My *first* first author paper is now online… http://www.sciencedirect.com/science/article/pii/S0019103516303517. If you go ahead and click on that link then you will see a genuine paper that I wrote with a lot of help from my supervisors and colleagues! It’s a real life published paper with my name on it, which you can download and everything! I’m really proud of this little paper, and I’m really grateful for all the help from my supervisors, colleagues and the anonymous reviewers. I’m well aware that the academic style of writing isn’t to everyone’s taste, so in this post I’m going to explain my paper in my own normalish words!
- So what’s this all about…?
As many of you already know I’m studying Jupiter’s aurora, but in this paper – plot twist – I investigate Jupiter’s equator. Initially the upper atmosphere of the equator may seem to pale in comparison to the dazzlingly bright lights of the aurora, but as my paper reveals, the equator of Jupiter is definitely important.
I study Jupiter in the infrared wavelengths. Jupiter looks especially excellent in the mid-infrared, where emission mainly comes from a charged molecule called H3+. This particular charged molecule is created from neutral hydrogen through a fast chain reaction that begins with ionisation. In the polar regions, fast electrons that have traveled from further out in Jupiter’s magnetic field, stream down the magnetic field lines and collide with hydrogen. This causes ionisation where the an electron is knocked out the neutral hydrogen molecule creating a charge molecule, or ion, called H2+. This quickly reacts with some more neutral hydrogen to make H3+.
Things go down a little different at the equator, where H3+ is made in a slightly different way. The ionisation of the neutral hydrogen is caused by extreme ultra-violet radiation, that has travelled to Jupiter from the Sun. After ionisation the H2+ quickly reacts with neutral hydrogen and makes the equatorial H3+. Radiation from the sun ionises the Earth’s upper atmosphere too but unfortunately doesn’t create H3+ due to different conditions in the atmosphere.
To observe H3+ at Jupiter we use the NASA Infrared Telescope Facility (IRTF) at the Mauna Kea observatories in Hawaii. Unfortunately I didn’t get to visit Hawaii this time (but I have been before…), the data was collected by my supervisor and colleagues in 1998, 2007 and 2012. This telescope has an instrument, known as a spectrometer, which can split up the wavelengths of light, allowing us to focus in on the mid-infrared and observe the wavelength at which H3+ gives out light.
- So why are we interested in the equator?
As someone who’s interested in the aurora, equator stuff intially seemed a bit boring to me but I shouldn’t have disgregarded the equator so quickly. It’s important to take a holistic approach when studying Jupiter, as the atmosphere and magentic field are connected in a complex way. In fact, most of the models that predict how Jupiter’s main aurora is created actually require the H3+ at the equator to boring. These models need the H3+ to be boring and simply move around the planet at the same rate as the planet spins. However there is this other idea…
So Jupiter has a equatorial bulge! When you look at Jupiter with an instrument capable of observing ultraviolet light, you’ll see a bright spot fixed in a position near to Jupiter’s equator. This spot was first discovered by Voyager on its journey out of the solar system, as it travelled past the gas giants. This is a really unusual feature, the origins of which remains a mystery…
But there is this one paper which suggests that the bulge is caused by supersonic jets in Jupiter’s upper atmosphere colliding and causing a brightening. They think that the two jets zoom down from Jupiter’s auroral regions and collide at the equator causing Eastward and Westward jets to emerge from the collision site, which causes brightening at the bulge position. These jets don’t exactly fit in with that boring picture of the equator that other scientists with other models had in mind. However no one has ever measured the velocity of the upper atmosphere at Jupiter’s equator, so who are we to know?
The tricky thing is the jets might exist higher up in Jupiter’s atmosphere than the H3+ population, and it is uncertain the exact altitude at which the peak H3+ emission comes from. Jupiter’s atomsphere is strongly coupled and so if there is some super strong winds high up, we might expect that to influence the layers of atomspheres below. So in this investigation measured the velocity of the H3+ ions at the equator to see if the supersonic jets exist and if there is any influence from the bulge.
- How do we measure the speed of the flows in Jupiter’s upper atmosphere?
Now the great thing about H3+ is not only does it give us temperatures of Jupiter’s upper atmosphere and amazing spectral images, it also allows the velocity of the H3+ ions to be calculated. This allows us to actually investigate the flows of H3+ in the upper atomsphere at Jupiter’s equator to see if the supersonic jets exist and work out if there is any effect from the bulge.
Even though you may claim not the know what Doppler shift is, you actually do! It’s that effect where an ambulance zooms past you and the pitch of the siren changes. We use this exact same principal to study the velocity of the H3+ ions. As they move around in Jupiter’s upper atmosphere the wavelength of the light they emit changes: when they move towards the observer the light is shifted towards the blue end of the spectrum and when they move away from the observer the light is shifted towards the red end of the spectrum. Using this we calculated the speed of the ions at Jupiter’s equator.
- And what did we find?
We found that the H3+ ions were rotating around with the planet and couldn’t find any evidence of flows relating to the supersonic jets or the bulge. We also did this thing where we added up a lot of measurements to get better signal, which was a kind of average of the velocities. This showed us that the general trend of the H3+ ions was to go round with the planet.
So it turns out that the equator is boring but that in itself is interesting! It’s interesting because no one else has ever measured the velocity of the H3+ ions at the equator before and our study was the first to do that. Its interesting because our results support the our current understanding of how the aurora is made, so the aurora modelling scientists can stay happy. Its interesting because the jets could still be a possibility, but not at the H3+ altitude, potentially existing at higher altiudes. And finally, it’s interesting because it leads onto further research questions, which my colleagues are already investigating.
So I hope, like me, you have been converted to finding Jupiter’s equator interesting and not boring! I’m currently writing another paper about the aurora so the next blog will have better pictures! Thanks for taking the time the read about my research, if you have any questions about this paper or Jupiter in general please ask away in the comments section 🙂