1. Nitrogen and Oxygen Budget ExpLoration (NOBEL)
M. Yamauchi (IRF, Kiruna, Sweden)
I. Dandouras and H. Rème (IRAP, Toulouse, France)
O. Marghitu (ISS, Bucharest-Magurele, Romania)
and the NOBEL proposal team
poster (EGU ), Tuesday ( )

2. Mission objectives
Study thermal and non-thermal escape of major atmospheric elements (N and O) from the Earth.
1. Required observations:
First-time exploration of the exosphere.
First-time examination of isotope ratios in the magnetosphere/ionosphere.
2. Required measurement quality:
Enable modeling of the escape on a geological time scale.
Be a good reference in understanding the evolution of planetary atmosphere from the isotope ratio and N/O ratio.
What is to be measured
Density, fluxes, and energy-angle distribution for N+, N2+, O+, and H+ in the magnetosphere;
Neutral and ion densities for N, N2, O, and O2 at exosphere/ionosphere (> 800 km);
Isotope ratios of neutrals and cold ions (17O/16O, 18O/16O, D/H, and if possible 15N/14N, ) in the ionosphere, exosphere, and magnetosphere;
for a wide range of solar wind and solar EUV conditions 2

3. Why exosphere? Mandatory for escape models
(For thermal and some non-thermal escape)
Poor knowledge
(No knowledge of > 800 km for nitrogen, > 1500 km for oxygen, and all altitude for isotope ratio)
Varies in both density/ionization
(Mars observation indicates unknown factors other than EUV)
Source of cold ions above the ionosphere
(They contribute feeding ions of non-thermal escape)
He < 800 km
O < 700 km
N2 < 500 km O2
One order of magnitude variation with only 20% change in Sun-Mars distance
appear for only < 7 hrs 3

4. Why isotope ratios? Why nitrogen?
Indicators of escape from planet
(the isotope ratios are different between different escape processes)
Isotope ratio of escape is unclear
(mass-filter depends on ionization altitude)
Poor knowledge
(in the magnetosphere/ionosphere/exosphere)
N2N2+N+ vs. O2O O+
(completely different solar/geomagnetic dependence)
Scientifically important
(a representative volatile, and essential for amino-acid formation)
Escaped amount could be significant for biosphere
(Escape matters for 5% change in atmospheric/oceanic O/N ratio, i.e., if ≥ 1026 ions/s in the past. Although a route from Ocean crust to Mantle is very large, escape to space alone can play role.)
Not well known, but now possible to measure
(impossible 5 years ago)
light
total estimated subduction of N from Ocean crust to Mantle is 9 x 1018 kg over 4 byr using current subduction rate.
content in continental crust is 2 x 1018 kg, and 5 times(2x1019 kg) more inventory in the Mantle
Mars atmosphere
Earth
Mars interior
Jupiter
heavy

5. Where is the optimum orbit?
1. Non-thermal escape can be estimated by covering both the exosphere and the inner magnetosphere.
2. ~100 km altitude resolution for both in-situ and remote sensing measurements of the exosphere within a single orbit

6. Payload S/C specification Baseline
* Cold ion/neutral mass spectrometer
(1) m/∆m ~ 2000 /slow (Bern)
(2) m/∆m ~ 50 / fast (optional?)
* Ion mass analyzers (0.01 – 30 keV):
(1) m/q < 20 (Toulouse)
(2) m/q > 10 (Kiruna)
* Energetic Ion mass analyzer (UNH)
* Magnetometer (Graz)
* Langmuir probe (Brussels)
* Electron analyzer (London)
* UV spectrometer (U Tokyo)
N+, N2+, N2, O+, O+
* Auroral / airglow camera (Tohoku)
* Potential control (SC subsystem)
Optional
* Waves analyser with search coil (Prague and Orleans)
* ENA monitoring (TBD)
* IR emissions (if sensitivity is high)
S/C specification
outreach for camera
attitude control
Spin (22-26 sec) + despun platform
attitude reference
Sun-pointing
resolution
1 min & 100 km
angular resolution
//, , and anti-//

7. Possible conjugate study
Covering area of EISCAT_3D
High sensitivity in more than 300 km diameter (white area) ≈ 10° longitudinal range. 
3% of polar orbits traverse this region in average.
With T~10 hours, NOBEL crosses once every 15 days in average. 7

8. Summary
With recently developed reliable instrumentation, NOBEL will systematically study
the exospheric conditions,
nitrogen budget,
isotope ratio of cold ions/neutrals above 1000 km.
The knowledge is mandatory in estimating present-day’s thermal/non-thermal escape as well as behavior of the exosphere.
The required instrumentation can also address extra science goals:
Planetary Evolution: meaning of isotope ratio and N/O ratio.
Exoplanet modeling: tuning interpretation of optical data on exoplanets by having both spectral and in-situ measurements.
Ionosphere Physics: ionization chemistry, transport, and 3-D dynamics at its upper part together with EISCAT_3D.
Inner Magnetospheric Dynamics: N+ as an independent tracer.
Space Plasma Physics: different V0 for similar masses. 8

9. If maximum nitrogen escape is > 1028/s
Comparable amount of escape between the Earth and Mars
 The interpretation of isotope ratio (e.g., 15N/14N) is questioned.
 Favors N2 delivery model than Outgassing model of NH3 unless escape mechanisms are different between the Earth and Mars.
Two competing models of N2
+ N2 delivery model (from comets, asteroids)
Solving the problem that volatiles are difficult to be included in proto-Earth (Temprature/EUV)
But amount of delivery is uncertain
– Outgassing model of NH3
Nitrogen is expected in the proto-Earth (as NH3 rather than N2 due to higher temperature)
But difficult to protect from hydrodynamic massive escape