DOCSLIB.ORG

An Upgraded Theory for Helene, Telesto, and Calypso

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
An Upgraded Theory for Helene, Telesto, and Calypso A&A 397, 353–359 (2003) Astronomy DOI: 10.1051/0004-6361:20021518 & c ESO 2003 Astrophysics An upgraded theory for Helene, Telesto, and Calypso P. Oberti1 and A. Vienne2 1 Observatoire de la Cˆote d’Azur, BP 4229, 06304 Nice Cedex 4, France e-mail: [email protected] 2 Institut de m´ecanique c´eleste et de calcul deseph´ ´ em´erides, UMR 8028 du CNRS and Universit´e de Lille, 1 impasse de l’Observatoire, 59000 Lille, France e-mail: [email protected] Received 1 August 2002 / Accepted 10 October 2002 Abstract. A tridimensional model including the perturbation due to Saturn’s oblateness provides accurate solutions for the motions of Tethys and Dione’s Lagrangian satellites Telesto, Calypso, and Helene. Expanded around the Lagrangian points and compared to numerical simulations to check their reliabilities, the solutions are fitted to almost twenty years of data thanks to recently published observations. User-friendly compact series give Telesto, Calypso, and Helene’s positions and velocities in the mean ecliptic and equinox of J2000. Key words. planets and satellites: individual: Saturn – planets and satellites: general – celestial mechanics 1. Introduction 2. Analytical model Recently published observations of Tethys and Dione’s For the sake of convenience, computations are carried out in di- Lagrangian satellites Telesto, Calypso, and Helene (Veiga & mensionless units (Szebehely 1967). The distance between the Vieira Martins 2000; Veiga et al. 2002), give an opportunity primaries, and the sum of their masses (called µ = m/(M + m) to revisit and improve the theory of their motions to face an for the second primary and 1 µ for Saturn), are assumed to be − almost 2-decade observation time span. unity. The reference frame is a barycentric rotating frame with 6 The mass ratios Tethys/Saturn (m/M = 1.20 10− )and a rotational period of 2π/k (in dimensionless time τ), where Dione/Saturn (m/M = 1.85 10 6) ensure the stability× of the the value of k will be computed in order to insure a consistent × − Lagrangian points L4 and L5 in the Restricted Circular 3-Body model involving fixed primaries. The xy-plane contains the pri- Problem. Due to the 1:1-resonance with the companion, a satel- maries, the x-axis being located along the primaries and posi- lite around these positions shows librations in its motion re- tively oriented from Saturn toward the second primary. sulting in a tadpole-shaped orbit in a rotating reference frame. The theory will be expanded around L4. Dealing with the Expansions around the equilibrium positions provided accurate symmetrical point L5 requires only slight modifications indi- solutions in the bidimensional case (Deprit & Rom 1970). cated in Sect. 7. γ √3 Pointed out as a significant perturbation by numerical sim- With γ = 1 2µ, L4 is located at the point , , 0 . − 2 2 ulations, Saturn’s oblateness (through the first zonal coefficient Let x, y, z be the satellite’s Cartesian coordinates and Px, of Saturn’s potential developed in spherical harmonics) was Py, Pz their conjugate variables in the barycentric rotating then introduced in the model by addition of perturbing terms frame. The Hamiltonian of the motion is: in the second and following orders of the previously expanded 1 non-perturbed Hamiltonian (Oberti 1990). H = P2 + P2 + P2 k xP yP 2 x y z y x This new theory, now developed in a tridimensional con- − − 1 µ J 3z2 µ text, deals with the perturbation at the uppermost level of the − 1 + 1 , − r r2 − r2 − ∆ expansion, the quadratic part of the Hamiltonian (generally " !