JEE2012

Modeling the Jovian dust field, moon atmospheres, and Io’s Torus

Introduction

JEE2012 is a great opportunity for amateur and professional astronomers to work together to accomplish something no one thought was possible. That is to actually detect and measure the tenuous atmospheres surrounding some of the moons of Jupiter as well as this same material that is captured in a torus ring around Jupiter, called the Torus of Io. The most exciting aspect of this project is since the moons of Jupiter are bright compared to most astronomical endeavors, the JEE work can be done in the smallest of telescopes, putting the ability to accomplish a real scientific measurement in virtually anybody’s hands. We have documented measurements of Io’s atmosphere in a small 80mm finderscope. Thus even the simplest amateur astronomer can perform some of the same measurements that our space probes have done flying out to Jupiter, and at a significant fraction of the cost. Add to that, the Juno Space Probe is on its way to Jupiter right now and they have expressed interest in some of our data. So here is the chance to actually contribute to real science. http://www.nasa.gov/mission_pages/juno/main/index.html

JEE stands for Jovian Extinction Event. This project has its roots in a discovery made in 2009 during the Jovian Mutual Event season where anomalous dimming and brightening occurred during the period of time outside of the actual mutual event. During this particular event of 20090807 Io was passing in front of Europa and occulting Europa with its body. But several 10s of minutes prior to the occultation a slow dimming occurred, and then following the occultation a reverse slow brightening began. Theorizing that this dimming and brightening occurred due to the extinction of the light of Europa by the tenuous material of the atmosphere surrounding Io, an observing program called the Io Atmospheric Extinction Project (IAEP) was launched to verify or refute this theory. Over a dozen folks from different countries submitted many dozen data sets and documented 28 events the indeed showed that extinction due to this tenuous material was being detected. We even then accidently discovered that Europa had an even larger and easily detectable atmosphere, as well as the Torus material that Io passes through constantly. This formed a new observing program we now refer to as JEE.

The results of IAEP were published here:

Degenhardt, S. et. al (2010), Io and Europa Atmosphere Detection through Jovian Mutual Events, The Society for Astronomical Science: Proceedings for the 29^th Annual Symposium on Telescope Science, p. 91-100

http://scottysmightymini.com/JEE/SAS2010_Io_Europa_Degenhardt.pdf

JEE Schematic cropped

The mechanics of the Jovian dust field

Without getting into specific technicalities, here is the basic understanding of how and where the material that makes up the Jovian dust is created and scattered. Io, the moon closest to Jupiter, is under a lot of stress from being so close to a super giant ball of gas. Io is geologically and electrically very active. Volcanoes constantly spew dust and gasses from Io, and the electrical and magnetic storm between Io and Jupiter trap this material for a short period of time. Io’s weak gravitational field will hold on to some of the material first, and our first order assumption is that we have detected this material out to about a dozen Io radii around Io. We have also found trails of it as many as 30 Io radii away from Io. Then the material slips away from Io into space. Some of it is trapped in a magnetic torus ring around Jupiter that Io passes through in its orbit, called the Torus of Io. It then eventually migrates out in space. Europa sweeps up some of the material and it is gravitationally bound temporarily out as far as 25 Europa radii. These numbers are preliminary and are what we hope to clarify and quantify with JEE2012.

The observation

The Jovian Mutual Event (JME) season occurs when the plane of the orbits of Jupiter’s four brightest moons is edge on so that they mutually eclipse and occult each other. This occurs at a frequency of about every six years and has about a dozen months of regular mutual events occurring. The difference and beauty of the JEE season is it lasts for years due to the outer reaches of the Europa and Io atmospheres. Actually the JEE season never ends because Io traverses through its torus nonstop, and about once a day is passing through the eastern or western tips of its torus where dimming are recordable.

During an occultation JME the body of one moon occults or blocks our view of another moon line of sight to earth. So far we have documented Io and Europa to have a tenuous but measurable atmosphere of material. If Io or Europa is the moon in front occulting a moon behind it, then the light from the moon behind Io or Europa will experience a slow dimming the closer it gets to the occultation, and then a slow brightening after the occultation. The total magnitude lost to extinction is very subtle, about 0.1 to 0.2 magnitude, but very measurable with quality imagery and a few basic techniques. The most important technique is time. This is the reason this has been overlooked for the 400 years since Galileo discovered the moons surrounding Jupiter. The dimming, which is miniscule, occurs over many 10s of minutes, and in some cases many hours. So collecting images over the right period of time is one of the most important aspects of the observation. The predictions made for JEE21012 are designed to facilitate the understanding of the right period to observe. It is likely you will only be able to record data over a very small portion of a total event, but your data combined with others is what will make up a total lightcurve. This lightcurve is almost 50 minutes long and you see the extinction dimming was over 20 minutes before the occultation and the length of the brightening is unknown afterwards because of incomplete data.

