Spatial heterogeneity in the radiogenic activity of the lunar interior: Inferences from CHACE and LLRI on Chandrayaan-1

In the past, clues on the potential radiogenic activity of the lunar interior have been obtained from the isotopic composition of noble gases like Argon. Excess Argon (40) relative to Argon (36), as compared to the solar wind composition, is generally ascribed to the radiogenic activity of the lunar interior. Almost all the previous estimates were based on, 'on-the-spot' measurements from the landing sites. Relative concentration of the isotopes of 40Ar and 36Ar along a meridian by the Chandra's Altitudinal Composition Explorer (CHACE) experiment, on the Moon Impact Probe (MIP) of India's first mission to Moon, has independently yielded clues on the possible spatial heterogeneity in the radiogenic activity of the lunar interior in addition to providing indicative 'antiquity' of the lunar surface along the ground track over the near side of the moon. These results are shown to broadly corroborate the independent topography measurements by the Lunar Laser Ranging Instrument (LLRI) in the main orbiter Chandrayaan-1. The unique combination of these experiments provided high spatial resolution data while indicating the possible close linkages between the lunar interior and the lunar ambience

MENCA experiment aboard India’s Mars Orbiter Mission

The Mars Exospheric Neutral Composition Analyser (MENCA) aboard the Indian Mars Orbiter Mission (MOM) is a quadrupole mass spectrometer-based experiment. Making use of the highly elliptical and low inclination (~150°) orbit of MOM, MENCA will conduct in situ measurements of the composition and radial distribution of the Martian neutral exosphere in the 1–300 amu mass range in the equatorial and low latitudes of Mars. The functionality of MENCA has been tested during the Earth-bound and heliocentric phases of MOM before its operation in the Martian orbit. This article describes the scientific objectives, instrument details, design and development, test and evaluation, and calibration of the MENCA instrument

SCIENCE FICTION

50-52The Machin

The spatial distribution of molecular Hydrogen in the lunar atmosphere—new results

The measurements carried out by Chandra׳s Altitudinal Composition Explorer (CHACE) onboard the Moon Impact Probe (MIP) of Chandrayaan I mission is used to obtain information on the 2-D distribution of the lunar atmospheric H2 by a novel approach that makes use of the basic fact that the Moon has a Surface Boundary Exosphere (SBE).These are the ‘first’ daytime in situ measurements of lunar H2 covering the 20°S to 88°S latitude region centered ~14°E longitude. A critical examination of the observed spatial features of the surface number density of H2 vis-à-vis the surface topography delineated from the Lunar Laser Ranging Instrument (LLRI) in the main orbiter Chandrayaan-I, indicates that that lunar surface process may be important in introducing small scale variations in the H2 number density. Another constituent which exhibited spatial variation in the observed partial pressure is 40Ar and it was hypothesized that it is indicative of the spatial heterogeneity in the radiogenic activity of the Lunar interior (Sridharan et al., 2013a). The absolute number density at the surface and also the latitude/altitude variation of the densities that are reported for the first time, highlight the complexities of the sunlit lunar atmosphere

'Direct' evidence for water (H<SUB>2</SUB>O) in the sunlit lunar ambience from CHACE on MIP of Chandrayaan I

Direct detection of water in its vapour phase in the tenuous lunar environment through in situ measurements carried out by the Chandra's Altitudinal Composition Explorer (CHACE) payload, onboard the Moon Impact Probe (MIP) of Chandrayaan I mission vindicates the presence of water on the surface of the moon in form of ice at higher lunar latitudes inferred from IR absorption spectroscopy, (especially that of OH), by the Moon Mineralogy Mapper (M<SUP>3</SUP>) of Chandrayaan I. The quadrupole mass spectrometer based payload, CHACE, sampled the lunar neutral atmosphere every 4 s with a broad latitudinal (&#732;40&#176; N to 90&#176; S, with a resolution of &#732;0.1&#176; ) and altitudinal (from 98 km up to impact on the lunar surface with a resolution of &#732;0.25 km) coverage in the sunlit side of the moon for the first time. These two (CHACE and M<SUP>3</SUP>) complementary experiments are shown to collectively provide unambiguous signatures for the distribution of water in solid and gaseous phases in Earth's moon

On the evening time exosphere of Mars: result from MENCA aboard Mars Orbiter Mission

The Mars Exospheric Neutral Composition Analyser (MENCA) aboard the Indian Mars Orbiter Mission (MOM) is a quadrupole mass spectrometer which provides in situ measurement of the composition of the low-latitude Martian neutral exosphere. The altitude profiles of the three major constituents, i.e., amu 44 (CO₂), amu 28 (N₂ + CO), and amu 16 (O) in the Martian exosphere during evening (close to sunset terminator) hours are reported using MENCA observations from four orbits of MOM during late December 2014, when MOM's periapsis altitude was the lowest. The altitude range of the observation encompasses the diffusively separated region much above the well-mixed atmosphere. The transition from CO₂ to O-dominated region is observed near 270 km. The mean exospheric temperature derived using these three mass numbers is 271 ± 5 K. These first observations corresponding to the Martian evening hours would help to provide constraints to the thermal escape models