The Satellites Of Jupiter

THE SATELLITES OF JUPITER ROBERTO BARTALI ABSTRACT In this project I will investigate the appearance and the motion of the satellites of Jupiter. I decide to start “from scratch”, as my knowledge of the Jovian System were almost cero, as for Galileo four centuries ago. My goal is the identification of each satellite in the pictures and then measure the position of each one and then, computing the orbital period to make some prediction of their positions in the near future. The reader can learn the basics of each satellite, how to collect and organize observational data and how to reduce data using a little of mathematics. INTRODUCTION

Figure 1 Galilean satellites from Earth

The purpose of this project is the determination of the orbits of the four major satellites of Jupiter called Galilean in honor to its discoverer, the Italian scientist Galileo Galilei in January 1610. As a complement, I will explain, briefly, the characteristics of them and I will also give the latest orbital data. For clarity reason I will first introduce the reader with each satellite, giving the most interesting and important physical data of it and its orbital characteristics, all complemented with some images rendering a better idea of what I am writing. The second section of this work is the presentation of the observation and the explanation of the method used to acquire and reduce data, then the way how I get the result. Late, in the conclusion I will compare published data with my measured data and discuss the difference obtained. The Jovian system is a little Solar System with Jupiter as the “Central Star” and a lot of satellites as “Planets” around. Due to the very small disk size of

them, as seen from Earth of about 1 arcsecond, (Figure 1), a few attention they collect in the past three centuries. After the Pioneer 10 spacecraft images, things changed dramatically, and they are now a priority in investigation and exploration projects for the near future together with Mars. Figure 2 The Galilean satellites. From left to right: Io, Europa, Ganymede, Callisto. Galileo spacecraft images

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GENERAL DESCRIPTION OF SATELLITES Each of the four satellites came from the same nebula around Jupiter, but they appears as worlds completely different one from each other (Figure 2). Detailed analysis of each one reveals their common nature and it is clear that the difference are because of the interaction between themselves and Jupiter. The two inner (Io and Europa) are denser than the other two (Ganymede and Callisto) because they are basically rocky and are also the smallest. The two outermost satellites are bigger and mostly icy, so less denser. All four are in synchronous rotation, as they present always the same “Face” to Jupiter, Io, Europa and Ganymede are also in resonance, that means the revolution of Io is half the period of Europa and Ganymede make a revolution in twice the time of Europa; eventually, Callisto also go in resonance some time in the future. It has to lowering its orbital period until reach a value 8 times the period of Io. Due to the resonance effect of the orbits, the tree closest Io, Europa and Ganymede, never get closer one to the other, when Europa is closer to Ganymede, Io is at the opposite side of its orbit. The Galilean satellites form a so called “regular satellite system” because their orbit are circular and placed on the equatorial plane of the planet. Now I present almost up to date information of each one in the distance from Jupiter order. IO The nearest of the Galilean is IO. If the “Hell” exist it is on this constant changing landscape satellite. The gravitational attraction and tidal heating it suffer from the interaction with Jupiter and the other satellites, generate a lot of energy and the heating of the interior and this is the reason for many active volcanoes, in fact this is the most active body of the solar system. The surface of IO is almost plain, because the lava flow cover quickly the possible impact craters and the effect of the enormous tides that breaks the surface every times. As Io cross the powerful magnetic field of Jupiter, a very high electric current is generated and every second there is a flow of one ton of matter from Io to Jupiter, some of these particles then fall in Amalthea, a closer satellite. This flow of particles generate a plasma that enlarge the magnetosphere of Jupiter, it is so wide that it is visible from Earth as a torus around the satellite. A constant electron beam of energetic level between 15 and 190 KeV maintain that cloud of ionized gas called the torus. The surface of Io is almost sulfuric, due to the volcanic activity, The ejection of lava (Figure 4) is Figure 3 Global Image of IO from Galileo Spacecraft

