Ahmed, S. M.

Bhardwaj, Anil

Das, Tirth Prathim

Sridharan, R.

English

Publications of the IAS Fellows

SCIENTIFIC CORRESPONDENCE 
 
CURRENT SCIENCE, VOL. 105, NO. 11, 10 DECEMBER 2013 1470 
Indicators for localized regions of heavier species in the lunar surface 
from CHACE on Chandrayaan-1 
 
Chandra’s Altitudinal Composition Ex-
plorer (CHACE) has been a unique  
experiment on the Moon Impact Probe 
(MIP) – a micro satellite riding piggyback 
on Chandrayaan-1, India’s first mission 
to the Moon. CHACE, based on a quad-
rupole mass spectrometer, was intended 
to get the altitudinal and latitudinal com-
position of the tenuous lunar ambience, a 
‘first of its kind’ attempt and has yielded 
significant results, including the first  
‘direct detection of water’, revealing the 
sunlit-side ambient pressure to be at least 
two orders of magnitude larger than  
expected and also showing the domi-
nance of CO2 and H2O in the lunar atmo-
sphere1,2. In addition, the relative 
composition of the noble gases and their 
isotopes revealed significant north–south 
asymmetry in the radiogenic activity of 
the lunar interior3. All the above results 
pertained to the dominant species and/or 
species for which identification is not an 
issue. 
 Careful analysis of the 650 spectra  
obtained from ~ 100 km to the lunar sur-
face and covering a latitude range (40 N–
85 S) with unprecedented spatial (~ 250 m) 
and temporal resolution (~ 4 sec) reveals 
significant grouping of heavier species 
(> 60 amu) in localized regions. Figure 1 
depicts some sample spectra correspond-
ing to different lunar latitudes in the lon-
gitude region 12–15 E. The mass spectra 
obtained from the quadrupole instrument 
have been subjected to all the instrumen-
tal corrections like mass discrimination 
of the analyser, relative sensitivity of the 
detector, etc. and have been normalized 
to the total pressure measured by the 
ionization gauge, which itself was cali-
brated for total pressure measurements. 
Due corrections to the dominant gas have 
also been made. Details of the data-
handling procedure, including ruling out 
the possible effects of instrument and the 
satellite-related contaminants have been 
dealt with in detail in the literature 1,2 
and will not be elaborated here. In this 
brief note, no attempt is made to identify 
the species either. They could be elemen-
tal or complex molecules. These heavier 
species start showing up from ~ 5 N lat. 
and continued their presence with vary-
ing strengths as the spacecraft moved 
towards the South Pole. A mass peak 
corresponding to 94 amu started appear-
ing at sweep number 190 (~ 8 N) with a 
partial pressure of 6 × 10–9 torr. It was at 
its maximum amplitude of 2 × 10–8 torr 
over a latitude of 5 S (sweep number 
250) and lasted up to scan number 321 
(~ 22 S), beyond which its intensity 
slowly decreased and eventually merged 
with the noise level. In general, 80 amu 
coexisted with 94 amu. However, there 
are occasions when 80 amu became 
stronger than 94 amu by nearly a factor 
of two (scan number 370 and beyond). 
Mass numbers 77, 78 and 79 that showed 
up in sweep number 210 (~ 3.5 N) are 
seen to become stronger intermittently 
during the MIP transit. All the above  
observations are believed to be a reflec-
tion of lunar surface heterogeneity and a 
positive indication for localized regions 
that are abundant with heavier elements/ 
species. This result has the potential to 
form a base for any future exploration. 
The above point becomes clearer in the 
following discussion. 
 The Earth’s moon is known to have a 
surface boundary exosphere (SBE), 
which means that there are no intera-
tomic/molecular collisions mainly due to 
the particle number density being ex-
tremely low and, as a consequence, each 
one of the atmospheric species has its 
own altitudinal distribution occupying 
the same volume. The atoms and mole-
cules would have ballistic trajectories 
and the lighter species, by virtue of their 
larger scale height are free to escape into 
the interplanetary medium once they 
have enough kinetic energy to overcome 
the gravitational pull of the Moon. Hav-
ing a background information on the  
lunar surface temperature both during 
sunlit conditions (~ 400 K) and otherwise 
(~ 150 K) and keeping in mind the latitu-
dinal variation of the surface tempera-
ture, it could be seen that only the 
lightest of the species, viz. hydrogen 
would have enough energy to escape into 
the interplanetary medium, that too only 
up to ~ 75° lat. All the other species 
would be gravitationally bound, unless 
some additional energy is supplied to 
them. This makes the lunar atmosphere 
unique in the sense that the atmospheric 
composition measurements directly reflect 
the lunar surface properties. After suc-
cessfully delineating the surface tempe-
ratures using the scale height of noble 
gases and showing excellent agreement 
with the spectroscopically determined 
values2 and after duly accounting for the 
scale height variations, the latitudinal 
distribution of the atmospheric species 
has been obtained and reported in the lit-
erature2. 
 In the present communication, empha-
sis is given to the higher mass numbers. 
As MIP raced towards the South Pole, 
appearance and disappearance of differ-
ent species in the amu range (65–100) 
became conspicuous. Though the relative 
concentration of these species is signifi-
cantly low, often forming less than a few 
percentage of the dominant species, due 
to the sensitivity of the instrument, their 
signatures are very clear. 
 In fact, Apollo-17 measurements using 
a mass spectrometer that was left on the 
lunar surface by the astronauts did show 
similar groups of heavier species4. How-
ever, the spectra were believed to have 
been contaminated due to degassing from 
the suits of the astronauts and also from 
the large quantity of materials taken and 
left behind by them on the lunar surface. 
Under such a notion, many of the genu-
ine species of lunar origin were also left 
out. After Apollo-17, which itself was 
the first attempt to measure the tenuous 
atmospheric composition of the Moon, it 
was the CHACE experiment on Chandra-
yaan-1’s MIP that made an attempt to 
measure the lunar atmospheric composi-
tion after more than four decades. This 
‘one shot’ experiment was free from 
many of the limitations of the LACE 
(Apollo-17) experiment and had clearly 
indicated a complex lunar atmosphere, 
though tenuous, with CO2 and H2O as the 
dominant species2. 
 Identification of the masses is a chal-
lenge in itself and no attempt is made 
here in this direction. Based on the  
arguments provided in the earlier cited 
publications, the observed masses are not 
contaminants as one tends to treat them 
at the first instant. If they had been so, 
they should have registered their pres-
ence all through with the same intensity 
and it cannot be intermittent or localized 
as had been observed. It should also be 
noted that even as the spacecraft was 
SCIENTIFIC CORRESPONDENCE 
 
