Magnetic Planets andMagnetic Planets and How Mars Lost Its Atmosphere

Bob LinPhysics Department & Space Sciences Laboratory

University of California, Berkeleyy f f , y

Also (visiting) School of Space Research Kyung Hee University, Korea

Thanks to the MGS, MAVEN, and LP teams

Earth’s Magnetic Field

The Earth’s Magnetosphere

Explorer 35 (1967)

Lunar Shadowing

Apollo 15 Mission -1971

Lunar Rover ->

Lunar Shadowing

Electron TrajectoryTrajectory

ConvergingMagnetic Fields

SecondaryElectron

- -- -- - - --

d [ ]EUeBB

αdsdB

μdsdU

edtdv

mSurf

LPc Δ-1=sin⇒0=++

2||Remotely Sensing Surface Magnetic Fields by Planetary Electron Reflection Magnetometry (PERM)

Apollo 15 & 16 Subsatellites Electron Reflectometry

One of the great surprises from Apollo was the discovery of paleomagnetic fields in the lunar crust Their existenceHowever, the Apollo 15 & 16 Subsatellite magnetic data set is very sparse and confined within 35 degrees of thepaleomagnetic fields in the lunar crust. Their existence suggests that magnetic fields at the Moon were much stronger in the past than they are today.

is very sparse and confined within 35 degrees of the equator. Attempts to correlate surface magnetic fields with specific geologic features were largely unsuccessful.

Mars Observer (1992-3) –disappeared 3 days before Mars orbit insertiondisappeared 3 days before Mars orbit insertion

Mars Global Surveyor (MGS) 1996-2006y ( )

MGS Mag/ER team

Current state of knowledge• Very strong crustal fields measured from orbit:

– Discovered by MGS: ~10 times stronger than terrestrial fields.Req ire h ge ol mes (>106 km3) of coherentl magneti ed cr st– Require huge volumes (>106 km3) of coherently magnetized crust.

– Crustal remnant of a strong dynamo-driven global magnetic field

MGS Aerobraking

Mars Magnetic Map (from Electron Reflection)

What do we Learn about Mars?No significant global field

Interior incapable of supporting dynamo todayInterior incapable of supporting dynamo today

Strong localized magnetic fieldsOldest crust magnetized in ancient dynamoImpacts/volcanism erased many sources

Variable solar wind field create randomness in mapAtmosphere exposed to solar wind in many regions

Current state of knowledge• Distribution of crustal fields:

– Follows the dichotomy to first-order: strong in South, weak in North.– Shock demagnetization by post-dynamo impacts– Thermal demagnetization by magmatic intrusions (e.g. Tharsis)

Current state of knowledge• The Martian dynamo:The Martian dynamo:

– Rapid cessation in basin magnetization around 4.1 Gyr ago (H&N).

E it ti h i i iti l h t i f ti i t– Excitation mechanisms: initial hot core, inner core formation, impact– Termination mechanisms: cooling core, giant impact – Lack of global field → increased atmospheric loss.

Wi hi 0 300 M f i li h d lik l b h d i ( d– Within 0-300 Myr of cessation, climate had likely become much drier (end of the Phyllosian era).

Martian Climate Evolution

Many lines of evidence point to a change in the Martian atmosphere from Earth-like to cold and thin

Where did the Atmosphere Go?

Up UPp UP

DDown

Pickup IonsIons

Ganymede

Aurora in the Solar System

Jupiter

Observations of Auroral Processes

QuickTime™ and a decompressor

are needed to see this picture.

Brain et al., 2006

QuickTime™ and a decompressor

are needed to see this picture.

Lundin et al., 2006

Bertaux et al., 2005

QuickTime™ and a decompressor

are needed to see this picture.

(Earth)

Consequences of Aurora?

(Earth)

ESAESA

MGS Atmospheric Probing ResultsAt h i t l d it fAtmospheric neutral density from MGS ER measurements, at latitudes of 0-30 S (diamonds), 50-55 S (triangles) and all latitudes (solid(triangles) and all latitudes (solid line). Dashed lines show aphelion and perihelion.

Atmospheric density

Solar Energetic Particles

Space Weather Effects on Atmosphere

• Solar Energetic Particle (SEP) events:– detectable in MGS ER background

deposit energy in atmosphere heating

Electrons

Protons

– deposit energy in atmosphere, heating atmospheric neutrals

– enhance atmospheric sputteringt ib t t M ’ di ti i t Electrons– contribute to Mars’ radiation environment

COUP: The Movie (courtesy Feigelson, 2007)

Extraordinary flares inanalogs of the young Sung y g

JW 7381 2

JW 738

K=10.5 Age ~ 10 Myrc

ts /

ks

Age ~ 10 Myr

log Lp = 32.6 erg/sX-ra

y c

Time (13.2 days)

Flare 1: Unusual slow-rise morphology.

Flare 2: One of the most powerful X-ray flares ever seen in any late-type star with Ex ~ 1036.8 erg.

Wolk & 7 others 2005 COUP #6

Mars Atmosphere and Volatile

EvolutioN (MAVEN)

Mars Scout Mission

Bruce Jakosky, Principal Investigator University of Colorado

Bob Lin, Deputy PI Univ. of California, Berkeley

MAVEN Team