# called H0), improving the convergence of the solution and of- where: fering an explicit generalization suitable for other studies. Moreover, the model could prove useful for the analysis of r = (x + µ)2 + y2 + z2, the CASSINI space probe’s accurate observations of these faint q satellites that should be obtained during its nearing exploration ∆= (x + µ 1)2 + y2 + z2, of the Saturnian system. − q 1 2 Send offprint requests to: P. Oberti, and J = 2 J2re stands for half the first Saturnian zonal harmonic e-mail: [email protected] coefficient J2 (Campbell & Anderson 1989) multiplied by the Article published by EDP Sciences and available at http://www.aanda.org or http://dx.doi.org/10.1051/0004-6361:20021518 354 P. Oberti and A. Vienne: An upgraded theory for Helene, Telesto, and Calypso square of Saturn’s equatorial radius (re = 60 268 km), appro- where: priately scaled. The value of J, depending then on the selected 4 4 2 2 2 second primary, is 3.4088 10− for Tethys and 2.0780 10− r = (ξ + S 1) + (η + C1) + ζ , × × for Dione. q L is no longer an equilibrium position (Sharma & Subba 2 2 2 4 ∆= (ξ + S 2) + (η + C2) + ζ , Rao 1976). The conditions: q γ √3 S √3 + C C √3 S x = ,y= , z = 0, x˙ = 0, y˙ = 0, z˙ = 0, S 1 = , C1 = − , 2 2 2 2 lead to: S √3 C C √3 + S γ 3J 1 + γ S 2 = − , C2 = P˙ = k2 1 , 2 2 · x − 2 − 2 2 ! 2 √3 3J √3 1 + γ 3. Local solutions P˙y = k 1 , − 2 − 2 2 Using, for example, the software Mathematica, we expand the ! P˙z = 0, functions of the coordinates in the vicinity of ξ = η = ζ = 0: where dots stand for derivation with respect to the dimension- 1 1 = 1 S ξ C η + 3S 2 1 ξ2 less time. Canceling the accelerations would require two differ- r − 1 − 1 2 1 − ent values of k: 3 1 2 2 1 2 + S 1C1ξη + 3 C1 1 η ζ + , 1 + γ 1 + γ 2 2 − − 2 ··· k1 = 1 + 3J , k2 = 1 + 3J 2 2γ · s ! s ! 1 3 = 1 3S ξ 3C η + 5S 2 1 ξ2 The value of k is in fact computed in order to immobilize r3 − 1 − 1 2 1 − the second primary, also perturbed by Saturn’s oblateness. The 15 3 3 + S C ξη + 5 C2 1 η2 ζ2 + , point (1, 0) (or any point on the unit circle) turns into an equi- 2 1 1 2 1 − − 2 ··· librium position for the Hamiltonian: 1 5 1 2 2 1 J 2 2 K = P + P k xP yP 1 + , = 1 5S 1ξ 5C1η + 7S 1 1 ξ 2 x y − y − x − r r2 r5 − − 2 − 35 5 5 where: + S C ξη + 7 C2 1 η2 ζ2 + , 2 1 1 2 1 − − 2 ··· r = x2 + y2, and similar expressions for ∆ with the second index. Then, scal- when:q ing with respect to the total power p + q + r of the monomi- als ξpηqζr, the Hamiltonian can be expanded up to an arbitrary k = √1 + 3J. order n. With k2 > k > k1, L4 becomes an almost-equilibrium position: Neglecting the remainder: 3J 3J √3 1 1 P˙ x = µ, P˙y = µ, P˙z = 0. H ) = H + H + H + + H , − 2 2 (n 0 1 2 2 ··· n! n A first canonical transformation defines a coordinate system in H containing the terms where p + q + r 2. 0 ≤ the vicinity of L4: Defining: γ √3 3 1 + γ 3 1 + γ x = + Cξ S η, Px = k + CPξ SPη, α = 1 + 5J ,β= γ + 5J , 2 − − 2 − 4 2 4 2 √3 γ " !# " !# y = + S ξ + Cη, Py = k + SPξ + CPη, the substitutions into H lead to: 2 2 0 z = ζ, Pz = Pζ, 1 2 2 2 H0 = Pξ + Pη + Pζ k ξPη ηPξ where S and C are the sine and cosine of a rotation devoted 2 − − 1 γ to removing a ξη-term in the expression of the zero-order 3J − (S ξ + C η) − 2 2 2 Hamiltonian below. This kind of coordinate system is gener- ! ally referred to as the normal frame at an equilibrium position. 