Stellar Occultation of P20120614 by Pluto

Stefan Réner, Ahmed Daassou and Zouhair Benkhaldoun took this image of Pluto and the target star, using the T60cm from Atlas Golf Marrakesh on the night 12 to 13 June. Credit

Although the suddenness of such an event is rather peculiar (as such an event should have been in ephemerides without such short notice), Pluto perhaps will occult the a star, P20120614 of the 13.7 magnitude during the night of June 13-14. In an alert entitled "Possible Pluto occultation Wednesday night (2012/06/14 03:28 UT) from US East coast" issued by Leslie Young, we find that Pluto's occultation hopefully will conclude to be helpful for more insight to Pluto, as it is a world of which we do not have much information from. The occultation is planned to last around sixty-eight seconds starting on June 14 at 3:22 UT (June 13 11:22 pm EDT) at a low altitude in the sky for the eastern United States and Canada. The RA (Right Ascension) of the star is 18h 35m 48.69s while declination is at –19° 17' '43.6".

From the alert, we learn that stellar occultations prove to help us learn more about Pluto, but particularly its atmosphere. "Pluto's thin, nitrogen atmosphere is in vapor-pressure equilibrium with the surface ice, and changes seasonally", so observable occultations will help astronomers learn more about the atmosphere. When Pluto passes in front of a star, we get a good view of the atmosphere by the light from the star behind the planet and meanwhile, at ~10 km resolution, temperature and pressure is measured accordingly. More information can be obtained here.

Visibility Map: Across the globe pictured above, the three solid lines correspond to the northern limit, centerline, and southern limit of Pluto's shadow. The northern and southern limits correspond to a radius of 1400 km. The upper and lower dashed lines indicate 3-sigma errors. The shaded area represents where the sun is more than 12 degrees below the horizon.

Table 1: Prediction Details
Pluto Geocentric Mid-time (yyyy month dd hh:mm:ss)	2012 June 14 03:26:12± 00:00:42 UT
Pluto Minimum Geocentric Separation	0.275± 0.025 arcsec
Position Angle (Pluto relative to the star; measured north through east)	–6.40 degrees
Geocentric Velocity	22.89 km/sec
Occultation Star R magnitude	13.8

Table 2: Reference Star Position
Reference star position: (at epoch of event)	RA (h:m:s; J2000)	Dec (d:m:s; J2000)		Notes
P20120614 Catalog	18 35 48.6931	–19 17 43.617
P20120614 Measured	18 35 48.6883 ± 0.002	–19 17 43.639 ± 0.009		From 5 SMARTS Telescope frames.
Table 3: Projected KBO Offsets from Reference Ephemeris at the Time of the Event
Body	RA (arcsec)		Dec (arcsec)
Pluto	–0.1392± 0.041		+0.225± 0.023

Above Tables and Visibility Map Thanks to P20120614 Occultation June 14, 2012. Below map credit same site the image of Pluto and Star (beneath the title) was accessed.

Dark gray is night and light gray is astronomical twilight (Sun at less than 18° below the horizon).
Shadow moves from right to left, each red dot is separated by one minute, the nominal occultation time on the map, is for the big red dot, the closest approach

The Cryptic World of the Satellites of Distant Pluto

Designated 134340 Pluto, this second-largest dwarf planet in the solar system is one with a history of no other planet, such as its downgrade and climatic discovery in the mid twentieth century; but one of the most remarkable aspects of this cryptic world are its specialized brood of moons which it harbors so well astronomers have never been able to photograph them, or even Pluto itself (in high resolution) to say the least! So what makes this distant, icy world so fascinating it's rather arcane? The answer to that question lies in your perspective of the planet: probably because we know nothing about it, or because of its hidden mystery and history of its creation (etc). Pluto is a rather special dwarf-planet; it lies within the Kuiper Belt, a belt of objects beyond the orbit of Neptune and orbit the sun in irregular orbits, along with many other know minor and dwarf planets such as Eris (the most massive dwarf planet in the solar system), Makemake, and Haumea to name a few.

The green objects represent the wide variety of objects in the Kuiper Belt, Pluto including. This map shows the area of the Kuiper Belt and the comparison of its distance from the gas giants (such as Jupiter) in the center.

