After travelling three billion kilometres, Juno reaches Jupiter

Friday 01 Jul 16


John Leif Jørgensen
Professor and Head of Measurement and Instrumentation
DTU Space
+45 45 25 34 48


Mathias Benn
Associate Professor
DTU Space
+45 45 25 34 56

Facts about Jupiter

  • Jupiter is 300 times bigger than Earth, and its mass is greater than that of all the other planets combined.
  • A storm which has lasted at least 350 years—making it the most persistent in the solar system—is found on Jupiter, where it covers an area larger than Earth.
  • Jupiter’s four largest moons include Io, the solar system’s most volcanic active planet, as well as Europa, which has a sea below a water-ice crust.

Juno mission

Juno was launched on 5 August 2011 from Cape Canaveral in Florida. It will orbit Jupiter for about two years. It travels at a speed of approx. 96,000 km/h in relation to Earth.

The main goal of the mission is to study how Jupiter was formed as well as its development by:

  • Looking at how much water its atmosphere contains, which may provide new knowledge about how the planets were formed.
  • Measuring temperatures, cloud formations and composition deep within its atmosphere.
  • Mapping out its magnetic and gravitational fields to identify its internal structure.
  • Examining the magnetosphere around its poles, among other things to find out more about how the planet’s enormous magnetic fields affect its atmosphere.

Read more about the mission:

One of the biggest missions that DTU has ever participated in reaches its destination—Jupiter—on 4 July. 

After a journey lasting almost five years, the unmanned spacecraft Juno is now about to enter its orbit around the planet Jupiter, more than 720 million kilometres from Earth.

Altogether, Juno has travelled nearly 3 billion kilometres through deep space to reach Jupiter, where it will try to answer some of the big questions about the universe using sophisticated equipment. Among other things, the planet’s enormous magnetic and gravitational fields will be mapped to an unprecedented level of detail. The mission will also look for water in the planet’s atmosphere as well as more unusual substances such as metallic hydrogen in its interior.

The National Aeronautics and Space Administration (NASA) has planned the mission so that the initial climax coincides with Independence Day celebrations in the US on 4 July. Professor John Leif Jørgensen from DTU Space has been appointed by NASA to the expert panel that will comment live to American TV viewers and radio listeners when Juno’s arrival is celebrated with a huge party at the Rose Bowl stadium in Pasadena, California.

“We have worked on this mission for many years, and now the goal is in sight. Consequently, it will be a really big day for everybody at DTU Space and—of course—for NASA, which is heading the mission,” says Professor and Head of Measurement and Instrumentation John Leif Jørgensen from DTU Space.

“The mission is really exciting because we will be looking at some of the big questions about the origins and evolution of the solar system. For example, Jupiter has a very strong gravitational field, and the most powerful magnetic field of any known planet. However, we don’t know exactly how this magnetic field was formed.”

“Jupiter is also the reason why we are able to survive on Earth, because its magnetic and gravitational fields pull many of the asteroids towards it that come from deep space.”
“If it wasn’t for Jupiter, many more asteroids from outer space would strike Earth, and then there would not be any life here as we know it. So it’s a very exciting planet to study,” says John Leif Jørgensen.

Precision equipment from DTU
DTU Space has supplied equipment to the mission in the form of four star cameras, which have been used for extremely precise navigation and for taking photographs of Jupiter and the areas in space which Juno has passed on its long journey. In addition, DTU Space has validated and calibrated the magnetometer that NASA Goddard Space Flight Center (GSFC) developed for studying the planet’s magnetic field.

“We enjoy a reputation for supplying the most precise and effective star cameras, and therefore we were invited on board, both as suppliers of technological hardware and on the scientific part of the mission,” says John Leif Jørgensen.

The mission is estimated to be costing in the region of DKK 13 billion, and DTU is responsible for approximately one tenth of the mission.

“It is one of DTU’s biggest assignments ever. We are extremely proud to be involved, and it shows that DTU and DTU Space are leading the way internationally within this field of research,” says John Leif Jørgensen.

Extreme environment—extreme demands
To date, there has only been a handful of missions in the vicinity of Jupiter. However, none have been this close or had the potential to conduct such detailed studies as is the case now. Juno will orbit Jupiter 37 times at a height of approx. 5,000 kilometres above its cloud layers. Each orbit takes 14 days.

“Juno will be navigating an extremely harsh environment around Jupiter, and it will be going closer than ever before. Due to the intense particle radiation around the planet, we have to let Juno whizz in under the magnetic field at Jupiter’s north pole to gather information, and then let it come out at the south pole, after which it can transmit data back to Earth before heading back in. If we allowed it to orbit continuously inside the cloud layer, our instruments would be destroyed by the radiation,” says John Leif Jørgensen.

"Juno will be navigating an extremely harsh environment around Jupiter, and it will be going closer than ever before."
Professor John Leif Jørgensen, DTU Space

About one kilogramme of 24 karat gold has been used to pack the instruments. Relative to its weight, pure gold is highly effective at stopping the invasive particles.

On the other hand, the mission offers the opportunity of studying and perhaps even answering a number of key questions.

Formation of the solar system
“Jupiter holds masses of knowledge that is key to understanding how our solar system was formed. Therefore we must basically examine how the planet is built up, its morphology, which elements are present, its atmospheric conditions, its core and many other things,” explains Professor Jørgensen.

“For example, we will be able to look at whether the hydrogen which makes up most of the planet is so compressed that it constitutes a sort of metallic hydrogen, and is therefore no longer gaseous. In this state, we believe it become superconductive, and may explain a number of processes elsewhere in the universe.”

As far as water is concerned, none has ever actually been discovered on Jupiter, but it might well be concealed deep in its atmosphere together with CO2. This will be investigated using radio waves.
“Via Jupiter, we can perhaps find indications of why there is water on Earth, which there shouldn’t be, and in this way test the explanatory models that we currently have.”

In addition, photographs will be taken of the large radiation belts of particles around Jupiter using the cameras from DTU. This profiling will provide knowledge that can be used in connection with future missions to one of Jupiter’s moons, Europa, one of the places in the universe where there is a relatively high probability that the conditions for life may be present.

On the trail of an unknown phenomenon
The star cameras will also take pictures of the clouds of gas and dust surrounding Jupiter in plate-shaped rings. This will be done by measuring how much light which is emitted by the stars behind the rings passes through them. Using this information, it will then be possible to create a profile of the dust and examine what it contains.

DTU’s star cameras have already been in action en route to Jupiter, photographing small meteorites that hit the spacecraft and then evaporate.

“Here we have discovered a phenomenon which has never previously been measured, and which can prove to be a new discovery,” says John Leif Jørgensen.

Right now, however, the team is busy getting ready to travel to the USA while helping to ensure that everything is functioning as it should when Juno, after its 3 billion kilometre journey, moves into position to start orbiting around the huge planet. If everything goes according to plan on 4 July—on 5 July in Denmark between 9:00 and 12:00—the signals will start to flow back to Earth with a 40 minute delay, which is the time it takes for data to be transmitted from Jupiter, 720 million kilometres away.

Jupiter photographed from Juno on 21 June at a distance of 10 million kilometres. (Photo: NASA/JPL)

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