CURRENT SCIENCE, VOL. 105, NO. 11, 10 DECEMBER 2013 1471
 
 
Figure 1. Sample mass spectra of the lunar ambience in the range 60–100 amu as the Moon Impact Probe of Chandrayaan-1 mission raced  
towards the South Pole. The sweep number and the corresponding lunar latitudes and altitudes are also given in each panel. 
 
 
steadily descending from 100 km, the 
partial pressure of these species did not 
build up as would have been the case  
if there had been some sort of uniform  
distribution; in fact, the partial pressure 
of 94 amu decreased significantly. 
 When the ground trajectory of MIP 
was projected over the lunar surface, it is 
interesting to see that the former crossed 
over the fringe of the KREEP region rich 
in potassium and rare earth elements that 
show large surface heterogeneity2,3. 
Since CHACE is the only experiment 
that has provided both latitudinal/ 
altitudinal variation of the lunar exo-
spheric composition so far, the variations 
recorded with respect to the heavier spe-
cies could be associated with the lunar 
surface heterogeneity. With the launch of 
Lunar Atmosphere and Dust Environ-
ment Experiment (LADEE) by NASA on 
7 September 2013, where emphasis is 
given to the lunar exospheric composi-
tion and also the near-lunar dusty  
SCIENTIFIC CORRESPONDENCE 
 
CURRENT SCIENCE, VOL. 105, NO. 11, 10 DECEMBER 2013 1472 
environment over the equatorial plane, 
some of the CHACE findings are likely 
to be vindicated. Further, unlike in the 
case of CHACE, which was a ‘one shot’ 
mission, the distinct advantage of 
LADEE which would be an orbiting 
spacecraft initially at around 250 km and 
later coming down as low as 20 km, with 
an anticipated lifetime of ~ 3 months, is 
that the whole of the lunar globe is likely 
to be covered over the equatorial plane. 
This would clearly bring out the spatial 
heterogeneity indicated by India’s CHACE 
experiment, in addition to the inferences 
on the lunar day and night pressure dif-
ferences. 
 
1. Sridharan, R., Ahmed, S. M., Das, T. P., 
Sreelatha, P., Pradeepkumar, P., Naik, N. 
and Supriya, G., Planet. Space Sci., 2010, 
58, 947–950. 
2. Sridharan, R., Ahmed, S. M., Das, T. P., 
Sreelatha, P., Pradeepkumar, P., Naik, N. 
and Supriya, G., Planet. Space Sci., 2010, 
58, 1567–1577. 
3. Sridharan, R., Das, T. P., Ahmed, S. M., 
Supriya, G., Bhardwaj, A. and Kamalakar, 
J. A., Adv. Space Res., 2013, 51, 168–178. 
4. Hoffman, J. H., Hodges Jr, R. R. and Evans, 
D. E., In Proceedings of the 4th Lunar Sci-
ence Conference, Geochim. Cosmochim. 
Acta, Suppl. 4, 1973, pp. 2865–2875. 
 
