Transcript Need for a mission to understand the Earth-Venus

Need for a mission to understand the
Earth-Venus-Mars difference
in Nitrogen
M. Yamauchi (IRF, Kiruna),
I. Dandouras (IRAP, Toulouse),
and the NITRO proposal team
4th SERENA – HEWG Meeting, Key Largo, May 2013
(A) Nitrogen as essential element of life
Miller’s experiment (Miller and Urey, 1959).
Model atmosphere + model lightning (discharge)
 amino acid was formed!
The result depends on the oxidation state of N
reduced form (NH3)
neutral form (N2)
oxidized form (NOx)
 Formation of pre-biotic molecules is most likely
related to the relative abundance of N, O, and H
near the surface (not only the amount!)
(B) N in the brother plants
Earth: 75% of atmospheric mass
(the amount in the soil, crust, and ocean are small)
Venus ~ 2.5 times as much as Earth
(3% of Patm.Venus = 90 x Patm.Earth)
Titan ~ 1.5 times as much as Earth
(98% of Patm.Titan)
Mars ~ only 0.01% of the Earth
(note: MMars ~ 10% of MEarth)
(B) N and O in the brother plants
N is missing at Mars but O is abundant in all
three planets (Martian case, exist in the crust
as oxidized rocks)
 Oxidation (O/N ratio for given Temperature)
of planet is
Mars > Venus > (Titan?) > Earth
Nitrogen (N/O ratio) Mystery
N < 0.01% of
Earth/Venus
rich in N
Venus
Earth
Mars
N/O ratio at Mars << at the Earth, Venus, Titan
(B) N in the brother plants
N/O ratio anomaly at Mars
 A mystery in the solar system because
(1) N is much more difficult to be ionised
than O, due to the triple chemical binding
(i.e., more difficult to escape).
(2) The evolution model (Lammer’s model)
cannot explain the N/O of both Venus and
Mars simultaneously.
How about observation of escape?
It is not easy to estimate the “value” of ancient
abundance.
 However, tendency of N/O ratio of escape
against solar forcing might be easier to
obtain ( see example).
Example: guessing O+/H+ ratio
ion escape
H+< 50 eV O+< 50 eV
H+> 10 eV O+> 10 eV
High UV
Low UV
Akebono/SMS
(Cully et al., 2003)
Polar/TIMAS
(Peterson, 2002)
Escape mechanisms
Type
Mechanism
Explanation
thermal,
neutral
Jeans escape +
momentum exchange
Thermal tail exceeds the escape velocity + Escaping
light molecules collide with heavier molecules.
thermal,
neutral/ion
Hydrodynamic blow off Same as the solar wind formation mechanism
(extreme EUV radiation during early Sun).
thermochemical,
neutral/ion
Photochemical heating
Release of e.g., recombination energy of the
excited state accelerate the atom.
thermal &
non-thermal,
ion
Ion pickup + secondary
sputtering of neutrals
Ions that are newly exposed to solar wind are
removed by the solar wind ExB.
non-thermal,
ion
Ion energisation by EM
waves and E//
EM disturbances and static E energize ions by, e.g.,
the ion cyclotron resonance.
non-thermal,
ion
Large-scale momentum The solar wind dynamic pressure and EM forces
transfer
push the planetary plasma anti-sunward at the
boundary region, by e.g., mass-loading, instability,
and reconnection
Quick rotation of early Sun
 stronger dynamo
 stronger solar maxium
 stronger CME
Ancient?
Dependence on the solar forcing
High UV flux of early Sun
 expansion of the ionosphere
beyond the magnetopause.
 Treat as non-magnetized
planet
Ancient
Guessing escape (Non-Magnetised)
Increase in
FUV (or T) Psw
Bsun
MeV e-
Pick-up
(important)
++
++
+
(unchanged?)
Non-thermal
heating
(++?)
++
++
+++
Jeans & photochemical
+++ for H+
unchanged
unchanged
(+?)
O+/H+ ratio of
escape
??
(+++?)
(+?)
(++?)
N+/O+ ratio of
escape
(?)
(?)
(?)
(++?)
Expected change in the escape of H, O, N (increase level +, ++, or +++) in
response to enhanced external forcing. () means no relevant observation
Guessing escape (Magnetised)
Increase in
FUV (or T)
Psw
Bsun
MeV e-
Pick-up (small)
unchanged
(+?)
unchanged
unchanged
Non-thermal
heating
+++
+++
++
(+?)
Jeans & photochemical
+++ for H+
unchanged
unchanged
(+?)
O+/H+ ratio of
escape
??
+++
++
(++?)
