INSIDE THE GIANT
Jupiter has been cooling ever since it formed, and inside,
it’s been stirring up elements that were around when the solar system itself
first formed. Studying the interior activity allows us to better understand how
Jupiter has evolved from the gaseous glob it once was to the majestic planet we
DOES JUPITER HAVE A SOLID CORE? HOW DOES IT CREATE THE LARGEST MAGNETIC FIELD IN THE SOLAR SYSTEM, APART FROM THE SUN?
Jupiter is a dynamic planet, with billowing clouds and swirling gases. But Juno won’t be able to dive deep into the clouds and gas, since the mounting pressure and heat would destroy the spacecraft. Instead, by measuring Jupiter’s gravitational and magnetic fields, Juno will allow scientists to do what no telescope has ever done – peer into the churning depths of the gas giant.
Gravity is caused by mass, and the nature of Jupiter’s gravitational field depends on how all of the stuff inside Jupiter is arranged. From its close orbit, Juno will feel even the tiniest shift caused by any variations in gravity, and these small displacements reveal details about Jupiter’s interior structure.
Precise measurements of Jupiter’s gravity will help answer a long-standing question: is there a solid core at the center, and if so, how big is it? Based on what we do know about Jupiter, we suspect that there is indeed a solid core, composed of heavy elements -such as carbon, nitrogen, and oxygen-and rock-forming elements – such as magnesium, silicon, and iron. Different theories as to how Jupiter formed make different predictions about the core’s size. If Juno can determine how big the core is, we can narrow down the possibilities.
Measuring Jupiter’s gravity will also reveal how the inner part of the planet rotates and how its gases swish around inside. The clouds that we see on the surface form bands that flow in alternating directions – west-ward and eastward. We don’t know whether these patterns are only surface deep or fundamentally related to what’s going on inside. One idea is that the interior consists of whirling cells, in which the gas rises and falls in a circular pattern. As a deeper cell rotates, it turns the one above it like a set of gears. The bands we see are just the outer edges of the top gears. Another hypothesis is that the entire planet rotates together, almost like a single, solid sphere.
Juno’s magnetometer will gauge Jupiter’s magnetic field more accurately than it’s ever been possible for any planet – including Earth. The engine behind Earth’s magnetic field is its rotating, molten core, but the crust and mantle slightly muffles the field, preventing us from taking detailed measurements. Jupiter, on the other hand, doesn’t have a solid surface, so Juno – due to its close orbit – can trace the magnetic field all the way down to its source. Not only will the spacecraft locate how deep the field begins, it might also be able to detect the motion of the fluids at that depth.
Juno will also learn what Jupiter’s made out of. For example, by seeing how much water is in the atmosphere, the spacecraft can determine how abundant is oxygen, which is expected to be one of Jupiter’s main ingredients.
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INVESTIGATING THE INTERIOR
Juno will reveal the internal structure of Jupiter.
INVESTIGATING THE INTERIOR
THE INCREDIBLE SHRINKING PLANET
Jupiter is still contracting and cooling from its formation – more than 4.5 billion years later.
THE INCREDIBLE SHRINKING PLANETHeat can travel via infrared radiation (light with wavelengths just a little longer than the light we can see), so by measuring the infrared radiation emanating from Jupiter, we can calculate how much it’s cooling and shrinking. We estimate that the planet shrinks at a rate of a few centimeters (about an inch) per century and cools by about one degree Celsius (1.8 F) every million years.
What is Jupiter made of?
JUPITER’S STRUCTURE1. ATMOSPHERE
Gases: Hydrogen, Helium, Methane, Water, Ammonia
Liquids: Water droplets
Solids: Ammonia ice particles
Pressure: 0-1000 Earth atmospheres pressure
Temperature: -150 to +1000 C
2. OUTER INTERIOR
Liquids: Hydrogen and Helium, small amounts of Methane, Water, and Ammonia
Pressure: 1000-2000,000 Earth atmospheres pressure
Temperature: 1000 to 8000 C
Liquid metallic Hydrogen, with Helium and small amounts of Methane, Water, and Ammonia
Pressure: 2000,000-45,000,000 Earth atmospheres pressure
Temperature: 8000 to 16,000 C
Solid or Liquid?: Oxygen, Carbon, and Nitrogen? Ice? Rock?
Pressure: More than 45,000,000 Earth atmospheres pressure
Temperature: 16,000 to 30,000+ C
WHAT’S IN JUPITER’S CORE?
The size of the core, if it exists, will help discriminate among the current theories of Jupiter’s origin and evolution.
