UV radiation is thought to have played an important role in the origin of life on Earth. To estimate these levels of UV radiation, we computed the UVC  uxes from
HST/STIS and IUE spectra of the young solar analogs κ 1 Cet and χ 1 Ori. In the future experiments with extremophilic microorganisms we will use these resulting UVC-levels to test the probability of the survival, and therefore, the existence of this kind of life at Early Earth, Early Mars and Early Europa.Fil: Abrevaya, Ximena Celeste. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Hanslmeier, A.. Institute of Physics; AustriaFil: Leitzinger, M.. Institute of Physics; AustriaFil: Odert, P.. Institute of Physics; Austria. Space Research Institute; AustriaFil: Mauas, Pablo Jacobo David. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Buccino, Andrea Paola. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin

Abrevaya, Ximena Celeste

Buccino, Andrea Paola

Hanslmeier, A.

Leitzinger, M.

Mauas, Pablo Jacobo David

Odert, P.

CONICET Digital

ISSN 18458319UV RADIATION OF THE YOUNG SUN AND ITSIMPLICATIONS FOR LIFE IN THE SOLAR SYSTEMX. C. ABREVAYA1; A. HANSLMEIER2 ; M. LEITZINGER2 ; P. ODERT2;3 ;P. J. D. MAUAS1 and A. P. BUCCINO1;41Instituto de Astronomía y Física del Espacio, UBA-CONICET,Pabelløn IAFE, CC 67, Suc. 28 (C1428ZAA), CABA, Argentina2Institute of Physics, Univ. Platz 5, 8010 Graz, Austria3Space Research Institute, Austrian Academy of Sciences,Schmiedlstr. 6, 8042 Graz, Austria4 Departamento de Física, FCEN, UBA, CABA, ArgentinaAbstract. UV radiation is thought to have played an important role in the origin of lifeon Earth. To estimate these levels of UV radiation, we computed the UVC uxes fromHST/STIS and IUE spectra of the young solar analogs 1 Cet and 1 Ori. In the futureexperiments with extremophilic microorganisms we will use these resulting UVC-levelsto test the probability of the survival, and therefore, the existence of this kind of life atEarly Earth, Early Mars and Early Europa.Key words: Solar analogs - Astrobiology - origin of life1. IntroductionThe current answer about when life originated on the Earth comes from in-direct evidences from the microbial fossil record. Accordingly, the rst cellsarose around 3.800-3.500 million years ago. However, there are some uncer-tainties about when rst cells could have aroused. Since it is well known thatradiation at certain doses could be very damaging for life, inducing dam-age to dierent cellular components which could lead to cell death, solarradiation could be an important constraint for the origin of life on Earth.At the Early Earth ages, the Sun was dierent in several aspects to thepresent Sun. Solar analogs could provide relevant information about theconditions of the Young Sun (0.8 Gyr). According to Dorren and Guinan(1994) and Ribas et al. (2005), the early Sun emitted a proportionally higherUV ux than at present. In particular, the UV continuum ux density of theCent. Eur.Astrophys. Bull. vol (2013) 1, 1 1UV RADIATION OF THE YOUNG SUN AND ORIGIN OF LIFEearly Sun exceeded the present one by a factor of 2 to 10 shortward of 200nm. However, at longer UV wavelengths, where the photospheric emissiondominates over that of the chromosphere, the UV ux of the young Suncould have been even lower than at present due to its lower luminosity, aspredicted by stellar models, even after accounting for chromospheric excessemission ?. However, if the predicted lower luminosity, which is inconsistentwith geological evidence (faint young Sun paradox), is mainly due to de-ciencies in the standard stellar models, the UV uxes would be higher (orat least