Posted on by Nancy Atkinson

One of Jupiter’s Moons is Melted!

The two outer moons of Jupiter, with the cutaway showing the extent of melting caused by an astroid/comet bombardment. Credit: Amy Barr, SWRI

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Jupiter’s two moons Ganymede and Callisto could be considered fraternal twins. They have a similar composition and size, but visually, they are different. Also, data from the Galileo and Voyager spacecraft reveal the two moons’ interiors are very dissimilar, as well. The reasons for the differences have eluded scientists for 30 years, but a new study provides an explanation. During the Late Heavy Bombardment, Callisto escaped relatively unscathed, while Ganymede was a battered child; so much so that the later moon melted. “Impacts during this period melted Ganymede so thoroughly and deeply that the heat could not be quickly removed,” said Dr. Amy Barr of the Southwest Research Institute. “All of Ganymede’s rock sank to its center the same way that all the chocolate chips sink to the bottom of a melted carton of ice cream. Callisto received fewer impacts at lower velocities and avoided complete melting.”

Barr and and Dr. Robin Canup created a model showing how Jupiter’s strong gravity focused cometary impactors onto Ganymede and Callisto 3.8 billion years ago, during the LHB period. Each impact onto Ganymede or Callisto’s mixed ice and rock surface creates a pool of liquid water, allowing rock in the melt pool to sink to the moon’s center.

But Ganymede is closer to Jupiter and therefore was hit by twice as many icy impactors as Callisto. Additionally, the impactors hitting Ganymede had a higher average velocity. Modeling by Barr and Canup shows that core formation begun during the late heavy bombardment becomes energetically self-sustaining in Ganymede but not Callisto.

Interior density structures created by an outer solar system late heavy bombardment onto Ganymede (top row) and Callisto (bottom row). Credit: SwRI

Watch a movie that shows the effect of an outer solar system late heavy bombardment on the interior structure of Callisto (top model in the movie) and Ganymede (bottom).

“Similar to Earth and Venus, Ganymede and Callisto are twins, and understanding how they were born the same and grew up to be so different is of tremendous interest to planetary scientists,” explains Barr. “Our study shows that Ganymede and Callisto record the fingerprints of the early evolution of the solar system, which is very exciting and not at all expected.”

The “Ganymede-Callisto dichotomy,” has been a classical problem in comparative planetology, a field of study that seeks to explain why some solar system objects with similar bulk characteristics have radically different appearances. The study by Barr and Canup also links the evolution of Jupiter’s moons to the orbital migration of the outer planets and the bombardment history of Earth’s moon.

Their article, “Origin of the Ganymede-Callisto dichotomy by impacts during the late heavy bombardment,” by Barr and Canup, appears online in Nature Geoscience on Jan. 24, 2010.

Source: SwRI

Posted on by Jerry Coffey

How Hot is Jupiter?

Jupiter in visible and infrared

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Given how far Jupiter is from the Sun, you might think that “how cold is Jupiter?” would be a more relevant question and you would be partially right. “How hot is Jupiter?” becomes more relevant the deeper into the planet’s atmosphere and core that you travel. Near the very center of the planet, scientists believe that temperatures can reach 35,500 C.

The outer edges of Jupiter’s atmosphere are much cooler than the core region. Temperatures in the atmosphere are thought to be as cold as -145 degrees C. The intense atmospheric pressure on Jupiter contributes to temperature increases as you descend. Not far into the atmosphere the pressure can be ten times what it is here on Earth and scientists speculate that the temperature is 20 degrees C(average room temperature on Earth). A few hundred km deeper into the planet and hydrogen becomes hot enough to turn into a liquid. The temperature at this point is believed to be over 9,700 C. The layer of dense molten hydrogen metal extends to the 78th percentile of the planet’s radius. Between the cold clouds and the molten lower regions is an interior atmosphere of hydrogen. The hydrogen in this region is at a temperature where there are no distinct liquid and gas phases, so the hydrogen is said to be in a supercritical fluid state.

