Planetary Magnetism

  • View
    22

  • Download
    1

Embed Size (px)

DESCRIPTION

Planetary Magnetism. How crucial is a planets magnetic field?. Relative sizes of Earth and Mars. Shape of their magnetic fields. Earth. Mars. Marss crust has small pockets with magnetic fields. The rest is unprotected many harmful effects from the Sun. - PowerPoint PPT Presentation

Transcript

Slide 1

Planetary MagnetismHow crucial is a planets magnetic field?

Relative sizes of Earth and MarsEarthMarsShape of their magnetic fieldsEarths global magnetic field is very strong compared to Marss small crustal fields.3

Marss crust has small pockets with magnetic fields.The rest is unprotected many harmful effects from the Sun.Magnetized rocks in the crust create these fieldsMost of the crustal magnetic fields are located on one half of Mars, in the southern hemisphere. Much of the northern hemisphere has little no magnetic fields.4All of Earth is protected by a very strong and global magnetic field

Earths magnetic field extends far out into space, way above its atmosphere, including the ionosphere.5

Where does Earths magnetic field come from?Its complicated, but simply put: its outer core. Movement of electrically conducting fluid creates the geodynamo.There are three requisites for a geodynamo to operate:1) An electrically conductive fluid medium,2) Kinetic energy provided by planetary rotation,3) An internal energy source to drive convective motions within the fluid.

6

A global magnetic field helps to protect a planets atmosphere from the harmful effects of the Suns magnetic field and solar wind.Earth MarsThere are many processes that can strip a planets atmosphere. The process weve just been learning about is called ion pickup but there are others. A strong magnet field can shield a planet from many of these processes.7

The atmosphere of Mars is less than 1% the thickness of Earths atmosphere. The atmosphere of Mars differs from the Earth's in many ways, and most of them don't bode well for humans living there. It's composed mostly of carbon dioxide (95.3 percent compared to less than 1 percent on Earth). Mars has much less nitrogen (2.7 percent compared to 78 percent on Earth). It has very little oxygen (0.13 percent compared to 21 percent on Earth). The red planet has about 1/1000 as much water vapor (0.03 percent). It exerts only 7 millibars of pressure (Earth's atmospheric pressure is 1,000 millibars).8

Many scientists think that Mars might have had a stronger global magnetic field billions of years ago, when water once flowed on its surface. It may have looked like this:There is a growing body of evidence showing that Mars once had a much thicker atmosphere with a lot of flowing water. One of the leading theories about where that atmosphere went involves Mars having, and then losing, a strong global magnetic field.9How is NASA continuing to study this?...So where did Marss atmosphere go?We think that magnetism has a lot to do with it, but we still dont completely understand

The 2013 Mars Atmosphere and Volatile EvolutioN (MAVEN) MissionThe Mars Atmosphere and Volatile Evolution Mission (MAVEN), set to launch in 2013, will explore the planets upper atmosphere, ionosphere and interactions with the sun and solar wind. Scientists will use MAVEN data to determine the role that loss of volatile compounds, such as CO2, N2, and H2O, from the Mars atmosphere to space has played over time, giving insight into the history of Mars atmosphere and climate, liquid water, and planetary habitability. http://lasp.colorado.edu/home/maven/

11The EndUnless you really want to know more.Marss atmosphere is cold and dry today, butThere was once liquid water flowing over the surface.Where did the water and early atmosphere go?

Where's the greenhouse atmosphere that allowed water to be liquid at the surface? H2O and CO2 can go into the crust or be lost to space. MAVEN will focus on the loss to space.Science Summary

Turn-off of the Martian magnetic field allowed turn-on of solar-extreme ultraviolet (EUV) and solar-wind stripping of the atmosphere approximately 3.7-4.1 billion years ago, resulting in the present thin, cold atmosphere.

Ancient Valleys#13Other science content relevant to MAVENIonosphere: Ultraviolet (UV) and Extreme Ultraviolet (EUV) light from the Sun strips off electrons from the atoms and molecules in atmospheres (ionizes the atoms and molecules), leaving many ions and electrons. UV and EUV light also breaks apart molecules. This mixture of the upper neutral atmosphere and ions and electrons is called the ionosphere. Charged particles from the solar wind (mostly electrons and protons) also ionize Mars atmosphere.