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violent and can reach hundreds of kilometers high and may last for weeks. From various spacecraft data, there are more than 200 calderas larger than 20 km, and many more smaller. The interior of Io is an iron core, surrounded of a silicate molten mantle and a thin silicate crust. The composition of this satellite is very similar to the Earth and the other terrestrial planets. The surface crust is composed basically of silicate lava and sulfur lava, with frosty sulfurs in places when there are not volcanic activity. The presence of an atmosphere is uncertain, if there is one, it is very thin with a pressure about one microbar or so. Only a fraction of the satellite may have some denser parts above greatest volcanoes. It seems that the atmosphere is variable with time and is directly related to volcanic activity. A very interesting fact is the presence of a Ionosphere at high altitude (up to 900 km). Previous observations and measurement fit the Ionosphere at altitudes no more than 60 km above the surface. Figure 4 Volcanic eruption on IO (Pillan Patera). Galileo Spacecraft image.

TABLE 1 Io orbital and physical data (from J.P.L., NASA)

Radius

1821.3km(+/- 0.2)

Density

3.53 g/cm3 (+/- 0.006)

Mass

8.933 x 10e22 kg (+/- 1.5)

Albedo

0.6

Semi-major axis, a

421769 km

Mean distance

421600 km

Distance from Jupiter

5.905 Jr

Orbital period

1.769138 days

Eccentricity, e

0.041

Rotational period

Synchronous

Inclination, I

0.036 degree

Gravity

0.183 G

Orbital speed

17.34 km/s

Escape velocity

2.56 km/s

Temperature Visual magnitude

135..350 K 5.0

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EUROPA This is a very interesting body, its surface is covered by ice and is highly reflective (Figure 5). Under the crust surface there is possibly an ocean of water ice. The landscape of Europa is constantly changing, due to the movement of the iced mass, the reddish color is probably because of the sulfurs coming from Io, accelerated by the Jupiter magnetosphere. The interior of Europa is composed of an iron rich core, surrounded by a silicate mantle covered by a thin iced crust and perhaps a subsurface ocean. Like Io is a denser satellite. During closer flybys of Galileo spacecraft, the instruments onboard detect some magnetic fields, but it is not well clear if it is generated by the satellite itself. The Figure 5 characteristic linear frames on the surface (figure 6) are ridges Europa Galileo Spacecraft image and fractures maybe generated by tectonics or by tidal effects, changing its direction many times. Data from Galileo wakeup the interest of scientist community and there is a space mission planned (called Europa Express) to study the satellite and the possibility of life there. Tidal heating, the presence of water, maybe liquid, and of some chemical compound compatibles for life evolution as we know (carbon based), makes Europa one of the very few places in the Solar System in which life can exist, maybe in the past or perhaps now. Galileo actually ends the exploration and the surface mapping at high resolution. Future missions have to be capable of Figure 6 Europa surface details. Galileo spacecraft image.

descending into the subsurface ocean and make experiments there and retrieve data of the composition and history of the satellite interior. There is also a thin atmosphere with oxygen.

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TABLE 2 Europa orbital and physical data (from JPL, NASA) Radius

1565 km (+/- 8)

Density

2.99 g/cm3 (+/- 0.05)

Mass

4.797 x 10e22 kg (+/- 1.5)

Albedo

0.6

Semi-major axis, a

671079 km

Mean distance

670900 km

Distance from Jupiter

9.5 Jr

Orbital period

3.55181 days

Eccentricity, e

0.0101

Rotational period

Synchronous

Inclination, I

0.464 degree

Gravity

0.135 G

Orbital speed

13.74 km/s

Escape velocity

2.02 km/s

Visual magnitude

5.3

GANYMEDE

Figure 7 Ganymede, the largest satellite known. Galileo spacecraft image.