ACKNOWLEDGEMENTS. This work is 
supported by the Department of Space, Gov-
ernment of India. R.S. thanks NASI for the 
Senior Scientist position and the Director, 
PRL, Ahmedabad for providing the necessary 
facilities. 
Received 9 October 2013; accepted 11 Octo-
ber 2013 
 
 
R. SRIDHARAN1,* 
TIRTHA PRATIM DAS2 
S. M. AHMED3 
ANIL BHARDWAJ2 
 
1Physical Research Laboratory, 
Ahmedabad 380 009, India 
2Space Physics Laboratory, 
Vikram Sarabhai Space Centre, 
Thiruvananthapuram 625 022, India 
3Central University, 
Hyderabad 500 046, India 
*For correspondence. 
e-mail: sridharan@prl.res.in 
 
 
 
 
Lessons from Kedarnath tragedy of Uttarakhand Himalaya, India 
 
The complete destruction by Mandakini 
River in Kedarnath on 16 and 17 June 
2013 could not have been avoided. Yet, 
the number of casualties would have 
been far less had the mushrooming growth 
of hotels, lodges and dharmshalas not 
been allowed in Kedarnath. This has 
been one of the worst Himalayan trage-
dies in recent years in which the exact 
number of people buried/perished is not 
known as thousands are still missing. 
Almost the entire Rambara and a large 
part of Gaurikund and many villages of 
Mandakini valley were also wiped out. 
The flash flood and attendant debris flow 
was undoubtedly an irrepressible natural 
hazard. However, its worst impact must 
be viewed in the perspective of high  
vulnerability (of this area) mainly attri-
buted to rampant construction activity 
for commercial purpose in Kedarnath, 
Rambara and Gaurikund in the close 
proximity of Mandakini River and also 
the uncontrolled floating population of 
pilgrims. It was the worst-case scenario 
with an area of very high vulnerability 
(man-made) experiencing flash floods 
and debris flow induced by torrential 
rains, Chorabari lake collapse and mobili-
zation of glacial material1. This corre-
spondence discusses the measures aimed 
at reducing the vulnerability of this area 
in the future. 
 About 131 years ago in 1882 only the 
Kedarnath temple and four to five huts 
(chhan in local parlance) existed in the 
region. 
 Some decades ago, the holy shrines of 
Uttarakhand did not witness heavy influx 
of floating population of pilgrims and 
tourists. Also, there was no rampant con-
struction activity on active and old flood 
plains and lower terraces of rivers and on 
critical hill slopes. Our rising population, 
economic growth and improved lodging 
facilities due to rapid transformation in 
the livelihood strategies of locals have 
drastically increased the influx of  
pilgrims and tourists in this region. 
 A few years back, the pilgrims used  
to start their journey from Gaurikund to 
Kedarnath on foot or by pony early in the 
morning just to ensure their return to 
Gaurikund by afternoon on the same day. 
This was because there were few lodges/ 
hotels in Kedarnath and even far lesser 
number of such facilities in Rambara, 
which is a transit point midway between 
the 14 km long pony route from Gauri-
kund to Kedarnath. 
 The area is geodynamically unstable 
with neotectonic movements and high 
frequency of landslides, including rock 
falls, debris flow and ground subsi-
dence2,3. The source of the Mandakini 
River is formed by Chorabari and an  
unnamed companion glacier. The settle-
ment of Kedarnath is just 500 m below 
the snout of these glaciers and the termi-
nal moraine hump is about 275 m high 
from the outwash plain over which  
Kedarnath is situated (GSI, unpublished). 
Examination of satellite images indicates 
that this outwash plain might have been 
reworked by the Mandakini River in the 
past and a major part of Kedarnath till 16 
June 2013 was located on the old flood 
plain (T1 terrace). However, the famous 
Kedarnath temple constructed on a man-
made raised platform seems to be located 
on a higher terrace of the Mandakini 
River. The moraine ridges running paral-
lel and subparallel to the upper Manda-
kini valley are conspicuous in Kedarnath 
and further downstream up to Garuriya 
and Ghindurpani. After the flash floods 
and debris flow of 16 and 17 June 2013 
(although flood water of the Mandakini 
River has receded), it would not be  
geologically incorrect to say that the 
completely devastated settlement of  
Kedarnath today lies on the active flood 
plain of Mandakini River that may be 
flooded again in the near or far future in 
the event of torrential rains and or due to 
mobilization of glacial material. 
 Critical slopes on the hillside and flash 
flood-prone banks on the river side restrict 
the capacity of the Himalayan shrines of 
Yamunotri, Gangotri, Kedarnath, Badri-
nath and a number of habitations such as 
Gaurikund and Rambara (on the way to 
Kedarnath) and Janki chatti (on the way 
to Yamunotri) to safely accommodate the 
growth of 3–4-storied hotels and lodges. 


Indicators for localized regions of heavier species in the lunar surface from CHACE on Chandrayaan-1

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Indicators for localized regions of heavier species in the lunar surface from CHACE on Chandrayaan-1

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