Science Society explores outer solar system

Dr Jackman is an Associate Professor of Space Physics at Southampton University. She holds an STFC Ernest Rutherford Fellowship to study planetary and stellar magnetospheres. Her research interests include large-scale structure of giant planet magnetospheres, the energy budget of Earth’s magnetosphere (with implications for ground-based technology and services), machine learning and complexity science. She is also very active in outreach and public engagement. 

In the1970s the voyager spacecraft took an iconic photograph of the Earth from far out in the solar system with the Earth appearing as a faint blue dot. We have created machines that can travel into deep space for many years, still sending information back to Earth from distant planets and now beyond our Solar System. It is hard to get to the outer solar system. One obvious obstacle could be the asteroid belt, a belt of rocks and debris between Mars and Jupiter. In fact, the rocks are far enough apart to navigate easily. We cannot go direct to the outer planets because we would need too much fuel and the spacecraft would be too heavy. So the planets are used as a gravity assist, pulling the spacecraft through space, calculating a path being a major mathematical challenge. Once you get to major planets you have to deal with strong radiation surrounding Jupiter, which can badly affect electronics.

Jupiter is an easy object to observe with the naked eye or a simple and cheap telescope or pair of binoculars. Galileo identified the four biggest moons of Jupiter, paving the way for the heliocentric model of the solar system. Jupiter has also been observed using its radio emissions, first discovered by Burke and Franklin in 1955. This showed that Jupiter had a magnetic field round it, and electrons trapped in the field emit radio waves that can be detected on the surface of the Earth. We have sent nine missions to Jupiter with New Horizons in 2007 and Juno from 2016 the most recent. The Juno mission has rewritten the book of understanding Jupiter. We still have many unanswered questions, such as why the atmosphere has dark and light bands and why is the Great Spot red.

Considering Jupiter’s moons, Io has active volcanoes because the gravitational pull of Jupiter and other nearby moons stretch the rocks, causing heating. The volcanic plumes can go hundreds of kilometres into space. Europa has a smooth icy surface covering a sub-surface ocean. Water vapour plumes have been observed escaping from the planet and that means it has a chance of containing life. 

The magnetosphere of Jupiter is where the plasma flowing from the Sun interacts with Jupiter’s magnetic field, accelerating particles and causing aurorae. The aurora on Jupiter is much more powerful than that of Earth. Studying this, and in particular magnetic reconnection, has been a big part of Dr Jackman’s research. It is a very energetic process with one event involving energy equivalent to boiling a billion kettles. These events happen every few days. At the moment the energy balance is not working and it is a continuing puzzle to work out where the missing mass and energy goes.

Saturn is the most beautiful planet with the rings changing aspect to us, making the planet look very different over time, especially to early astronomers with weaker telescopes. Four missions have passed by Saturn, finishing with Cassini from 2004 to 2017. Cassini revolutionised our understanding of Saturn, launched in 1997 and reaching Saturn in 2004, having swung by the Earth, Venus and Mars multiple times. As part of the mission we landed the Huygens lander on Titan, one of Saturn’s moons. We saw rivers, mountains and lakes, but lakes of liquid methane, not water. Enceladus was the biggest surprise for the mission, with a covering of fresh, clean ice. Strong stripes near one pole are striking. A flyby revealed Enceladus had a strong magnetic field, and there was no idea why. It was decided this must be explored further and the mission plan was changed. It turned out there were plumes of gas ejected from the stripes near the pole and the temperature was much hotter than expected. The plume is water ice and the stripes are cracks shifting with gravitational pull, like the heating of Io. The last flyby went very close to the surface near the plume. It discovered molecular hydrogen, which suggests hydrothermal vents are active under an ocean of water below the icy surface of Enceladus and that gives the potential for life. This generated a lot of unwanted headlines about finding alien life but offers a lot of possibilities. Saturn has a large magnetosphere and powerful aurorae and it has the same energy imbalance from magnetic reconnection.

Juno was launched in 2011 and took just five years to get to Jupiter. It is flying through the radiation belts and has to be protected from the harsh environment. The trajectory planned was compromised by a stuck thruster so it is taking longer to get around the planet sufficient times to map it all. Juno is looking to explain the origin of Jupiter, its interior structure, its atmospheric composition and its magnetosphere. Junocam is a public controlled camera that anyone can vote for what it should take a picture of, so log on and your vote counts the same as anyone else, expert or not. We are finding the magnetic field, of Jupiter is much stronger than thought and theories about aurorae are having to be revised. There is a lot of work to be done and places for future researchers!