Solar wind interaction with the inner, Earth-like, planets (Venus and Mars) Stas Barabash Swedish Inst. of Space Physics Kiruna, Sweden Let us beging from the basic ideas on how the solar wind interacts with nonmagnetized atmospheric planets

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 The ionosphere is highy conductive media. A complicated interctaion occurs.

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=-VxB 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.

Solar wind interaction with a nonmagnetized planet (3) The thermal pressure in the ionosphere, nkT, is generally sufficient to balance the dynamic pressure in the solar wind,rv2 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.

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

Pressure balance at Mars. Mars Express observations IMB Ne (cold, MARSIS) Ne, cm-3 Ne (hot, ASPERA) P, dyn/cm2 R, Rm UT Ptot=B2/8p+ kNeTe Pi=kNeTp Pd=NempV2cos2(f) Pe(Te =0.3 eV) Pe(Te =1.0 eV) Dubinin et al., 2008

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.

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 800-1500 km long with alternative magnetic field polarity The anomaly’s field affects locally the solar wind interaction region

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 Why is it important to study how the solar wind interacts with nonmagnetized planets?

Processes leading to escape To escape atoms / molecurlars of the atm. Gass should gain extra energy exceeding the escape energy.

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. Despite, … To correctly propagate backwards the variation of the escape rate on the solar and solar wind conditions should be established.

Escape and the evolution of Martian atmosphere Past Mars (~3.5 Gy) “warm and wet” Wet, warm place, 1-3 bars CO2 atmosphere, strong green house effect Water and CO2 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, CO2 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 CO2 atmosphere The choice between these two scenarios depends in certain extent on the escape (or aeronomy) studies.

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 This is my lis of unsolved problems of the solar wind Mars interaction. First of all, we know too little on the …mass analyzers. But first of all where we are in terms data available

Evolution of the solar wind

Solar conditions for the solar wind interaction missions Mars-5 Phobos-2 MEX Coverageof the measurements relevant for the escape problem in terms of solar conditios is also limited. Very short period of the ions measurements at solar maximum. Mars-5 to be mentioned here. For Venus the situation is even worse because no plasma measurements at solar maximum is available.

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

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. Simialrly, we still do not understand .. Recent analysis of the simultaneous MGS - MEX measurements indices indeed the size of IM decreases with the dynamic pressure. Dubinin et al, 1996 Lundin et al, 2007

Plasma composition in the induced magnetosphere. Mars O+, CO2+, O2++ : CO2+/O+ = 20%, O2+/O+ ~1 (Carlsson et al., 2005) He+ : escape rate 1.2·1024 s-1 (Barabash, 1995) H+ and H2+: cold (Norberg, Barabash, 1992; Lundin et al., this meeting). Double charged O++ (Norberg, Barabash, 1992) O++ Observations of O++. Never systematically investigated only reported Attributed to Phobos outgassing , Most certainly Mars’ ions in the plasma sheet

Solar cycle variations. Ionospheric supply (Fox, 1997)

Plasma composition in the induced magnetosphere. Venus Now back to ions. ASPERA established the composition of the escaping plasma which consists of tree main ions H+, He+, and O+. The plot shows intergated and averaged energy - mass matrixes obtained in the three areas inside the wake. As on the overall plot we see ions acclelrated up to few hundred one keV energy in the reagion close to the plasma sheet. The energy shows clearly depenends on mass that indicate acclelration via pick-up (but yet not ful assimilation with the flow). Energy does not depend on mass: polarization electric field Energy depends on mass: ion-pick up Barabash, Fedorov et al., 2007

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. Green cover shows the distance Energy, eV/e Dubinin et al., 2005

Ion acceleration in the tail Classical pick-up operates in the magnetospheath. The ion energy proportional to the ion mass JxB 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(O2+)~0.5 E(O++). Once ions extracted from the ionosphere with sufficient energy (> few eV), they are can be accelerated up to few keV Lundin and Dubinin et al., 1992

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

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, CO2+, and O (180-240nm, 289nm, 297.2nm) observed above the strong magnetic anomalies.

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 If the anomalies regions can be considered as minimagnetospheres, one may search for phenomena expected in large scale magnetospheres, namely, partcile acceleration along field lines and related aurora phenomena as well as recoonection processes.

History of the Mars and Venus exploration Collaboration with Japan at IRF Collaboration with Japan I briefly reviewed the solar wind interaction with non-magnetized Mars and Venus. All results I reported were obtained by in-situ measurements from the spacecraft. I would now like to review IRF’s program on the Mars and Venus exploration and with the focus on collaboration with Japan, following the spirit of this colloquium

Plasma measurements at Mars In all 13 Martian missions carrying payload for the solar wind interaction since 1964. IRF participated in 4! Non-American

IRF missions to Mars and Venus Phobos, 1988 VEX, 2005 Mars-96, 1996 1990 2000 2010 Nozomi, 1998 2009 Phobos-Grunt Of those 4 misisons to Mars two were successfully. Currently, MEX and Vex luanched in 2003 and 2005 continue data collection and we continue our Mars exploration with the Russian / Chinese Phgobos-Grunt MEX, 2003

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. Everything started back to the beginning of 80-s.

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 The first IRF experiment at Mars was unique in many respects.

Sven Olsen (1934 - 2005) The success of ASPERA on Phobos would not be possible without outstanding engineer and person Sven Olsen who is not with us any more. Sven was also technical leader for our next experiment to Mars flown on the Japanese Martian mision Nozomi.

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

Nozomi missed Mars in Dec. 2003, 5 years after launch. While m-96..The fight for Nozomi continued for almost 5 years after a malfunction of the main engine. Mars-96 with ASPERA-C sunk in the Pacific (Nov. 1996) after malfunction of the kick-off (4th) stage

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. The heroic saga of attempt to save Nozomi would to take too much time and deserve a separat talk but not all stories have happy-ends. Despite really outstanding work of the Nozomi team at ISAS who was fighting to the end

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).

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

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 The new times came 2005 ASPERA-4 / Venus Express

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

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

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! The limitation of the present measurements prompted us to develop ideas microsat missions to study mars, Moon, and asteroids.

Future cooperation with Japan. Joint instruments Ultra light mass analyzers (< 500g) 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 eV - few keV Solutions of joint plasma packages Currently we see a lot of areas of joint interests in the field of research on the solar wind . Mars / venus interaction. Collaboration on new instruments, such

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 (HPC2N) 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. Collaborative projects in the area simulations of solar wind interctaion with the moon and mars are possible

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 (O7+, O6+, .., C5+, C6+, ,…) charge exchanging on the Martian exosphere produces X-rays (0.3 - 1 keV) The satellite borne X-ray telescope Suzaki performs X-ray imaging from an Earth orbit Mars Express/ASPERA-3 monitors local plasma conditions Other examples of the successful copertaion isSuch kind of supporting and monitoring missions are pssible

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