The molten inner regions of the planet serve to heat the rest of the planet through convection, so Jupiter gives off more heat than it receives from the Sun. This heating prevents it from being an ice giant instead of a gas giant, but wreaks havoc in the atmosphere. Storms and high winds are generated by cool air and warm air mixing here on Earth. Scientist think that the same holds true on Jupiter. The Galileo spacecraft observed winds in excess of 600 kph. One difference is that the jet streams that drive storms and winds on Earth are caused by the Sun heating the atmosphere. On Jupiter it seems that the jet streams are driven by the planets’ own heat. Storms on Jupiter are as out-sized as the planet. The Great Red Spot is a single storm that has been raging for hundreds of years. Other storms have been observed to grow to more than 2,000 km in diameter in a single day.

“How hot is Jupiter?” is more relevant than you may have thought. The planet’s inner heat seems to be the basis for its identity as a stormy world. The actual temperatures of the different areas of the planet may not be a mystery much longer. Hopefully, the recently launched JUNO space mission will clear up many of the Jovian theories that scientists currently have.

We’ve written many articles about the temperature of planets for Universe Today. Here’s an article about how hot Mercury is, and here’s an article about how hot Venus is.

If you’d like more information on Jupiter, check out Hubblesite’s News Releases about Jupiter, and here’s a link to NASA’s Solar System Exploration Guide to Jupiter.

We’ve also recorded an episode of Astronomy Cast just about Jupiter. Listen here, Episode 56: Jupiter.

Sources:
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Jupiter
http://www.nasa.gov/mission_pages/juno/main/index.html

Posted on by Jerry Coffey

Jupiter’s Core



Jupiter probably does not have a solid core. Jupiter’s core contains some rock and hydrogen metals. Scientists can not be 100 percent certain if deep within the planet there is a solid core or not, but based on gravitational measurements compared with Earth’s, the best educated guesses possible based on those measurements say there is no solid core. Those measurements make them think that the core is a thick, super hot soup.

Jupiter’s composition is more of a mystery than anything else. The accepted theory holds that it consists of a dense core made of a mixture of elements, the core is thought to be surrounded by a layer of liquid metallic hydrogen and helium, then the outer layer is to be dominated by molecular hydrogen. The core is often speculated to be rocky. It wasn’t until 1997 that the existence of the core was even theorized. Gravitational measurements were taken, indicating a mass in the neighborhood of 12 to 45 times the Earth’s mass, so the proposed core accounts for about 3–15% of the total mass of the planet. The presence of a planetary core follows accepted knowledge of planetary formation. According to this knowledge base, Jupiter would have had to form a rocky or icy core with enough mass in order to capture such a high percentage of gasses from the early solar nebula. Scientists admit that the planet may lack a core at this time due to the high heat and as hot liquid metallic hydrogen mixed with the molten core, carrying it to higher levels of the planet’s interior.

The layer of dense molten hydrogen metal extends to the 78th percentile of the planet’s radius. Just above the layer of metallic hydrogen is an interior atmosphere of hydrogen. The hydrogen at this point is at a temperature where there are no distinct liquid and gas phases, so the hydrogen is in a supercritical fluid state. The temperature and pressure increase steadily toward the core. In the region where hydrogen becomes metallic, the temperatures are thought to be up to 10,000 K and the pressure is 200GPa. The temperature at the core boundary is estimated to be 36,000 K and the pressure is believed to be 3,000 to 4,500 Gpa.

Since very little is known about the composition of Jupiter’s core or even if it still exists, the JUNO space mission was launched on August of 2011. It should arrive in orbit around Jupiter in 2016. The purpose of the mission is to orbit the poles and clear up some of the mysteries surrounding the planet and the entire Jovian system.

We’ve written several articles about planetary cores for Universe Today. Here’s an article about the Earth’s core, and here’s an article about the core of Mercury.

If you’d like more information on Jupiter, check out Hubblesite’s News Releases about Jupiter, and here’s a link to NASA’s Solar System Exploration Guide to Jupiter.

We’ve also recorded an episode of Astronomy Cast all about Jupiter. Listen here, Episode 56: Jupiter.

