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LPI Technical Report 93-03, Parrl 23 Icarus, 56 476-495. [5] Pieri D. C. (1980) Science, 210, 895-897. The most promising nonclimatic evidence for main sequence [6] Schunml S. A. (1956) GSA, 67. 597-646. [7] Cook F. A. (1967) mass loss from the early Sun isthe direct observation of similar mass Geo. Bull., 9. 262-268. [8] French H. M. (1976) The Periglacial loss from young naain-sequence G stars. Detection of stellar mass Enviromnent. 309. [9] Washburn A. L. (1980) Geocryology. 406. loss£rom late dwarfs atthe predicted rate (less than-I 0-10M® yr-L) by optical techniques is generally not possible. However, in one [10] Budel_41_t_)Cl_ima_ic_l_eo_orp_olo_. _4. unique case where it could be measured, an outflow 1000x that of the preseat Sun was found in a K2V dwarf [11]. Recently, huge winds have been reported from several M dwarfs [12]. This tech- MARS AND THE EARLY SUN. _, ?P. Whitmire, L.R.Doyle-, R. T.Reynolds _,and P.G. Whitman t iUniversity of Southwestern nique involves detections over awide range of radio and millimeter Louisiana, Lafayette LA 70504-4210. USA. 2SETI Institute, NASA wavelengths and the fact that free-free emission from an optically Ames Research Center, Moffett Field CA 94035, USA, 3Theoretical thick wind has acharacteristic spectrum inwhich the flux ispropor- Studies, NASA Ames Research Center, Moffett Field CA 94035, tional to the 2./3 power of the frequency. As afirst step inextending USA. this technique to solar-type stars we have recently used the VLA to obtain the radio emission at2and 6cm infour nearby young G-type Global meantemperatures near 273 Konearly Mars are difficult stars. to explain in the context of standard solar evolution models. Even in the second model-(ecliptic focusing)we assume standard solar assuming maximum CO_, greenhouse warming, the required flux is evolution. Young G stars__are often observed to be heavily spotted -15% too low [1]. Here we consider two astrophysical models that (10-50%). In contrast to m_ature Gstars like the Sun, which typically could increase the flux bythis amount. The first model isanonstand- have only amaximum cove_ge of-0.1%, the net effect ofstar spots ard solar model in which the early Sun had anrass somewhat greater on young G stars is toreduce the radiated flux at the location of the than today's mass (1.02-1.06 Mo). The second model is based on spot. Since the total stellar l_fftinosity is determined by nuclear a standard evolutionary solar model, but the ecliptic flux is in- reactions inthe core, the flux mr]st increase inregions without spots. creased due to focu sing by ,an(expected) heavily spotted early Sun. Such variations influx are obse_d on short (days) and long (years) The relation between stellar mass M and luminosity L for stars timescales [13]. These observations measure the anisotropy in the near IM® is L- M"t.75[2]. If'the Sun's original mass were larger than distribution of spots. Amore significant effect would be the average at present, the early planetaLy flux would be further increased_ due increase in the equatorial flux if the time-averaged location of the to migration of orbits. Isolropic mass loss does not produce _t-orque spotted regions was nearer to the stellar poles than to the equator. on aplanet and so angular momentum is conserved. Cons_e_luently, This is not the case in today's Sun, but fsobserved to occur inyoung semimajor axes increase inversely with mass loss and the flux is stars such as the G2V star SV Camelopardalis, in which there is a proportional to M6.75.To increase the flux atMars by 15% requires -10% coverage, localized in latitude andlongitude, toward one of that the Sun's mass be _>1.02M®. On the otherhand, the flux cannot the poles. be so large (!.1x that of the flux at IAU today) that Earth would have We have investigated asimple model irtwhich polar cap block- lost its water [3]. This imposes an upper masslimit of 1.06 Me. ing focuses the stellar flux in the equatorial plane. The equatorial Nonclimatic evidence for mass loss of this magnitude might be, fluxcan be enhanced amaximum of afactor of 2over the uncapped found in the ion implantation record of meteorites and Moon rocks. case. Fora time-averaged polar coverage of 10% the equatorial flux Such evidence does exist, but isinconclu__sive due touncertainties in enhancement factor is 1.17. Refinements inthismodel and areview exposure times and dating [4.5]. The dynamical record of adiabatic of the relevant observational data will be presented. mass loss isalso inconclusive. The adiabatic invariance of the action Acknowledgments: D.P.W. and P.G.W. thank the Louisiana variables implies that the eccentt_ities and inclinations of plan- Educational Quality Support Fund for partial support of this work. etary orbits remain constant as!he semimajor axes increase. The D.P.W. also acknowledges aNASA Ames/Stanford ASEE summer dynamical drag of the wind would have no effect on planets, but research fellowship. would cause anet inward migration of bodies of sizes less than about References: [l]KastingJ.(1991)lcarus, 94,1-13.[2]Ibenl. 1 km [6]. Whether the c_ratering record is consistent with this (1967) Annu. Rev. Astron. Astrophys., 5.571-626. [3] Kasting J. dynamical consequence is unclear. Mass loss could also be an (1988) Icarus. 74. 472-494. [4] Caffee M. et al. (1987) Astrophys. additional process comributing to bringing organics into the inner J.. 313, L31-L35. [5] Geiss J. and Bochsler P. (19cJ!) The Sun in solar system. Time (C. Sonett etal., eds.). 99-117, Univ. of Arizona.:[6] Whitmire Amass loss of 0_.1Mohas been suggested as an explanation for D. et al. (1991) Intl. Co_ on Asteroids, Comets. Meteors. 238, the depletion of Li in the Sun by 2 orders of magnitude over Flagstaff, Arizona [7]Graedel T. etal. (1991)GRL, 18, [881 - 1884. primordial values [7]. However, this explanation has been reconsid- [8] Swenson F. and Faulkner J. (1992) Astrphys. J.. 395,654-674. ered by [8], who find that mass loss cannot explain the depletion of [9] Pinsonneault M. et al. (1989) Astrophys. J., 338. 424-452. Li inHyades G dwarfs. Although it isgenerally believed that young [10] Bohigas J. et al. (1986) AAS. 157, 278-296. [11] Mullan D. G stars a_ spun down by mass loss. most models are insensitive to et al. (1989) Astrophys. J., 339, L33-L36. [12] Mullan D, et al. the total mass loss required [e.g.. 9]: An exception is the model by (1992) Astrophys. J. [13] Radick R. (1991) The Sun in Time (C. [10] which predicts amass loss comparable to our lower limit. Sone_!t et al., eds.). 787-808, Univ. of Arizona.