Is There Lightning on Venus? Are the Result of the Solar Wind Interaction

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=2~~------N8NSANDVI8NS------~N~A~T~U~R=E~v~o=L~.3~19~2=3~JA~N~U=A=R=Y~1~98~6 the Lehner and Murray Springs mammoth does not fit a climatic extinction hypoth occur in conjunction with the vertical kill sites were apparently ambushes at esis but coincides suspiciously with the magnetic field present during the 100-Hz streams. A realistic painting of mammoth period of the Clovis hunters. It is also bursts, but that the vertical fields associ hunting should show warmly clad profes suspicious that the abundant mammoths ated with the longer duration troughs do sionals calmly spearing a mammoth and many other large New World mam not map preferentially to the highlands. already crippled by a trap or ambush. mals survived at least 22 Pleistocene gla They point out that several other studies Did hunting really exterminate mam cial cycles, to disappear about the time show that the vertical magnetic fields are moths or did they die out solely because of that Clovis hunters arrived. Using tandem related to the solar wind interaction with late-Pleistocene climatic changes and re accelerator mass spectroscopy to date the planetary ionosphere causing the in treat of tundra? These alternatives have more precisely the last mammoths will terplanetary field to become 'hung up' in been much debated, not only for mam provide a test of this suspicion. 0 the ionosphere'2,13, and that it is unlikely moths but also for other large extinct I. Agenbroad, L.D. in Quaternary Extinctions (eds Martin, that these fields penetrate to the ground. Pleistocene mammals'. The accurate P.S. & Klein, R.G.) 113 (University of Arizona Press, Tuc Moreover, the ion-density depletions son, 1984). radiocarbon dating of very small fossil 2. Vereshchagin, N.K. & Baryshnikov, G.F. in Quaternary must also result from the interaction be samples by tandem accelerator mass Extinctions ( eds Martin, P .S. & Klein, R.G.) 438 (Universi tween the solar wind and the ionosphere". ty of Arizona Press, Tucson, 1984). spectrometry' may provide some of the 3. Vereshchagin, N.K. Vestnik zoologii 3, 32 (1982). Similar ion troughs occur in the Earth's answers. With this technique, Mead et at. 4. Martin, P.S. & Klein, R.G., Quaternary Extinctions (Uni· ionosphere at mid- and high latitudes in versity of Arizona Press, Tucson, 1984). have just shown that a species derived 5. Haynes, C.V. Can. J. Anthrop. 1, liS (1980). response to magnetosphere - ionosphere from cold climates, Harrington's mountain 6. Johnson, D.L. et al. Can. J. Anthrop. 1, 107 (1980). coupling. As plasma instabilities can re 7. Haynes, C.V. et al. Archaeol. Eastern North. Am. 12, 184 sult from gradients in the plasma prop goat, and a species derived from warm (1984). climates, the Shasta ground sloth, both 8. Mead, J. eta/. Proc. natn. Acad. Sci. U.S.A. (in the press). erties, it is not surprising that plasma disappeared in Arizona at essentially the Jared Diamond is Professor of Physiology at the waves occur in conjunction with the iono same time- 11,160 ± 125 and 11,018 ± University of California Medical School, Los spheric density gradients on Venus. 50 years BP, respectively". This pairing Angeles, California 90024, USA. Lightning need not be invoked; therefore the argument for volcanism is moot. Planetary meteorology Indeed, evidence continues to accumu late showing that the vertical magnetic fields in the nightside ionosphere of Venus Is there lightning on Venus? are the result of the solar wind interaction. The ion-density depletions and density Janet G. Luhmann and Andrew F. Nagy gradients are associated with the vertical fields" but this does not mean that the Is lightning unique to Earth, or does the optical data, although a search with the vertical fields and ionosphere troughs phenomenon occur on other planets? The star tracker on the US spacecraft Pioneer produced by the solar wind interaction answer to this question will have implica Venus Orbiter had failed to show any cannot duct lightning-induced whistlers to tions for matters ranging from the nature evidence for lightning'. However, the the spacecraft when there is a favourable of the atmospheric chemistry and the plasma-wave experiment on that space connection