Source: NASA

Posted on by Jerry Coffey

Weight on Jupiter

Jupiter's Red Spot

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If you are worried about your weight, do not go to Jupiter. The Jovian gravity is much more intense than Earth’s. 2.528 times more intense to be exact. That means if you weigh 100 kg on Earth, your weight on Jupiter would be 252.8 kg.

Of course, you can not stand on the surface of Jupiter. Jupiter is composed of about 90% hydrogen and 9.99% helium. The gaseous nature of the planet makes a solid surface impossible. Scientists have devised a way to define the surface of Jupiter, though. The surface of the planet is defined as the point where the pressure of the atmosphere is 1 bar, which is equal to the atmospheric pressure at Earth’s surface. That point is at the tops of Jupiter’s clouds.

Now that we have defined your weight on Jupiter, let’s move to on some other interesting facts about the planet. To start off, even though it is the largest planet in our Solar System, it is not the largest planet that we know of. While there are several planets larger than Jupiter, the largest known to man is TrES-4. TrES-4 is 70% larger than Jupiter, but is quite a bit less massive. Scientists think that it has a structure similar to cotton candy for lack of a better analogy.

Since Jupiter’s gravity is so intense, it has trapped quite a few moons. The are 63 acknowledged Jovian moons and there are a few others being studied, so that number could go up at any time.

Jupiter has a system of rings. Many people are surprised to find out that Saturn is not the only ringed planet in our Solar System. In addition to Saturn; Jupiter, Uranus, and Neptune have rings. Rings are generally formed by dust and debris left orbiting after a meteorite impact on a moon. With so many moons, you would think that Jupiter would have a bunch of rings. It only has four defined rings, though.

A day on Jupiter is just under 10 Earth hours long, but a single years lasts 11.86 Earth years.

Some scientists think that Jupiter’s gravity is intense enough to affect the Sun. They believe that when Jupiter is at its closest approach to the Sun, solar flare activity increases. Others believe that Jupiter’s gravity may eventually push Mercury our of our Solar System.

Now that you know what your weight on Jupiter would be, we hope that you will want to research more Jovian facts.

We’ve written several articles about your weight on other planets. Here’s an article about your weight on the Moon, and here’s a link about your weight on Mercury.

If you’d like more information on Jupiter, check out Hubblesite’s News Releases about Jupiter, and here’s a link to NASA’s Solar System Exploration Guide to Jupiter.

We’ve also recorded an episode of Astronomy Cast just about Jupiter. Listen here, Episode 56: Jupiter.

Source: NASA

Posted on by Fraser Cain

What is the Surface of Jupiter Like?

A true-color image of Jupiter taken by the Cassini spacecraft. The Galilean moon Europa casts a shadow on the planet's cloud tops. Credit: NASA/JPL/University of Arizona

Have you ever wondered what it might feel like to stand on Jupiter’s surface? Well, there’s a problem. Jupiter is made up almost entirely of hydrogen and helium, with some other trace gases. There is no firm surface on Jupiter, so if you tried to stand on the planet, you sink down and be crushed by the intense pressure inside the planet.

When we look at Jupiter, we’re actually seeing the outermost layer of its clouds. Jupiter upper atmosphere is made of up to 90% hydrogen, with 10% helium, and then other gases like ammonia. The bands and storms that we can see on the planet are all generated in the upper atmosphere. The cloud layer we can see is made of ammonia, and only extends down for about 50 km or so. The large storms like the Great Red Spot occur within this layer; although it’s thought they may dredge up material from deeper down inside the planet.

If you could stand on the surface of Jupiter, you would experience intense gravity. The gravity at Jupiter’s surface is 2.5 times the gravity on Earth. If you weighed 100 pounds on Jupiter, you’d weigh 250 pounds on Jupiter. Of course, there’s no actual surface, so you’d just sink into the planet if you tried to stand on it.

We’ve written many articles about Jupiter for Universe Today. Here’s an article about how Jupiter might have captured a comet as a temporary moon, and does Jupiter have a solid core?

If you’d like more info on Jupiter, check out Hubblesite’s News Releases about Jupiter, and here’s a link to NASA’s Solar System Exploration Guide to Jupiter.