As large as a little terrestrial planet, Ganymede is the biggest satellite of the Solar System (figure 7). The low density show that the interior is mostly liquid. The core is rocky, instead of metallic as for Io and Europa, and is about the 60% of the satellite. The mantle, composed of water or ice, is about 40% of the satellite diameter. The crust is though to be a thick layer of water ice. The interior is well differentiated, this is maybe due to the formation story, it has to be very hot and all interior material melted, so the denser rocky matter drop in, freeing the liquid and this way they are floating in the upper mantle. Like Io and Europa, Ganymede is locked in a resonance orbit, this was the cause for the heating by tidal distortion and stresses. There are a thin layer of ozone in the atmosphere, probably this is due to the destruction of water molecule by charged particles falling 5

and penetrating the surface, freeing oxygen and lead its recombination as ozone. There is a presence also of oxygen in the atmosphere. Opposite to the other two Galilean satellites, previously described, Ganymede, has many craters, proof of the old aged geological activity. The surface is not refurbished by heavy volcanism or lava flows from its interior. The surface is covered by a layer of ice or water ice, as seen in figure 8, the landscape resembles the one of Europa, with many fractures. We see two kind of Figure 8 surfaces, bright and dark, each one with its own history. Craters and fractured surface of Ganymede. The dark zones are highly covered by impact craters this Galileo spacecraft image. imply the age of this part of Ganymede, as old as the Solar System. The bright regions are less cratered because are covered by ice or water ice. The contrast from dark and bright terrain is evident and well defined like two countries separated by a river. Bright areas are filled of parallel ridges and valleys, many times crisscrossing each one creating a very complicated figures. The orbit of Ganymede is nearly circular with a very low eccentricity. The self generated magnetic field is low but strong enough to react with the stronger one of Jupiter. TABLE 3 Ganymede orbital and physical data (From JPL, NASA) Radius

2634 km (+/- 10)

Density

1.94 g/cm3 (+/- 0.02)

Mass

1.482 x 10e23 kg

Albedo

0.4

Semi-major axis, a

1,070,042.8 km

Mean distance

1,070,000 km

Distance from Jupiter

15.1 Jr

Orbital period

7.154553 days

Eccentricity, e

0.0006

Rotational period

Synchronous

Inclination, I

0.186 degree

Gravity

0.145 G

Orbital speed

10.9 km/s

Escape velocity

2.74 km/s

Temperature Visual magnitude

156 K 4.6

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CALLISTO The Galilean are unique objects and, Callisto is not an exception: it is the most cratered body of the Solar system. There is no evidence of resurfacing in the past four billion years, it seems that most of the craters was formed by impact of tiny planetesimals in the Jupiter System primordial nebula (Figure 9). The very low albedo is because of the dark surface covered by dirty ice. The core of Callisto is similar to that of Ganymede, but smaller, so the icy mantle is proportionally bigger, and its density is the lowest of the Solar System objects. Another difference with Ganymede is the poor differentiated interior. Rocks and ices in the Figure 9 Callisto cratered satellite. Galileo spacecraft image

Figure 10 Many craters on Callisto Galileo spacecraft image

interior are mixed together, because Callisto never was hot enough to completely differentiate, is has not a magnetic field also Major impact craters have a central dome, the reason is not well understood, but probably are due to warmer icy in the interior ejected when the impactor penetrated deeply. Less diameter craters have a kind of pedestal, other have long bright lines extended for hundreds of km. These long lines represent fractures in the iced surface, they are bright because the ice exposed is clean, not covered by dust and particles from meteorites and space debris. They are proof of relatively new impacts. The large distance from Jupiter, save Callisto to the locked resonance orbit, and from strong tidal interaction that may cause the heating of the interior. But mathematical models shows that in the future it has to slow down its revolution period and finally go into a locked orbit 8 times the one of Io.