WHAT’S IN JUPITER’S CORE?According to most theories, Jupiter has a dense core of heavy elements that formed during the early solar system. The solid core of ice, rock, and metal grew from a nearby collection of debris, icy material, and other small objects like the many comets and asteroids that were zipping around four billion years ago. These bits of matter clumped together due to their mutual gravity, becoming larger chunks called planetesimals, which, in turn, collided and stuck together to form Jupiter’s core.
The core grew big enough so that it had enough gravity to attract even hydrogen and helium, the lightest elements that exist. More and more gas accumulated until it became what we now know as Jupiter. Although most scientists agree on this general story, many details remain unknown. For example, we’re still not sure where all the icy matter comes from.
Another theory, however, suggests that there is no core at all. Instead, Jupiter formed from the large cloud of gas and dust that surrounded the sun soon after its birth. As this cloud cooled and condensed, gas and dust particles lumped together so that some regions were denser than others. One of these dense splotches was able to gravitationally pull more and more gas and dust together, swelling into a full-fledged planet.
By measuring Jupiter’s gravitational and magnetic fields, Juno will be able to determine whether a core exists. If it does, exactly what the fields look like will depend on how big the core is, and knowing it’s size will help determine which of the many theories – if any – are most likely to be correct.
If Juno finds no evidence of a core, that could strengthen the condensed-cloud theory. Another possibility is that Jupiter once had a core, but has since eroded away. Or maybe, whatever Juno finds won’t fit any theory, and scientists will have to come up with completely new ideas.
A DIVE INTO JUPITER
As a gas giant planet, Jupiter has no solid surface. So what would it be like to dive into the planet’s alien atmosphere?
A DIVE INTO JUPITERYou jump from your spaceship and fall toward Jupiter below. In space, the temperature is around -270 degrees Celsius – just about three degrees above absolute zero. But as you reach the tops of Jupiter’s atmosphere, things start to heat up.
Don’t take off your coat just yet, though – it’s still -130 degrees Celsius (-200 F). The wisps of clouds around you produce a pressure of only about a fifth of one bar (the pressure at Earth’s sea level).
The clouds consist of ammonia and ammonium hydrosulfide, and are very bright. Jupiter reflects more than half the sunlight that hits it, making it the solar system’s second most reflective planet after Venus.
As you continue to plummet, the clouds thicken and warm up. After 30 kilometers, the pressure around you is about one bar and the temperature is now a balmy -100 degrees Celsius (-150 F). After another 40 kilometers, you hit a thick layer of clouds made from water.
Soon, the pressure will be crushing and the temperature searing. Fortunately, your special space suit keeps you alive as you descend farther, and after a few hundred kilometers, you reach what’s considered the bottom of the atmosphere.
Earth’s atmosphere ends where the ground begins, but since there’s no surface on Jupiter, its atmosphere ends where the gas – mainly hydrogen at this point – acts less like a gas and more like a liquid. This transition probably happens gradually, as the rising pressure squeezes the hydrogen molecules together. It’s like sinking through increasingly heavy fog that gets wetter and wetter until you find yourself swimming in liquid.
You’ve only traveled a distance less than one percent of Jupiter’s radius, but the pressure is already 1,000 bars – a thousand times what you would feel on a beach on Earth – and the thermometer reads just over 1,000 degrees Celsius (2,000 F). This depth is the limit of Juno’s Microwave Radiometer, which measures the micro- wave-wavelength radiation from Jupiter’s atmosphere.
Maybe around a third of the way down – a depth of more than three Earth diameters – when the pressure climbs to two million bars and the temperature soars to between 8,000 and 10,000 degrees Celsius (18,000 F), something extraordinary happens to the liquid hydrogen around you. The intense pressure squeezes the atoms so tightly that their previously bound electrons break free. The electrons can then flow throughout the liquid, generating electrical current and, we believe, Jupiter’s magnetic field. The liquid hydrogen can now conduct electricity like a metal. Called liquid metallic hydrogen, this form of hydrogen fills the rest of Jupiter’s interior until you hit the core.
At last, you’ve arrived at your final destination: the core. Here, the pressure is probably around 45 million bars – as much as that of 1,000 elephants standing on a stiletto heel. The temperature is about 20,000 degrees Celsius (35,000 F), more than three and a half times hotter than the surface of the sun. But what you see is anyone’s guess. No one knows where exactly the core begins nor does anyone know whether the boundary is well-defined or gradual – yet another mystery Juno hopes to solve.
WHAT IS A MAGNETIC FIELD?
Co-investigators Fran Bagenal and Jeremy Bloxham describe the source of Jupiter’s magnetic personality.
WHAT IS A MAGNETIC FIELD?