We’ve also recorded an entire episode of Astronomy Cast all about Jupiter. Listen here, Episode 56: Jupiter.

Posted on by Fraser Cain

Planet Jupiter

Jupiter photo. Image credit: NASA/SSI

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Jupiter is the 5th planet in the Solar System, and by far the largest, containing 2.5 times the mass of the rest of the planets in the Solar System. Everything about planet Jupiter is big. It has the most moons in the Solar System, including the largest moon, Ganymede. It has the largest storm: the Great Red Spot; the most extreme gravity, and the biggest temperature extremes.

Because you can see Jupiter with the unaided eye, it’s impossible to say who actually discovered Jupiter. But it was Galileo Galilei who first turned his rudimentary telescope on Jupiter in 1610. Even with its dim optics, Galileo was able to make out the fact that Jupiter had 4 bright moons and bands across the planet. Since astronomers believed that everything orbited around the Earth, finding moons orbiting Jupiter threw the Earth-centered theory of the Universe into doubt. Even the smallest telescope will show you what Galileo saw.

Planet Jupiter orbits the Sun at an average distance of 779 million km (484 million miles), and it takes 4,333 Earth days to complete one orbit around the Sun; that’s almost 12 years. But Jupiter rotates once on its axis every 9 hours and 56 minutes. This high rotation speed has flattened out the planet, so that its equator is much further from the center of Jupiter than the poles. Jupiter’s also the largest plane in the Solar System, with an equatorial diameter of 142,984 kilometers (88,846 miles) – 11 times the diameter of Earth.

Jupiter has 318 times more mass than Earth, but it has a relatively low density; only 1/4 the density of Earth. It has such a low density because Jupiter is made up almost entirely of hydrogen with a little bit of helium. The upper atmosphere has tiny amounts of ammonia and other chemicals, which create the bands and clouds we see in photographs. The most familiar feature in Jupiter’s atmosphere is the planet’s Great Red Spot. This is a long-lived storm large enough to swallow up three planets the size of Earth.

It also has the largest number of moons in the Solar System: 63 at last count. The 4 largest moons are the Galilean moons, named after Galileo who discovered them. Ganymede measures 3,273 km across, and it’s the largest moon in the Solar System. Io orbits the closest of these moons and its undergoing almost constant volcanic activity because of tidal flexing being so close to Jupiter. Europa and Callisto probably have oceans of liquid water underneath thick shells of ice, and could be the home to exotic forms of life. Jupiter also has its own set of rings.

Seven spacecraft from Earth have made the journey to Jupiter: Pioneer 10, Pioneer-Saturn, Voyager 1, Voyager 2, Ulysses, Galileo, and New Horizons. Pioneer 10 was the first to reach the planet, making its flyby in 1972. The Galileo spacecraft actually went into orbit around Jupiter, to study the planet and its moons in great detail.

We’ve written many articles about Jupiter for Universe Today. Here’s an article about how Jupiter might protect us in the Solar System, and here’s an article about how you can see Jupiter in a telescope.

If you’d like more info on Jupiter, check out Hubblesite’s News Releases about Jupiter, and here’s a link to NASA’s Solar System Exploration Guide to Jupiter.

We’ve also recorded an episode of Astronomy Cast just about Jupiter. Listen here, Episode 56: Jupiter.

Reference:
NASA

Posted on by Fraser Cain

How Big is Jupiter?

Hubble Jupiter

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I’m sure you’ve heard that Jupiter is the largest planet in the Solar System, but just how big is Jupiter?

In terms of size, Jupiter is 142,984 km (88,846 miles) in diameter across its equator. If you just compare that to Earth, it’s 11.2 times the diameter of Earth. But then, it’s only 10% the diameter of the Sun.

The volume of Jupiter is 1.43128×1015 km3. That’s enough to fit inside 1321 planets the size of Earth, and still have room left over.

The surface area of Jupiter is 6.21796×1010 km2. And just for comparison, that’s 122 times more surface area than Earth.

And finally, the mass of Jupiter is 1.8986×1027 kg. That’s enough mass for 318 Earths. In fact, Jupiter is 2.5 times more than the mass of all the other planets in the Solar System. But then, the Sun accounts for 99.9% of the mass of the Solar System.