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TABLE 4 Callisto orbital and physical data (From JPL, NASA) Radius

2403 km(+/- 5)

Density

1.851 g/cm3 (+/- 0.004)

Mass

1.076 x 10e23kg

Albedo

0.2

Semi-major axis, a

1,883,000 km

Distance from Jupiter

26.6 Jr

Orbital period

16.689018 days

Eccentricity, e

0.007

Rotational period

Synchronous

Inclination, I

0.281 degree

Gravity

0.127 G

Orbital speed

18.21 km/s

Visual magnitude

5.7

OBSERVATIONS I start to observe with my own telescope, a 60 mm refractor at 80x (Figure 11), but due to atmospheric condition and poor seeing, I decide to use a telescope rent service located in Arizona (USA) and operate it online by internet (*1). Most data is acquired with

Figure 11 My own 60 mm refracting efracting telescope

Figure 12 Arizona observatory with Takahashi TRC300 in first plane. Courtesy of Arnie Rosner Enterprise

a Takahashi TRC300 (Figure 12)(*2) telescope equipped with a Santa Barbara Instrument Group ST8XE (1530x1020 pixels) CCD camera (*3) cooled at –20 degree centigrade. Some images are taken with another 300 mm telescope a Mewlon300 (*4) equipped with a 1024x1024 pixel CCD camera from Dream Machine (*5), but due to the extremely sensitive CCD, the impossibility to do very short exposures and the lack of antiblooming system, I decided to use this telescope only when the main instrument was unavailable. Fortunately very few bright stars are in the field of view interfering with satellites, so I can recognize every satellite with no doubt.

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After taking some pictures I find the right exposure time to give a bright satellite image, but, ufortunately, loosing Jupiter cloud details, but the planet it is not the purpose of this project. Each image is recorded in FITS format and its data stored in an Excel ™ spreadsheet. The coordinate position of each satellite relative to the field of view and of Jupiter itself are taken using SAO DS9 image processing software, I get a free trial version for the realization of this project. After a few pictures I find a big difference in brightness of each satellite, so I decide to track each one detecting its magnitude. The orbital speed of each one is proportional to the distance to the planet, so the innermost satellite moves faster than the outermost one. Then I assign a number to each one in accord to the relative distance from planet as seen in the pictures beginning from the leftmost. Soon I could identify the farthest satellite, Callisto, as the less luminous because it moves day a day a few pixels in the field. Due to the magnitude difference it is simple to detect Ganymede, the third, because it is the brightest of the four. It moves some faster than Callisto and it go far from Jupiter, and even in the case when Callisto is closer to Jupiter than Ganymede, the magnitude difference show clearly which is one or the other. The real problem is to identify Io and Europa. The magnitude criterion works well but due to the closer position to the planet, the energy captured by the pixels in the CCD, is influenced by the brightness of the planet. The high orbital speed of Io is easy to detect, but most of the time it is in front or behind the planet. It take me almost three weeks to identify these two satellites, and in some pictures I have some doubt yet. The next step is trying to get a picture when the satellite is at maximum distance from the planet because I need to find the radius of the orbit, so when it is at that position, the movement change in direction. As more precisely that point is, more accurate will be the orbit parameter determination. If it is not possible to take a picture right when the satellite is at greatest distance, because it occurs during daylight or a bad seeing night, data interpolation can help. Fortunately I take a picture of each satellite at very close time before or after the maximum elongation. Sometimes due to the not-so-good stability of the telescope mounting and some vibration of the CCD, other times due to the brightness of the background sky and short exposure, I have to do some image processing. For this purpose I get trial versions of some Image Processing Software like IRIS (*6), CADET (*7), AVIS (*8) and, as previously mentioned, SAO DS9 (*9). All the pictures for measuring purpose are processed with IRIS and DS9, the pictures presented here are processed with AVIS and Microsoft Photo Editor™ (*10). VISUAL OBSERVATIONS

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CCD PICTURES All of this pictures are only a representative JPEG format sample, the original FITS files are available in a CD Rom.

