ESS 7 Lectures 21 and 22 November 21 and 24, 2008 The PlanetsSlide 2What will we do on the Moon?High Priority Heliophysics ScienceMore High Priority Lunar ScienceSlide 6The Magnetic Field and Plasma at the MoonPlanetary MagnetospheresInteraction of the Solar Wind with PlanetsInteraction Between Solar Wind and PlanetsMercuryMercury’s MagnetosphereSubstorms at Mercury?Mars Showing Polar Ice CapSlide 15Slide 16Slide 17VenusSlide 19Slide 20Slide 21Slide 22Slide 23JupiterSlide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Ganymede’s Mini-magnetosphereThe Surface of EuropaSlide 34Detecting oceans - inductionSlide 36Slide 37Slide 38Slide 39HomeworkESS 7ESS 7Lectures 21 and 22Lectures 21 and 22November 21 and 24, 2008November 21 and 24, 2008The PlanetsThe Planets•Moon in 2015•Stepping Stone to MarsExploration InitiativeWhat will we do on the Moon?•Heliophysics Science of the Moon – investigating fundamental space plasma processes using the Moon as a laboratory.•Space Weather; Safeguarding the Journey- understanding the drivers and dominant mechanisms of lunar radiation and plasma-dust environment that affect human and robotic explorers.•The Moon as a Historical Record – history and evolution of the Sun and Solar System using lunar soil data.•The Moon as a Heliophysics Science platform – remote sensing of plasmas from the Moon.High Priority Heliophysics Science•Dynamics of the magnetotail as it crosses the moon – plasmoids, energy transport down the tail.•Impact of the Moon on the plasma environment. Study fundamental plasma physics at the fluid-kinetic interface.•Characterize the lunar atmosphere. Study charged dust environment.•Map and study surface magnetic field of the Moon.•Study the dust environment at several locations on the Moon. •Monitor space weather in real time to determine and mitigate risks to lunar operations.•Monitor lunar environment variables (radiation, electrodynamic/plasma environment, dust dynamics and adhesion.More High Priority Lunar Science•Understand the nature and history of solar emissions and galactic cosmic rays.•Perform low frequency radio astronomy of the Sun to improve our understanding of space weather. •Analyze the composition of the solar wind.•Image the Earth’s magnetosphere and ionosphere from the Moon.•Analyze the Sun’s role in climate change.•A body like our moon composed of insulating material and embedded in a flowing plasma absorbs the plasma particles that hit it.•The lunar soil contains a record of the solar wind.•There is no bow shock at the moon because there is no obstacle to the flow.•The magnetic field diffuses into the outer layers of the moon quickly.The MoonThe Magnetic Field and Plasma at the Moon•If the flow is slow compared to the thermal speed a short wake forms behind the obstacle.•If there is no magnetic field (or the flow is parallel to the magnetic field) and the flow speed is large compared to the thermal velocity a wake will persist to large distances.•For perpendicular flow the wake will be shorter.Planetary Magnetospheres•In addition to the direct space weather applications to astronaut and equipment safety investigating other planets helps us test the concepts we are using to study space weather at Earth. •Fortunately planetary magnetospheres cover a wide variety of parameters.•Mercury, Jupiter, Saturn, Uranus and Neptune have an interaction similar to that at Earth - a supersonic solar wind interacts with a magnetic field to form a magnetospheric cavity but the nature of the obstacle differs greatly as do the solar wind parameters.Interaction of the Solar Wind with Planets•Jupiter’s moon Ganymede has an intrinsic magnetic field however it interacts with a plasma wind within Jupiter’s vast magnetosphere rather than the solar wind.•Jupiter’s moon Io provides the main source of plasma for Jupiter’s magnetosphere. Saturn’s moon Enceladus is the major source for Saturn’s magnetosphere.•Europa and Callisto have induced magnetospheres possibly related to a subsurface ocean. (Ganymede too may have an induced field but it is small compared to the intrinsic magnetic field.)Interaction Between Solar Wind and Planets•The ionospheres of Venus and Titan (when outside Saturn’s magnetosphere) interact with the solar wind flow to form an induced magnetospheric cavity.•The small size and large amount of gas that evaporates from a comet make its interaction with the solar wind unique.Mercury•Visited twice by Mariner 10 •In January 2008 Messenger flew by Mercury – will go into orbit around Mercury.Mercury’s Magnetosphere•Mercury has an intrinsic magnetic field with a dipole moment of ~300 nT RM3 (3X1012 T m3) and a dipole tilt of ~100.•The magnetic field is strong enough to stand off the solar wind at a radial distance of about 2RM.•Mercury’s magnetosphere contrasts that at the Earth because it has no significant atmosphere or ionosphere.Substorms at Mercury?•Mariner 10 flew through the tail of Mercury’s magnetosphere and found evidence of substorm activity although this is controversial. MESSENGER will probe the magnetosphere from orbit. •Magnetic field changes consistent with field aligned currents have been reported.Mars Showing Polar Ice Cap•Mars does not have a global magnetic field but is thought to have had one in the distant past.•Mars Global Surveyor found evidence of crustal magnetization mainly in ancient cratered Martian highlands.•The magnetic signatures are thought to be caused by remanent magnetism (when a hot body cools below the Curie temperature in the presence of a strong magnetic field the body can become magnetized).•The surface magnetic field is organized in a series of quasi-parallel linear features of opposite polarity.•One explanation of this is tectonic activity similar to sea floor spreading and crustal genesis at Earth. The field reversals result from reversals in Mar’s magnetic field.•The north-south dichotomy is not understood. MarsMaps of Magnetic Signatures at Mars•To be an obstacle to the solar wind a body must be conducting. •Imagine a planet with an atmosphere. –In sunlight some of the neutral atoms and molecules can be ionized.–If the solar wind is magnetized currents can be generated in the ionosphere that will keep the magnetic field from penetrating the planet. –This condition will persist as long at the magnetic field keeps changing (otherwise it will