Saturn's Atmosphere Studies with LOFAR

Philippe Zarka

Transcript

1. Saturn's Atmosphere Studies with LOFAR: a « pot-pourri » P. Zarka & the TKP Planet Working Group R. Courtin and the LC0_005 team J.-M. Griessmeier and the LC0_023 team
2. Saturn’s lightning commissioning observations • 2010/04/08 : (3h) incoherent sum of 10 stations, 30-78 MHz, 81 μsec x12 kHz, Stokes I, On only • 2010/12/17-18 : (16h) incoherent sum of 22 stations, 15-75 MHz, 81 μsec x12 kHz, Stokes I, Off=PSR1133 (TBB in //) • 2011/07/07-08 : (12h) coherent sum of 5 superterp stations, 20-70 MHz, 1.3 msec x12 kHz UIOWA 20100413 2010-04-08 (098) 19:00 2010-04-09 (099) 01:00 15,98 267,44 0,22 15,59 15,98 16,34 300,38 0,23 15,64 16,34 16,69 333,36 0,23 15,70 16,69 17,04 6,37 0,23 15,75 17,04 17,38 39,41 0,24 15,80 17,38 17,72 72,48 0,24 15,85 17,72 18,05 105,57 0,24 15,89 18,05 19:00 20:00 21:00 22:00 23:00 00:00 01:00 Orbit 129 R S Lon Lat LT L 2, 4, 6, 8, 10, 12, 14, 16, Frequency (Hz) 0, 2, 4, 6, 8, 10, 12, 14, dB Above Background (30%) Cassini Incoherent Stokes - I 0 10 20 30 40 50 60 seconds since 20:30:00 30 40 50 60 70 MHz dB 0.2 0.4 0.6 0.8 1.0 Incoherent Stokes - I 10 20 30 40 50 60 seconds since 20:31:00 30 40 50 60 70 MHz dB 0.2 0.4 0.6 0.8 1.0 1.2 LOFAR
3. Nb of Stations f b τ σsky 1 station 30 MHz 195 kHz 82µs 104 Jy 10 stations 30 MHz 6 MHz 20ms 37 Jy Saturn’s  lightning  @  Earth  ~  10-­‐1000  Jy   (1  Jy  =  10-­‐26  W.m-­‐2.Hz-­‐1) σsky  =  2kTsky/(  A  (bτ)1/2) with Tsky ~  1.15×108/f2.5   and  A1  Sta/on ~  48λ2/3 • 2010/04/08 : (3h) incoherent sum of 10 stations, 30-78 MHz, 81 μsec x12 kHz, Stokes I, On only • 2010/12/17-18 : (16h) incoherent sum of 22 stations, 15-75 MHz, 81 μsec x12 kHz, Stokes I, Off=PSR1133 (TBB in //) • 2011/07/07-08 : (12h) coherent sum of 5 superterp stations, 20-70 MHz, 1.3 msec x12 kHz RFI  +  SED raw  data  (6  MHz)  "On" clean  data  (6  MHz) raw  data  (195  kHz)  "~Off" Saturn’s lightning commissioning observations
4. • 2010/04/08 : (3h) incoherent sum of 10 stations, 30-78 MHz, 81 μsec x12 kHz, Stokes I, On only • 2010/12/17-18 : (16h) incoherent sum of 22 stations, 15-75 MHz, 81 μsec x12 kHz, Stokes I, 24 Mz On & 24 MHz Off (=PSR1133) (TBB in //) • 2011/07/07-08 : (12h) coherent sum of 5 superterp stations, 20-70 MHz, 1.3 msec x12 kHz 18/12/2010 03:00 11:00 SB# 17/12/2010 - SubBand 50 Time steps Intensity Saturn’s lightning commissioning observations
5. • 2010/04/08 : (3h) incoherent sum of 10 stations, 30-78 MHz, 81 μsec x12 kHz, Stokes I, On only • 2010/12/17-18 : (16h) incoherent sum of 22 stations, 15-75 MHz, 81 μsec x12 kHz, Stokes I, 24 Mz On & 24 MHz Off (=PSR1133) (TBB in //) • 2011/07/07-08 : (12h) coherent sum of 5 superterp stations, 20-70 MHz, 1.3 msec x12 kHz UIOWA 20110627 2010-12-18 (352) 00:00 2010-12-18 (352) 16:00 27,47 292,56 -0,06 20,06 27,47 26,78 33,01 -0,06 20,11 26,78 26,08 133,41 -0,07 20,18 26,08 25,35 233,76 -0,07 20,24 25,35 24,60 334,05 -0,07 20,32 24,60 23,83 74,27 -0,07 20,39 23,83 00:00 03:00 06:00 09:00 12:00 15:00 Orbit 142 R S Lon Lat LT L 2, 4, 6, 8, 10, 12, 14, 16, Frequency (Hz) 0, 5, 10, 15, 20, dB Above Background (7%) PSR 1133 in Off beam on 2010/12/18 Saturn’s lightning commissioning observations
6. • 2010/04/08 : (3h) incoherent sum of 10 stations, 30-78 MHz, 81 μsec x12 kHz, Stokes I, On only • 2010/12/17-18 : (2x8h) incoherent sum of 22 stations, 15-75 MHz, 81 μsec x12 kHz, Stokes I, 24 Mz On & 24 MHz Off (=PSR1133) (TBB in //) • 2011/07/07-08 : (2x6h) coherent sum of 5 superterp stations, 20-70 MHz, 1.3 msec x12 kHz 20 70 MHz 0 1600 sec 20 70 MHz 0 1600 sec Saturn’s lightning commissioning observations