to the highlands. meteorology of the planets' to the exist craft, showing a whistler-type electric Because the Pioneer Venus mission has ence of life. Because aerosols of volcanic field noise in the 100-Hz channel in the continued to accumulate data, Scarf and origin enhance lightning production, geo nightside ionosphere~, reinforced the coworkers can look for further support for logical processes must also be involved in Venera results. (Whistlers are a well their claims as new areas of venusian 2 this familiar phenomenon • known electromagnetic signature of light topography rotate into the nightside re Venus is particularly fascinating, both ning discharges on Earth.) gion of vertical magnetic fields. Mean because of its proximity and because of its Scarf and Russell' have extended the while, theoretical investigations of the na permanent obscuring cloud layers. Be interpretation of the electric field observa ture of the alleged plasma instabilities in cause lightning on the Earth is associated tions of lightning by demonstrating that the ion troughs may help finally to resolve with the generation of electrical charges in well-ordered magnetic fields with approx the question. 0 convective clouds, there seems a good imately vertical orientation 'duct' the whist I. Rinnert, K. J. geophys. Res. 90,6225 (1985). chance that Venus is also a candidate for lers from the lower nightside atmosphere 2. Veimeister, P.E. The Lightning Book (MIT, Boston, this type of meteorological activity. But to the spacecraft located at altitudes above 1%1). the dynamic and thermal conditions in the 150 km. Moreover, these ducts, when 3. Ksanfomality, L.V. et al. Pisma Astron. Zh.S, 229 (1979). 4. Krasnopolsky, V.A. Cosmic Research 18,429 (1980). venusian atmosphere are probably quite traced along straight lines in the direction S. Borucki, W.J. Icarus 52, 354(1982). different from those on Earth; the clouds, along the magnetic field towards the 6. Taylor, W.W.L., Scarf, F.L., Russell, C.T. & Brace, L.H. Nature 279,614 (1979). for example, are composed of sulphuric planet, all appear to intersect the ground 7. Scarf, F.L., Taylor, W.W.L., Russell, C.T. & Brace, L.H. acid instead of water vapour. If the neces near regions identified as volcanic high J. geophys. Res. 85, 8158 (1980). 8. Ksanfomality, L.V., Scarf, F.L. & Taylor, W.W.L. in sary ingredient of strong convection is lands by radar experiments'". On this Venus (ed. Hunten, D.) 565 (Univ. Arizona Press, 1983). absent, and the electrical properties of the basis, Scarf and Russell concluded that the 9. Scarf, F.L. & Russell, C.T. Geophys. Res. Lett. 10, 1192 cloud constituents or other environmental lightning sources on Venus are clustered (1983). 10. Mazursky, H. Lunar and Planetary Science XIV part 2, ~ conditions are not appropriate, venusian near specific topographical features where (LPUUSRA, Houston, 1983). clouds should never be brightened by the aerosols, such as those associated with 11. Taylor, H.A., Jr, Grabowsky, J.M. & Cloutier, P.A. J. geophys. Res. 90, 7415 (1985). types of discharges found on Earth. Yet active volcanism, may be present. 12. Luhmann, J.G. & Russell, C.T. Geophys. Res. Lett. 10, there have been inferences that lightning Taylor and coworkers" have now sug 409 (1983). 13. Marubashi, K. et al. J. geophys. Res. 90, 1385 (1985). does occur on Venus. gested that Scarf and Russell's results are 14. Brace, L.H., Theis, R.F., Mayr, H.G., Curtis S.A. & The Soviet space probes Venera 11 and simply a coincidence arising from the com Luhmann, J.G.,J. geophys. Res. 87, 199 (1982). 12 first detected impulsive very low fre bination of the sampling bias imposed by quency electric fields below the cloud tops the spacecraft orbit, planetary rotation Janet G. Luhmann is at the Institute of Geo which resemble the lightning-generated and the magnetic field geometry at Venus. physics and Planetary Physics, University of California, Los Angeles, California 90024; 'sferics' seen in terrestrial data'. A more Their main arguments stem from the Andrew F. Nagy is in the Department ofAtmos recent reanalysis of Venera 9 spectro observation that depletions or troughs in pheric and Oceanic Science, University of meter measurements' found supporting the observed ionospheric ion densities Michigan, Ann Arbor, Michigan 48109, USA.