NASA’s Juno Mission — Looking Inside Jupiter

Juno was launched in 2011, arrived at Jupiter in 2016, and spent the next nine years changing many things scientists thought they knew about the giant planet. To learn about Jupiter itself, see our Jupiter facts for kids page.

📋 Juno — Quick Facts

• Mission typeJupiter orbiter and explorer
• AgencyNASA (built by Lockheed Martin)
• Launched5 August 2011 — Cape Canaveral, Florida
• Arrived at Jupiter4 July 2016
• Funded mission end30 September 2025 (extended mission)
• Current statusExtended mission planned through September 2025 — check NASA/JPL before publishing
• Orbit typePolar — the first spacecraft ever to circle both of Jupiter’s poles
• Closest pass to JupiterAs close as about 3,500 km above the cloud tops — closer than any Jupiter orbiter before
• Closest pass to IoAbout 1,500 km (December 2023 and February 2024)
• PowerThree giant solar panels — the first solar-powered spacecraft designed to operate at Jupiter’s distance from the Sun
• ProtectionTitanium “radiation vault” shielding its computer and instruments
• Named afterJuno, queen of the Roman gods (Jupiter’s wife in mythology)

What is Juno?

Juno is a robotic spacecraft about the size of a basketball court (including its solar panels). It was built and launched by NASA to answer some of the biggest mysteries about Jupiter:

• What is Jupiter made of deep below the clouds?
• How big and heavy is Jupiter’s core?
• How does Jupiter’s incredible magnetic field work?
• How does Jupiter’s weather behave — especially at the poles, which no spacecraft had ever seen up close?

To answer these, Juno carries nine instruments — microwave radiometers, magnetometers, cameras, gravity-measuring radios, plus the famous JunoCam, a colour camera built mainly for the public to share Jupiter’s beauty with the world.

Juno is named after the Roman goddess Juno, who in mythology was the wife of the king of the gods, Jupiter. The story goes that Jupiter wrapped himself in clouds to hide his mischief, but Juno could see through them. Just like NASA’s Juno spacecraft, which was built to see through Jupiter’s clouds and find out what the planet is really doing.

Juno’s journey to Jupiter

Jupiter is hundreds of millions of kilometres from Earth. To get there, Juno took a long looping path:

• 5 August 2011 — Juno launched from Cape Canaveral aboard an Atlas V rocket
• August–September 2012 — Deep space manoeuvres far from the Sun
• October 2013 — Juno flew past Earth, using our planet’s gravity to speed up (a “gravity assist”)
• 4 July 2016 — Juno arrived at Jupiter and fired its engine for 35 minutes to slow down and enter orbit

That 35-minute engine burn was one of the tensest moments in the mission. At Jupiter, Juno was hundreds of millions of kilometres from Earth, so it had to follow its instructions on its own. NASA had to trust Juno to do the manoeuvre entirely on its own, because radio signals take nearly an hour to travel between Earth and Jupiter. If something went wrong, there was no time to fix it.

Why Juno was different from other spacecraft

Before Juno, eight spacecraft had visited Jupiter — mostly flying past on their way to somewhere else. NASA’s Galileo orbiter did spend 1995 to 2003 orbiting Jupiter, but its orbit kept it in Jupiter’s equatorial belt. Juno did three things no spacecraft before it had managed:

1. Juno flew over Jupiter’s poles

Every previous Jupiter spacecraft had circled Jupiter’s equator. Juno orbits over the north and south poles — swooping past one pole, racing low across the planet, then swinging up over the other pole. This was the first time anyone had seen Jupiter’s poles up close — and what Juno saw was strange and beautiful: groups of giant cyclones in neat geometric patterns.

2. Juno flew closer than any Jupiter orbiter before

On each pass, Juno dives to as close as about 3,500 km above Jupiter’s cloud tops — closer than any Jupiter orbiter before. From that close, its instruments can peer through the clouds and measure what is underneath.

3. Juno was the first solar-powered spacecraft built for Jupiter

Most spacecraft going beyond Mars use nuclear power, because sunlight is too weak that far from the Sun. Juno was the first solar-powered spacecraft designed to operate at Jupiter’s distance — about 778 million km from the Sun. Its three solar panels stretch about 9 metres long each, with a total surface area larger than a tennis court.

What Juno discovered

Juno turned Jupiter from a planet we thought we understood into one of the most surprising worlds in the solar system. Here are some of the biggest discoveries:

The polar cyclones

Both of Jupiter’s poles are home to rings of giant cyclones in neat geometric patterns. Jupiter’s north pole has eight cyclones surrounding a central one. The south pole has five cyclones around a central one. These storms are each the size of large countries and have been spinning in formation for years.

