SAVS: Week 3

image showing Emily's laptop which is displaying a polar projection image plot using Python code
Emily successfully plotting a polar projection image using Python code


All my homies hate Python.

(Not actually – Emily and Michelle seem to have it working, so our group is saved… for now at least…)

On a more serious note, we’ve spent this week practising our Python coding so that we could create images from raw data that we have sourced. Emily and Jude have focused on this, and are compiling the information so that the rest of the team can make observations and comparisons. They also attended our Physics department’s Space and Planetary Physics discussion about Gas Giants, in the hopes that we might learn something to help us with our own gas giant. Not only did they introduce our project to some researchers but they also gained some contacts who may be able to help us with the coding and overall direction of our project.

Meanwhile, Michelle & Diyura have started making a skeleton for our report paper so that we know what we want to include within it and in what sections. They were also able to sort and organize some journal papers that we’ve found will be useful for our project.

We’ve decided that we can potentially examine how the intensity of the aurora changes with local time, for a full rotation in each season (Summer and Winter), likely within each hemisphere. We can also compare the morphological changes over time, and any detectable variations in the magnetic field during that time period.

Leah has been able to determine the optimal time periods to focus on, based on the investigations we are aiming to carry out on the aurora. She recorded which images were clearly displaying the whole aurora, rather than a fraction.

She noticed that there is an overlap of data from Cassini and Hubble Space Telescope (HST) over Northern Summers only. The lack of Southern Summer data means that we may need to do some approximations using earlier HST Southern projections and later Cassini data on the Southern Hemisphere. The position of HST prevents it from viewing any of the Winter seasonal events on either hemisphere, so we can only use Cassini’s data for this period. With all of this in mind, we have concluded that we will focus on Cassini’s data for 2004, 2013-14, 2017 and Hubble’s data for 2008, 2013, 2016, 2017.

FUN FACT: The Cassini orbiter spacecraft carried 12 different science instruments. One of them was the Ultraviolet Imaging Spectrograph (UVIS), an optical remote sensing device acting like our eyes and ears. This allowed us to get information from remote objects without actually being in direct contact with them. It had two spectrographic channels, which observed light over wavelengths from 56 to 118 nm (extreme ultraviolet) and 110 to 190 nm (far ultraviolet). UVIS created images using these measurements.

The mission continues next week but until then “Goodbye, for now, until you read again!”

SAVS: Week 2

Our presentation went well! We’ve received some useful feedback, and had a private meeting with our Supervisor. It has been suggested that we utilise Auroral Planetary Imaging and Spectroscopy (APIS), so we have registered for access to this data so that Emily and Jude could practice/better understand everything relating to APIS in time for our Week 3 project plans.

FUN FACT: The Cassini-Huygens mission was the first to orbit Saturn. It spent 13, of its 20 years in space, exploring Saturn and its environments. On 15th September 2017, 294 orbits later, Cassini plunged into Saturn's atmosphere while transmitting new and unique data to scientists the entire time. It's "Grand Finale" consisted of 22 elliptical orbits between the rings of Saturn. Over 4000 science papers have been written so far, using the data Cassini collected, and ours will be next.

We have decided to use Cassini’s Ultraviolet Imaging Spectrum (UVIS) data on Saturn and data collected by the Hubble’s Space Telescope Imaging Spectrum (STIS) to aid our investigation since the seasons change very slowly on Saturn. Both Cassini and Hubble have been able to take images of Saturn’s auroras, so we will have data available to us that has been collected over a broad time period. Since Hubble first saw Saturn’s aurora in 1994, we should have enough data for a decent comparison of auroral differences for at least 3 seasons on Saturn.

Specifically, we’re looking for morphological differences such as size (by modelling our data as circles) and visual appearance (brightness, etc.). We also intend to do this quantitatively. We want to see what causes these differences and determine whether it may be influenced by temperature or some other local source.