comparable) to the present solar value.In this work we use the UV uxes of several solar analogs with dierentages to simulate the radiation environment of planetary bodies which arerelevant from an astrobiological point of view (Early Earth, Early Mars,Early Europa). These values will be used to conduct biological experimentswith microorganisms, simulating the radiation environment on these plan-etary bodies in order to test the probability of the survival, and therefore,the existence of this kind of life at these ages on these planetary bodies.2000 2200 2400 2600 2800 3000wavelength [Å]020406080100120140flux [erg s−1 cm−2 Å−1 ]Figure 1: UV Spectra of the Sun and Solar Analogs.2 Cent. Eur. Astrophys. Bull. vol (2013) 1, 2UV RADIATION OF THE YOUNG SUN AND ITS IMPLICATIONS FOR LIFE IN THE SOLAR SYSTEM2. Methodology2.1. Solar analogs and UV fluxesFor the present study we calculated the UV uxes of three stellar analogswith dierent ages. We selected the stars 1 Cet (G5 V) and 1 Ori (G1 V)because their ages of 0.3 Gyr and 0.75 Gyr respectively are representativeof the Young Sun when life arose on Earth. We also included the best solartwin 18 Sco (G2V) in this study which has nearly the same age as the Sun.In a future analysis we will expand our sample based on the list of solaranalogs from Güdel (2007). As we are interested in the UV radiation of thesestars we will use data from the International Ultraviolet Explorer (IUE)and the Hubble Space Telescope (HST), especially from the Space TelescopeImaging Spectrograph (STIS) and the Cosmic Origins Spectrograph (COS).The obtained uxes will then be scaled to the distances of Earth, Mars, andEuropa. The shown spectra (Fig. 1) are scaled to a distance of 1AU and weretaken from StarCat (see Ayres (2010)). The solar spectrum was recorded bythe SORCE/Solstice instrument during solar quiescence.In Fig. 2 we show the solar analogs selected in this work and the Sunin the context of the origin of life on Earth. In particular, UVC radiation(2000-2800 Å) is relevant on the Early Earth due to the absence of the ozonelayer in the atmosphere.In Fig. 3 we show the temporal evolution of stellar ux in dierentwavelength bands normalized to the present solar values. The evolution ofthe UVC uxes was obtained by tting a power law to the integrated uxesin the UVC range derived from the spectra shown in Fig. 1, whereas theevolution of the uxes in the shorter wavelength bands were calculated fromthe power laws given in Ribas et al. (2005). Here the UV-C band shows theweakest correlation with stellar age and is therefore not closely related tostellar activity. The UV-C wavelength band includes already a part of thecontinuum of our solar-like stars.2.2. Irradiation experiments with microorganismsThe experiments with microorganisms will include extremophilic microor-ganisms such as dierent species of halophilic archaea or haloarchaea (or-ganisms that live at very high salt concentrations as hypersaline environ-Cent. Eur.Astrophys. Bull. vol (2013) 1, 3 3UV RADIATION OF THE YOUNG SUN AND ORIGIN OF LIFEFigure 2: Solar analogues, stellar ages and timescale relevant to the origin of life (LHB:Late Heavy Bombardment period).ments) and also several species of cyanobacteria (photosynthetic bacteria).The relevance of these microorganisms for this project is related to dierentfacts:- They are known as UV-tolerant (apart from other harsh conditions)(Garcia-Pichel, 1998; Abrevaya et al., 2010, 2011, 2012)- Cyanobacterial group contains the oldest entries in the fossil recordthat can be assigned to any extant group of organisms- Haloarchaea were found in old salt rocks (evaporites) of