Although not the only minor planet to have a collection of moons, Pluto has the most known of all dwarf planets. With a count from March 2012, Pluto has four moons, three of which have been named officially by the International Astronomical Union (IAU). Its most famous would be Charon, which was discovered June 22, 1978 (publicly announced July 7) by James Christy at the United States Naval Observatory Flagstaff Station while he was carefully observing photographic plates of the minor planet. A bulge was noticed periodically while plates were being taken and it was obvious this bulge was not a result of an error on the plate, but rather a moon orbiting the planet. Although this was rather controversial for a while, any doubt of no lunar presence was annulled during the eclipse period of Charon during the 1980s (specifically 1985-90).

"It was fortuitous that one of these intervals happened to occur so soon after Charon's discovery," Swarthmore College Computer Society writes in their article of Charon, and it was beneficial! The eclipses of Pluto are an extremely rare phenomena which can occur only twice per the planet's 248 year revolution around the sun, the next ones to occur start October 2103, peak in 2110, and will end January 2117, as observed from earth. It will be Charon who does most of the eclipsing for Pluto. More can be read here about the phenomena.

The Sun disappears behind Charon's surface during the total solar eclipse on Pluto of 23rd December 2111 (computer simulation) Thanks to Wikipedia and JPL simulator

The complete Plutonian system (as of 2005) thanks to the Hubble

Charon is not the only moon Pluto has, however! Three others have been discovered since the days of Charon's discovery and people are becoming less and less more skeptical about the existence of such objects. Nix (also spelled Nyx) and Hydra are two others discovered in July of 2005 by the HST Pluto Companion Search Team. The discoveries of both were publicly announced on October 31, 2005 after more than five works of research and confirmation from precoveries done in 2002.

Nyx, named after the Greek goddess of the night (all moons of Pluto were named in accordance to deities of the Underworld, as Pluto was the god of the Underworld in Greek mythology; Charon was named after the ferryman who took souls into Hades across the river Styx), orbits in the same plane Charon does and orbits every 24.9 days with a unique 1:4 orbital resonance with Charon (although not quite). The Nictian surface is quite unknown (like Pluto's) and is usually at the measured magnitudes of 23.38 to 23.7, almost 6300 times dimmer than the dwarf planet itself! But, its orbital resonance was a problem (because it was not perfect). In a paper presented by the discoverers of the moons entitled Orbits and Photometry of Pluto's Satellites: Charon, S/2005 P1, and S/2005 P2. This paper explained that although the orbital resonance between these objects were mostly 1:4, there was a 2.7% timing discrepancy, proving no resonance existed. The below portion of text discusses this on a higher level. 

The orbital period of P1 is 38.2065 ± 0.0014 days, while 6 times the period of Charon is 38.3234 days. This is the period ratio most nearly commensurate, and from the 0.3% difference from a 6 : 1 period ratio we get a circulation of the resonant argument in 2090 ± 80 days, less than 6 yr. Likewise, our period of P2 is 24.8562 ± 0.0013 days, compared with 4 times the period of Charon, which is 25.5489 days. This difference corresponds to a 2.7% difference, and thus, the resonant argument will circulate in only 229 ± 2 days. Comparing the periods of P1 and P2, we find that their ratio is 1.53710 ± 0.00006, not the exact ratio of 3/2. Again, circulation would be quite rapid, at just 515 ± 6 days. These circulation periods are all of comparable timescales to the duration of the constraining astrometry for the two-body orbits we have derived. We do not see any obvious periodic deviations from a two-body Keplerian orbit and thus argue that perhaps there are no active resonances.

Hydra (named after the chthonic beast of nine heads in the Grecian underworld) was discovered with Nyx and remains virtually unknown as the others. Its magnitude is just a tad brighter than Nyxs' at 22.9 to 23.3, and its orbital resonance with Charon made an issue as well as Nyx's. The Hydrian revolution was 1:6 to the Charonian one and (not suprisingly!) there was a 03.% timing discrepancy between the two, making no resonance at last.  

With that having been said, Pluto's three moons discovered 2005 and before have become a pivotal part of the history of Pluto, the planet we know almost nothing about. But then, in July of 2011, another moon was discovered. This moon was not the farthest moon out, as most moons are discovered in their order from closest to out-most of the planet [probably because the closest moons are the largest and most prominent and the outer are less-brighter and more hard to detect], but rather it was found to orbit between Hydra and Nyx. This moon, labeled S/2011 P1 was discovered (announced) on July 20, 2011, and is relatively dimmer than the other moons, at magnitude 26.1 ± 0.3. The plus/minus symbols details that the magnitude has been seen to shift as it orbits the planet. You can read more about Pluto's fourth in our article we published back in July when it was discovered. [Below is an image of P4 orbiting the planet]. 

