Jupiter
Large enough to fit every other planet inside, it’s no surprise Jupiter holds the title of “King of the planets”.
Last year the European Space Agency sent the Jupiter Icy Moons Explorer (JUICE for short) on the long journey towards the planet, and this October NASA will launch the Europa Clipper to join it on its way. The trip will take five and a half years, because Jupiter lies around 484 million miles from the Sun – five times further away than Earth.
With its century-long storms, deadly radiation and a glittering assortment of moons, the solar system’s largest planet is a fascinating – and deadly – place to visit.
A giant gassy ball: Jupiter is around 86,881 miles wide and it contains more than twice as much mass as every other planet put together. The more material a planet has, the stronger its gravity. So, if you stood on a set of scales on Jupiter you would be nearly two and a half times heavier than you are on Earth. You wouldn’t be any bigger – the planet is just pulling down on you more.
You’d have a tough time standing anywhere on Jupiter though, because it’s a gas giant. The solar system’s inner planets – Mercury, Venus, Earth and Mars – are mostly made of rock, but Jupiter is entirely made of its atmosphere.
The planet is about 90% hydrogen gas, the lightest known element in the universe. Most of the remaining 10% is helium, the gas used to fill balloons so they float. There are also trace amounts of other chemicals, such as water and ammonia (which is used on Earth to make plant fertilisers), which form Jupiter’s clouds.
Jupiter’s outer atmosphere is about 30 miles thick. Below this, there is a layer of hydrogen and helium 13,000 miles thick, which changes from gas to liquid as the depth and pressure increase. Under this lies a deep sea – 25,000 miles deep – of liquid metallic hydrogen.
Scientists don’t yet know if a solid surface exists on Jupiter, but if there is one, you wouldn’t be able to walk on it.
Stormy weather: If you looked at Jupiter through a large enough telescope, you’d see the planet has alternating brown and white stripes running from side to side. These are bands of swirling clouds, moving around the planet in opposite directions. The cream coloured stripes are known as “zones”, while the darker ones are called “belts”.
The belts and zones are created because Jupiter spins incredibly quickly. Pinning down exactly how long the gas giant takes to rotate – and the length of its day – is surprisingly complicated. Because it isn’t solid, different parts of the planet rotate at different speeds. While the equator zips around in just nine hours and 50 minutes, material at the poles takes six minutes longer to catch up. This rapid spinning creates strong currents in the atmosphere, which help create the planet’s distinctive belts and zones.
Dotted among these stripes are bright spots that are white or red. These are immense storms, which can last from a few days to decades. The biggest of them is called the Great Red Spot, and it has been a permanent fixture on the face of Jupiter for over 190 years.
Today, the Spot is 8,700 miles across, wide enough to swallow Earth whole. Violent winds roar at 425 miles per hour, more than double a Category 5 hurricane. The fastest winds, though, are at the poles, where storms whip gusts at over 900 miles per hour.
Jupiter’s most dangerous feature (to spacecraft, at least) is its magnetic field. Around 20,000 times stronger than Earth’s, the field traps charged particles and accelerates them towards the planet. When they strike the atmosphere they make it glow, creating beautiful aurorae (northern and southern lights), that ring the poles like a crown.
Visiting Jupiter:
The trapped particles also create deadly radiation around the planet. The first spacecraft to visit Jupiter in the 1970s – Pioneer 10 and Pioneer 11 – avoided this by blazing past the planet at 78,000 miles per hour. They found the radiation was 100 times stronger than expected, and it fried several onboard instruments. The next visitors – Voyager 1 and Voyager 2 – in 1979, fared much better. They took 33,000 pictures of Jupiter and its moons, found the planet had a thin ring around its waist like Saturn, and also spotted a volcano erupting on one of Jupiter’s moons, Io.
Other spacecraft have passed the planet on their journeys elsewhere, such as New Horizons on its way to Pluto. Only two have stayed longer, surviving the radiation by spending most of their time at a safe distance from Jupiter and occasionally swinging in for a short visit.
The Galileo spacecraft orbited Jupiter from 1995 to 2003. It spotted bright flashes that turned out to be lightning strikes leaping between the clouds. It even dropped off a probe that fell through the planet’s atmosphere for 58 minutes before it was crushed by the intense pressure. Juno arrived in 2016 and is still watching over the mighty gas giant today. The spacecraft has been mapping out the strength of size of States.
Jupiter’s gravity and magnetic field, hoping to reveal more about what the planet looks like underneath the clouds. It also found evidence of helium rain falling through the layers deep in the atmosphere, where the pressure is so high that hydrogen and helium act like liquids.
A new hope for alien life: When JUICE and Europa Clipper arrive at Jupiter in the 2030s, however, their main focus will be on Jupiter’s moons, rather than the planet itself. Jupiter has 95 moons (that we know of, as new ones are still being discovered), but both missions will focus their attention on three – Europa, Ganymede and Callisto. Mostly made of water ice, each moon is thought to hide a liquid water ocean beneath its surface. On Earth, wherever there’s water there’s life, so the icy moons are great places to look for life beyond Earth.
Neither JUICE nor Europa Clipper are directly searching for alien lifeforms, but they will be looking for signs that the moons could be habitable (possible to live there). In doing so, astrobiologists (scientists who study the origins of life in the universe) hope to understand more about how life might have begun on our own planet and elsewhere in the galaxy.
Jupiter may be the King of the Solar System, but its moons are set to shine in the coming years. Will alien life be finally found in our solar system, hiding on one of Jupiter’s many moons? Watch this space!
Europa Clipper - a journey to an ocean world: NASA's Europa Clipper is set to launch in October 2024 and arrive at Jupiter in April 2030. The spacecraft hopes to unlock some of the secrets of the planet's icy moon Europa and find out if it is capable of hosting alien life. Here are five mysteries the mission is seeking to solve:
1 Salty ocean
The key question scientists want to answer is whether Europa has an ocean of salty water hidden beneath its icy surface, and if so, how big it is. Europa Clipper will use radar to survey under the moon's surface.
2 Ingredients for life
Although scientists are almost certain that a vast ocean lies under Europa's surface, they want to know if it has other essential ingredients for life. The spacecraft will search for these, and investigate whether they come from Europa's icy shell or from the moon's rocky interior.
3 Plumes of water
Water jets have been seen shooting into space from Europa's surface. Europa Clipper will search for these and attempt to fly through one of them to give scientists a glimpse into the ocean beneath.
4 Smooth surface
Europa's surface is the smoothest object in the solar system, with no impact craters. The spacecraft will study the moon's surface to understand what is keeping it so fresh-faced, and whether volcanoes or Jupiter's gravity could provide the energy for life.
5 Landing site
Future missions to Europa might want to land on the surface to study its ocean. During its mission, Europa Clipper will aim to map the moon's surface in detail, allowing NASA to locate the best landing spot.
