Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.mrao.cam.ac.uk/wp-content/uploads/2014/04/GHodosan.pdf Äàòà èçìåíåíèÿ: Wed Apr 16 18:57:16 2014 Äàòà èíäåêñèðîâàíèÿ: Sun Apr 10 13:29:34 2016 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï ï

Radio signatures of lightning discharges originated on exoplanets and brown dwarfs
Gabriella HodosÀn
gh53@st-
andrews.ac.uk
1

Supervisor: Chris.ane Helling1
­ 53 ­ 1University of St Andrews, UK

Can exoplanetary lightning induced radio signatures be observed from the Earth or from the inner Solar System?
Lightning related signatures can be found in the whole spectral range from radio to gamma-
rays. While for example UV, visible or IR molecular emission (as the lightning discharge causes changes in the local chemistry) depends on the composiGon of the atmosphere of the extrasolar body, radio signatures do not have this limitaGon, so they may give us a universal tool for lightning observaGons both on exoplanets and brown dwarfs. Table 1. summarizes the signatures of lightning discharges observed in the Solar System and lists the instruments that could possibly observe signatures origina.ng from extrasolar planets or brown dwarfs based on their opera.ng wavelength range. The red box frames two types of radio signatures.
Pro cess Signature Wavelength Celestial b o dy References Instrument with suitable wavelength range Fermi GBM, Meegan et al. (2009) AGILE, Tavani et al. (2006) AGILE Astrosat-SXT1 Astrosat-LAXPC2 VLT - X-SHOOTER Vernet et al. (2011) VLT - VIMOS, Le F` evre et al. (2003) Astrosat - UVIT, Kumar et al. (2012) Swift-UVOT, Roming et al. (2005) VLT - X-SHOOTER VLT - VIMOS HARPS, Mayor et al. (2003) HST-NICMOS, Viana (2009) IRTF - TEXES, Lacy et al. (2002) Spitzer IRS, Houck et al. (2004) LOFAR, van Haarlem et al. (2013) UTR 2, Braude et al. (1978) LWA, Kassim et al. (2005) LOFAR UTR 2 LWA HST-STIS Hernandez & et al. (2012) VLT -X-SHOOTER VLT - VIMOS HARPS HST - NICMOS IRTF-TEXES Spitzer IRS

Direct lightning emission

- ray (TGF) X - ray

20 eV - 40 MeV 30 250 keV Earth

Lu et al. (2011); Yair (2012) Marisaldi et al. (2010) Dwyer et al. (2004) Dwyer et al. (2012) Borucki et al. 1996 Aplin (2013) Wallace (1964) Baines et al. 2007

He

588 nm

Jupiter

NUV to NIR many lines of N2 , N(I I), O(I), O(I I)

See: Wallace (1964) (310-980 nm) 0.35-0.85 µm (direct imaging)

Earth Jupiter

whistlers

tens of Hz - kHz

Earth Saturn Jupiter Earth Saturn Uranus Earth Venus Earth

Desch et al. (2002) Yair et al. (2008); Yair (2012) Akalin et al. (2006) Fischer et al. (2008) Desch et al. (2002) Yair et al. (2008) Fischer et al. (2008) Zarka & Pedersen (1986) Lorenz (2008) Noxon (1976) Krasnop olsky (2006) Tessenyi et al. (2013)

sferics

1 kHz - 100 M Hz

Radio signatures:

Eect on lo cal chemistry

NOx

439 nm (NO2 ) 445 nm (NO2 ) 5.3 µm (NO) 9.6 µm 14.3 µm 200 350 nm 420 830 nm

Sferics (atmospherics): emission in the low-
frequency (LF) Ehrenreich et al. (2006) range with a power density peak at 10 kHz. (Aplin, K. L., HCN 2.97525 µm `Electrifying atmospheres', Springer 2013) Desch et al. (2002) VLT - CRIRES, K¨ fl et al. (2004) au 3.00155 µm Jupiter Mandell et al. (2012) Keck - NIRSPEC, McLean et al. (1998) CH 2.998 µm 3.0137 µm Whistlers: electromagne.c waves propaga.ng along magne.c HST - STIS 1PN 609 753 nm Emission caused VLT - X-SHOOTER field lines and emiYng in the very low-
frequency (VLF) range. by secondary 1NN 391.4 nm VLT - VIMOS Pasko (2007) events Earth HARPS 2PN 337 nm They have got their name from the typical sound they give (e.g. sprites) Liu & Pasko (2007) LBH N 150 280 nm HST-COS,Green et al. (2012) through a speaker while the waves travel more quickly at higher HST-STIS http://astrosat.iucaa.in/?q=no de/14 frequencies and more slowly at lower frequencies. (Desch, S. J. http://astrosat.iucaa.in/?q=no de/12 1PN is the first, 2PN is the second p ositive, LBH N is the Lyman-Birge-Hopfield N band system. 1NN is the first negative band system of N . et al. 2002, Rep. Prog. Phys. 65, 955) Table 1: Lightning discharges signatures observed in the Solar System. The right column lists ng ar g re o n the ol Sys m. The g Sc hum ann-
r e sonanc e s : VLF lig htning disc har g e -
induc e d potentially Table 1.i:nLigrhtnientdischobge sie natutnsngbservedriasolarSplar ets ter b rownridht column lists usefuln.ally useful instruments lto observe nigext ing on extrn olar planets orwaofs.n dwarfs a as o pote st um s to serv igh i o l htn br r w electromagne.c oscilla.ons of the earth-
ionosphere cavity. (R. L. Bailey, Ch. Helling, G. HodosÀn, C. Bilger, C. R. Stark 2013, ApJ, accepted) (SimÓes, F. et al. 2012, LPICo 1683, 1052) (Table 2.)
2 2 2 + 2 2 3 2 1 2 3 2 2 2 2 + 2 + 2

O3

Limits of detec3on:
Low cutoff frequency:

Celestial body Venus Earth Mars Jupiter Saturn Titan Uranus Neptun

1st mode f [Hz] 7.9 - 9.5 7.8 7.3 - 14 0.6 - 0.76 0.75 - 0.93 8.2 - 26 1 - 2.5 1 - 2.6 Q 4.8 - 10.5 5 1.9 - 4 5 - 10 3.5 - 7.8 0.92 - 6 2 - 21 1 - 16

2nd mode f [Hz] 14.17 - 16.3 14.3 13 - 26 1.2 - 1.35 1.63 14.3 - 45 1.99 - 4.27 2 - 4.12 Q 5 - 11.3 5 1.8 - 3.8 7.2 - 8.6 6.8 0.8 - 6 1.9 - 19.4 1 - 9.4

3rd mode f [Hz] 20.37 - 23.3 20.8 19.2 - 38 1.74 - 1.93 2.34 26.7 - 64 2.96 - 5.9 2.96 - 5.9 Q 5.2 - 22.7 5 1.8 - 40 7.3 - 8.7 6.5 1 - 4.7 0.9 - 9.5 0.9 - 9.5

ne ­ electron number density me ­ electron mass 0 ­ permiYvity of free space e ­ elementary charge

EM waves propagate through the ionosphere if:
(Lammer, H. et al. 2001, PSS 49, 561)

Natural background noises: es of Schumann resonances of the major planets and the Titan. Schumann resonances are very low frequency lightningGalac.c radio (electromagne.c) background · dischargeTable 2.: theeearth-ionosphereecavity.chSimÓes -
real. nances The Q- fmajormeasuresand thaveitan. Theion in the cavity. (SimÓes et Th first three mod s of S ( umann et so 2012a) of the actor planets the w e T attenuat illations of · Q 1asi-
the Q-
fac were easur f s th SimÓes aden (2011). n th eferences SimÓe , F. e planets and the Titan see SimÓes et al. (2012a) (ust modermal noise e Earth tor mtaken erome wave et al. ua.on iFor re cavity. (for thesother t al. 2012, ApJ 750, 85) The · Photo-
electron (electrosta.c) noise 8) values foences Earth wFor Titann from SimÓes, et al. (2012). 11, GeoRL 38, L22101). For references and referr the within. ere take see also BÈghin F. et al. (20
for the other planets and the Titan see SimÓes, F. et al. (2012, LPICo 1683, 1052) (1st mode only) and SimÓes, F. et al. (2008, SSRv 137, 455) and references within. For Titan see also BÈghin et al. (2012, Icarus 218, 1028).

(Zarka et al. 2012, PSS 74, 156)

Conclusions, future work:
ü From the surface of the Earth only sferics in the MHz frequency range would be detectable because of the low cutoff frequency of the ionosphere. ü From Space (or from the surface of the Moon ­ see: Zarka et al. 2012, PSS 74, 156) even whistlers of few tens of kHz might be observable. ü Schumann-
resonances of a few Hz may not be detectable at all, although on extrasolar bodies (especially on brown dwarfs) they might appear in higher frequency range. ü Further inves.ga.on and simula.ons are needed to determine if the lightning produced radio emission on extrasolar bodies can reach high enough frequencies to propagate through their ionosphere and reaching the inner Solar System.

For Earth: fpl = 5-
10 MHz < ~10 MHz detectable only from space < 30 kHz cannot reach the inner Solar System
(Zarka et al. 2012, PSS 74, 156)