1 + γ ξ2 α 1 + 2S 2 + 2β √3SC 1 3J Applying the transformation turns the Hamiltonian into: − − − 2 2 " !# 1 2 2 2 2 2 1 + γ η H = Pξ + Pη + Pζ k ξPη ηPξ α 1 + 2C 2β √3SC 1 3J 2 − − − − − − 2 2 " !# 1 2 1 2 k Cγ + S √3 ξ + k S γ C √3 η 2αSC+ β √3 C2 S 2 ξη −2 2 − − − 1 + γ J 3 ζ2 1 γ 1 + γ ζ2 1 + 1 − , 1 9J − 2r r2 − r2 − 2∆ − − − 2 2 · " !# " !# P. Oberti and A. Vienne: An upgraded theory for Helene, Telesto, and Calypso 355 The terms in ξ and η, resulting from the fact that L4 is not ex- The required expression for H0 and the canonicity of the trans- actly an equilibrium position, are small because J (1 γ) /2 = formation provide ten relations leading to: − Jµ. At the precision required by the observations, they can 1 1 safely be ignored, transforming this way the Lagrangian a13 = , a14 = , √v2 2kv a √a + 2ku u2 point L4 in an actual equilibrium position for the theory. − − − Removing the ξη-term leads to: ω1 ω2 a21 = − , a22 = , √u2 + 2ku b √b 2kv v2 − − − δ 1 δ + 1 β 2 a = ua , a = va , a = va , a = ua , S = − , C = ,δ= 1 + 3 , 31 21 32 22 43 13 44 14 − 2 δ 2 δ s α r r where: and H0 finally reads: b a + d b a d u = − ,v= − − 1 4k 4k · H = P2 + P2 + P2 0 2 ξ η ζ Finally, the canonical transformation: a 2 b 2 c 2 2I k ξPη ηPξ ξ η ζ , Q = 1 sin ϕ , P = 2I ω cos ϕ , − − − 2 − 2 − 2 1 ω 1 1 1 1 1 r 1 where: p 2I Q = 2 sin ϕ , P = 2I ω cos ϕ , 1 3 1 + γ 5 2 ω 2 2 2 2 2 a = 1 δ + 3J 3 δ , r 2 2 − 2 2 − 2 p " ! !# 2I3 Q3 = sin ϕ3, P3 = 2I3ω3 cos ϕ3 1 3 1 + γ 5 ω3 b = 1 + δ + 3J 3 + δ , r 2 2 2 2 p " ! !# leads to: 1 + γ H0 = I1ω1 I2ω2 + I3ω3.
Load more

Recommended publications
  • Arxiv:1912.09192V2 [Astro-Ph.EP] 24 Feb 2020
    Draft version February 25, 2020 Typeset using LATEX preprint style in AASTeX62 Photometric analyses of Saturn's small moons: Aegaeon, Methone and Pallene are dark; Helene and Calypso are bright. M. M. Hedman,1 P. Helfenstein,2 R. O. Chancia,1, 3 P. Thomas,2 E. Roussos,4 C. Paranicas,5 and A. J. Verbiscer6 1Department of Physics, University of Idaho, Moscow, ID 83844 2Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca NY 14853 3Center for Imaging Science, Rochester Institute of Technology, Rochester NY 14623 4Max Planck Institute for Solar System Research, G¨ottingen,Germany 37077 5APL, John Hopkins University, Laurel MD 20723 6Department of Astronomy, University of Virginia, Charlottesville, VA 22904 ABSTRACT We examine the surface brightnesses of Saturn's smaller satellites using a photometric model that explicitly accounts for their elongated shapes and thus facilitates compar- isons among different moons. Analyses of Cassini imaging data with this model reveals that the moons Aegaeon, Methone and Pallene are darker than one would expect given trends previously observed among the nearby mid-sized satellites. On the other hand, the trojan moons Calypso and Helene have substantially brighter surfaces than their co-orbital companions Tethys and Dione. These observations are inconsistent with the moons' surface brightnesses being entirely controlled by the local flux of E-ring par- ticles, and therefore strongly imply that other phenomena are affecting their surface properties. The darkness of Aegaeon, Methone and Pallene is correlated with the fluxes of high-energy protons, implying that high-energy radiation is responsible for darkening these small moons. Meanwhile, Prometheus and Pandora appear to be brightened by their interactions with nearby dusty F ring, implying that enhanced dust fluxes are most likely responsible for Calypso's and Helene's excess brightness.