N+/O+ ratio of
escape
(+?)
(+?)
(?)
(++?)
Expected change in the escape of H, O, N (increase level +, ++, or +++) in
response to enhanced input from the sun
Present knowledge on N+ escape
(1) Akebono (1989 launch): cold ions < 0.05 keV
N+
N+
N++
N++
// direction to B
ram direction =
ambient plasma
Present knowledge on N+ escape
More drastic change of N+ than O+ for < 0.05 keV
N+
N+ N +
2
But destination and acceleration is not clear
Present knowledge on N+ escape
(2) AMPTE (1984 launch): energetic ions > 30 keV
(Hamilton et al., 1988)
But no observations of N/O
at 0.1 - 30 keV
All past magnetospheric (and Mars / Venus)
missions failed to separate N+ from O+ at
0.05~10 keV range.
This is because the time-of-flight (TOF)
instruments use “start” foils, where ion energy
losses (ion velocity scatter) merge the O+ TOF
and the N+ TOF.
Technology is within reach!
MEX / IMA, IRF
Technology is within reach!
MEX/IMA detected C+/N+/O+ group in 4 mass channels
(ch.10, 11, 12, 13) out of total 32 channels.
* IMA uses only 5 cm magnet to separate mass-percharge, and by doubling the magnet to 10 cm, we could
separate C-N-O.
CESR/IRAP Time-of-Flight R&D:
Grazing-incidence MCP as “start foil”
Beam energy
of 10 keV
P. Devoto, J.-L.Médale, and
J.-A. Sauvaud, Rev. Sci. Instru., 2008
Need for a mission
(1) Understanding the non-thermal nitrogen escape is
important in modeling both the ancient atmosphere of
the Earth and the Martian nitrogen mystery.
(2) Unfortunately, past magnetospheric missions could
not separate N+/O+ for > 50 eV because of high crosstalk in TOF instruments.
(3) Now, the technology to separate N+ and O+ with
light-weight instrument just became available.
(4) Therefore, we need a dedicated mission to
understand N+.
This is the Nitro mission, that was proposed to ESA.
North
Mission orbit and Payload
In-situ obs.
All types of ion mass
Imaging
analysers:
(1) Magnet
(2) Grazing-incidence
ENA of 1-10 keV
(substorm injections)
MCP as “start foil”
(3) Shutter TOF
(4) Reflection TOF
(various types)
Optical (emission)
South
(1) N+ : 91nm, 108nm
(2) N2+ : 391 nm, 428nm
(3) NO+
cf. Auroral N2+ emission
e- collisions ionise N2 to make
exited N2+ that emits blue line
(but N2 is exited or even N2+
pre-exists by solar UV during
equinox)
Spin-offs of N & O observations
Qualitative differences between O+ & N+
(1) Transport: Magnetospheric Physics
+
H
O+
 How about N+ and N2+?
In-situ Payload Requirements
#1: N+- O+ separation (M / ∆M ≥ 8 for narrow mass range) and
H+- He+- O+ separation (M/∆M ≥ 2 for wide mass) at  and //
directions at 10-1000 eV (11 km/s~9 eV for N) with ∆E/E ≤ 7%
((EO+-EN+) / EN+ = 15%).
Science Question
What and where to
measure?
requirement
N+ escape history vs
O+ or H+
N+, O+ and H+ at different
solar and magnetospheric
conditions.
#1, ∆t<1min
Ion filling route to the same as above.
inner magnetosphere
#1, ∆t<1min
N-O difference in
N+, O+, H+, J//, and e- at
energy re-distribution different solar conditions.
in the ionosphere
#1, keV e-, J//,
eV ions
Ion energisation
mechanisms
energy difference among N+, #1, ∆t<1min
O+ and H+ at different altitudes
Nitrogen is our future
Nitrogen is an essential element of life
N/O ratio is quite different between brother plants
No observations of N+/O+ ratio at 0.1 - 10 keV range
 New Mission with the first-time measurement of N+ and
N+ / O+ ratio of the escape (>50 eV) for interdisciplinary
purposes:
(a) History of oxidation state of the atmospheric nitrogen,
(b) Mars mystery on N/O ratio,
(c) ion injections and dynamics in the magnetosphere
(d) acceleration mechanisms,
(e) re-distribution of energy in the upper ionosphere.
N/O ratio at Mars << at the Earth, Venus, Titan:
We Need a Nitrogen mission
Proposal for a Small Mission,
submitted to ESA: June 2012
“Quad Chart” submitted to
NASA (Heliophysics):
January 2013
Preparation for a proposal to
ESA, in response to the
forthcoming M-4 call.