Solar wind interaction with the inner Earth-like planets

Solar wind interaction with the inner, Earth-like, planets (Venus and Mars) Stas Barabash Swedish Inst. of Space Physics Kiruna, Sweden 1

Solar wind interaction with a nonmagnetized planet (1) • A sufficiently large planet with a sufficiently cool upper atmosphere will retain its heaviest atmospheric constituents against thermal or Jean’s escape for the age of the solar system • Solar radiation extends into the EUV range where these atoms and molecules can be ionized and dissociated • If the solar wind were unmagnetized the solar wind would be absorbed • The presence of the solar wind magnetic field enables the solar wind to be deflected and enables atmospheric loss 2

Solar wind interaction with a nonmagnetized planet (2) • • • Basic physics of the interaction is similar for Venus and Mars The convective electric field of the solar wind E=-Vx. B results in ionospheric currents. The currents create magnetic field to deviate the solar wind plasma flow. A solar wind plasma void, an induced magnetosphere, is formed. The induced currents decay with time depending on the electrical conductivity that varies with height and solar cycle. 3

Solar wind interaction with a nonmagnetized planet (3) • The thermal pressure in the ionosphere, nk. T, is generally sufficient to balance the dynamic pressure in the solar wind, rv 2 • The induced magnetosphere acts as a cap on the ionosphere and an obstacle to the solar wind flow • The magnetic pressure in the induced magnetosphere above the ionosphere reaches a value strong enough to hold the ionosphere down and deflect the solar wind • The induced magnetosphere is immersed into the planet’s exosphere. 4

Bow shock formation • The solar wind magnetic field is draped over the highly electrically conducting ionosphere forming a magnetic barrier • This barrier deflects the flow around the ionosphere • The necessary pressure gradient to cause the deflection cannot be created in the supersonic flow • The shock forms to deflect and heat the solar wind so that the pressure gradient can steer the solar wind around the induced magnetosphere 5

Pressure balance at Mars Express observations IMB Ne, cm-3 Ne (cold, MARSIS) P, dyn/cm 2 Ne (hot, ASPERA) R, Rm UT Dubinin et al. , 2008 Ptot=B 2/8 p+ k. Ne. Te Pe(Te =0. 3 e. V) Pe(Te =1. 0 e. V) Pi=k. Ne. Tp Pd=Nemp. V 2 cos 2(f) 6

Tail formation • • • Magnetic flux tubes that become “hung-up” deep in the night and day ionosphere are heavily mass-loaded and contribute to the central region of the tail Magnetic flux tubes at higher altitudes that may only be lightly mass loaded also become tail-like Magnetic pressure and curvature force act to accelerate the ionospheric plasma in the tail and straighten the magnetic field lines. 7

Magnetic anomalies on Mars • • The Martian crust was magnetized by the ancient intrinsic magnetic field The Martian dynamo ceased to operated ca. 3. 5 billion years ago due to too small size of the planet. The crust magnetization remained. The magnetization forms east - west stripes of 100 -200 km wide and 8001500 km long with alternative magnetic field polarity The anomaly’s field affects locally the solar wind interaction region 8

Unique phenomena for nonmagnetized planets • • • Bow shocks in mass loaded plasmas with neutral background Waves and instabilities in plasma (solar wind) with neutral background Physics of minimagnetospheres: magnetic anomalies (Mars) Kinetic effects (Mars): the interaction region and bow shock size are comparable with the Larmour radius for protons Impact of the interaction on the atmospheres • Energy transfer to the upper atmosphere: higher temperatures on Mars than predicted • Mass transfer: helium in the Martian and Venusian atmospheres are from captured solar wind a-particles • Atmospheric loss: 0. 01 - 1. 0 kg/s 9

Processes leading to escape 10

Escape and planetary atmosphere evolution • • The escape due to the solar wind interaction is the dominant channel for the atmospheric loss at Venus but it is small relative to the mass of the atmosphere. It is also significant for Mars both relative to the other channel and relative to the atmosphere mass. 11

Escape and the evolution of Martian atmosphere • Past Mars (~3. 5 Gy) “warm and wet” • Wet, warm place, 1 -3 bars CO 2 atmosphere, strong green house effect • Water and CO 2 escaped or stored in unknown undersurface / surface storage • Effective escape to space, if no reservoirs are found • Past Mars (~3. 5 Gy) “cold and dry” • Cold place, CO 2 gone early in the history, no green house effect • Water frozen and released sporadically during volcanoes eruptions and/or meteor impacts • No effective escape to space • Present Mars: dry desert, with 0. 01 bar CO 2 atmosphere 12

Four main scientific questions on the escape • Induced magnetosphere response to the solar and solar wind conditions • Variation of the atmospheric loss • Detailed composition of the escaping plasma • Mechanisms of ion extraction from the ionosphere • Plasma physics of the magnetic anomalies at Mars and their role in the escape 13

