NASA’s Juno Mission: Unlocking Jupiter and Planetary Origins

Think of Jupiter as a locked box. Thick clouds hide what is inside. Juno was built to look past them.

What kind of spacecraft is Juno?

• Juno is a solar-powered NASA spacecraft that orbits Jupiter, the largest planet in the solar system.
• Builder: Lockheed Martin built and runs it. NASA’s Jet Propulsion Laboratory manages the mission.
• Leader: Scott Bolton of the Southwest Research Institute in San Antonio is the principal investigator.
• Programme: Juno belongs to NASA’s New Frontiers Program.

When did it fly?

Juno was proposed in 2003. It lifted off on an Atlas V rocket from Cape Canaveral on 5 August 2011. It reached Jupiter on 4 July 2016. The trip covered about 1.7 billion miles, or 2.8 billion km.

Why is it named Juno?

In Roman myth, the god Jupiter hid behind clouds. His wife Juno could see through them. The Planetary Society says the craft lives up to that name.

Is Juno the first spacecraft to visit Jupiter?

No. NASA’s Galileo orbiter went there first and worked from 1995 to 2003. Juno was the first to fly over both of Jupiter’s poles.

Juno does not circle Jupiter like a ring. It swings in a long, stretched loop that passes over the poles.

Why a polar orbit?

Jupiter is wrapped in belts of harmful radiation. Juno dives between the belts and the planet over the north pole. At times it comes within 3,500 km of the cloud tops. Then it exits over the south pole.

How long is one loop?

• First orbit: about 53 days, from just above the clouds to the far reaches of Jupiter’s magnetic field.
• Pass: the trip from pole to pole takes about two hours.
• Prime mission: 35 orbits, which ended in 2021.
• Far point: Juno goes out beyond the orbit of the moon Callisto.

Why does Juno spin?

Juno spins twice a minute. The spin keeps it steady, like a spinning top. Its instruments are fixed in place. The spin gives each one a turn at the planet.

Did earlier probes fly the same way?

No. Earlier craft stayed near Jupiter’s equator plane. That is the same view we get from Earth. Juno’s polar path shows the poles and the deep interior.

Sunlight is weak at Jupiter. Juno needed huge panels to make enough power.

How weak is the sunlight?

Jupiter is five times farther from the Sun than Earth. Light spreads out as it travels. Five times the distance means one part in 25 of the light. NASA gives this as 4% of the sunlight Earth gets.

How big are the panels?

• Arrays: Juno has three. Each reaches about 9 m from the body.
• Span: The craft is more than 20 m wide with the panels out.
• Body: The six-sided body is about 3.5 m across.
• Folding: Each array has hinged parts, so it folded up for launch.

NASA says Juno is the first solar-powered NASA craft built to work this far from the Sun. Think of a lamp across a large hall. You need a big sheet of cells to catch enough light.

What protects it from radiation?

Jupiter’s magnetic field is about 15 times stronger than Earth’s. In some places it is over 50 times stronger. The field traps charged particles. Juno keeps its electronics inside a titanium vault of about 180 kg.

Juno carries nine science instruments. Each one has a clear job.

Which instrument does what?

• Microwave Radiometer (MWR) measures water and ammonia deep in the atmosphere.
• Gravity Science (GS) maps how mass is spread inside Jupiter.
• Magnetometer (MAG) maps the magnetic field.
• JADE and JEDI count low-energy and high-energy charged particles near the auroras.
• Waves finds the regions where auroral currents flow.
• Ultraviolet Spectrograph (UVS) images the ultraviolet auroras.
• JIRAM images auroras in infrared. The Italian Space Agency supplied it.
• JunoCam is a visible-light camera.

Is JunoCam a science camera?

It is built for the public. JPL calls it NASA’s first camera dedicated to public outreach. Volunteers process its raw images. A separate Stellar Reference Unit is an engineering camera that helps point the craft.

Juno’s biggest results come from below the clouds.

How deep do the bands go?

Juno measured Jupiter’s gravity. The data show that the belts and zones reach about 3,000 km below the cloud tops. The bands are jet streams that flow east and west. They are not a thin skin.

What is the fuzzy core?

Scientists once expected a small, hard core. Juno data suggest the core is larger than expected. It is partly dissolved, with no clear edge. Researchers call it dilute, or fuzzy.

How much water does Jupiter hold?

• Result: water makes up about 0.25% of the molecules at the equator.
• Compared: that is almost three times the Sun’s share.
• Depth: the radiometer reached about 150 km down, where pressure is about 33 bar.
• Earlier clue: NASA’s Galileo probe in 1995 hinted that Jupiter was dry.

Why does water matter?

Theories of how Jupiter formed lean on its water amount. NASA calls it a missing piece of the puzzle of the solar system’s formation.