20090807 IoIInIII O-C plot

The most important technique is time. This is the reason this has been overlooked for the 400 years since Galileo discovered the moons surrounding Jupiter. The dimming, which is miniscule, occurs over many 10s of minutes, and in some cases many hours. So collecting images over the right period of time is one of the most important aspects of the observation. The predictions made for JEE21012 are designed to facilitate the understanding of the right period to observe. It is likely you will only be able to record data over a very small portion of a total event, but your data combined with others is what will make up a total lightcurve.

The key to making a successful observation is a few basic methods. First and foremost, try to keep Jupiter out of the field of view of your recording at all times. Jupiter provides glare that makes photometric reductions more difficult (but not impossible). This is not always possible due to different observing systems, but try to keep that in mind.

Next, understand the predictions to know ahead of time which moon is the target, i.e. the one that will experience the dimming. Know which one is causing the extinction, i.e. the moon in front for our line of sight. In the early parts of the upcoming JEE season all you need are those two moons in the FOV if at all possible. At reduction time I will simply compare the intensity of the front moon to the back moon and get something like this:

So in some cases you will want high magnification to get just the target and front moon in the FOV and exclude Jupiter. In the case where a JME occurs, it will require a third or fourth moon in order to do a photometric reduction because your target and front moon actually merge to a single spot.

The past observing complain was imaged unfiltered in what is called photographic magnitude. We have desired photometry in other colors given that JEEs involve extinction phenomenon, which certainly implies varied colors are being extinguished by the dust and gasses that make up Io and Europa’s atmosphere. I would predict, for instance, that given the large amount of sodium and sulfur one would expect to see a deeper occultation in the red portion of the spectrum. But with Rayleigh scattering the moons may lose blue. B, V, and R imaging would help answer this. So it is desirable to have different spectrum data. If you are able to include filtered data, that would be bonus data for this round of observations in 2012. The AAVSO will likely participate in JEE2012, and they are quite capable of multicolor photometry. http://www.aavso.org/

You will see “wing data” length of time suggestions in the predictions. Wind data means taking measurements outside of an event before and after the event occurs in order to get a good baseline of the intensities. The longer you can record before and after the better, because one never knows what else exists outside of the predictions. This is in some cases unchartered territory and methodology. That is why it is an “experiment”.

The next concept to understand is saturation. If you make a recording or snapshot of Jupiter’s moons and the gain of the camera or the exposure is too long, the disc of the moons will saturate the pixels. The intensity profile of the moons will be clipped or chopped off at the top. When clipping or saturation occurs information is lost. It is important to know to back off from saturation when making a JEE data recording (or any photometric data run). Here is an example of a JEE that was accidently left in saturation. Note the small window on the right showing the intensity profile of the moons circle in the video image on the left and that their tops are flat or clipped due to saturation. If you are new to this concept you will want to make some practice runs to learn how to image out of saturation.

The next issue is time associated with your data. Given that JEE events occur over 10s of minutes to hours millisecond timing accuracy is not a must. But it is desirable that your intensity data be accurate to at least a second of UT. There are ways to accomplish this in crude manners. You could for instance log into the Naval Observatory Master Clock and record the screen prior to and after your video recording without stopping your recording (http://tycho.usno.navy.mil/what.html). Another preferred more accurate way would be to record a WWV time clock recording on your audio from a shortwave radio at 2.5, 5, 10, 15, or 20MHZ. Or if you own a GPS based video timestamp device like an IOTA VTI (http://videotimers.com/home.html) then you are as accurate as you can get for one of these recordings, as it will lay the UT time from the GPS atomic clocks onto your recording. As a last ditch effort your cell phone time is likely accurate to within a second, but only use that as a last resort. It is important in the end to report how you assigned the time to your recording, so keep good notes.