Evolution of the solar wind 14

Solar conditions for the solar wind interaction missions Mars-5 Phobos-2 MEX 15

Solar cycle variations. Escape rates Phobos-2 Venus Express PVO Mars-5 Mars Express Mars Venus Mars-5: Vaisber, 1986; Phobos-2: Lundin, 1990; Verigin, 1990; MEX: Barabash, 2007; Fedorov, 2008 PVO: Mc. Comass, 1986; Brace, 1987; VEX: Fedorov, 2008 16

Dependence of the escape on the upstream conditions • The planetary ion fluxes increases with the SW dynamic pressure (Lundin et al. , 2007) but the obstacle size decreases (Dubinin et al, 1996, 2007; Crider et al. , 2003). The net effect on the total escape is not yet clear. • To determine the dependence of the escape rate requires sufficient coverage of the escape region at a fixed upstream and XUV conditions. Dubinin et al, 1996 Lundin et al, 2007 17

Plasma composition in the induced magnetosphere. Mars • • O+, CO 2+, O 2++ : CO 2+/O+ = 20%, O 2+/O+ ~1 (Carlsson et al. , 2005) He+ : escape rate 1. 2· 1024 s-1 (Barabash, 1995) H+ and H 2+: cold (Norberg, Barabash, 1992; Lundin et al. , this meeting). Double charged O++ (Norberg, Barabash, 1992) O++ 18

Solar cycle variations. Ionospheric supply (Fox, 1997) 19

Plasma composition in the induced magnetosphere. Venus Energy depends on mass: ion-pick up Energy does not depend on mass: polarization electric field Barabash, Fedorov et al. , 200720

Ion extraction from the ionosphere. E-field and scavenging If the ionosphere is separated from the solar wind by the magnetic barrier region, how ions can be extracted from the ionosphere? • Penetration of the solar wind and convective electric field through IMB near terminator results in acceleration of ion in the form of narrow (energy/angle) beams. The energy increases with altitude (Dubinin et al. , 2005). • Cold plasma scavenging is observed on Phobos-2 and MEX. Mechanism is not clear. Plasma clouds up 700 cm-3 observed at 1000 km at SZA=60° (Pedersen et al. , 1991). Bulk velocity is unknown. Energy, e. V/e • Dubinin et al. , 2005 21

Ion acceleration in the tail • Classical pick-up operates in the magnetospheath. The ion energy proportional to the ion mass • Jx. B force acting on magnetized electrons, due to magnetic field stress in the kink of the draping field, accelerates ions due to the ambipolar electric field. It operates mainly in the plasma sheet. The ion energy does not depend on mass, E(O+)~E(O 2+)~0. 5 E(O++). Lundin and Dubinin et al. , 1992 22

Magnetic anomalies. Morphology • Anomalies are minimagnetospheres (Mitchel et al. , 2001). • Close field lines of the magnetic anomalies screen-off the solar wind and prohibit vertical transport of the ionospheric plasma. Open field lines connect the ionosphere with the solar wind. Soobiah et al. , 2005 23

Magnetic anomalies. Aurora • • • Reconnection signatures observed in the MGS magnetometer data (Brain et al. , 2003). Reconnection regions occupy 7% of the Martian surface. Cusp-like structures results in aurora-like emissions (Bertaux et al. , 2005) Martian aurora is a highly localized (~10 km along LOS), sporadic, low intensity (20. . 50 -700 R) emissions of CO, CO 2+, and O (180 -240 nm, 289 nm, 297. 2 nm) observed above the strong magnetic anomalies. 24

Magnetic anomalies. Particle acceleration (1) • Aurora-like electron spectra were observed above the anomalies (Lundin et al. , 2006; Brain et al. , 2006). • The acceleration mechanism is not clear because the field-aligned field cannot be maintained due to high Pedersen conductivity in the ionosphere (Dubinin et al. , 2007). • No statistically significant correlation between the occurrence of the ion beams and beam intensity and magnetic anomaly (Nilsson et al. , 2005). • Role of the anomalies for the ion acceleration and escape is still not clear 25

History of the Mars and Venus exploration at IRF Collaboration with Japan 26

Plasma measurements at Mars 27

IRF missions to Mars and Venus Phobos, 1988 VEX, 2005 Mars-96, 1996 1990 2000 2010 Nozomi, 1998 MEX, 2003 2009 Phobos-Grunt 28

The beginning (ca. 1983 - 1989). Phobos / ASPERA • Following successful ion mass spectrometers PROMICS-1 and 2 on the Soviet Prognoz 7 and 8 missions (1979 and 1980) our USSR colleagues at IKI (Space Research Institute, Moscow) invited IRF to participate in Venera-15/16 missions (1983). But we were not ready yet! • In 1983 Academician Roald Sagdeev (IKI director) invited Prof. Rickard Lundin to participate in the PHOBOS project. 29

ASPERA the first instrument at Mars • ASPERA is the first IRF experiment at Mars • Two ion mass analyzers and an electron spectrometer • Mechanical scanner: first IRF mechanics in space • Own solar arrays (30% power) • Two microprocessors 30