Although both UVIS and STIS capture ultraviolet (UV) and infrared (IR) imaging, the UV data is more abundant so this is primarily what we will be considering. The recent launch of the James Webb Space Telescope (JWST) would have offered more data on the IR imaging of Saturn’s auroras. Unfortunately, it has not gathered such information as yet.

We are also considering acquiring direct data ourselves. If this cannot be collected from our University’s lab, then we will use a simulation to collect data of the aurora based on Saturn’s axis tilt, the solar wind speed, the position of Saturn’s moons, the intensity of weather conditions and any other relevant factors which may be discovered as we continue our research.

It is common that polar projection images are used in Physics research papers. This includes ‘local time’ (LT) based on the planet’s position relative to the Sun (this allows for consistent comparisons since features fixed relative to the Sun will always appear at the same location). The direction of the Sun (12 LT) is toward the bottom of the image while dusk (18 LT) is to the right, as seen in our diagram below. Here, we can see a Southern polar projection image (right) which has been created using original data gathered by HST (left).

Comparison of original data from HST and a Northern polar projection image derived from it (source: APIS/LESIA/ESA/NASA-HST)
Comparison of original data from HST and a Northern polar projection image derived from it (Credit: APIS/LESIA/ESA/NASA HST)

Within our research so far, Leah has also found a very useful image comparing HST images and solar wind conditions over a specific time period on Saturn. We will be using this concept to model our own images, using data from Cassini and Hubble, to compare how the morphology of the auroras change with the dynamics taking place such as changes in magnetic field strength, temperature, solar wind levels and brightness/luminosity. We may also include infrared imagine to allow for a potential investigation of temperature differences.

It may even be possible to examine different aurora regions such as the:

  1. Main Emission Ring
  2. Emission Polarward
  3. Emission Equatorward
  4. Enceladus Footprint (less likely since it is so difficult to detect)

We’ll make these decisions as our research progresses, and keep you updated on the process.

The team is logging off for now, so look out for our post next week!

We thank the APIS service at LESIA/Paris Astronomical Data Centre (Observatoire de Paris, CNRS) for providing value-added data derived from UV observations of the ESA/NASA Hubble Space Telescope.

SAVS: Week 1

Just in case you didn’t know what an aurora is — it is a result of the emission of photons, due to interactions in a planet’s upper atmosphere. Variations in the plasma environment release trapped electrons, which then stream along the magnetic field lines into the upper atmosphere. They then collide with atoms and molecules, exciting them to higher energies. The atoms and molecules release this extra energy by radiating light at particular characteristic colours and wavelengths. On Earth, we frequently see a green colour, a result of the green Oxygen line. On Saturn, emissions are from molecular and atomic Hydrogen. From our research, we know that the photons released on Saturn are into the UV spectrum. This means they can best be observed using special filters, not our naked eyes.

FUN FACT: Saturn has an axial tilt of 27°, meaning that one hemisphere will be tilted toward the sun (experiencing summer) and the other away from it (experiencing winter).
This means that Saturn has seasons. One summer on Saturn lasts more than seven Earth years!
This is why we'll be looking at the auroras' seasonal changes.

Now that you know a little more about auroras and the planet we’ll be investigating, let’s get you up to speed.

SAVS research includes sources from NASA ADS and Google Scholar

This week, we’ve focused on finding information. Each member of our team has been scouring the World Wide Web for everything that could possibly help us along our journey. We’ve looked at many sources, including Google Scholar and NASA ADS (Astrophysics Data System), so that we could devise a more structured method for research, analysis and report writing.

So far we’ve found many articles, including some based on the changing seasons on Saturn and a comparison between planets and their aurorae. We’ve also found that imaging is typically done in the UV spectrum, so this could aid us in structuring our project.

We were also able to gain access to our assigned lab room so that we can meet and continue working easily. Next week, we will be presenting our project idea to the rest of the PHYS369 group (and our module supervisors — Sarah Badman and David Sobral). We’ll be able to get some feedback on our direction, as well as answer any general questions our audience might have.

Wish us luck!