7. • Statistical detection seems positive ... BUT ... • Unsuccessful one-to-one correlation of individual flashes seen by LOFAR and Cassini (for the moment tested on 2010/04/08), in spite of severe RFI mitigation Saturn’s lightning commissioning observations Ex: NDA observations, 14-28 MHz, 90 sec, 20 msec x 4 kHz resolutions
8. « If you torture data enough, they will confess » (޸ࢠ ~500 BC) « Sometimes there is just too much RFI » (Ter Veen, 3/12/2012) → NOT NECESSARILY ! → INDEED !
9. [Konovalenko et al., Icarus, 2012] Ground-based detection of Saturn’s lightning • Dec. 2010 observation at UTR-2/Kharkov with DSP receivers 10 microsec resolution (from waveform capture) DM ~ 3x10-5 pc.cm-3 ∫1 10(5/L2)dL ~ 5 cm-3/Lmin(UA)
10. Jean-Mathias Griessmeier LPC2E / OSUC France Philippe Zarka LESIA / Observatoire de Paris France Julien Girard LESIA / Observatoire de Paris France Walid Majid JPL / Caltech USA Heino Falcke Radboud Univ. Nijmegen NL Alexander Konovalenko IRA Kharkov Ukraine LC0_023 : Measuring the energy of Saturn's lightning LOFAR TAB data analysis / LOFAR TBB / UTR-2 observations Semester : LOFAR Cycle 0 Abstract Lightning-generated radio emission from Saturn has been observed by spacecraft missions (1980, 1981, and since 2004) and from the ground (since 2006). The highest frequency covered by these instruments is 40 MHz; at higher frequencies, the spectrum of Saturn lightning remains unknown. LOFAR observations at >40 MHz with high time resolution (5 microsec) would allow to measure the slope of the SED spectrum, the fine structure of discharges, and thus determine the energy of the discharge, which is currently unknown by many orders of magnitude. This energy is an important input for atmospheric chemistry. Extending the observation to lower frequencies (10-40 MHz) would allow to study the ionosphere of Saturn. Telescopes Telescope Modes LOFAR Beam Observation Applicants Name Affiliation Email Country Potential observer Dr Jean-Mathias Griessmeier LPC2E & OSUC & Obs. Paris Nancay jean-mathias.griessmeier@cnrs -orleans.fr France Pi Yes Dr Philippe Zarka CNRS - Observatoire de Paris (LESIA) philippe.zarka@obspm.fr France Phd student Julien Girard LESIA - Observatoire de Paris Meudon (LESIA - julien.girard@obspm.fr France Griessmeier LC0_023 Measuring the energy of Saturn's lightning [Farrell et al., 2007] - ToO / Saturn (Cassini) - measure spectrum across LBA band with 5 microsec resolution + TBB (5 nsec on bright spikes) - « HF » (>30 MHz) spectrum + hi-res time profile 㱺 flash energy - Mars ?
11. After the giant storm in 2011 ... • Storm lasted from 12/2010 to 8/2011, in Northern (summer) hemisphere • up to 10 flashes / sec, intensity up to 104 Earth's [Fischer et al., 2011]
12. After the giant storm in 2011 ... 2011-07-01 (182) 00:00 2011-07-10 (191) 00:00 44,47 152,56 0,27 15,37 44,47 41,05 328,05 0,29 15,77 41,05 35,07 141,94 0,32 16,28 35,08 25,68 311,35 0,35 17,09 25,68 10,14 93,49 0,33 19,72 10,14 2011-07-02 2011-07-04 2011-07-06 2011-07-08 2011-07-10 R S Lon Lat LT L 2, 4, 6, 8, 10, 12, 14, 16, Frequency (Hz) 0, 2, 4, 6, 8, 10, dB Above Background (10%)
13. ... Saturn’s amosphere has been quiet for months ... 2012-11-20 (325) 00:00 2012-12-04 (339) 00:00 27,72 321,97 -44,55 18,03 54,59 11,49 157,00 28,24 11,29 14,80 28,34 192,96 -31,35 15,14 38,86 2012-11-23 2012-11-28 2012-12-03 R S Lon Lat LT L 2, 4, 6, 8, 10, 12, 14, 16, Frequency (Hz) 0, 2, 4, 6, 8, 10, dB Above Background (10%)