million years,dating from Permic and Triassic and this kind of evaporites have beendetected in meteorites, including the martian meteorites (Gooding,1992; Rieder et al., 2004), these organisms have been proposed aspossible inhabitants of Mars or other planetary bodies with salineenvironments like the jovian moon Europa. Moreover, several speciesof haloarchaea were found in living stromatolites which are considered4 Cent. Eur. Astrophys. Bull. vol (2013) 1, 4UV RADIATION OF THE YOUNG SUN AND ITS IMPLICATIONS FOR LIFE IN THE SOLAR SYSTEM0.1 1.0 10.0age [Gyr]0.11.010.0100.01000.0F/F SunF/F SunX−ray: 1−20 ÅSXR: 20−100 ÅEUV: 100−920 ÅFUV: 920−1180 ÅLyα: 1216 ÅUVC: 2000−2800 ÅFigure 3: Temporal evolution of uxes in dierent wavelength bands normalized to thepresent solar values.analogs of the older stromatolites on the Earth (Burns et al., 2004).As a rst approach the microorganisms will be irradiated with UVC radi-ation (max. emission at 254nm). The doses will be obtained using the uxvalue for each star considering dierent intervals of time. The survival ofthe microorganisms will be measured using dierent techniques as dier-ential uorescent staining using specic dyes to detect live and dead cellsand classical methods in parallel as growth curves and plate counting, ifpossible.3. Expected resultsPrevious results obtained by Abrevaya et al. (2010, 2012) showed that somespecies of haloarchaea are capable to suvive UVC doses up to 13320 Jm 2.If we consider the UVC uxes calculated in this work it is possible to esti-mate that these microorganisms could survive up to 48 hours of continuousirradiation considering these uxes. However, further experiments are re-quired and future work will also consider the uxes reaching the surface ofthe Early Earth, Mars and Europa and the eect of the atmosphere in thecalculation of these uxes.Cent. Eur.Astrophys. Bull. vol (2013) 1, 5 5UV RADIATION OF THE YOUNG SUN AND ORIGIN OF LIFE4. AcknowledgmentsM.L, P.O., and A.H. gratefully acknowledge FWF grant P22950-N16.P.O. acknowledges the Helmholtz Association through the research al-liance Planetary Evolution and Life.X.C.A and A.P.B gratefully acknowledge MINCyT - BMWF bilateralcooperation grant.All authors thank the Österreichischer Akademischer Austauschdienst(ÖAD) with grant 11/2011 for supporting this work.ReferencesAbrevaya, X. C., Cortón, E., and Mauas, P. J. D.: 2010, in A. G. Kosovichev,A. H. Andrei, and J.-P. Rozelot (eds), IAU Symposium, Vol. 264 of IAUSymposium, pp. 443445.Abrevaya, X. C., Cortón, E., and Mauas, P. J. D.: 2012, in C. H. Mandrini, andD. F. Webb (eds), IAU Symposium, Vol. 286 of IAU Symposium, pp. 405409.Abrevaya, X. C., Paulino-Lima, I. G., Galante, D., Rodrigues, F., Mauas, P. J. D.,Cortón, E., and Lage, C. D. A. S.: 2011, Astrobiology 11, 10341040.Ayres, T. R.: 2010, ApJS 187, 149171.Burns, B.P., Goh, F., Allen, M.A., Neilan, B.A.: 2004, Environmental Microbi-ology 6, 10961101.Claire, M. W., Sheets, J., Cohen, M., Ribas, I., Meadows, V. S. and Catling,D. C.: 2012, ApJ 757, article id. 95, 12 pp.Dorren, J. D., and Guinan, E. F.: 1994, ApJ 428, 805818.Garcia-Pichel, F.: 1998, Origins of Life and Evolution of the Biosphere 28, 321347.Gooding, J. L.: 1992, Icarus 99, 2841.Güdel, M.: 2007, Living Reviews in Solar Physics 4, 3.Ribas, I., Guinan, E. F., Güdel, M., and Audard, M.: 2005, ApJ 622, 680694.Rieder, R., Gellert, R., Anderson, R. C., Brückner, J., Clark, B. C., Dreibus, G.,Economou, T., Klingelhöfer, G., Lugmair, G. W., Ming, D. W., Squyres,S. W., d'Uston, C., Wänke, H., Yen, A., and Zipfel, J.: 2004, Science306, 17461749.6 Cent. Eur. Astrophys. Bull. vol (2013) 1, 6

