The Solar Wind in Time

Stellar Winds and their Interaction with the Interstellar Medium Brian E. Wood (Naval Research Laboratory)Jeffrey L. Linsky (JILA, University of Colorado)

OUTLINEAstrospheric and Heliospheric Evolution Associated with Solar/Stellar Wind EvolutionIntro to Basic Heliospheric StructureHow Can We Detect Stellar Winds and/or Astrospheres?Inferring Wind Evolution from Astrospheric AbsorptionPlanetary Implications for Wind EvolutionAstrospheric and Heliospheric Evolution Associated with ISM Variability (Linsky)Neutrals interact through simple charge exchange processes (e.g., Ho+H+ H++Ho)1

Neutral Diagnostics of the Outer HeliosphereBow Shock?HeliopauseTermination ShockVISMBISMPost-TS NeutralizedPick-Up IonsTailSolar WindSchwadron et al. 2011, ApJ, 731, 56

Neutral Diagnostics of the Outer HeliosphereBow Shock?HeliopauseTermination ShockVISMBISMPost-TS NeutralizedPick-Up IonsTailSolar WindSchwadron et al. 2011, ApJ, 731, 56

Schwadron et al. 2011, ApJ, 731, 56The Ribbon, presumablywhere BISM n=0

Neutral Diagnostics of the Outer HeliosphereBow Shock?HeliopauseTermination ShockVISMBISM CenHydrogen Wall, orPost-BS Neutralized ISMPost-TS NeutralizedPick-Up IonsTailSolar WindSchwadron et al. 2011, ApJ, 731, 56Linsky & Wood 1996, ApJ, 463, 254

Schwadron et al. 2011, ApJ, 731, 56The Ribbon, presumablywhere BISM n=0

Neutral Diagnostics of the Outer HeliosphereBow Shock?HeliopauseTermination ShockVISMBISM Cen1 OriPost-TS NeutralizedBulk Solar WindHydrogen Wall, orPost-BS Neutralized ISMPost-TS NeutralizedPick-Up IonsTailSolar WindSchwadron et al. 2011, ApJ, 731, 56Linsky & Wood 1996, ApJ, 463, 254Wood et al. 2007, ApJ, 657, 609

Schwadron et al. 2011, ApJ, 731, 56The Ribbon, presumablywhere BISM n=0

Astrosphere ImagesYoung Star (LL Ori)Red Supergiant (Mira)Red Supergiant (Betelgeuse)Massive Hot StarPulsarBut unfortunately we cannot detect the astrosphere of a Sun-like star like this!

Mg IIHD151515 (O7 II)C IV

Spectroscopic Diagnostics of Stellar Winds

ACE (Advanced Composition Explorer)Methods for Detecting and Studying the Solar WindAuroraComet tailsDirect spacecraft measurement

Coronal imaging

Evolution of the Solar X-ray and EUV FLux

Ribas et al. 2005, ApJ, 622, 680The Case for a Very Strong Wind for the Young SunThe young Sun would have been much more coronally active, with higher coronal densities, so one would intuitively expect a stronger wind.Aside from the quiescent wind, the stronger and more frequent flares of the young Sun should by themselves lead to a massive CME-dominated wind. Example: Due to CMEs alone, Drake et al. (2013) predict =150 for the 500 Myr old solar analog 1 UMa.

Conclusion: There is every reason to believe the solar wind must have been much stronger in the past.Drake et al. 2013, ApJ, 764, 170

The Case for a Relatively Weak Wind for the Young Sun

Solar activity varies significantly over the course of its activity cycle, but:Voyager has observed little variation from the canonical solar mass loss rate of =210-14 M/yr.There is no strong correlation between solar X-ray flux and mass loss rate.

Conclusion: Perhaps the solar wind is relatively constant over time.Cohen 2011, MNRAS, 417, 2592

astrosphericabsorptionheliosphericabsorption12

=0.2 =0.5 =1.0 =2.0 Models of the Cen Astrosphere

Wood et al. 2001, ApJ, 547, L49Astrospheric Absorption Predictions for Cen

Wood et al. 2002, ApJ, 574, 412

Astrospheric Models

The Eri astrosphere is comparable in size to the full moon in the night sky!

The New 1 UMa Measurement1 UMa and 3 other young Sun analogs observed by HST in 2012.Only 1 UMa provided an astrospheric detection.1 UMa (G1.5 V) is a 500 Myr solar analog.The absorption suggests a mass loss rate of only 0.5 (Wood et al. 2014, ApJ, 781, L33).

List of Astrospheric Measurements

Mass Loss/X-ray RelationRed: Solar-like GK main sequence starsGreen: M dwarfsFX1.340.18Wood et al. 2014, ApJ, 781, L33

Rice & Strassmeier 2001, A&A, 377, 264Is Magnetic Topology Inhibiting the Winds of Young, Active Stars?

t-2.330.55Wind Evolution for a Sun-like Star

Evolution of the Martian AtmosphereMars TodayMars 4 Gyr ago

Lundin 2001, Science, 291, 1909What Role do Magnetospheres Play in Atmospheric Evolution?

Earth is protected by a magnetosphere, but Mars is not!

Stellar Wind Erosion of a Hot JupiterThis is just an artists conception of a stellar wind eroding a planetary atmosphere, but Ly absorption from such an eroding atmosphere may have actually been detected for the transiting exoplanet HD 209458b (Vidal-Madjar et al. 2003, Nature, 422, 143; Linsky et al. 2010, ApJ, 717, 1291).

Bahcall et al. 2001, ApJ, 555, 990The Faint Young Sun Problem (FYSP)(first defined by Sagan & Mullen 1972, Science, 177, 52)

Sackmann & Boothroyd 2003, ApJ, 583, 1084Could the FYSP be Resolved by a More Massive Young Sun?

Mass Lost due to Solar Wind Inferred from Astrospheric Measurements

Shaviv 2003, JGR, 108, 1437Could a Stronger Wind for the Young Sun Explain the FYSP Via Cosmic Ray Cooling?SUMMARYCurrently the only way to study the astrospheres and winds of solar-like stars is through astrospheric Ly absorption observed by HST.Analysis of the astrospheric absorption suggests that for solar-like GK dwarfs, mass loss and activity are correlated such that FX1.340.18.However, this relation does not extend to high activity levels (FX>106 ergs cm-2 s-1), possibly indicating a fundamental change in magnetic structure for more active stars.The mass-loss/activity relation described above suggests that mass loss decreases with time as t-2.330.55. However, the apparent high activity cutoff means that this mass loss evolution law doesnt extend to times earlier than t~0.7 Gyr.Despite the higher mass loss rates predicted for the young Sun by our mass loss evolution law, the total mass lost by the Sun in its lifetime is still insignificant, so this stronger young wind cant directly solve the Faint Young Sun problem, though there is speculation that it could indirectly via cosmic ray attenuation.The existence of generally stronger winds at younger stellar ages makes it more likely that solar/stellar wind erosion plays an important role in the evolution of planetary atmospheres.