Jupiter’s fuzzy, mushy core

Scientists used to think Jupiter had a small, dense, rocky core, like a marble at the centre of a fluffy ball. Juno’s gravity measurements showed something completely different: Jupiter’s core is “fuzzy” and “diluted” — spread out over a huge volume, with rock and metal mixed in with the gas. The boundary between core and not-core isn’t sharp; it’s gradual.

The deep weather

Jupiter’s famous cloud bands and stripes are not just on the surface. Juno measured their winds reaching down about 3,000 km into the planet. Below that, Jupiter rotates almost like a solid object — because at those pressures, the hydrogen gas turns into a strange liquid metal.

The Great Red Spot is deeper than expected

Juno flew over the Great Red Spot in July 2017, becoming the first spacecraft ever to do so. Its instruments showed that this giant storm reaches at least 300 km below the cloud tops, with gravity data suggesting it may extend down to 500 km. The Great Red Spot is much bigger in 3D than it looks in pictures. Read more about the Great Red Spot →

Lightning higher in the clouds

Juno’s instruments detected lightning happening much higher in Jupiter’s atmosphere than scientists expected — evidence that the weather is even stranger than the swirling clouds suggest.

Io’s record-breaking eruption

On 27 December 2024, Juno’s infrared instrument detected the most powerful volcanic activity ever recorded on Io — a hotspot larger than Earth’s Lake Superior, releasing roughly six times the energy of all of Earth’s power plants combined. The signal was so strong it briefly saturated the spacecraft’s detector. Read more about Io →

Juno’s tour of Jupiter’s moons

In its extended mission, Juno did something its mission designers never planned: it became a Jupiter system explorer instead of just a Jupiter probe. By bouncing off Jupiter’s moons’ gravity, Juno shifted its orbit to make close passes of three of the four Galilean moons. Each flyby gave us close-ups we hadn’t had in over 20 years.

• Ganymede — 7 June 2021, within 1,038 km of the surface
• Europa — 29 September 2022, within 352 km of the surface
• Io — December 2023 and February 2024, within about 1,500 km of the surface (twice)
• Io — a series of more distant Io flybys throughout 2024, including the December 2024 eruption discovery

Each flyby pulled Juno’s orbit a little tighter around Jupiter. By the time of the late Io passes, Juno was orbiting Jupiter once every 33 days — much faster than its original 53-day orbit.

Read more about the Galilean moons →

The end of Juno’s mission

Juno’s extended mission was planned through 30 September 2025, after nearly nine years at Jupiter. NASA’s most recent extension was funded through that date. As of writing, NASA’s public Juno pages should be checked for the spacecraft’s current operational status — mission updates can lag behind real spacecraft events, and the status should always be verified before publishing.

Eventually, Juno will fall into Jupiter’s atmosphere and be crushed by the pressure. This is on purpose. NASA does not want Juno to accidentally crash into Europa or Ganymede, because tiny Earth microbes could still be on the spacecraft — and contaminating those icy moons could ruin the scientific search for life there.

Whatever Juno’s status now, its scientific legacy is already enormous. The mission collected:

• More than 70 close passes of Jupiter
• Thousands of detailed images from JunoCam
• Decades worth of new data that scientists are still working through

Why Juno mattered

Juno was supposed to be a short, focused mission. Its prime mission was scheduled to end in 2017. Instead, the spacecraft kept performing far beyond what NASA planned. It survived radiation that should have broken it, sent back data that changed textbooks, and helped pave the way for two new Jupiter missions.

• Europa Clipper (NASA, launched 2024) — Juno’s discoveries helped scientists prepare important questions and conditions for Clipper’s study of Europa’s habitability — read more →
• JUICE (ESA, launched 2023) — Juno’s long observations of Jupiter’s system gave JUICE planners a better picture of what their spacecraft will encounter — read more →

Juno became the kind of mission that changes a whole field of science. There are not many of those.

Frequently asked questions about Juno

Quick recap

• Juno is NASA’s spacecraft built to study Jupiter from the inside out
• It launched in August 2011, arrived at Jupiter on 4 July 2016
• Juno was the first spacecraft to orbit Jupiter’s poles
• Funded mission ended September 2025; current status uncertain
• Discovered polar cyclones, a fuzzy core, deep weather, lightning high in the clouds, and the most powerful Io volcanic activity ever recorded
• Famously made all JunoCam images public for anyone to process
• Helped prepare NASA’s Europa Clipper and ESA’s JUICE missions