UV Radiation of the Young Sun and its Implications for Life in the Solar System

LAReferencia - Red Federada de Repositorios Institucionales de Publicaciones Científicas Latinoamericanas

ISSN 18458319UV RADIATION OF THE YOUNG SUN AND ITSIMPLICATIONS FOR LIFE IN THE SOLAR SYSTEMX. C. ABREVAYA1; A. HANSLMEIER2 ; M. LEITZINGER2 ; P. ODERT2,3 ;P. J. D. MAUAS1 and A. P. BUCCINO1,41Instituto de Astronomía y Física del Espacio, UBA-CONICET,Pabelløn IAFE, CC 67, Suc. 28 (C1428ZAA), CABA, Argentina2Institute of Physics, Univ. Platz 5, 8010 Graz, Austria3Space Research Institute, Austrian Academy of Sciences,Schmiedlstr. 6, 8042 Graz, Austria4 Departamento de Física, FCEN, UBA, CABA, ArgentinaAbstract. UV radiation is thought to have played an important role in the origin of lifeon Earth. To estimate these levels of UV radiation, we computed the UVC uxes fromHST/STIS and IUE spectra of the young solar analogs κ1 Cet and χ1 Ori. In the futureexperiments with extremophilic microorganisms we will use these resulting UVC-levelsto test the probability of the survival, and therefore, the existence of this kind of life atEarly Earth, Early Mars and Early Europa.Key words: Solar analogs - Astrobiology - origin of life1. IntroductionThe current answer about when life originated on the Earth comes from in-direct evidences from the microbial fossil record. Accordingly, the rst cellsarose around 3.800-3.500 million years ago. However, there are some uncer-tainties about when rst cells could have aroused. Since it is well known thatradiation at certain doses could be very damaging for life, inducing dam-age to dierent cellular components which could lead to cell death, solarradiation could be an important constraint for the origin of life on Earth.At the Early Earth ages, the Sun was dierent in several aspects to thepresent Sun. Solar analogs could provide relevant information about theconditions of the Young Sun (∼0.8 Gyr). According to Dorren and Guinan(1994) and Ribas et al. (2005), the early Sun emitted a proportionally higherUV ux than at present. In particular, the UV continuum ux density of theCent. Eur.Astrophys. Bull. vol (2013) 1, 1 1UV RADIATION OF THE YOUNG SUN AND ORIGIN OF LIFEearly Sun exceeded the present one by a factor of 2 to 10 shortward of 200nm. However, at longer UV wavelengths, where the photospheric emissiondominates over that of the chromosphere, the UV ux of the young Suncould have been even lower than at present due to its lower luminosity, aspredicted by stellar models, even after accounting for chromospheric excessemission ?. However, if the predicted lower luminosity, which is inconsistentwith geological evidence (faint young Sun paradox), is mainly due to de-ciencies in the standard stellar models, the UV uxes would be higher (orat least comparable) to the present solar value.In this work we use the UV uxes of several solar analogs with dierentages to simulate the radiation environment of planetary bodies which arerelevant from an astrobiological point of view (Early Earth, Early Mars,Early Europa). These values will be used to conduct biological experimentswith microorganisms, simulating the radiation environment on these plan-etary bodies in order to test the probability of the survival, and therefore,the existence of this kind of life at these ages on these planetary bodies.2000 2200 2400 2600 2800 3000wavelength [Å]020406080100120140flux [erg s−1 cm−2 Å−1 ]Figure 1: UV Spectra of the Sun and Solar Analogs.2 Cent. Eur. Astrophys. Bull. vol (2013) 1, 2UV RADIATION OF THE YOUNG SUN AND ITS IMPLICATIONS FOR LIFE IN THE SOLAR SYSTEM2. Methodology2.1. Solar analogs and UV fluxesFor the present study we calculated the UV uxes of three stellar analogswith dierent ages. We selected the stars κ1 Cet (G5 V) and χ1 Ori (G1 V)because their ages of 0.3 Gyr and 0.75 Gyr respectively are representativeof the Young Sun when life arose on Earth. We also included the best solartwin 18 Sco (G2V) in this study which has nearly the same age as the Sun.In a future analysis we will expand our sample based on the list of solaranalogs from Güdel (2007). As we are interested in the UV radiation of thesestars we will use data from the International Ultraviolet Explorer (IUE)and the Hubble Space Telescope (HST), especially from the Space TelescopeImaging Spectrograph (STIS) and the Cosmic Origins Spectrograph (COS).The obtained uxes will then be scaled to the distances of Earth, Mars, andEuropa. The shown spectra (Fig. 1) are scaled to a distance of 1AU and weretaken from StarCat (see Ayres (2010)). The solar spectrum was recorded bythe SORCE/Solstice instrument during solar quiescence.In Fig. 2 we show the solar analogs selected in this work and the Sunin the context of the origin of life on Earth. In particular, UVC radiation(2000-2800 Å) is relevant on the Early Earth due to the absence of the ozonelayer in the atmosphere.In Fig. 3 we show the temporal evolution of stellar ux in dierentwavelength bands normalized to the present solar values. The evolution ofthe UVC uxes was obtained by tting a power law to the integrated uxesin the UVC range derived