Need for a mission to understand the Earth-Venus
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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.