    [Show full text]
  • Cassini Update
    Cassini Update Dr. Linda Spilker Cassini Project Scientist Outer Planets Assessment Group 22 February 2017 Sols%ce Mission Inclina%on Profile equator Saturn wrt Inclination 22 February 2017 LJS-3 Year 3 Key Flybys Since Aug. 2016 OPAG T124 – Titan flyby (1584 km) • November 13, 2016 • LAST Radio Science flyby • One of only two (cf. T106) ideal bistatic observations capturing Titan’s Northern Seas • First and only bistatic observation of Punga Mare • Western Kraken Mare not explored by RSS before T125 – Titan flyby (3158 km) • November 29, 2016 • LAST Optical Remote Sensing targeted flyby • VIMS high-resolution map of the North Pole looking for variations at and around the seas and lakes. • CIRS last opportunity for vertical profile determination of gases (e.g. water, aerosols) • UVIS limb viewing opportunity at the highest spatial resolution available outside of occultations 22 February 2017 4 Interior of Hexagon Turning “Less Blue” • Bluish to golden haze results from increased production of photochemical hazes as north pole approaches summer solstice. • Hexagon acts as a barrier that prevents haze particles outside hexagon from migrating inward. • 5 Refracting Atmosphere Saturn's• 22unlit February rings appear 2017 to bend as they pass behind the planet’s darkened limb due• 6 to refraction by Saturn's upper atmosphere. (Resolution 5 km/pixel) Dione Harbors A Subsurface Ocean Researchers at the Royal Observatory of Belgium reanalyzed Cassini RSS gravity data• 7 of Dione and predict a crust 100 km thick with a global ocean 10’s of km deep. Titan’s Summer Clouds Pose a Mystery Why would clouds on Titan be visible in VIMS images, but not in ISS images? ISS ISS VIMS High, thin cirrus clouds that are optically thicker than Titan’s atmospheric haze at longer VIMS wavelengths,• 22 February but optically 2017 thinner than the haze at shorter ISS wavelengths, could be• 8 detected by VIMS while simultaneously lost in the haze to ISS.
    [Show full text]
  • The Orbits of Saturn's Small Satellites Derived From
    The Astronomical Journal, 132:692–710, 2006 August A # 2006. The American Astronomical Society. All rights reserved. Printed in U.S.A. THE ORBITS OF SATURN’S SMALL SATELLITES DERIVED FROM COMBINED HISTORIC AND CASSINI IMAGING OBSERVATIONS J. N. Spitale CICLOPS, Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301; [email protected] R. A. Jacobson Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099 C. C. Porco CICLOPS, Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301 and W. M. Owen, Jr. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099 Received 2006 February 28; accepted 2006 April 12 ABSTRACT We report on the orbits of the small, inner Saturnian satellites, either recovered or newly discovered in recent Cassini imaging observations. The orbits presented here reflect improvements over our previously published values in that the time base of Cassini observations has been extended, and numerical orbital integrations have been performed in those cases in which simple precessing elliptical, inclined orbit solutions were found to be inadequate. Using combined Cassini and Voyager observations, we obtain an eccentricity for Pan 7 times smaller than previously reported because of the predominance of higher quality Cassini data in the fit. The orbit of the small satellite (S/2005 S1 [Daphnis]) discovered by Cassini in the Keeler gap in the outer A ring appears to be circular and coplanar; no external perturbations are appar- ent. Refined orbits of Atlas, Prometheus, Pandora, Janus, and Epimetheus are based on Cassini , Voyager, Hubble Space Telescope, and Earth-based data and a numerical integration perturbed by all the massive satellites and each other.
