Very Low Frequency Observation On The Moon. H. Noda, N. Kawano, et al. NAOJ, Japan

Transcription

1 Very Low Frequency Observation On The Moon H. Noda, N. Kawano, et al. NAOJ, Japan

2 LLFAST Japan Lunar Low Frequency Astronomy Study Team A study team of voluntary base in Japan A subgroup of the study team for lunar exploration astronomers, planetary scientists, technologists, engineers N. Kawano 1, M. Inoue 1, T. Iwata 2, T. Ono 3, T. Kondo 4, H. Takeuchi 4, F. Tsuchiya 3, M. Tokumaru 5, T. Hirosaki 6, Y. Matsufuji 7, K. Matsumoto 2, H. Misawa 3, A. Miyahara 2, A. Morioka 3, K. Imai 8, and H. Noda 1 1 NAOJ 2 JAXA 3 Tohoku U. 4 NICT 5 Nagoya U. 6 SSD 7 NTS 8 Kouch NCT

3 Lunar Low Frequency Array on far-side (20XX) Lunar far-side taken by NOZOMI MIC (JAXA/ISAS) Tsiolkovsky crater (21.2S/128.9E) (NASA report, 1987) 20km

4 Why moon? Astronomy on the MOON? Advantages stable surface, thin( or no) ionosphere no terrestrial radio interference on the far side vacuum Disadvantages Need to land, move and deploy Temperature differences at day-night(280k), long night (14days),power supply Regolith dust (contamination, change in thermal properties, solar cell panel)

5 Why moon? near far near Spectrum in lunar near/far side by RAE2 (Alexander et al, 1975)

6 Why moon? Lunar far-side is protected for astronomical observation ITU-R RA.479 Thus, as a first requirement all frequencies below 2 GHz in the SZM should be accessible to radio astronomy. SZM = shielded zone of the Moon Earth SZM

7 science Radio astronomy ground-based observation must use atmospheric/ionospheric windows high resolution high freq. / long baseline (ex. VLBI) low freq. (~MHz) astronomy few high-resolution observations last window for radio astronomy

8 science Low frequency astronomy Physical processes Low temperature/density Absorption by cold electron Synchrotron self absorption free-free absorption Phenomena SNR (super nova remnant) Spatial distribution of electron in our galaxy

9 science Cane (1979) Galactic background ground & space obs. with low resolution break Free-free absorption by low temperature/low density plasmas in the galactic plane? FFA? <5MHz Te=6000[K] Ne=0.1/cc?? Spectrum of galactic background in the polar areas Electron density distribution in our galaxy would be obtained with high resolution telescope.

10 science Sources (UTR-2) (Braude et al., 1978d) dec. +10~+20 Free-free absorption / synchrotron self absorption?

11 Current status of low frequency astronomy ~ ~ ~ in operation~ ~ ~ UTR-2 GMRT VLA ~ ~ ~near future~ ~ ~ LOFAR SKA Proposals of the lunar interferometer NASA(1987), ESA(1997) Freq.(Hz) UTR-2 10M - 25M GMRT 50M - 1.4G VLA 74M - 50G LOFAR 10M - 240M SKA 150M - 20G Lunar observatory (ESA) 0.5M - 16M

12 30MHz map by ITS LOFAR Germany The Netherlands location prototypes

13 Artificial noises and auroral emission from the Earth Solar burst can be avoided on the far-side. Earth(auroral) Jupiter Solar type III Planetary Earth (ESA report, 1997)

14 Step by step for lunar observatory Step 1 Earth Moon interferometer (30MHz, at equator or polar region) fine structure of the Jupiter technical demonstration (landing, setting, survival at night) Step 2 multi-element interferometer on the lunar near side interferometer technique Step 3 multi-element interferometer on the lunar far side full-fledged observation

15 LLFAST: the first step Source regions of Jovian radio waves source locations of Jovian decameter waves radiation mechanisms Earth Moon interferometer (30MHz) 5 m cross dipole with inflatable (or stem antenna) Technical demonstration (Imai) Wire antenna FOV should be in the equatorial plane inflatable Cold setting compos

16 summary The lunar far-side is -- suitable site for radio astronomy -- protected for astronomy as shielded zone of the Moon (SZM) Low frequency (<10MHz) is the last electromagnetic window for astronomy and is becoming in vogue Absorption processes are important in low frequency astronomy Earth-Moon interferometer for Jovian decameter wave -- Elucidation of source locations and radiation mechanisms -- Technical demonstration