When we image what Pluto may look like, we imagine a gelid, ice-ridden world void of life and any consolation. But amid the depression that lurks throughout the planet, we will always have the exciting anticipation of one thing: New Horizons. This discussion of Pluto's moons would never be complete without NASA's excellent space-probe sent out to explore than planet and its moons, hoping to discover new ones. It won't reach the planet until (proposed) July of 2015, so although the wait is burdensome, the rewards will be plenty! Pluto is not an icy world but a world of discovery, something we can all take part in.

Astronomical Events Calendar: A Year In Review

Out Favorite Posts from whence the beginning of this emporium began:

Stjernedannelse I Carinatåken: Star Formation in the Carina Nebula

Occultation of 136199 Eris Gives Significant Data

Ens Sidus Quod non Debet Esse: The Star Which Should not ße

Hubble Discovers Fourth Moon of Dwarf Planet Pluto
 
Hubble Transits Jupiter

Seventeenth Anniversary of Jupiter's Impact by Comet Shoemaker-Levy

New Moonlets for Jupiter - How Many Are There Now?

Conjunction of Jupiter and Phobos

Wise Infrared Gives Us A Sample of Galaxies to Come

Four Planet Dance of 2011 - What Happened?

Occultation of Minor Planet 136199 Eris Gives Significant Data

Last November 6, 2010, minor planet 136199 Eris occulted the star USNOA2 0825-00375767 in the constellation Cetus. What significance does this relate to? Before this occultation, trans-Neptunian object Eris was assumed to be smaller than Pluto, its presumably larger contemporary. But now, Eris' diameter has been measured and not guesstimated, but rather an exact measurement. The video below shows the occultation, as astronomers would have seen it on that November day.

http://www.youtube.com/watch?v=HxQ0b8p4cGY&feature=player_embedded

USNOA2 0825-00375767, with a magnitude of 17.25 is a very faint star, but nothing is too dim for the Belgian TRAPPIST telescope at ESO’s La Silla Observatory to see. This event has been described by ESO as a "very rare and difficult to observe" event becasue minor planets are very small - and an occultation is even rarer. But these things do occur, for Eris will occult again in 2013, ESO reports. Astronomers first observed the star using the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory, and a another team carefully predicted the time and what would occur during the occultation. "Observing occultations by the tiny bodies beyond Neptune in the Solar System requires great precision and very careful planning. This is the best way to measure Eris’s size, short of actually going there," explains Bruno Sicardy, the lead author.

Twenty-six places global observed the occultation and were henceforth able to determine the diameter of Eris, which had not yet been accurately determined.  Eris is a dwarft planet, today known to be the most massive, of the Kuiper Belt - the region of the solar system which contains the "remains," as astronomers call it. Eris is a dwarf planet, as well as other well-known objects such as Pluto, Sedna, and Makemake. The planet itself is magnitude 18.7 and it orbits 97.56 AU, or 9,068,768,557.0108 miles from earth. It has one moon, Dysnomia, as shown in the picture below. This moon was used to help determine the mass of Eris - which is 27% heavier than Pluto, astronomers found.

Artist's conception of Eris (with Dysnomia above)

Previously estimated was the diameter of Eris at around 3000 km (or 25% larger than Pluto), but now, the research has proved that both minor planets are essentially the same size, as Eris' predicted diameter was 2326 km. (Pluto's diameter is approximately 2300 or 2400 km, as New Horizons will find out in 2016. Pluto's obstructive atmosphere makes occultation predictions hard to accurately define).

The below picture shows trajectories of the occultation, "the three oblique solid lines show the star trajectories relative to Eris, as seen from San Pedro, La Silla and CASLEO, with the arrow pointing towards the direction of motion," as multiple authors of A Pluto-like radius and a high albedo for the dwarf planet Eris from an occultation, a paper presenting their discoveries, write. The names below are observatories in Chile where this occultation was viewed.

 
“This density means that Eris is probably a large rocky body covered in a relatively thin mantle of ice,” comments Emmanuel Jehin, who contributed to the study. “It is extraordinary how much we can find out about a small and distant object such as Eris by watching it pass in front of a faint star, using relatively small telescopes. Five years after the creation of the new class of dwarf planets, we are finally really getting to know one of its founding members,” concludes Bruno Sicardy.

