Jovian Extinction Event (JEE) Main Page
Modeling the Jovian dust field, moon atmospheres, flux tubes and Io’s Torus through JEE
Jovian Extinction Events (JEE) occur when an object experiences a loss of intensity as it passes behind dust or gas in the Jovian system. This loss of light or extinction can be caused by material gravitationally bound around one of Jupiter’s four major moons, material trapped in the magnetosphere or torus ring that surrounds Jupiter near Io’s orbit, or possibly material streaming in the flux tubes that connect the four major moons to Jupiter’s poles. One can use an object passing behind a target of interest to probe the material around the object in front by measuring the change in light of the object behind as its light passes through the this material.
The extinction phenomenon was first detected in 2009 during the end of the Jupiter Mutual Event (JME) season when Jupiter’s orbital plane was still edge on enough that the major moons were eclipsing and occulting each other (Degenhardt et. al, 2010). It was noted then that an anomalous photometric dimming began many minutes prior to Io occulting Europa or when Europa occulted Io, and an anomalous brightening was observed over many minutes post occultation.
The material surrounding Io migrates away and is captured for a period of time in Io’s Torus ring. When Io passes through the tips of the torus where the extinctive material is collimated to our line of sight that Io experiences a self extinction of its reflected light. During the IAEP2009 and JEE2010 Observing Campaigns it was established that Io suffers a sort of “self-extinction” while it transits its own orbit at the tips inside the Torus of Io. There is enough stray gas and particles to cause detectable magnitude loss with standard unfiltered observing equipment via extinction of the reflected sunlight from Io as it is diminished by the collimated line of sight Torus material at the most extreme eastern and western tips of the Torus. In 2010 John Talbot of New Zealand captured 5 hours of video during most of an Io transit of its western Torus tip. At that time in November of 2010 the orbit of Io was only 0.4 degrees inclined to our view from earth. This presented a large amount of Torus material collimated to our view which caused a very notable 0.13 unfiltered magnitude dimming during its transit through the western torus tip. The data from that run enabled us to derive a 5th order polynomial fit to Western Torus Tip transits of Io and has enabled us to create reliable predictions of future Io Torus JEE.
2009 JEE events were detected around JME occultations where the body of the target moon in front passed directly in front of the probing moon in back. In 2012 there were no JME occultations involved. Instead conjunctions occurred where the target moon passed in front of the probing moon from our line of sight and the probing moon was separated by 10 to 30 arc seconds. Thus the moon in back was probing regions above or below the poles of the target moon. New repeatable anomalous photometric trends occurred in these outer regions. Predictions of dimming were initially based on a first order assumption of a spherical distribution of material around a target using trends observed in 2009 at the equators. In some alignments we expected to see gradual dimming in the outer regions based on this spherical distribution model, but instead in some cases no dimming extinction would occur. In other observations instead of faint dimming we found repeatable sharp magnitude dips exceeding anything expected symmetrically surrounding the target moon. The initial JEE2012 Observing Campaign yielded new and repeatable anomalies. During this Campaign we were probing the outer limits of the atmosphere of Europa. We found initially that the expected extinction rates based on a 1st order assumption of a spherical distribution of dust did not exist in the north polar region of Europa. Instead of finding a linear type of extinction rate there were spikes in the dimming of the moon passing behind Europa that at the moment appear to potentially be caused by the walls of the flux tube(s) that connect Jupiter to Europa.
Here is one of several events displaying such sharp dips surrounding the target moon Europa. Io passed behind the target at about 14 Europa radii line of sight above Europa’s northern pole, and the minima of these dips occurred at approximately 7.5 Europa radii east and west of the target. Such sharp features seem indicative of a boundary layer of some sort. It is understood that flux tubes emerge from a pole of Jupiter, goes through all four major moons, and reconnects back to the opposite pole of Jupiter. A high rate of electrical current flows through these flux tubes (Lang, 2010). One working theory is that these charged particles may carry ionized dust and gas from Europa’s atmosphere with it and the sharp photometric dips in lightcurves represent the walls of this flux tube that are detectable through extinction by this material flowing inside that flux tube. Much more data needs to be collected to validate this theory. With enough data one might eventually be able to trace out the flux tube all the way back to Jupiter.
In an effort to verify if the source of these brief dimming are from the walls of the flux tubes I have generated predictions through 2014 of what I am now calling “JEE Window of Opportunities”. Using JPL ephemeris I have created a macro that tells me when any of the four major Jovian moons are within 30 radii of the moon closest to earth (i.e. in front) at the time of this conjunction. Since the orbits of the Jovian moon are not edge on until 2014 each of these conjunctions will allow us to trace out the flux tubes via extinction from far above each moon to the equator of each moon as we get close to edge on in. Then as the orbit of the moons opens up in the opposite orientation after 2016 we will be able to use these conjunctions to trace out the flux tubes below the moons. These conjunctions will both validate the new anomaly source as the flux tubes and provide us new measurements, or it will refute this theory. Given the surprisingly brief minima of this new anomaly (on the order of a few minutes) it seems essential that all imaging be done via video, which provides streams of images instead of CCD which is usually spaced out over time and may miss one of these brief minima. But any images are accepted. I have added to the conjunction opportunities events where Callisto passes over the pole of Jupiter. If indeed we are seeing flux tube extinction in our lightcurves at the individual moons, that same anomaly in the lightcurve should be visible at Jupiter’s poles. All four flux tubes extend out of the pole of Jupiter to each moon. Look for “J in front” and “IV in rear” events and observe these with very high magnification (to get Callisto out of Jupiter’s glare), but make sure you keep one other moon in the FOV as a photometric reference.
In addition to body to body occultation and occultation near miss type conjunctions, an updated version of predictions now contains solar shadow eclipse and near miss eclipse JEE windows of opportunity. Collaborators with the Juno Space Probe have asked us to include these in our predictions effectively doubling the number of JEE observation possible. However I must point out that eclipse JEE reductions are not as straight forward as occultation JEE. The main reason being that the Jovian moons in an eclipse situation experience up to four distinctly different illumination scenarios making the deconvolution of events in their observed eclipse lightcurve complex to solve. For instance, if you have ever stood on Io (using planetarium software) and looked down at the surface you would see that you have two distinct shadows! One shadow is from the sun and the other from Jupiter. Both objects are greater than -20th magnitude in intensity. So even when the sunlight is being slightly extinguished by material from another moon between say Io and the sun, Jupiter’s illuminating light is unaffected by the extinction, and possibly to the point of washing out the subtle change in the sunlight at Io. Add another problem in the mix, since the sun is not a pinpoint of light at Jupiter there are both umbral and penumbral shading. Thus any eclipse JEE is quite difficult to resolve all these variant sources. In an occultation JEE all the light from the moon in the rear is suffering extinction all at once, quite simple to resolve in most cases. Where occultation JEE become complex is when more than one extinction source is involved. For instance, if Io is entering its Torus Tip at the same time Europa passes in front of it, Io will suffer extinction from the Torus material at one rate added to the extinction from Europa’s debris. Only multiple data sets will eventually provide enough information to resolve the Jovian system, and potentially in 3D with enough data one day.
Also added to the Version 2 prediction set are opportunities where stars pass behind the Jovian moons. There are a few opportunities through 2014 where stars have potentially enough brightness to get photometric and potentially spectroscopic data from these stellar conjunctions and occultations.