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.

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