14. But there is more about Saturn’s atmosphere with LOFAR ...
15. Saturn’s observable atmosphere from the UV to the microwave domains
16. Saturn’s temperature profile as a function of the H2 O abundance
17. LOFAR is expected to probe much deeper in Saturn’s atmosphere down to pressures of a few kbar ν=300 MHz ; λ=100 cm Opacity: NH3 + H2 O ν=100 MHz ; λ=300 cm Opacity: neutral & weakly-ionized H2 O
18. LOFAR HBA H2 O = 0.2×VF (O/H~0.7×solar) H2 O = 5×VF (O/H~17×solar) H2 O = 10×VF (O/H~34×solar) Briggs and Sackett (1989) Saturn’s brightness temperature spectrum between 10 cm and 300 cm
19. H2 O = 0.2×VF (O/H~0.7×solar) H2 O = 5×VF (O/H~17×solar) H2 O = 10×VF (O/H~34×solar) Saturn’s disk-integrated flux density in the LOFAR HBA range Δt = 5h per band
20. 1 MeV 0.028 MeV Flux (cm-2.sr-1.s-1.MeV-1) Flux (cm-2.sr-1.s-1.MeV-1) ! Electrons fluxes Salammbô-3D Modeled synchrotron radiation in the LOFAR HBA range Computed 2-D maps at 110-300 MHz 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 100 150 200 250 300 350 Fréquence (MHz) Densité de flux (mJy) DE=0° DE=26° @ 8.8 UA Computed disk- integrated spectrum
21. Objectives • Determine the deep atmospheric water vapor abundance, hence the O/H ratio in Saturn’s interior • Obtain better constraints for interior models of Saturn, i.e. the contribution of H2 O to the heavy-element component (z) • Check the prediction of a negligible level of synchrotron radiation • Assess the existence of a weakly-ionized region below 30 kbar Expectations • good signal-to-noise is expected at least in 3 of the bands above 160 MHz (160-172 + 210-222 + 238-250 MHz) • a 10% accuracy should allow us to discriminate between "under-solar" and "over-solar" H2 O distributions • the accuracy of the O/H determination will strongly depend on the quality of the imaging processing and calibration
22. Régis Courtin LESIA / Observatoire de Paris France Daniel Gautier LESIA / Observatoire de Paris France Franck Hersant LAB / Observatoire de Bordeaux France Mark Hofstadter Jet Propulsion Laboratory USA Tobias Owen IfA / University of Hawaii USA Nadine Nettelmann Rostock University Germany Philippe Zarka LESIA / Observatoire de Paris France Cyril Tasse GEPI / Observatoire de Paris France Julien Girard LESIA / Observatoire de Paris France Jean-Mathias Griessmeier LPC2E / OSUC France Angélica Sicard-Piet ONERA Toulouse France Lise Lorenzato ONERA / IRAP Toulouse France Daniel Santos-Costa SWRI San Antonio USA LC0_005 : A determination of the abundance of water in Saturn’s deep atmosphere with LOFAR Saturn’s Atmosphere & Interior / LOFAR Imaging / Saturn’s Synchrotron Radiation Semester : LOFAR Cycle 0 Abstract Lightning-generated radio emission from Saturn has been observed by spacecraft missions (1980, 1981, and since 2004) and from the ground (since 2006). The highest frequency covered by these instruments is 40 MHz; at higher frequencies, the spectrum of Saturn lightning remains unknown. LOFAR observations at >40 MHz with high time resolution (5 microsec) would allow to measure the slope of the SED spectrum, the fine structure of discharges, and thus determine the energy of the discharge, which is currently unknown by many orders of magnitude. This energy is an important input for atmospheric chemistry. Extending the observation to lower frequencies (10-40 MHz) would allow to study the ionosphere of Saturn. Telescopes Telescope Modes LOFAR Beam Observation Applicants Name Affiliation Email Country Potential observer Dr Jean-Mathias Griessmeier LPC2E & OSUC & Obs. Paris Nancay jean-mathias.griessmeier@cnrs -orleans.fr France Pi Yes Dr Philippe Zarka CNRS - Observatoire de Paris (LESIA) philippe.zarka@obspm.fr France Phd student Julien Girard LESIA - Observatoire de Paris Meudon (LESIA - julien.girard@obspm.fr France Griessmeier LC0_023 Measuring the energy of Saturn's lightning
23.