Figure 13 File: Júpiter_1704_3 From left to right: Callisto, Europa, Io, Jupiter, Ganymede

Figure 14 File: Júpiter_1804_1 From left to right: Callisto, Europa, Io, Jupiter, Ganymede

Figure 15 File: Júpiter_2404_1 From left to right: Europa, Jupiter, Io, Ganymede, Callisto

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Figure 16 File: Júpiter_2604_3 From left to right: Ganymede, Io, Jupiter, Europa, Callisto

Figure 17 File: Júpiter_3004_1 From left to right: Ganymede, Júpiter, Europa, Io, Callisto

Figure 18 File: Júpiter_0205_1 From left to right: Callisto, Io, Jupiter, Ganymede, Europa

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Figure 19 File: Júpiter_0205_5 From left to right: Callisto, Europa, Jupiter, Io, Ganymede

Figure 20 File: Júpiter_0205_6 From Left to right: Calisto, Jupiter, Ganymede, Europa

Figure 21 File: Júpiter_0405_1 From left to right: Ganymede, Callisto, Europa, Jupiter, Io

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Figure 22 File: Júpiter_0405_2 From left to right: Ganymede, Europa, Callisto, Jupiter, Io

Figure 23 File: Júpiter_0705_2 From left to right: Io, Europs, Jupiter, Ganymede, Callisto

Figure 24 File: Júpiter_1905_1 From Left to right: Callisto, Ganymede, Europa, Io, Jupiter

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Figure 25 File: Júpiter_2405_1 From left to right: Jupiter, Io, Europa, Callisto

DATA REDUCTION

CONCLUSION

REFERENCES • • • •

Beatty J. Kelly et al, THE NEW SOLAR SYSTEM, 4th edition 1999, Cambridge University Press Freedman R., Kaufmann III, UNIVERSE, 6th edition 2002, W.H. Freeman Co. Rosino L, LEZIONI DI ASTRONOMIA, Cedam ed. 1979 Buil C., CCD ASTRONOMY, Willmann-Bell Inc. 1991

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• • • • • • •

Meeus J., ASTRONOMIA CON IL COMPUTER, Hoepli ed. 1990 Doggett L. et al, ALMANAC FOR COMPUTERS FOR THE YEAR 1978, United State Naval Observatory 1978 Morrison D., Samz J., VOYAGE TO JUPITER, SP439, NASA 1980 Leone A., IL MOTO DEI CORPI CELESTI, Franco Muzzio ed.1982 Carboni E, Ventola F., CORSO DI MATEMÁTICA Vol. III, Paccagnella ed. 1973 Wittaker Sir E., Robinson G., THE CALCULUS OF OBSERVATIONS, 4th ed. Dover, 1944 Leithold L., EL CALCULO CON GEOMETRIA ANALITICA, Harla ed., 1973

INTERNET REFERENCES Images, data and information: http://seds.lpl.arizona.edu/billa/tnp/io.html http://www.jpl.nasa.gov/galileo/status960503.html http://www.jpl.nasa.gov/galileo/moons/io.html http://www.jpl.nasa.gov/galileo/moons/europa.html http://www.jpl.nasa.gov/galileo/moons/ganymede.html http://www.jpl.nasa.gov/galileo/moons/callisto.html http://www.ifa.hawaii.edu/~sheppard/satellites/ Instrumentation: (*1) (*2) (*3) (*4) (*5) Image Processing Software (*6) www.astrosurf.com/buil (*7) (*8) www.sira.it/msb/avis.htm (*9) http://hea-www.harvard.edu/RD/ds9/ (*10) www.microsoft.com

IMAGES CREDITS Figure 1: Roberto Bartali Figure 2: http://photojournal.jpl.nasa.gov/catalog/PIA01299 Figure 3..10: http://seds.lpl.arizona.edu/billa/tnp/io.html Figure 11, 12..31: Roberto Bartali Figure 12: www.arnierosner.com

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