from the spectra shown in Fig. 1, whereas theevolution of the uxes in the shorter wavelength bands were calculated fromthe power laws given in Ribas et al. (2005). Here the UV-C band shows theweakest correlation with stellar age and is therefore not closely related tostellar activity. The UV-C wavelength band includes already a part of thecontinuum of our solar-like stars.2.2. Irradiation experiments with microorganismsThe experiments with microorganisms will include extremophilic microor-ganisms such as dierent species of halophilic archaea or haloarchaea (or-ganisms that live at very high salt concentrations as hypersaline environ-Cent. Eur.Astrophys. Bull. vol (2013) 1, 3 3UV RADIATION OF THE YOUNG SUN AND ORIGIN OF LIFEFigure 2: Solar analogues, stellar ages and timescale relevant to the origin of life (LHB:Late Heavy Bombardment period).ments) and also several species of cyanobacteria (photosynthetic bacteria).The relevance of these microorganisms for this project is related to dierentfacts:- They are known as UV-tolerant (apart from other harsh conditions)(Garcia-Pichel, 1998; Abrevaya et al., 2010, 2011, 2012)- Cyanobacterial group contains the oldest entries in the fossil recordthat can be assigned to any extant group of organisms- Haloarchaea were found in old salt rocks (evaporites) of million years,dating from Permic and Triassic and this kind of evaporites have beendetected in meteorites, including the martian meteorites (Gooding,1992; Rieder et al., 2004), these organisms have been proposed aspossible inhabitants of Mars or other planetary bodies with salineenvironments like the jovian moon Europa. Moreover, several speciesof haloarchaea were found in living stromatolites which are considered4 Cent. Eur. Astrophys. Bull. vol (2013) 1, 4UV RADIATION OF THE YOUNG SUN AND ITS IMPLICATIONS FOR LIFE IN THE SOLAR SYSTEM0.1 1.0 10.0age [Gyr]0.11.010.0100.01000.0F/FSunF/FSunX−ray: 1−20 ÅSXR: 20−100 ÅEUV: 100−920 ÅFUV: 920−1180 ÅLyα: 1216 ÅUVC: 2000−2800 ÅFigure 3: Temporal evolution of uxes in dierent wavelength bands normalized to thepresent solar values.analogs of the older stromatolites on the Earth (Burns et al., 2004).As a rst approach the microorganisms will be irradiated with UVC radi-ation (max. emission at 254nm). The doses will be obtained using the uxvalue for each star considering dierent intervals of time. The survival ofthe microorganisms will be measured using dierent techniques as dier-ential uorescent staining using specic dyes to detect live and dead cellsand classical methods in parallel as growth curves and plate counting, ifpossible.3. Expected resultsPrevious results obtained by Abrevaya et al. (2010, 2012) showed that somespecies of haloarchaea are capable to suvive UVC doses up to 13320 Jm−2.If we consider the UVC uxes calculated in this work it is possible to esti-mate that these microorganisms could survive up to 48 hours of continuousirradiation considering these uxes. However, further experiments are re-quired and future work will also consider the uxes reaching the surface ofthe Early Earth, Mars and Europa and the eect of the atmosphere in thecalculation of these uxes.Cent. Eur.Astrophys. Bull. vol (2013) 1, 5 5UV RADIATION OF THE YOUNG SUN AND ORIGIN OF LIFE4. AcknowledgmentsM.L, P.O., and A.H. gratefully acknowledge FWF grant P22950-N16.P.O. acknowledges the Helmholtz Association through the research al-liance Planetary Evolution and Life.X.C.A and A.P.B gratefully acknowledge MINCyT - BMWF bilateralcooperation grant.All authors thank the Österreichischer Akademischer Austauschdienst(ÖAD) with grant 11/2011 for supporting this work.ReferencesAbrevaya, X. C., Cortón, E., and Mauas, P. J. D.: 2010, in A. G. Kosovichev,A. H. Andrei, and J.-P. Rozelot (eds), IAU Symposium, Vol. 264 of IAUSymposium, pp. 443445.Abrevaya, X. C., Cortón, E., and Mauas, P. J. D.: 2012, in C. H. Mandrini, andD. F. Webb (eds), IAU Symposium, Vol. 286 of IAU Symposium, pp. 405409.Abrevaya, X. C., Paulino-Lima, I. G., Galante, D., Rodrigues, F., Mauas, P. J. D.,Cortón, E., and Lage, C. D. A. S.: 2011, Astrobiology 11, 10341040.Ayres, T. R.: 2010, ApJS 187, 149171.Burns, B.P., Goh, F., Allen, M.A., Neilan, B.A.: 2004, Environmental Microbi-ology 6, 10961101.Claire, M. W., Sheets, J., Cohen, M., Ribas, I., Meadows, V. S. and Catling,D. C.: 2012, ApJ 757, article id. 95, 12 pp.Dorren, J. D., and Guinan, E. F.: 1994, ApJ 428, 805818.Garcia-Pichel, F.: 1998, Origins of Life and Evolution of the Biosphere 28, 321347.Gooding, J. L.: 1992, Icarus 99, 2841.Güdel, M.: 2007, Living Reviews in Solar Physics 4, 3.Ribas, I., Guinan, E. F., Güdel, M., and Audard, M.: 2005, ApJ 622, 680694.Rieder, R., Gellert, R., Anderson, R. C., Brückner, J., Clark, B. C., Dreibus, G.,Economou, T., Klingelhöfer, G., Lugmair, G. W., Ming, D. W., Squyres,S. W., d'Uston, C., Wänke, H., Yen, A., and Zipfel, J.: 2004, Science306, 17461749.6 Cent. Eur. Astrophys. Bull. vol (2013) 1, 6

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UV Radiation of the Young Sun and its Implications for Life in the Solar System

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