    [Show full text]
  • The Gravity Field and Interior Structure of Dione
    The gravity field and interior structure of Dione Marco Zannoni1*, Douglas Hemingway2,3, Luis Gomez Casajus1, Paolo Tortora1 1Dipartimento di Ingegneria Industriale, Università di Bologna, Forlì, Italy 2Department of Earth & Planetary Science, University of California Berkeley, Berkeley, California, USA 3Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington, DC, USA *Corresponding author. Abstract During its mission in the Saturn system, Cassini performed five close flybys of Dione. During three of them, radio tracking data were collected during the closest approach, allowing estimation of the full degree-2 gravity field by precise spacecraft orbit determination. 6 The gravity field of Dione is dominated by J2 and C22, for which our best estimates are J2 x 10 = 1496 ± 11 and 6 C22 x 10 = 364.8 ± 1.8 (unnormalized coefficients, 1-σ uncertainty). Their ratio is J2/C22 = 4.102 ± 0.044, showing a significative departure (about 17-σ) from the theoretical value of 10/3, predicted for a relaxed body in slow, synchronous rotation around a planet. Therefore, it is not possible to retrieve the moment of inertia directly from the measured gravitational field. The interior structure of Dione is investigated by a combined analysis of its gravity and topography, which exhibits an even larger deviation from hydrostatic equilibrium, suggesting some degree of compensation. The gravity of Dione is far from the expectation for an undifferentiated hydrostatic body, so we built a series of three-layer models, and considered both Airy and Pratt compensation mechanisms. The interpretation is non-unique, but Dione’s excess topography may suggest some degree of Airy-type isostasy, meaning that the outer ice shell is underlain by a higher density, lower viscosity layer, such as a subsurface liquid water ocean.
    [Show full text]
  • The Sources and Dynamical Mechanisms Responsible for Differing Regolith Cover on Satellites Embedded in Saturn’S E Ring
    50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132) 2790.pdf WHY SO MUTED? THE SOURCES AND DYNAMICAL MECHANISMS RESPONSIBLE FOR DIFFERING REGOLITH COVER ON SATELLITES EMBEDDED IN SATURN’S E RING. S. J. Morrison1 and S. G. Zaidi1, 1Center for Exoplanets and Habitable Worlds, 525 Davey Laboratory, The Pennsylvania State Uni- versity, University Park, PA, 16802, USA ([email protected]) Introduction: Saturn’s E ring, sourced primarily by resonances with Tethys and Dione. We also numerically cryovolcanic material erupted from Enceladus, extends integrate E ring particle trajectories including these outward from Enceladus’ orbit to beyond Dione’s orbit forces using the integrator package REBOUND and RE- [1][2]. Amongst the satellites embedded in this ring, BOUNDx [10-12]. We use initial orbits for the Satur- there are observed differences in regolith cover. In par- nian System from [13] and estimated masses for the tad- ticular, the small satellites Telesto, Calypso, Helene, pole moons from [7] that assume an average density of and Polydeuces have more muted surfaces, an absence 0.6 g/cc. We include Saturn’s gravitational harmonics of small craters, and downslope transport of regolith up to J4 and plasma drag forces arising from collisions within large craters than observed on Tethys and Dione with co-rotating O+ ions, the primary constituent of on similar distance scales [3][4]. However, these small plasma in the region of the Saturnian system of interest. satellites orbit in a different dynamical environment: Results: To provide insight into whether outwardly Telesto and Calypso are on leading and trailing tadpole drifting E ring particles should accumulate in the 1:1 orbits about the L4 and L5 Lagrange points in the co- resonances with Tethys and Dione, we compare the orbital 1:1 mean motion resonance with Tethys, respec- timescale for a particle of a given size to drift across the tively, as are Helene and Polydeuces tadpoles of Dione maximum libration width of this resonance to the corre- [e.g.
    [Show full text]
  • Observing the Universe
    ObservingObserving thethe UniverseUniverse :: aa TravelTravel ThroughThrough SpaceSpace andand TimeTime Enrico Flamini Agenzia Spaziale Italiana Tokyo 2009 When you rise your head to the night sky, what your eyes are observing may be astonishing. However it is only a small portion of the electromagnetic spectrum of the Universe: the visible . But any electromagnetic signal, indipendently from its frequency, travels at the speed of light. When we observe a star or a galaxy we see the photons produced at the moment of their production, their travel could have been incredibly long: it may be lasted millions or billions of years. Looking at the sky at frequencies much higher then visible, like in the X-ray or gamma-ray energy range, we can observe the so called “violent sky” where extremely energetic fenoena occurs.like Pulsar, quasars, AGN, Supernova CosmicCosmic RaysRays:: messengersmessengers fromfrom thethe extremeextreme universeuniverse We cannot see the deep universe at E > few TeV, since photons are attenuated through →e± on the CMB + IR backgrounds. But using cosmic rays we should be able to ‘see’ up to ~ 6 x 1010 GeV before they get attenuated by other interaction. Sources Sources → Primordial origin Primordial 7 Redshift z = 0 (t = 13.7 Gyr = now ! ) Going to a frequency lower then the visible light, and cooling down the instrument nearby absolute zero, it’s possible to observe signals produced millions or billions of years ago: we may travel near the instant of the formation of our universe: 13.7 By. Redshift z = 1.4 (t = 4.7 Gyr) Credits A. Cimatti Univ. Bologna Redshift z = 5.7 (t = 1 Gyr) Credits A.
