Category: Guide to Space

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

We all known that Saturn has rings, but does Jupiter have rings? Yes, it does. Four planets have a rings system: Saturn, Jupiter, Uranus, and Neptune. Saturn is best know because it has the brightest and most extensive rings system in the Solar System.

The rings around Jupiter had never been seen before Voyager 1 arrived in 1979. Since then the rings have been observed by the largest telescopes on Earth, the Hubble Space Telescope, and the New Horizons spacecraft. So far, only four rings have been observed: the halo ring, the main ring, the Amalthea gossamer ring, and the Thebe gossamer ring.

Jupiter’s rings and moons exist within an intense radiation belt of electrons and ions trapped in the planet’s magnetic field. These particles and fields comprise the Jovian magnetosphere or magnetic environment, which extends 3 to 7 million km toward the sun, and stretches in a windsock shape at least 750 million km, which puts it inside of Saturn’s orbit.

The main ring is about 7,000 km wide and has an abrupt outer boundary 129,130 km from the center of the planet. The main ring encompasses the orbits of two small moons, Adrastea and Metis, which may act as the source for the dust that makes up most of the ring. The ring needs a constant source of dust because small particles can only exist for 100 to 1000 years. The dust is thought to rise from moons within the rings due to micrometeoroid impacts. The main ring merges gradually into the Halo ring. The halo is a broad, faint torus of material about 20,000 km thick and extending halfway from the main ring down to the planet’s cloudtops.

On the outer edge of the main ring and opposite of the halo ring, is the broad and extremely faint Amalthea gossamer ring. This ring extends out beyond the orbit of the moon Amalthea. Scientists believe that it is composed of dust particles smaller than 10 microns. 10 microns is about the size of cigarette smoke particles. It extends to an outer edge of about 129,000 km from the center of the planet and inward to about 30,000 km. The origin of the ring is probably from micrometeorite bombardment of the tiny moons orbiting within the ring. Last, is the Thebe gossamer ring. This is the faintest of the Jovian rings and extended from the orbit of the moon Thebe at about 226,000 km towards the planet, ending at about 129,000 km. The exact inner edges of the two gossamer rings are hard to define because they overlap the brighter main ring.

So, the answer to ”does Jupiter have rings” is yes, it has four known rings. Be sure to read about the ring systems of Neptune and Uranus as well.

Here’s a news article from Universe Today about the rings of Jupiter, and information about New Horizon’s observations of Jupiter’s rings.

Here’s NASA’s Solar System explorer information about Jupiter’s rings, and a cool image from Astronomy Picture of the Day of Jupiter’s rings.

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=Rings

The diameter of Jupiter at its equator is 142,984 km. Since it rotates very quickly, completing a full rotation in just 10 hours, it is an oblate spheroid and bulges at the equator. If you measure the diameter through the poles it is 9,276 km smaller at 133,708 km. Solely based on diameter, Jupiter is 11.2 times the size of the Earth and larger than any other body in our Solar System other than the Sun.

The diameter of Jupiter is amazingly large for our Solar System, but is easily eclipsed by some extrasolar planets. According to Dr. Sean Raymond at the Center for Astrophysics and Space Astronomy at the University of Colorado the largest terrestrial(rocky like Earth) planets can be up to 10 times the size of Earth. Since Jupiter is a gas giant, let’s compare apples to apples and talk about the largest known gas giant in the universe. As of this time(August, 2011) the largest gas giant known is TrES-4. This planet is 1,400 light years away in the constellation Hercules. It has been measured to be 1.4 times the size of Jupiter, but it only has 0.84 times Jupiter’s mass. A gas giant can get about 14 times more massive than Jupiter before they ignite fusion and become brown dwarf stars.

A common question that people ask is ”can Jupiter ever become a star?”. That is a reasonable question given its size and mass. Fortunately for humans, the answer is no. Jupiter would need to add about 80 times its current mass in order to ignite fusion. While the planet occasionally accretes more matter, there is not enough available in our Solar System to add that much mass. If it did ignite, it would scorch our world

Jupiter interests scientists for many reasons. Its moons are a major draw for research. The planet has 64 moons that have been confirmed and a few more that have rarely been observed. The moons in the Jovian system account for 50% of all of the moons in our Solar System. A few of those moons are larger than some dwarf planets and others show evidence of subsurface oceans. Scientist are not sure if they are oceans of water as we know it, but they do believe that they exist.

The diameter of Jupiter is an awesome number in itself, but, once you consider the planet as a whole, you see that knowing the diameter is just scratching the surface. Hopefully, it is enough to spark an interest in researching the planet further.

Here’s more information on the diameter of Earth, if you’d like to compare and see how big Jupiter really is. Jupiter’s big, but extrasolar planets are thought to be able to get even bigger. Here’s an article about how big planets can get.

As I’ve mentioned above, Jupiter is the biggest planet in the Solar System, and here’s Hubblesite’s News Releases about 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=OverviewLong
http://planetquest.jpl.nasa.gov/news/tres4.cfm

The Universe Today readers are always asking great questions. ”How long is a day on Jupiter?”, is one of them. A day on Jupiter, also known as the sidereal rotation period, lasts 9.92496 hours. Jupiter is the fastest rotating body in our Solar System. Determining the length of a day on Jupiter was very difficult, because, unlike the terrestrial planets, it does not have surface features that scientists could use to determine its rotational speed.

Scientists cast about for ways to judge the planet’s rotational speed. An early attempt was to do some storm watching. Jupiter is constantly buffeted by atmospheric storms, so the theory was that you could locate the center of a storm and get some idea of the length of a day. The problem scientists encountered was that the storms on Jupiter are very fast moving, making them an inaccurate source of rotational information. Scientist were finally able to use radio emissions from Jupiter’s magnetic field to calculate the planet’s rotational period and speed. While other parts of the planet rotate at different speeds, the speed as measured by the magnetosphere is used as the official rotational speed and period.

All of the planets are oblate spheroids with varying degrees of flattening. Jupiter’s extremely fast rotation flattens it more than any other planet. The diameter of the equator is 9275 km more than the distance from pole to pole. Another interesting effect of Jupiter’s rotational speed is that, because Jupiter is not a solid body, its upper atmosphere features differential rotation. The atmosphere above the poles rotates about five minutes slower than the atmosphere at the equator.

Jupiter is almost a solar system unto itself. Many astronomers believe the the planet is simply a failed star, just lacking the mass needed to ignite fusion. Many people are aware of its four largest moons, the Galilean moons Io, Europa, Ganymede, and Callisto, but few realize that Jupiter has 50 confirmed moons and at least 14 provisional moons. The four largest moons are all very interesting to scientists. Io is a volcanic nightmare. Europa is covered in water ice and may have oceans of slushy ice underneath. Ganymede is the largest moon in the Solar System, even bigger than Mercury, and is the only moon known to have an internally generated magnetic field like Earth’s. Callisto is interesting because its surface is thought to be very ancient; perhaps original material from the birth of the Solar System.

Knowing ”how long is a day on Jupiter” just scratches the surface of the intrigue that is the Jovian system. You could spend months researching the planet and its moons, yet have more to research to do.

Here’s an article on Universe Today that shows how Jupiter can be very flattened, and an article about how the powerful windstorms are generated from its rotation.

NASA’s Ask an Astronomer also has an answer for the question, “how long is a day on Jupiter?” And a cool video of Jupiter’s rotation.

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
Caltech Cool Cosmos