Category: Guide to Space

It takes Saturn 10,832 Earth days to complete one orbit around the Sun. That means the answer to ”how long is a year on Saturn” is 29.7 Earth years. The length of Saturn’s year is a direct effect of its orbital distance from the Sun. Saturn orbits at an average of 1.43 billion km, or 9.58 AU, from the Sun.

Knowing how long a year is on Saturn might make one wonder if the planet experiences seasons like we do here on Earth. Yes, Saturn experiences seasons. Saturn has an axial tilt of 26.73 degrees, allowing different hemisphere to experience varying levels of sunlight. Of course, the seasons only go from cold to a whole lot colder. Also, the seasons last nearly 30 times longer because of the length of the planet’s year. Can you imagine a seven year summer that never reaches higher than -23 C?

The length of a day on Saturn is 10.656 hours. While that number seems to be pretty precise, it took a lot of study to arrive at that figure. There is no way to observe the planet’s surface region, so a way had to be found to estimate the planets rotational speed. Scientists first turned to radio emissions for an estimate, then observation by space craft. They then found that the rotational period varied by as much as 1% over the span of a week. The current stated length of a day on Saturn is an average from all observations.

Saturn’s movement through its orbit occasionally causes its rings to disappear. The phenomenon is called ”ring plane crossing”. Ring plane crossings occur when the tilt of the planet and its position in its orbit combine to allow a side-on view of the rings. The rings seem to disappear, but, without the glare from the rings, the planet’s moons are more easily observed. Also, these crossings are the best time to see Saturn’s blue north pole.

29.7 Earth years is the answer to ”how long is a year on Saturn”, but it leads to many other questions about our mysterious neighbor. Direct observation is the answer, but there have only been four missions to visit the planet as of today(October, 2011). The Casinni-Huygens mission is currently in orbit sending data on a regular basis. Hopefully, it will expand our knowledge of Saturn beyond expectations.

Here’s an article that discusses how Saturn’s rings can seem to disappear, and here’s how long a day is on Saturn.

Here’s a great photo collage of Saturn’s rings seen at various angles to the Earth, and some general Saturn facts.

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://solarsystem.nasa.gov/planets/profile.cfm?Object=Saturn
http://www2.jpl.nasa.gov/saturn/faq.html#what

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

Words are one thing, but to really appreciate Jupiter, we’re going to want to see pictures.

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This is a picture of Jupiter captured by NASA’s Cassini spacecraft, on its way to its final destination: Saturn. The black spot is a shadow cast by Jupiter’s moon Europa. Cassini was never able to capture this detailed a resolution image of Jupiter because the planet was too big to fit into its camera field of view. Instead, the spacecraft took 4 separate images which were then combined together on computer.

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This Jupiter pic is a montage of the planet and its moon Io, captured by NASA’s New Horizons spacecraft on its way out to Pluto. The two objects were never actually lined up like this, instead, the separate images were combined together on computer.

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Although this picture of Jupiter looks like it was taken by a spacecraft, it was actually taken by the Hubble Space Telescope, currently in orbit around the Earth. The photograph of Jupiter was taken to show the Great Red Spot, which has been decreasing in size over the last century.

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This image of Jupiter was captured by NASA’s Galileo spacecraft. As Galileo was orbiting Jupiter, it didn’t take many large images of the planet. This photograph is a mosaic of many images stitched together, showing the boundary between a zone and a belt on Jupiter.

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This is one of the most famous pictures of Jupiter and its Great Red Spot. This was captured by NASA’s Voyager 1 spacecraft as it was speeding past the giant planet.

Did you enjoy these images of Jupiter? There are many more on Universe Today. For example, this is a picture of Jupiter’s south pole captured by Cassini. And here’s Jupiter seen from Saturn.

Probably the best resource for pictures of Jupiter is from NASA’s Planetary Photojournal. You can access it here.

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.

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