Jupiter’s big, no question, but don’t worry about the possibility that Jupiter might become a star. It would need another 80 times its own mass to be able to ignite solar fusion.

We’ve written several articles about Jupiter for Universe Today. Here’s an article about an impact that recently happened on Jupiter, and here’s an article about how Jupiter might protect us in the Solar System.

If you’d like more information on Jupiter, check out Hubblesite’s News Releases about Jupiter, and here’s a link to NASA’s Solar System Exploration Guide to Jupiter.

We’ve also recorded a whole episode of Astronomy Cast just about Jupiter. Listen here, Episode 56: Jupiter.

Posted on by Fraser Cain

What is Jupiter’s Great Red Spot?

Jupiter's Red Spot

One of the most prominent features in the Solar System is Jupiter’s Red Spot. This is a massive storm three times the size of the Earth that has been raging across the cloud tops of Jupiter since astronomers first looked at it with a telescope.

Known as the Great Red Spot, this is an anticyclonic (high pressure) storm that rotates around the planet at about 22°. Astronomers think that its darker red color comes from how it dredges up sulfur and ammonia particles from deeper down in Jupiter’s atmosphere. These chemicals start out dark and then lighten as they’re exposed to sunlight. Smaller storms on Jupiter are usually white, and then darken as they get larger. The recently formed Red Spot Jr. storm turned from white to red as it grew in size and intensity.

Astronomers aren’t sure if Jupiter’s Red Spot is temporary or permanent. It has been visible since astronomers started making detailed observations in the 1600s, and it’s still on Jupiter today. Some simulations have predicted that this a storm like this might be a permanent fixture on Jupiter. You can still see the Red Spot with a small telescope larger than about 15 cm (6 inches).

The edge of the Red Spot is turning at a speed of about 360 km/h (225 mph). The whole size of the spot is ranges from 24,000 km x 12,000 km to as wide as 40,000 km. You could fit two or three Earths inside the storm. The actual edge of the storm lifts up about 8 km above the surrounding cloud tops.

Astronomers have noticed that it’s been slowly shrinking over the last decade or so, losing about 15% of its total size. This might be a temporary situation, or Jupiter’s Red Spot might go on losing its size. If it continues, it should look almost round by 2040.

We’ve written many articles about Jupiter’s Red Spot for Universe Today. Here’s an article about Jupiter’s little red spot, and here’s an article about Jupiter’s red spot colliding together.

If you’d like more info on Jupiter, check out Hubblesite’s News Releases about Jupiter, and here’s a link to NASA’s Solar System Exploration Guide to Jupiter.

We’ve also recorded an episode of Astronomy Cast all about Jupiter. Listen here, Episode 56: Jupiter.

Posted on by Fraser Cain

When Was Jupiter Discovered?

Jupiter's Red Spot

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Were you wondering when was Jupiter discovered? Well, there’s no way to know. Jupiter is one of the 5 planets visible with the unaided eye. If you go outside and Jupiter is up in the sky, it’s probably the brightest object up there, brighter than any star; only Venus is brighter. So the ancient people have known about Jupiter for thousands of years, and there’s no way to know when the first person noticed the planet.

Perhaps a better question to ask is, when did we realize that Jupiter was a planet? In ancient times, astronomers used to think that the Earth was the center of the Universe. This was the geocentric model. The Sun, the Moon, the planets, and even the stars all orbited around the Earth in a series of crystal shells. But one thing that was hard to explain was the strange movements of the planets. They would move in one direction, then stop and go backwards in a retrograde motion. Astronomers created ever more elaborate models to explain these bizarre movements.

But then in the 1500s Nicolaus Copernicus developed his model of a Sun-centered, or heliospheric model of the Solar System. The Sun was center of the Solar System, and the planets, including Earth and Jupiter orbited around it. This nicely explained the strange movements of the planets in the sky. They were really following a circular path around the Sun, but the Earth was also traveling around the Sun, and this created different speeds based on our perspective.