It remains possible that an image from your digital camera shot through your eyepiece may suffice as a data point. You will need to shoot many of these thought to statistically reduce the noise and increase the signal. This is why video is the preferred method of recording. The cheapest easiest way is to buy a Supercircuits PC164CEX-2 high sensitive security camera (http://www.supercircuits.com/Security-Cameras/Fixed-Security-Cameras/PC164CEX-2) and put it in place of your eyepiece in your telescope. This camera has an automatic gain, so to prevent saturation you will need to stop the aperture of your telescope down. Another technique to avoid saturate is to put your image out of focus until it is unsaturated. This is less desirable though as it can blur the target and front moon to the point they overlap at closest approach making it impossible to do photometry on them individually. Stoping down the front of your scope with something like cardboard is the best method here, unless you do use a video camera with controllable gain that you can raise the shutter speed.

Here is an older page with some “How To” tips:

http://scottysmightymini.com/JEE/HowToJEE.htm

For advance observers with spectroscopy capabilities it is very desirable to get spectra of these JEEs to add to the understanding of the structures and components of the dust surrounding Jupiter.

What to do with your data

At this time Scott Degenhardt has a standing offer to reduce your data. If you take the time and effort make the recording or the snapshots he will reduce the data for you. He has tools he has developed that expedite the process while maintaining accuracy.

Contact Scott at this email scotty@scottysmightymini.com to discuss data reduction (or acquisition). All the data will go into a soon to be formed JEE database. Papers will be published so it is very important that you maintain good record keeping. Please be ready to provide the observers name, location, instrumentation, timing methods, and contact information and associations to go into a paper.

Mission statement

The call for observations for JEE2012 serves the main purpose of getting as many people to observe whenever they can and provide basic video or picture sequences over time during a predicted JEE so that the photometric reduction of those data samples may one day collectively yield a high resolution 3D model of the material scattered throughout the Jovian system. Anyone willing to do spectroscopic observations during a JEE may also contribute an accurate accounting of the specific molecules and their ratios in these clouds of material.

Prediction

A complete current prediction kit through Aug 2102 is available here:

http://scottysmightymini.com/JEE/JEE2012_Jun_Aug.zip

JEE predictions are made by me (Scott Degenhardt) who with the assistance of Wayne Green learned about the plethora of data available at JPL’s Horizons data base:

http://ssd.jpl.nasa.gov/horizons.cgi

Using Horizons I download ephemeris that allows me to make the following calculations in an Excel spreadsheet:

Horizon’s provides the X, Y offset from Jupiter’s center giving me a mutual reference point for all four moons at any given time. To determine the distance in arc seconds between Io (I), Europa (II), Ganymede (III), or Callisto (IV) I take a pair of moons at a time and perform a hypotenuse calculation as such:

SQRT((X_I - X_II)^2+(Y_I - Y_II)^2)

The answer to this would be the true separation in arc seconds of Io and Europa. Horizons also provides me with the angular diameter of each moon at that reference point of time. Knowing the diameter means I can divide that by 2 and get the radius, which means I can set up a filter to look for any moons that pass within a certain radius of another moon. Horizons provides Range data, i.e. the distance the moon is from earth, so I can do a set of comparisons that is basically like this:

· Show me when Europa or Io is in front of another moon.

· Highlight an event whenever Europa is in front and any object passes within 25 Europa radii

· Highlight an event when Io is in front and an object passes within 12 Io radii

So this gives me predictions of when an object may experience extinction based on models we have surmised from the IAEP study and other papers we have read.

Intensity data for each moon is provided by Horizons. This allows me to take our estimates of predicted photometric magnitude during a JEE by applying estimated extinction and predict the rate of dimming as an object passes inside the boundary of the atmospheric models we are currently using.

Using the X, Y offset of Io to Jupiter I can set up a filter that highlights when Io is at its most eastern or western elongation from Jupiter. At that time Io is in the center of its Torus tip material. I have derived a 4^th order polynomial fit to the expected lightcurve during a passage through the tips of the Torus. I can take the time from the center of the tip and predict the dimming and brightening rates and then apply those to the photometric intensity provided by Horizons.

Most importantly… THESE ARE PREDICTIONS! Anything can happen differently than predicted. So it is important to observe long before and long after an event. We wouldn’t be making this study and observations if we already had the answers. In fact, I suspect there will be new answers not even thought of before this is all completed…

Here are some credits for data used in the predictions: