Pluto System Occults UCAC 2603 9859

June 12, 2006, 16h 25min UTC

The Web site:

http://www.iota-es.de/pluto384.html

General overview

The Pluto system will occult the star UCAC 2603 9859 (15mag) on June 12th, 2006 around 16h 25min UTC, as first pointed out by Dave Herald (WINOCCULT, DE405) and Jean Lecacheux in early March. A new prediction for this important occultation has been done by Bruno Sicardy, Observatoire d Paris/Meudon using DE413 and an improved ephemeris of P1 and P2. The main visibility areas of the occultation by Pluto itself will be New Zealand, Tasmania, southern Australia and Reunion.

Even more important, following the discovery of the recently discovered small satellites P2, an occultation of this small body will take place about 1000km north of Pluto's occultation track.

The scientific goals of an observation of this important occultation are:

For Pluto,

to determine the atmospheric static conditions (Temperature, Pressure etc.) and to compare it with data from past occultations, to get an idea of the development of Pluto's atmosphere during the loss of energy due to the increasing distance from the sun.

to determine winds in Pluto's atmosphere by a possible measurement of a central flash from Tasmania or New Zealand.

For P2 and other possible objects as well

to determine the diameter of P2

to determine the mean density of P2

to determine a possible ring system around Pluto

The results are of special interest to the New Horizons mission to Pluto, because possible smaller bodies and/or a ring system around Pluto may have a significant impact on the mission.

In order to observe the small satellite P2 by this occultation, a lot of stations are necessary. The approximate diameter of P2 is only around 100 km. So it will be a real challenge. Everybody in the area of Central and Southern Australia, Tasmania but also on Reunion is encouraged to observe! IOTA-ES will try to coordinate together with other organizations as well the preparations and obervations for the event. Obervations by the team around Bruno Sicardy are planned in Tasmania and New Zealand.

Looks like New Zealand got snowed out for this one. Hope things went better in Australia.

[Edit: Sorry about the lack of a reference... I got this info from Google News today by searching on something along the lines of "pluto occultation".]

I predict no rings for Pluto.

Over longish time spans (even shortish ones) Pluto has wafty atmosphere drag effects probably up to top of Roche limit.

Charon on the other hand . . . . .

There's another possibility, though: P1 and/or P2 may be associated with dusty rings, similar to the newly discovered ring of Uranus that is associated with its moon Mab. These rings, if they exist, would circle both Pluto and Charon.

It would be really neat if this turned out to be the case, because any such rings would have very unique shapes. However, the very low mass of the Pluto-Charon system is probably a strike against their existence. Any material knocked off of P1 or P2 would be less likely to stay gravitationally bound to the system (and in the same orbit) than similar material knocked off of Mab. Uranus, being seven thousand times heavier than Pluto, can provide fragments of Mab with a lot more incentive to stick around...

I wonder if any previous Pluto occultations recorded the new moons
blocking starlight but was not noticed at the time? Or perhaps even
other moons we have yet to discover?

That's certainly possible, but it would depend on whether the apparatus was turned on at the time. P1 and P2 are quite a bit further away from Pluto than Charon is... during occultations, their shadows might not be noticed simply because nobody happened to be looking for them.

The Pluto system has been nearly "edge-on" to the inner Solar System for quite a while now, though... there's probably at least some chance that one or two occultations have happened while P1 or P2 happened to be (visually) close enough to Pluto or Charon to get picked up. It might be worth looking over some old data to see if there was anything there that got dismissed as "glitches" at the time.

This actually sort of begs the question of whether we can, in cases like this, consider the star that is being occulted to really be a point source. A 50-km satellite, at Pluto's distance from Earth, has an angular diameter of only about 0.0022 arc-seconds. That's less than a third of Alpha Centauri A's apparent angular diameter, and it's plenty less than the apparent angular diameters of giant stars like Arcturus, Aldebaran, Antares and Betelgeuse. If P1 or P2 were to pass in front of one of those monsters the result would look like a transit of Venus.

These are of course some of the nearest and brightest stars in the sky, far more prominent than a 15th magnitude star. Nonetheless, this is worth considering, and presumably the folks doing the math have done so.

I wrote to Jim Elliot (jle@MIT.EDU), part of the MIT team who observed
the Pluto system occultation. This was his response:

> Hello,

> I was wondering if you have any information regarding the Pluto
> occultation of June 12, 2006? Were there successful observations?


Yes, the MIT-Williams team had successful observations at several of our stations.

> Do you know if in any of the previous occultations there were
> detections that later turned out to be the new moons of Pluto,
> or perhaps ones we have otherwise yet to find?


So far I have heard of no reports of new moons. We have yet to look at our data carefully.

Jim Elliot


So not much for now, but at least they did observe the occultation.

Ah. Good thinkin'. Anyways, with any luck, we'll see the results of that within the next few months. It's no surprise that they haven't had the chance to analyze the data -- it's only been a couple of days, after all.

Quoted from the IOTA Web site:

On the night of 5/6 August 2006, the newly discovered Pluto satellite Hydra (alias 2005/P1) will occult a star, 2UCAC 26034796, with magnitudes respectively

mK = 12.7 , mH = 12.9, mJ = 13.7, mI =14.8, (rUCAC = 16.2) mV = 16.5.

This rare event might be seen from somewhere in Spain, Portugal (00h04), or Canary Islands (00h05), or Africa and South America (00h13). The faintness of the star requires a large enough telescope and a sensitive camera. The star and Hydra will be about 3 arcsec south of Pluto (mK = 12.9, mV = 13.9) : it is a MUST to resolve the images of Pluto and the star on different pixels.

Depending on Hydra's albedo (m = 22.9), the satellite brightness implies a diameter ranging from 50 to 150 km, i.e. a poorly constrained size. Observing such occultation would provide constraints on the satellite size, an important step in determining its albedo, hence its nature (bright icy body vs dark cometary material) and origin. Size can also constrain Hydra's mass, with important consequences for better estimating its resonant interaction with Nix (see under).

http://www.iota-es.de/hydra.html

It just so happens that there is a 4.2M telescope in the Canary islands...
http://www.ing.iac.es/PR/wht_info/