Essential Information

Royal Observatory

25 Jun 2020

Juno is a space probe developed by NASA which is currently orbiting around Jupiter. Now 4 years into its mission, what has the Juno probe revealed about the largest planet in our solar system?

Why is it called Juno?

In roman mythology Jupiter was the king of the gods and the Juno probe is named after the Roman goddess Juno - the wife of Jupiter and the queen of the gods. Jupiter was a bit of a flirtatious character and had many lady friends that Juno was not pleased by.

To hide his mischief, Jupiter drew a veil of clouds around himself, but Juno was able to lift the clouds and reveal his true nature.

Aptly named, the Juno probe’s mission is to reveal some of the secrets of Jupiter - notably how it originated and evolved which in turn may give us a better understanding of the solar system’s beginnings.


Juno and Jupiter

What are the main aims of the Juno mission?

  1. To work out how much water is in Jupiter’s atmosphere (something that will tell us which of the current planet formation theories is likely to be correct or highlight that we need new ones).
  2. To peer deep into Jupiter’s atmosphere to give us a better understanding of what it’s made of (composition), its temperature and its cloud motions amongst other things.
  3. To map the gravity field and magnetic field around this monster planet which will hint at what Jupiter’s deep structure is like.
  4. To explore Jupiter’s magnetosphere (the region surrounding the planet in which charged particles are affected by its magnetic field) especially near its poles. This will provide new insights into how Jupiter’s gigantic magnetic field affects its atmosphere and the creation of its aurorae.

Alternative mission objectives

Although this was a robotic mission, the Juno spacecraft did have some passengers. Onboard were three miniature Lego figures of Jupiter, Juno and the Italian astronomer Galileo Galilei - the discoverer of the four largest moons around Jupiter. Made of aluminium (a non-magnetic metal which wouldn’t interfere with the onboard equipment), these 4 cm figures were sent with an alternative mission in mind – to inspire young people to explore and develop an interest in STEM (Science, Technology, Engineering and Mathematics) and to encourage them to imagine and dream about journeying to the king of the planets ourselves, a feat that may seem impossible now but may one day become a reality.


Juno Lego figures

Launch, journey and arriving at Jupiter

The Juno probe was launched from Cape Canaveral Air Force Station on 5th August 2011 but the mission itself began back in 2005 when it was approved by NASA after several years of a strong desire for a Jupiter probe. The average distance to Jupiter is around 800 million km but the Juno probe travelled roughly 2.8 billion km to get there taking just under 5 years, due to a trajectory that used a gravity assist (speed boost) from the Earth. After the gravity assist in October 2013 which gave it a speed boost of more than 14,000 km/h, the probe headed for Jupiter. Accelerated by Jupiter’s gravity on approach, it arrived with a speed of around 210,000 km/h and so the spacecraft underwent insertion burns (firing of its engines) to decelerate it and finally entered Jupiter orbit on 5th July 2016.

The Juno probe has a highly elliptical polar orbit which means that its orbit is not perfectly circular around Jupiter and it is able to view Jupiter’s poles clearly (something that hasn’t been done before). The 53-day orbit brings it up close before taking it back far out from Jupiter and although it was intended for the probe to drop into a shorter 14-day orbit, instrumental problems that could jeopardise the engine burns required to achieve this meant that the scientists opted to keep Juno in its original 53-day orbit which is slowly moving northward, as intended. So with each orbital flyby, we’ll be able to see more and more of Jupiter’s northern hemisphere with better clarity.