Where does the magnetic field come from?

Deep pressure turns hydrogen into liquid metallic hydrogen. It conducts electricity like a metal. Scientists believe it is the source of Jupiter’s strong field. Juno also tracked the Great Blue Spot, a patch of intense field on the equator.

Juno gave the first clear close-up pictures of the north pole. The poles are crowded with storms.

What lives at the north pole?

A central cyclone sits at the north pole. Eight more surround it. NASA says these cyclones stretch more than 4,000 km across. Their spiral arms touch, but the storms do not merge.

What about the south pole?

At the south pole, Juno saw a pattern of six cyclones with one in the centre. During one close flyby it spotted a new giant cyclone that had pushed into the region.

How deep is the Great Red Spot?

Juno probed the huge storm. Its roots run about 320 km deep. NASA compares that to 50 to 100 times the depth of Earth’s oceans.

Does Jupiter have lightning?

Yes. On Jupiter it likely comes from clouds of an ammonia-water mix. It is seen most often near the poles. On Earth, lightning comes from water clouds and strikes most often near the equator.

NASA planned Juno’s prime mission to end in July 2021. In January 2021 it approved more time. The extension ran to September 2025, or to the end of the spacecraft’s life.

What did the extension add?

• Orbits: 42 more, as set out in January 2021.
• Flybys planned: Ganymede (2), Europa (3) and Io (11).
• New targets: Jupiter’s faint rings and the Great Blue Spot.
• Aim: to prepare the way for Europa Clipper and ESA’s Juice mission.

What did each flyby do to the orbit?

Each moon flyby acts as a gravity assist. It shortens the orbit and saves fuel. The period fell step by step.

• Ganymede, 7 June 2021: Juno came within 1,038 km. The period fell from about 53 to 43 days.
• Europa, 29 September 2022: Juno came within 352 km. The period fell to 38 days.
• Io, 30 December 2023 and 3 February 2024: the period fell to 33 days.

Did Juno orbit the moons?

No. Juno always orbits Jupiter. It only passes close to the moons. Callisto, the fourth Galilean moon, was not on its list.

This card separates what is confirmed from what is not. The date to remember is 30 September 2025.

What do NASA’s pages say?

NASA’s mission pages, read on 9 October 2026, say the extension ran through September 2025, or until the spacecraft’s end of life. The JPL page still shows the mission as in an extended phase.

What did the news say in 2025?

• 6 October 2025: Space.com reported that the extension ended on 30 September 2025. A US government shutdown began the same day.
• NASA’s reply: the 2021 extension was “the most recent update”. NASA could not say if Juno was still working.
• Gap: the NASA pages read did not give a later outcome.

Treat Juno’s status after September 2025 as unconfirmed. Do not write that it has ended or that it is still working.

What was the first plan for the end?

The team first expected 33 orbits, ending by October 2017. Juno would then be steered into Jupiter. That protects ocean moons like Europa from Earth microbes. NASA says the later path no longer put those moons at risk.

Who follows Juno?

Europa Clipper launched in October 2024 and is due at Jupiter in April 2030. ESA’s Juice launched in April 2023 and is due in July 2031.

Juno’s main goal is to learn how Jupiter formed and changed. That story reaches far beyond one planet.

Why study Jupiter first?

Jupiter is mostly hydrogen and helium, like the Sun. So it must have formed early. It grabbed most of the gas and dust left after the Sun formed.

What is the time-capsule idea?

Unlike Earth, Jupiter’s huge mass let it hold onto its original mix. Studying that mix lets scientists trace the solar system’s history.

How does that reach Earth?

NASA says understanding Jupiter helps explain how the rest of the solar system formed. That includes how Earth came to be and how it became a home for life. Jupiter also helps us read the planet systems found around other stars.

Does Juno study Earth?

No. Juno studies Jupiter. The link to Earth is indirect. It comes through the formation of the solar system.

UPSC asked about Juno in the 2017 Mains. This card gives the wording, an outline and the traps.

What did the past paper ask?

How could you answer it?

• Start: name Juno, its 2011 launch and its 2016 arrival.
• Link: Jupiter formed early and kept its original mix.
• Findings: a fuzzy core, deep bands and water at the equator.
• Close: the link to Earth is indirect, through how the solar system formed.

What are the traps?

1. Years. Launch 2011. Arrival 2016.
2. Orbit. 53 days at first. Then 43, 38 and 33.
3. Sunlight. 4%, not half.
4. Count. Nine science instruments.
5. Depth. Bands reach about 3,000 km. The Great Red Spot reaches about 320 km.
6. Water. About 0.25% of molecules at the equator.
7. Status. The last NASA extension ran to September 2025.