Transcript Sungrazing Comets

Solar wind interaction with
the comet Halley and Venus
K. Murawski
University of M. Curie Skłodowska
Outline
• Overview of solar wind interaction with
magnetic and non-magnetic bodies
• Numerical simulations of the solar wind
interaction with Venus
• Numerical simulations of the solar wind
interaction with the comet Halley
• Summary
A global view of the Heliosphere
Solar system - Icy Matter ...
Jan Oort’s Cometary Cloud
Outskirts of the Solar system - Comets
Properties of the solar wind
 highly conducting plasma
 magnetic field “frozen” in the plasma
 electrons, protons + alpha-particles
 SW = super-sonic + super-alfvénic
 radial expansion
 ne
T
 |BIMF|
Solar
Rotation
 vsw ≈ 400 km/s
 vA ≈ 30 - 50 km/s
 cS ≈
60 km/s
Radial
Plasma
Outflow
Interplanetary
Magnetic
Field
≈ 5 cm-3
≈ 105 K
≈ 5 nT
Planetary
Obstacle
1 AU
TYPES OF INTERACTION
WITH THE SOLAR WIND
MERCURY
VENUS
NEPTUN
SATURN
ATMOSPHERE
JUPITER
INTERNAL
MAGNETIC
FIELD
EARTH
COMETS
URANUS
MARS
GANIMEDE
EARTH'S
MOON
Simplest case:
Earth's MOON
NO magnetic field
NO atmosphere
MOON – type

no magnetic field

negligibly thin atmosphere
 insulating material
 submerged in a flowing plasma
 absorption of particles
 no bow shock upstream
 plasma – absorption wake
 magnetic field parallel to the upstream flow →
no effect
 magnetic field perpendicular to the flow →
minimal effect
Illustration of the interplanetary plasma flow and magnetic-field
perturbation by the nonconducting moon.
The wake created by solar-wind absorption closes more quickly when
the magnetic field is not aligned with the undisturbed flow.
SW interactions with magnetized
bodies
and an atmosphere
Obstacle = magnetosphere
EARTH – type (Jupiter, Saturn)
 strong magnetic field
 substantial atmosphere
magnetosheath
magnetopause
cusp
solar
wind
plasma sheet
trapping region
ionosphere
neutral sheet
lobes
plasmasphere
Plasma structures of the Earth's magnetosphere
SW interactions with magnetized
bodies
but without an atmosphere
Obstacle = magnetosphere
MERCURY - type
 strong magnetic field
 no gravitationally bound atmosphere





Similarities and differences
with Earth
Magnetosphere
Absence of an atmosphere
and ionosphere
Solar wind conditions
Mercury has a larger
fractional volume of its
magnetosphere
 no stable trapping regions
 closed magnetic flux tubes


Solar wind – primary source
of magnetospheric plasma
Plasma sheet – higher
densities
magnetosheath
magnetopause
cusp
solar
wind
lobes
0.382 AU
Mercury
Plasma structures of the Mercury's magnetosphere
COMETS
NO internal magnetic field
but atmosphere
Obstacle = exosphere
WhatCOMETS
is Solar Wind?
Comet Structure
• Nucleus: main solid core of
the comet.
• Tail: gas and dust particles
released by the comet.
• Coma: gases and dust
released by the comet when
energy from the sun heats
the comet and causes the
solid materials to turn into a
gas.
Comet Tails
•
•
Comets develop tails
only when the get
close enough to the
Sun.
Comet tails always
point away from the
Sun—This is how
scientists first realized
the existence of solar
wind.
Comet – type
 no internal magnetic field
 substantial atmosphere
Bow Shock
Ionosphere
Solar Wind
Contact
Surface
Nucleus
Cometo-pause
Numerical model - MHD
Numerical results
Numerical results
Numerical results
Numerical results
Numerical results
Numerical results
SW interactions with
unmagnetized bodies
with a substantial atmosphere
Obstacle = ionosphere
Venus
VENUS – type
 weak magnetic field or non at all
 substantial atmosphere
Planetary
Atmosphere
(neutral
atoms and
molecules)
Ionosphere
(photoions)
Solar
radiation
Bow
Shock
Solar
Wind
Wake
Interplanetary
Magnetic Field
Magnetic
Barrier
Ionosphere
induced
Magnetotail
Magnetosheath
Illustration of the steps that lead to the formation of an ionospheric planetary obstacle in a flowing
plasma like the solar wind. Ionization by solar radiation, for example, is followed by diversion of the
external plasma flow only if that flow is magnetized.
Structure of the Ionosphere
Brace and Kliore,
1991
Location of the obstacle boundary
magnetic pressure of the
interplanetary magnetic
field
Bow
Shock
Streamlines
of Solar
Wind Plasma
Flow
ionospheric
pressure
ni k Ti
thermal
pressure
Ionosphere
external pressure
nswkTsw + ρv2 + B2 / 2μ0
solar wind
dynamic
pressure
Ionopause
Magnetic
Barrier
Magnetic Field
Lines
Induced magnetotail
Bow
Shock
Z_vso
X_vso
Y_vso
Magnetotail
Pick – up and escape processes
Escape
Photoion
Energetic
neutral atoms
(ENAs)
Escape
Illustration of planetary pickup – ion trajectories of Venus. The cycloid
sizes are approximately scaled for O+ (oxygen is the main constituent of
the Venus upper atmosphere).
Ionospheric magnetic field
Ne(cm-3)
102
104
103
105
102
106
103
104
105
106
102
103
104
105
106
500
Ionopause
Altitude (km)
400
Ionopause
Orbit 177
Orbit 186
Orbit 176
300
Ionopause
200
100
0
20
40
60
80 100
0
20
40
60
80 100
80
120
160
200
Examples of observed altitude profiles for the ionospheric electron densities (points) and magnetic fields
(solid line) at Venus. The ionopause is located where the magnetosheath field decreases and the plasma
density increases.
Altitude (Km)
Number Density (cm-3)
Numerical model - Draping magnetic field lines
Solar wind
Physical model – 2 component MHD
Parameters of the physical model
Pressure distribution
Interaction
region
IMF
bow shock
magnetic
barrier
ionosphere
Pressure profiles in the
subsolar region
X
Plasma profiles
X
Magnetic field lines and
nightside ionosphere
Z
XZ plane
Solar wind
X
IMF
Y
XY plane
Concluding remarks
 Flowing plasma interactions with various types of
 magnetized planets or
 unmagnetized / weakly magnetized bodies
 Each plasma interaction has distinctive features
 Earth:
magnetic field and atmosphere
 Mercury:
magnetic field but NO atmosphere
 Moon like bodies:
neither a magnetic field nor an atmosphere
 Venus and Mars: no internal magnetic field but a substantial
atmosphere
 Comets:
atmospheres with insignificant bodies
Thank you!
44
Marco.Rademacher@in
f.fu-berlin.de
[email protected]