Oxygen atoms, O + EUV-> Oxygen Ions, O+ + e-CO2 atoms + EUV -> CO+ + O + e-Carbon atoms, C + EUV -> C+ + e-Helium atoms, He + EUV -> He++ + e- etcIonosphere#14MAVEN Science Questions

What is the current state of the upper atmosphere?What is the escape rate at the current epoch and how does it relate to the controlling processes?What has the total loss to space been over time?MAVEN will answer questions about the history of Martian volatiles and atmosphere and help us to understand the nature of planetary habitability.#15The MAVEN Spacecraft

MAG (2)Gull-Wing Solar ArraysLPW (2)SWEAArticulated Payload Platform (IUVS/STATIC/NGIMS)Fixed HGASWIASEPSEP#16Atmosphere Escape Routes

Key:#17There are a lot of ways that Marss atmosphere can escape to space. Many of them are related to magnetism (black, yellow, and red), but not all of them.

Instruments Sample all the Relevant Physics#MAVENs instruments studies all of these processes.18AtomsWhat three subatomic particles make up atoms?

Lesson OverviewThe Nature of MatterAtomsWhat three subatomic particles make up atoms?

The subatomic particles that make up atoms are protons, neutrons, and electrons.

Lesson OverviewThe Nature of MatterAtomsAtoms are incredibly small. Placed side by side, 100 million atoms would make a row only about 1 centimeter longabout the width of your little finger!

The subatomic particles that make up atoms are protons, neutrons, and electrons.

The subatomic particles in a carbon atom are shown.

Lesson OverviewThe Nature of Matter

Protons and Neutrons Protons and neutrons have about the same mass.

Protons are positively charged particles (+) and neutrons carry no charge at all.

Strong forces bind protons and neutrons together to form the nucleus, at the center of the atom. Lesson OverviewThe Nature of Matter

Electrons The electron is a negatively charged particle () with only 1/1840 the mass of a proton.

Electrons are in constant motion in the space surrounding the nucleus. They are attracted to the positively charged nucleus but remain outside the nucleus because of the energy of their motion.

Lesson OverviewThe Nature of Matter

Electrons Because atoms have equal numbers of electrons and protons, their positive and negative charges balance out, and atoms themselves are electrically neutral. The carbon atom shown has 6 protons and 6 electrons.An atom that loses electrons becomes positively charged. An atom that gains electrons has a negative charge. These positively and negatively charged atoms are known as ions. Lesson OverviewThe Nature of MatterWhy the Ionosphere?

(+)UV light from the sun hits atoms in Earths upper atmosphere. The energy from this light knocks an electron off the atom, leaving a free electron and an Ion. This type of ionized gas is called a plasma. Unlike other gases, it can conduct an electric charge and is affected by magnetic fields. (+)

Lesson OverviewThe Nature of Matter

27Solar Wind Interaction with a Body with an AtmosphereThe sunlight partially ionizes the dayside atmosphere. Some of this flows to night side.The solar wind is absorbed by the planetary atmosphere.If the solar wind is magnetized, it cannot immediately enter the ionosphere, so the planet becomes an obstacle to the solar wind flow.

2728Pressure Balance between Solar Wind and IonosphereThe solar wind exerts dynamic pressure (u2) plus some magnetic and thermal pressure.The ionosphere exerts thermal pressure force against the solar wind at the ionopause.The pressure at the peak of the ionosphere is generally greater than that of the solar wind.If the standoff distance is well above the collisional region, then the magnetic field will not diffuse into the ionosphere.

28The remaining slides illustrate some of the technical details related to the Suns magnetic field, how it picks up and carries an ion away from Mars, and how the same basic process can cause sputtering.

The underlying physical concepts are typically taught in college-level coursesMars orbitSlow solar wind IMFFast solar wind IMFThe interplanetary magnetic field (IMF) from the Sun moves similar to the animations shown on this webpage:http://www.swpc.noaa.gov/wmo/solar-wind.php Marss orbit would be close to the edge of the imagesSunMarsThere are lots of other related visualizations here:http://iswa.ccmc.gsfc.nasa.gov:8080/IswaSystemWebApp/

30Slow solar wind IMF moving left to rightMars orbitLooking down on Mars, Sun to the left, IMF lines in the plane parallel to page and above Marss north pole (north pole is designated by the star)Slow solar wind IMF (lines coming out of page [mostly]) moving left to rightLooking at Mars from the side, sun to the left, Mars orbit going into page. IMF moving left to right.Slow solar wind IMF (lines coming out of page [mostly]) moving left to rightLooking at Mars from the side, sun to the left, Mars orbit going into page. IMF moving left to right.Ion suddenly created, becomes swept up by the IMF (ion starts orbiting/gyrating around the field lines and get carried away by the moving IMF)Ion PickupA charged particle that is moving relative to a magnetic field (or vice versa) moves like 0:36-0:53 in this video: http://www.youtube.com/watch?v=slmV2IlluAM

Zoomed outLooking at Mars from the side, sun to the left, Mars orbit going into page. IMF moving left to right.Ion PickupAs the ion spins aro