The Latest Among The Planets

Much has been happening these days, concerning the planets, that is. MESSENGER found a lot of what Mars is like, needless to mention Dawn's secrets from Vesta. Mars and Venus have some stories of their own to tell, again, let alone Uranus. Ever since the beginning when MESSENGER started spewing our information about Mars, much more was happening than I though; nothing is of the sort redundant - the planets can never lie! (Although this is not in the least a comprehensive study of each of the planet's latest 'whereabouts,' this article does bring forth the best of each planet.)

MESSENGER Spreads the Real Mercury

Six months have gone by since MESSENGER was put into orbit around Mercury, and has finished a set of orbits that have been necessary for astronomers to learn more about this baked planet. Sky & Telescope write this about Mars: "its exterior bears only slight geochemical resemblance to the outer layer of Mars and to the seafloor crust on Earth and none at all to the Moon's low-density, metal-poor crust. Instead, the combination of a high magnesium-to-silicon ratio and an abundance of the 'volatile' rock-forming elements sodium, potassium, and sulfur make Mercury unique among the terrestrial worlds."

There are many radioactive isotopes in the crust, as MESSENGER has found potassium and uranium to name a few. MESSENGER would not have found these foundational elements if not for the strong gamma ray flow they produced - quite amazing for Mercury. But, what really shocked astronomers was the core of this sullen planet. It takes up three-fourths the diameter of the planet (and nearly half Mercury's entire volume!), and is very metallic, to leave alone to the fact that the surface is very low in metallics (specifically iron). This view changed the entire way astronomers now thing about this planet - you can read and see more at MESSENGER's website, where feeds of images report back to earth daily.

Venus' New Ozone Layer

"The European Space Agency's Venus Express spacecraft has discovered an ozone layer high in the atmosphere of Venus," Science Daily tells us. Now we know that like earth, Venus too has an ozone layer; maybe this is to blame for the cloudy atmosphere? Although astronomers aren't sure of it yet, they are hoping this may lead them to finding life on other planets, which is rather amazing to note, considering how Venus Express made this fascinating discovery. "Venus Express made the discovery while watching stars seen right at the edge of the planet set through its atmosphere. Its SPICAV instrument analysed the starlight, looking for the characteristic fingerprints of gases in the atmosphere as they absorbed light at specific wavelengths."

It's a very incredible thing that Venus Express could see Venus occult stars, and then noticing that they weren't fully occulted! (they could still be seen through the atmosphere). This is what astronomers have been waiting for, becasue it may show us how they can see if there is life on other planets - the presence of ozone. We now know that three planets in the solar system block the powerful rays of radiation the Sun emits, earth, Mars, and now Venus. Through the different chemicals, astrobiologists believe that this (simultaneous) presence of those different chemicals, respectively oxygen, carbon dioxide, etc., may tell us if there could be life on a planet.

"This ozone detection tells us a lot about the circulation and the chemistry of Venus' atmosphere" says Håkan Svedhem, ESA Project Scientist for the Venus Express mission. "Beyond that, it is yet more evidence of the fundamental similarity between the rocky planets, and shows the importance of studying Venus to understand them all."

Mars' Supersaturated Water Vapor: the Red Planet has Water After All!

European Space Agency's Mars Express spacecraft (I presume it's twin is European Space Agency's Venus Express spacecraft, above) has found water on Mars. Although this is a little too bluntly stated, the spacecraft does show us that there is supersaturated water on the planet, in it's atmosphere, respectively. To define things clearer, "supersaturated" is the past participle (or as us Latinists would call it the 'perfect passive participle') of the verb, to "supersaturate" and is defined from Merriam-Webster, "to increase the concentration of (a solution) beyond saturation point," or in a more astronomical sense, "water that is suspended in Mars' atmosphere, with increased concentration beyond the saturation point."

Hypothetical water transport in the Martian atmosphere

You may ask, how can this be? To show correlation, on earth, water vapor in the atmosphere condenses when the temperature is lower than the standard dew-point. When the atmosphere is so saturated with all this condensed water attaching to dust particles (which make it heavier), it rains. This is not what happens on Mars. Science Daily writes, "condensation may sometimes be much slower, especially when particles and dust are scarce. Unable to condense, the excess water vapor therefore remains in the gaseous state: this is known as supersaturation. Until now, it was assumed that this phenomenon could not occur in the Martian atmosphere, although this had never been proved."

(Hence, later on, Science Daily writes that this hypothesis needs revising, but is a good start to this never-ending debate: does Mars have water, (or more spontaneously) life!?)

