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Guest post: Marco Vedovato, “Jupiter: a little analysis about the GRS-LRS encounter” February 15, 2009

Posted by dorigo in astronomy, news, physics, science.
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Marco Vedovato, in his daily life, is a structural engineer. As an amateur astronomer, when his children allow him to do this, his main interest is the atmosphere of Jupiter, the giant planet of the Solar System, and he partecipates, as a measurer, to the Jupos Project, an international investigation about Jupiter. He is also the vice-manager of the Jupiter Program for the Italian Amateur Astronomic Union. When I saw his extremely interesting analysis of the Jovian atmosphere I begged him to write about it for this site. You can find the resulting piece below.

Last year I amused myself to analyze one aspect of the encounter between two Jupiter spots. For this aim, I used WinJupos, a software for measuring the Jupiter images (see here). In the following picture, a map composed by using some very good images, the reader will be able to meet the protagonists of this tale (click on the picture to get the full image!):

The first one is the famous Great Red Spot (GRS), a long-lived anticyclonic circulation, centered around -22,5ΓΈ South latitude, existing at least since the second half of 18th century. The second one is a smaller reddish spot (LRS, Little Red Spot), probably born around the end of 2007 and the beginning of 2008, a residue of a previous “Tropical Disturbance”, observed during the 2007.

It is well-known that the GRS has a 90-days oscillation around its mean motion in the Jupiter outer atmosphere; having a look to the map above, GRS is moving very slowly in longitude (with the same latitude) from left to right, forward to the increasing longitudes (retrograde motion). This lazy motion is not constant but presents an oscillation around the main drift. In the following graph the red points are the GRS center, the ones on the left (blue) and right (green) side are the ends of GRS; it is easy to note a period close to 90 days.

Instead the LRS moved in the opposite direction (prograde motion) than the GRS (and with higher speed), so an encounter was inevitable. In the the picture below, a graph I obtained before the encounter, using few points but from very good images (i.e. those of C. Go, F. Carvalho, A. Wesley, G. Grassman and others). I noted, also in the LRS case, an oscillation around the interpolating line.

After the encounter the LRS was quickly destroyed. The following graph documents the collision.

I was interested to see if this LRS oscillation were similar to the GRS one, with the same period and if in phase or not. So I matched “in parallel” the relative motions (by using a modified reference system for the LRS, artificially changing its speed, to have more or less the same slope for both the drifts); a light correlation between the two oscillations seems noticeable. I do not know whether the effect is casual or if it is real. In this last case, are the two oscillations determined by a same cause, hidden in atmospheric currents embedded in deeper layers?

John Rogers, Jupiter director of the British Astronomical Association, wrote me this comment: “Very interesting. Perhaps the oscillation of the GRS has an effect on the nearby LRS? Or perhaps the synchrony is a coincidence — it is difficult to say!

I’ll have to prepare further analysis when there will be similar opportunities.

(Marco Vedovato)