    [Show full text]
  • 1247 (Created: Wednesday, April 14, 2021 at 1:32:54 PM Eastern Standard Time) - Overview
    JWST Proposal 1247 (Created: Wednesday, April 14, 2021 at 1:32:54 PM Eastern Standard Time) - Overview 1247 - Saturn Cycle: 1, Proposal Category: GTO INVESTIGATORS Name Institution E-Mail Dr. Leigh Fletcher (PI) (ESA Member) University of Leicester [email protected] Matthew Tiscareno (CoI) SETI Institute [email protected] Dr. Stefanie N. Milam (CoI) (US Admin CoI) NASA Goddard Space Flight Center [email protected] OBSERVATIONS Folder Observation Label Observing Template Science Target Saturn Observations 301 System NIRCam 1 NIRCam Imaging (637) SATURN-CENTRE 312 Pandora NIRSpec NIRSpec IFU Spectroscopy (617) PANDORA 314 Epimetheus NIRSpec NIRSpec IFU Spectroscopy (611) EPIMETHEUS 318 Pallene NIRSpec NIRSpec IFU Spectroscopy (633) PALLENE 319 Telesto NIRSpec NIRSpec IFU Spectroscopy (613) TELESTO 341 System NIRCam 2 NIRCam Imaging (637) SATURN-CENTRE 665 Saturn Background MI MIRI Medium Resolution Spectroscopy (2) SATURN-OFFSET RI 330 Saturn Rings MIRI MIRI Medium Resolution Spectroscopy (600) SATURN-RINGS 666 Saturn North Pole MIR MIRI Medium Resolution Spectroscopy (634) SATURN-75N I 667 Saturn 45N MIRI MIRI Medium Resolution Spectroscopy (635) SATURN-45N 668 Saturn 15N MIRI MIRI Medium Resolution Spectroscopy (636) SATURN-15N ABSTRACT 1 JWST Proposal 1247 (Created: Wednesday, April 14, 2021 at 1:32:54 PM Eastern Standard Time) - Overview Reconnaissance of the Saturn system with NIRCam will test the capacity of JWST to detect faint moons around bright planets, via comparison to the faint targets already detected by Cassini, which will be useful for ERS and GO observers of other planetary systems. Furthermore, the NIRCam images should be sensitive to discovering new moons significantly fainter than any that Cassini has discovered.
    [Show full text]
  • Moons of Saturn
    National Aeronautics and Space Administration 0 300,000,000 900,000,000 1,500,000,000 2,100,000,000 2,700,000,000 3,300,000,000 3,900,000,000 4,500,000,000 5,100,000,000 5,700,000,000 kilometers Moons of Saturn www.nasa.gov Saturn, the sixth planet from the Sun, is home to a vast array • Phoebe orbits the planet in a direction opposite that of Saturn’s • Fastest Orbit Pan of intriguing and unique satellites — 53 plus 9 awaiting official larger moons, as do several of the recently discovered moons. Pan’s Orbit Around Saturn 13.8 hours confirmation. Christiaan Huygens discovered the first known • Mimas has an enormous crater on one side, the result of an • Number of Moons Discovered by Voyager 3 moon of Saturn. The year was 1655 and the moon is Titan. impact that nearly split the moon apart. (Atlas, Prometheus, and Pandora) Jean-Dominique Cassini made the next four discoveries: Iapetus (1671), Rhea (1672), Dione (1684), and Tethys (1684). Mimas and • Enceladus displays evidence of active ice volcanism: Cassini • Number of Moons Discovered by Cassini 6 Enceladus were both discovered by William Herschel in 1789. observed warm fractures where evaporating ice evidently es- (Methone, Pallene, Polydeuces, Daphnis, Anthe, and Aegaeon) The next two discoveries came at intervals of 50 or more years capes and forms a huge cloud of water vapor over the south — Hyperion (1848) and Phoebe (1898). pole. ABOUT THE IMAGES As telescopic resolving power improved, Saturn’s family of • Hyperion has an odd flattened shape and rotates chaotically, 1 2 3 1 Cassini’s visual known moons grew.