As we reminisce on the planets, astronomers look now at Mercury's formation in a different way, Venus' atmosphere may help them find more life, and so might the "water vapor" on Mars. Although nothing big happens with Saturn, Neptune, Pluto (and/or Ceres & Eris), we will start some Jovian transits soon, respectively on Jupiter... Uranus has another story as well. Astronomers think that Uranus' tilt was casued by a different way...you can read here. (It is written in an evolutionary perspective).

(Credit: Lawrence Sromovsky, (Univ. Wisconsin-Madison), Keck Observatory)

Events for the Week 08/20 through 08/27

From our past weeks of same-old events, we have now decided to do events differently...from weekly viewings, to a Solar-System events Calendar, and from a planet observation line, to a section. Be amazed and observe!

SOLAR-SYSTEM EVENTS FOR THE WEEK OF 08/20 THROUGH 08/27, 2011.

19 Aug 2011 01:03:35 Aphelion of Asteroid 2 Pallas, 3.41195 AU from Sun

20 Aug 2011 09:51:38 Conjunction of Jupiter with the Moon, 4.6°

21 Aug 2011 05:45:32 (Quebec, Canada) Stellar Occultation of Delta Aries*^

21 Aug 2011 21:54:29 Last Quarter

22 Aug 2011 04:00:00 Moon Conjunction with the Pleiades, 4°

22 Aug 2011 06:36:32 (Washington DC) Stellar Occultation 37 Taurus*^

22 Aug 2011 09:21:49 Closest Approach of Neptune, 28.99519 AU from Earth

22 Aug 2011 23:25:59 Opposition of Neptune, 7.8m*

23 Aug 2011 12:19:52 Max. South Declination of the Moon, 23.1°

23 Aug 2011 17:23:27 Descending Knot Passage of the Moon

25 Aug 2011 12:38:46 Conjunction of Mars with the Moon, 2.6°

26 Aug 2011 04:04:34 Mercury stationary: getting prograde

27 Aug 2011 04:15:07 Max. South Declination of Jupiter, 13.6°

27 Aug 2011 23:32:17 Conjunction of Mercury with the Moon, 2.4°

(All times and dates are UT (Universal Time). *This is a major event. ^There will be a post published approx. 1-2 days event occurs.)

SPECIAL VIEWINGS FOR THE WEEK OF 08/20 THROUGH 08/27, 2011.
MOON & PLEIADES CONJUNCTION - Just after the moon is at last quarter, shortly before midnight, the moon will just be about four degrees away from the Pleiades, and will be a remarkable sight: a half lit moon with a cluster not very far away. Jupiter will also conjunct tonight, giving us something like this:

 OR

NEPTUNE OPPOSITION - On the night that Neptune is at opposition, astronomers and many other observers will be viewing this distant world at its brightest. At magnitude 7.8 (technically 7.78), Neptune is brighter than its darkest mag 8.02. It will be in the sky the highest at 1 am, but you'll be able to see it around 10 pm. To help locate Neptune, try looking for Iota Aquarii, just 1.6 degrees due south. Remember Neptune's birthday?...

DAWN & VESTA - as NASA probe Dawn is circling the planet, Vesta recently passed opposition and was a great target for many observers August 5. But, still it remains bright and you too can view the protoplanet if you have binoculars, telescope, etc. Come to our Minor Planets Viewing Page, and look under the header titled: "Viewing 1 Ceres and 4 Vesta through the rest of 2011. There is a nice dissertation on how to view them, thanks to Sky&Telescope.

Below is the sky for August 25-27. 

PLANET VIEWINGS FOR THE WEEK OF 08/20 THROUGH 08/27, 2011.


Mercury - (NV)* Hidden in the Sun's glare
Venus - (NV) Hidden in the Sun's glare
Mars - (N) magnitude +1.4; constellation: Gemini; up around 2am EDT

Jupiter - (N & D) magnitude -2.6; constellation: south Aires; rises at 11pm, and sets as the Sun rises. Best to view around 1am.
Saturn - (E & N) magnitude +0.9; constellation: Virgo; sinking into the evening, earlier each night.
Uranus - (E & N) magnitude +5.8; constellation: in the Circlet of Pisces
Neptune - (E & N) magnitude +7.78 (opposition this week!); constellation: Aquarius. Both Uranus and Neptune are high before midnight.
Pluto - (N) magnitude +14.0 in Sagittarius.
Minor Planets - come to this page.

*(E) Evening, (N) Night, (D) Dawn, (NV) Not Visible.
Have a great viewing this week!!