywhere except as a floating microscopic organism.

Free floating organisms could only exist at the very tops of the clouds due to atmospheric pressure that is progressively more intense than anything seen on Earth. While the cloud tops could harbor life that is resistant to solar radiation, the atmosphere is in constant chaos. Convection forces the lower atmosphere upwards and colder areas of the atmosphere are constantly being sucked closer to the core. The churning would eventually expose any organisms to the extreme pressures nearer the core, thus killing any that may develop.

Should an organism find a way to resist atmospheric pressure that reaches 1,000 times what it is here on Earth, there are the temperatures close to the planet’s core. Gravitational compression has heated areas near the core to over 10,000 degrees Celsius. It is so hot in some areas that hydrogen is in a liquid metallic state. While organisms on Earth live in areas near volcanoes, the temperatures there do not approach Jovian levels.

Jupiter is completely inhospitable to life as we understand it, but its moon Europa has been proposed as a possible habitable zone. It is thought to have a large amount of water ice on its surface. Some of which covers a proposed ocean of water slush. The conditions under the water ice could be harboring microscopic life according to some scientists.

The question ”is there life on Jupiter” seems pretty well decided. There is no way that life as we understand it could exist on the gas giant. The possibility of life within the Jovian system is still being explored. Some debate exists about Europa. NASA’s Jupiter Icy Moons Orbiter was set to answer those questions before it was canceled. Hopefully, another mission like it will be launched soon and end all of the debate.

Here’s an article about the search for life on Europa. Not so fast, though. Here’s an article about how Europa might be corrosive to life.

Here’s a classic article from Time Magazine in 1961 about the possibilities of life on Jupiter, and the search for life on Jupiter’s moon Europa.

We’ve also recorded an entire show just on Jupiter for Astronomy Cast. Listen to it here, Episode 56: Jupiter, and Episode 57: Jupiter’s Moons.

Sources:
http://www.nasa.gov/vision/universe/starsgalaxies/frozenworlds.html
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Jupiter
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Jup_Europa
NASA Jimo MIssion

The orbit of Jupiter, like that of all the planets, is elliptical instead of circular. At perihelion(closest approach) Jupiter comes within 741 million km, or 4.95 astronomical units(AU), of the Sun. An astronomical unit is the average distance from the Earth to the Sun and is used to make astronomical distances easier to communicate. At its most distant point, called aphelion, Jupiter is 817 million km, or 5.46 AU from the Sun. The average between perihelion and aphelion is called the semi-major axis. Jupiter’s semi-major axis is 778 million km, or 5.2 AU.

Jupiter is the fifth planet from the Sun, but it is the third brightest object in the night sky here on Earth. Since Jupiter is farther from the Sun, you would expect it to take longer to orbit, but did you know that it takes 11.86 Earth years, or 4331 Earth days for Jupiter to complete one orbit? Jupiter travels at 47,002 km/h through ts orbit. Its orbit is inclined 6.09 degrees from the the Sun’s equator. Several of the planets have seasons, similar to Earth’s, but Jupiter does not. It rotates too fast for seasonal variations(Jupiter rotates every 10 hours).

Jupiter has several companions in its orbit. By companions, I mean moons. There are 64 known moons in orbit around Jupiter with a few more being suspected. The largest four(Io, Europa, Ganymede, and Callisto) are are called the Galilean satellites. They are diverse and interesting worlds of their own. Io is the most volcanically active body in our Solar System. Europa is covered in water ice which may be covering an ocean of slushy water. Ganymede is larger than Mercury and it is the only moon in the Solar System that generates its own magnetic field. Callisto’s surface is heavily cratered and some of the larger craters may have been in place shortly after the creation of the Solar System, yet some small craters show indications of recent geologic activity. Four of Jupiter’s moons are thought to be the source of its rings. Adrastea and Metis contribute to the main ring and the halo ring. Amalthea and Thebe contribute to two separate gossamer rings.

The orbit of Jupiter is beyond comparison in our Solar System. The Jovian influence can be felt well beyond its orbit. There is so much within that orbit that scientists can make an entire career out of studying the Jovian system.

Here’s an article on Universe Today about how Jupiter might have caught one of its moons while orbiting the Sun, and more detailed information about how long a year is on Jupiter.

Here’s Hubblesite’s News Releases about Jupiter, and more information on Jupiter in NASA’s Solar System Exploration pages.

We’ve also recorded an entire show just on Jupiter for Astronomy Cast. Listen to it here, Episode 56: Jupiter, and Episode 57: Jupiter’s Moons.

Source:
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Jupiter&Display=Facts