    [Show full text]
  • Rev 214 SOST Segment Titan Rainclouds 2015-100T20:13:00-102T20:13:00 Rhea No Targeted Flybys; Highlights
    Rev 214 SOST Segment Titan rainclouds 2015-100T20:13:00-102T20:13:00 Rhea No targeted flybys; Highlights: CIRS and ISS observation (16.5hours) starting at 101T05:00 of Tethys to image and derive composition of poorly observed regions and to characterize its spatially resolved thermal inertia, “Pacman” shape, and global energy balance. UVIS observation of trailing side to understand UV absorber; ~54, 000 km C/A at moderate solar Tethys (above); Dione (below) phase angles (~30-50°); VIMS ridealongs; 3 PIEs ORS observations of Dione at ~110,000 km focusing on bright wispy streaks. CIRS PDT Design Two observations of Paaliaq to determine rotation state and pole position (another observation later in sequence) Helene The Tethys observations will focus on the above area. Iapetus observing campaign (No PIES) Rhea On rev 213-214 (XD Segment) there are five distant (~1 million km) ORS Iapetus observations designed to cover regions that are poorly imaged. The solar phase angle is ~40 degrees throughout the observing period, which is ideal for mapping geologic features. Composition and thermal properties will also be studied. Tethys The observations extend from 2015- 085T21:52-091T20:17 and cover the N. trailing (bright) hemisphere. ISS is CIRS PDT Design prime except for one observation, which is CIRS prime. Iapetus is about 240 ISS pixels at 6 VIMS (hi-res) pixels. Iapetus Helene This part of the campaign will focus on the above area. Plume Observation in S88 (not a PIE) XD_214_215 Rhea ISS_214EN_PLMHPMR001_PRIME 2015-103T23:10-104T09:00 VIMS and UVIS in ridealong; pointing requirements (must point within 15 ° of Saturn center ; added to spreadsheet) Science Goals:recap To obtain different viewing geometries which better characterize plume morphology, Tethys particle size, and the relationship between plumes and surface features and thermal anomalies.
    [Show full text]
  • Arxiv:1603.07071V1
    Dynamical Evidence for a Late Formation of Saturn’s Moons Matija Cuk´ Carl Sagan Center, SETI Institute, 189 North Bernardo Avenue, Mountain View, CA 94043 [email protected] Luke Dones Southwest Research Institute, Boulder, CO 80302 and David Nesvorn´y Southwest Research Institute, Boulder, CO 80302 Received ; accepted Revised and submitted to The Astrophysical Journal arXiv:1603.07071v1 [astro-ph.EP] 23 Mar 2016 –2– ABSTRACT We explore the past evolution of Saturn’s moons using direct numerical in- tegrations. We find that the past Tethys-Dione 3:2 orbital resonance predicted in standard models likely did not occur, implying that the system is less evolved than previously thought. On the other hand, the orbital inclinations of Tethys, Dione and Rhea suggest that the system did cross the Dione-Rhea 5:3 resonance, which is closely followed by a Tethys-Dione secular resonance. A clear implica- tion is that either the moons are significantly younger than the planet, or that their tidal evolution must be extremely slow (Q > 80, 000). As an extremely slow-evolving system is incompatible with intense tidal heating of Enceladus, we conclude that the moons interior to Titan are not primordial, and we present a plausible scenario for the system’s recent formation. We propose that the mid-sized moons re-accreted from a disk about 100 Myr ago, during which time Titan acquired its significant orbital eccentricity. We speculate that this disk has formed through orbital instability and massive collisions involving the previous generation of Saturn’s mid-sized moons. We identify the solar evection resonance perturbing a pair of mid-sized moons as the most likely trigger of such an insta- bility.