Sven Olsen (1934 - 2005) 31

The difficult 90 -s. Mars - 96 / Nozomi • Beginning of 90 -s the group in Kiruna was already known for its light weight plasma mass analyzers • In 1992 the invitation came to participate in the Japanese Nozomi mission (Planet-B) with the IMI instrument (Ion Mass Imager). At that time we were already working on ASPERA-C for the Russian Mars -96. Nozomi / IMI, 1998 Mars-96 / ASPERA-C, 1996 32

Nozomi missed Mars in Dec. 2003, 5 years after launch. Mars-96 with ASPERA-C sunk in the Pacific (Nov. 1996) after malfunction of the kick-off (4 th) stage 33

Nozomi heroic story (1) • • Nozomi (Planet-B) was launched in July, 1998. Performing powered swing -by at the Earth on December 20, 1998 (after two Moon swing-by’s) a main engine malfunction occurred and too much fuel was consumed. The remaining fuel was not sufficient for the planned Mars orbit insertion in October 1999. New trajectory was devised but it would require 4 more years in space. The insertion would occur in December 2003 at the time of the ESA Mars Express insertion. 34

Nozomi heroic story (2) • • Spring 2002 radiation caused by a solar flare hit Nozomi affecting its power distribution system. Since April 26, 2002 no TM could be sent and the spacecraft thermal control system could not function. Our ISAS colleague devised a beacon mode (ON/OFF) to receive at least some knowledge on the Nozomi state. The mode was extremely time and man-power consuming but the Nozomi team did not give up In August 2002 the team regain control over attitude and orbit maneuver capabilities. 4 orbit corrections and 2 earth swing-by’s were performed (the last in June 2003). Nozomi was on its way to Mars with the hope the power distribution system recovers. The Nozomi team was fighting until October 2003, when a new orbit correction maneuver was performed to avoid any potential collisions with Mars (Originally planned as an orbiter, the spacecraft did not go through sterilization). 35

Nozomi heroic story (3) While not fully successful, Nozomi provided extremely important experience and paved the way for the other planetary missions in Japan, new instruments, and international collaboration. Farewell image, Earth as seen by a Nozomi camera 36

The new times (1998 - 2007) • ESA Mars Express was initiated as a recovery for European instruments from the Mars-96 failure. • Venus Express was a follow-on of the successful Mars Express • Following the participation in Soviet Phobos, Japanes Nozomi, and Russian Mars-96 IRF led team including colleagues from ISAS (Japan) was selected to provide ASPERA-3 and ASPERA 4 experiments for Mars and Venus Express missions. 2003 ASPERA-3 / Mars Express 2005 ASPERA-4 / 37 Venus Express

Mars Express Venus Express Nya tiderna (1998 - 2007). Venus Express / ASPERA - 4 38

MEX, 2003 VEX, 2005 Nya tiderna (1998 - 2007). Venus Express / ASPERA - 4 39

The future. Swedish satellites at the other planets • IRF together with the Swedish Space Corporation, other Swedish groups and international partners, Japan being the major one, is developing ideas on microsatellites to study Mars, Venus, the Moon, and asteroids. • Such missions are indeed feasible! 40

Future cooperation with Japan. Joint instruments • • Ultra light mass analyzers (< 500 g) with the functionality and performance of the Nozomi and Mars Express type of instruments Neutral gas mass spectrometers (M/DM > 1000, up to 100 amu) (in cooperation with University of Bern) Energetic Neutral Atom (ENA) imagers for the energy range 10 e. V - few ke. V Solutions of joint plasma packages 41

Future cooperation with Japan. Joint simulation projects • Uses software built on the public FLASH software from University of Chicago. Parallel, adaptive grid. Handles fluid (MHD) and particle (hybrid and DSMC) simulations. Uses the Akka cluster with 5376 cores at the High Performance Computing Center North (HPC 2 N) in Umeå • Hybrid model of the Mars-solar wind interaction under development. • Moon hybrid modeling. Will be used to interpret the observations of an IRF instrument on the Indian Chandrayaan-1. We are also open on collaboration in the frame of the Japanese Moon mission Kaguya. 42

Future cooperation with Japan. Data analysis • Data analysis: all our Mars and Venus Express data sets are open. We are ready to provide Japanese users all necessary support. • Collaboration with the X-ray telescope Suzaki team to observe charge exchange X-rays from Mars • Solar wind multi-charged ions (O 7+, O 6+, . . , C 5+, C 6+, , …) charge exchanging on the Martian exosphere produces X-rays (0. 3 - 1 ke. V) • The satellite borne X-ray telescope Suzaki performs X-ray imaging from an Earth orbit • Mars Express/ASPERA-3 monitors local plasma conditions 43

A lot of joint research can be made in the area of the solar wind - Mars/Venus interaction. We are open for collaboration! 44