The first person to actually view Jupiter in a telescope was Galileo. Even with his rudimentary telescope, he was able to see bands across the planet, and the 4 large Galilean moons that have been named after him. The moons clearly were orbiting Jupiter, which broke the theory that everything in the Universe was orbiting the Earth.

With bigger telescopes, astronomers were able to see more details in Jupiter’s cloud tops and discover more moons. But it wasn’t until the space age that scientists got to really study Jupiter close up. NASA’s Pioneer 10 was the first spacecraft to fly past Jupiter in 1973. It passed within 34,000 km of the cloud tops.

We’ve written several articles about when the planets of the Solar System were discovered. Here’s an article about the discovery of Uranus, and here’s an article about the discovery of Neptune.

If you’d like more information on Jupiter, check out Hubblesite’s News Releases about Jupiter, and here’s a link to NASA’s Solar System Exploration Guide to Jupiter.

We’ve also recorded an entire episode of Astronomy Cast just about Jupiter. Listen here, Episode 56: Jupiter.

Reference:
NASA

Posted on by Jon Voisey

Jupiter – Our Silent Guardian?

Jupiter photo. Image credit: NASA/SSI

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We live in a cosmic shooting gallery. In Phil Plait’s Death From the Skies, he lays out the dangers of a massive impact: destructive shockwaves, tsunamis, flash fires, atmospheric darkening…. The scenario isn’t pretty should a big one come our way. Fortunately, we may have a silent guardian: Jupiter.


Although many astronomers have assumed that Jupiter would likely sweep out dangerous interlopers (an important feat if we want life to gain a toehold), little work has been done to actually test the idea. To explore the hypothesis, a recent series of papers by J. Horner and B. W. Jones explores the effects of Jupiter’s gravitational pull on three different types of objects: main belt asteroids (which orbit between Mars and Jupiter), short period comets, and in their newest publication, submitted to the International Journal of Astrobiology, the Oort cloud comets (long period comets with the most distant part of their orbits far out in the solar system). In each paper, they simulated the primitive solar systems with the bodies in question with an Earth like planet, and gas giants of varying masses to determine the effect on the impact rate.

Somewhat surprisingly, for main belt asteroids, they determined, “that the notion that any ‘Jupiter’ would provide more shielding than no ‘Jupiter’ at all is incorrect.” Even without the simulation, the astronomers say that this should be expected and explain it by noting that, although Jupiter may shepherd some asteroids, it is also the main gravitational force perturbing their orbits and causing them to move into the inner solar system, where they may collide with Earth.

Contrary to the popular wisdom (which expected that the more massive the planet, the better it would shield us), there were notably fewer asteroids pushed into our line of sight for lower masses of the test Jupiter. Also surprisingly, they found that the most dangerous scenario was an instance in which the test Jupiter had 20% in which the planet “is massive enough to efficiently inject objects to Earth-crossing orbits.” However, they note that this 20% mass is dependent on how they chose to model the primordial asteroid belt and would likely change had they chosen a different model.

When the simulation was redone for for short period comets, they again found that, although Jupiter (and the other gas giants) may be effective at removing these dangerous objects, quite often they did so by sending them our way. As such, they again concluded that, as with asteroids, Jupiter’s gravitational jiggling was more dangerous than it was helpful.

Their most recent treatise explored Oort cloud objects. These objects are generally considered the largest potential threat since they normally reside so far out in the solar system’s gravitational well and thus, will have a greater distance to fall in and pick up momentum. From this situation, the researchers determined that the more massive the planet in Jupiter’s orbit, the better it does protect us from Oort cloud comets. The attribute this to the fact that these objects are initially so far from the Sun, that they are scarcely bound to the solar system. Even a little bit of extra momentum gained if they swing by Jupiter will likely be sufficient to eject them from the solar system all together, preventing them from settling into a closed orbit that would endanger the Earth every time it passed.

So whether or not Jupiter truly defends us or surreptitiously nudges danger our way depends on the type of object. For asteroids and short period comets, Jupiter’s gravitational agitation shoves more our direction, but for the ones that would potentially hurt is the most, the long period comets, Jupiter does provide some relief.