    [Show full text]
  • Icy Moons Highlights June 2011-August 2012
    Icy Moons Scientific Highlights June 2011-August 2012 Bonnie J. Buratti SOST Lead CHARM telecon August 28, 2012 Summary of targeted flybys Flyby Date C/A(km) Flavor Comments E14 Oct. 1, 2011 103 MAPS (INMS) E15 Oct. 19, 2011 1235 UVIS double Successful occ Nov. 6, 2011 500 RADAR On thrusters; E16 successful E17 March 27, 2012 78 MAPS (INMS) April 14, 2012 78 MAPS ORS drag – E18 VIMS data E19 May 2, 2012 77 RSS gravity One of a pair Dec. 12, 2011 100 RSS (gravity) CO2, O2 atm D3 MAPS detected by ridealong INMS D1-D3; (O2+ by CAPS previously) Scientific Highlights • Activity on Dione? • Double occultation of Enceladus plumes • First high resolution RADAR images of an icy satellite (Enceladus) • Heat detected by VIMS on Enceladus • Small satellite observations • Pacmen • Theory on colors of the satellites • Small satellite observations; Hyperion and Iapetus campaigns • Plumes galore • MAPS: Auroral hiss and electron beams on Enceladus; “Van Allen” belts and moon cavities Dione 8461 km ISS image on May 3, 2012 Activity on Dione? • There are multiple lines of evidence for some sort of recent and/or ongoing activity on Dione. • These include detection of a tenuous atmosphere by multiple instruments; MAPS observations that indicate an atmosphere or “plume” is altering the fields and particles environment; “paleo” tiger stripes; possible cryovolcanoes; and highly crystalline ice. Paul Schenk: Volcanism Smooth plains on Dione • Lower crater density • Linear grooves and scarps • Rampart craters • Anomalous crater pair: Possible volcanic vent! E15: UVIS Double Occultation 2011-292T09:22:11.57 Rhea (19 Oct 2011) 1234.8 km The main goal of this flyby was to obtain a double UVIS occultation by Enceladus of two stars in Orion’s Belt, epsilon Ori and zeta Ori, as they pass behind the plume of Enceladus.
    [Show full text]
  • PDS4 Context List
    Target Context List Name Type LID 136108 HAUMEA Planet urn:nasa:pds:context:target:planet.136108_haumea 136472 MAKEMAKE Planet urn:nasa:pds:context:target:planet.136472_makemake 1989N1 Satellite urn:nasa:pds:context:target:satellite.1989n1 1989N2 Satellite urn:nasa:pds:context:target:satellite.1989n2 ADRASTEA Satellite urn:nasa:pds:context:target:satellite.adrastea AEGAEON Satellite urn:nasa:pds:context:target:satellite.aegaeon AEGIR Satellite urn:nasa:pds:context:target:satellite.aegir ALBIORIX Satellite urn:nasa:pds:context:target:satellite.albiorix AMALTHEA Satellite urn:nasa:pds:context:target:satellite.amalthea ANTHE Satellite urn:nasa:pds:context:target:satellite.anthe APXSSITE Equipment urn:nasa:pds:context:target:equipment.apxssite ARIEL Satellite urn:nasa:pds:context:target:satellite.ariel ATLAS Satellite urn:nasa:pds:context:target:satellite.atlas BEBHIONN Satellite urn:nasa:pds:context:target:satellite.bebhionn BERGELMIR Satellite urn:nasa:pds:context:target:satellite.bergelmir BESTIA Satellite urn:nasa:pds:context:target:satellite.bestia BESTLA Satellite urn:nasa:pds:context:target:satellite.bestla BIAS Calibrator urn:nasa:pds:context:target:calibrator.bias BLACK SKY Calibration Field urn:nasa:pds:context:target:calibration_field.black_sky CAL Calibrator urn:nasa:pds:context:target:calibrator.cal CALIBRATION Calibrator urn:nasa:pds:context:target:calibrator.calibration CALIMG Calibrator urn:nasa:pds:context:target:calibrator.calimg CAL LAMPS Calibrator urn:nasa:pds:context:target:calibrator.cal_lamps CALLISTO Satellite urn:nasa:pds:context:target:satellite.callisto
    [Show full text]