interpretation of magnetic noise component in lunar sample magnetic


Kamenikova, T.

(1), Kletetschka, G. (2)

(1) Faculty of Science, Charles University, Czech

Republic; Institute of Geology, Academy of Sciences of the Czech

Republic, Czech Republic; (2) Institute of Geology, Academy of

Sciences of the Czech Republic, Czech Republic; Faculty of Science,

Charles University, Czech Republic; Department of Geology and

Geophysics, University of Alaska Fairbanks, USA,



The paleomagnetic

measurements of the lunar samples were based on Natural Remanent

Magnetization (NRM). Because it was shown that any heating of Lunar

samples causes irreversible changes to their paleomagnetic record, new

methods were designed, analyzing NRM without heating [1]. Magnetic

characteristics stem from magnetic minerals involved in sample, their

grain size, temperature, strain and aspect ratio [2, 3]. There are two

existing ways for the crustal rock sample how to record the

paleomagnetic information. The chemical process when magnetic grain is

growing through the blocking volume of homogeneously distributed

magnetic dipoles. The magnetic minerals will interact with the

magnetic field, in case the field will be present at the stationary

temperature. The acquired magnetization by this process is called

chemical remanent magnetization (CRM). The second process is for

cooling magnetic grain of constant volume through the blocking

temperature, when fluctuation of the magnetic moments interacts with

the external magnetic field, in case the field is present. This

acquired magnetization is called thermal remanent magnetization (TRM).

Both magnetizations achieve similar efficiency for specific magnetic

mineral [4].

This work develops a new method which don’t involve the sample

heating and estimates an amount of magnetic noise in the Lunar

samples. This method is based on the following logic.

Lets assume that the sample A has not seen magnetic field, when it was

formed. The sample should be completely demagnetized and contain just

magnetic background M(A). The first step of our approach is to take

sample A and demagnetize it by 1 mT, 10 mT, 100 mT, 1000 mT and the

overall magnetization M(A(AF)) should be constant magnetic background

[5], magnetic noise.

Then we check if this sample contains magnetizing magnetic carriers.

When the sample is saturated by pulse or constant external homogeneous

magnetic field, all of the demagnetized magnetic grains of the sample

are contributing towards one overall magnetic dipolar field that can

be detected from out side of the sample. Such sample contains maximum

saturation remanence MS(A). When sample is step-wise demagnetized,

observation of its monotonous magnetic decay is evidence that sample

contains magnetizable magnetic carriers. Demagnetizing curve itself

from its saturated value is monotonous down to its demagnetized state

MS(A(AF)). Ratio between these two sequences M(A(AF))/MS(A(AF)) has a

special case when M(A(AF)) function is constant (=magnetic noise) and

is divided by monotonously decreasing function MS(A(AF)). Then the

overall result is function that monotonously increases. And this

monotonous trend is central for our test for magnetic noise presence

in lunar samples [5]. The proposed method is modification of the

method for establishing paleomagnetic field intensity [6].

The lunar rocks magnetic carrier is mostly iron minerals [7]. In case

these minerals contain superparamagnetic grains, they are vulnerable

to viscous magnetization when is exposed to geomagnetic field.

Carriers of this magnetization have very low magnetic coercivity. Such

magnetization is removed when demagnetizing the sample by using the

lowest amplitude of the demagnetizing alternating field (usually up to

5 mT) [5].

We tested sample of lunar breccia chipped by Apollo 15 mission. The

sample 15445.277 was fragmented. We had 7 subsamples, one thin

section, one of these subsamples contained only dust as a residue from

separation for control of magnetic noise.

The noise/viscosity detection procedure was applied for all fragments.

Surprisingly, all subsamples displayed monotonously increasing

function. The 4 fragments and thin section showed a magnetic noise

only (monotonously increasing function), 3 fragments with the highest

sample masses were partly induced by viscous magnetization and

contained superparamagnetic component overprinted on magnetic noise.

It was possible to show with magnetic data that all sub-fragments of

15445 without SP that they contain magnetic noise and did not record

any level of magnetic field during their formation [5]. We discuss

that the level of magnetic noise depends on magnetic carrier [8].

Kamacite provides noise level at 30000 nT, taenite 10000 microtesla,

and Troilite 3 nT.


[1] Weiss B. P. and Tikoo S. M. (2014) Science 346, 1198.

[2] Kletetschka G. et al. (2004) EPSL 226, 521-528.

[3] Kletetschka G. and Wieczorek M. A. (2017) PEPI 272, 44-49.

[4] Kletetschka G. et al. (2002) Tectonophysics 347, 167-177.

[5] Kamenikova T. et al. (2018) LPSC 49, No. 1389.

[6] Kohout, T., et al, (2008) Studia Geophysica Et Geodaetica, 52(2),

225-235, doi:10.1007/s11200-008-0015-1.

[7] Oliveira J. S. et al. (2017) JGRPlanets 122,


[8] Kletetschka G. et al. (2017) PEPI, 272, 44-49,