Cold plasma: a previously hidden solar system particle population

Mats André and Chris Cully

Swedish Institute of Space Physics, Uppsala

Cold plasma

• Cold: thermal energy, and drift energy,

less than a few eV.• From the Terrestrial ionosphere, planets or moons.• Cold ions hard to detect on SC charged to

a few Volts• The more we look for cold plasmas,

the more we find…

Cold plasma: The ionosphere

Atmosphere + sunlight/precipitating particles

Observations:• Groundbased: magnetometers (currents),

radio/ionosonds (density),

radars/incoherent scatter radars…• Low altitude SC (not much charged,

but instr. threshold, SC velocity…)

Cold flowing plasma: Wake behind a charged SC

Tail lobes

Density from

SC potential (calibrated)

Cluster

Engwall et al., (2009)

Cold plasma: Particle instrument vs wake detection

Cluster SC 4

SC potential control

(60 V => 7 V) -50 50vX

50

-50

vZ

km/sH+

Particles (black) SC 4

Wake E (red) SC 307:40 08:20 UT

-20

+20

km/s

Engwall et al., (2006)

Outflowing cold plasma

H+ outflow about 1026 ions/s Cluster

Engwall et al. (2009)

High altitude, high energy – likely to escape (ion detector)2×1025 /s (0.5 kg/s) 0+ (Nilsson et al., 2010)

Path to the lobes, where cold ion outflow has been detected (E-field instr.)1026 /s H+ (Engwall et al., 2009)

Oxygen ion heating and outflow (Cluster)

Cold plasma: Total vs hot density

Just inside the magnetopause

Total density from plasma frequency (WHISPER instrument)

Cluster

Sauvaud et al., 2001

2001-01-31

1000eV

10

cm-3

10

0.105:50 06:00 UT

Magnetic

reconnection,

Cluster

(magnetopause)

20 min

10s

6000km2 min

Reconnection jet

Magnetic reconnection,

Cluster (magnetopause)

Cold (eV) ions at the magnetopause

Important for EN at edge of recon. jet (acceleration)EN

30 s (1500 km)

4 s (200 km)

André et al. (2010)

Cold plasma: Recent results from the magnetopause

Cluster SC 4, 2008

Total about

150 MP crossings

Percent of crossings

Status report, to be continued…

10

30

1 4Time from MP (hours)

Cold ions, from

wake E, within

certain time inside MP

Red: high lat

Blue: low lat

Black: total

Cold plasma: Titan

0.1

cm-31000.1

Te (eV)0.1

10.0

18:00 19:00 UT 2009-06-22

Cassini Langmuir probe

Edberg et al., 2011

Cold plasma• How much cold plasma is there?• Cold plasma missing in estimates of ion outflow? Cold plasma changes dynamics. How can cold plasma stay cold?Always stay tuned to find cold plasma when

anywhere near a planet, moon or comet!