Chandrayaan-2's Orbiter Entered Lunar Orbit on 20 August 2019, and Its Eight Instruments Have Since Reported Hydroxyl, Sodium, Argon-40 and Possible Polar Ice

The Chandrayaan-2 orbiter entered lunar orbit on 20 August 2019 with eight instruments that map the Moon’s surface, its thin atmosphere and the Sun’s X-rays. ISRO’s August 2021 compilation of results says the mission was planned to last one year and that precise launch and mission management gave the orbiter a life of almost seven.

Papers from its data have kept arriving since: the first global-scale sodium measurement in 2022, a coronal mass ejection recorded in the lunar atmosphere in 2025, and a radar study of possible ice in south polar craters announced on 27 May 2026.

From launch to the 7 September descent

A GSLV Mk III rocket launched Chandrayaan-2 from Sriharikota on 22 July 2019, with the lander stacked on the orbiter at a combined mass of 3,846 kilograms. Orbit insertion at the Moon came on 20 August, according to the compilation, followed by four manoeuvres down to a 100 by 100 kilometre orbit and the separation of the lander, Vikram, on 2 September.

The orbiter also helped with the landing itself. Its high-resolution camera, ISRO says, imaged the landing site about ten hours before touchdown, and hazards found in the images were uplinked to Vikram four hours before landing.

Vikram’s descent went as planned down to 2.1 kilometres above the surface, ISRO’s compilation says. Then communication was lost and the lander hit the surface hard. In a written reply to the Lok Sabha, reported on 21 November 2019, the government said the velocity reduction in the second phase of the descent exceeded the design value and that Vikram came down within 500 metres of the intended site. The Chandrayaan-3 article covers what ISRO changed afterwards.

On 8 September 2019 the ISRO chairman, K. Sivan, said, “We have found the location of Vikram lander on lunar surface and orbiter has clicked a thermal image of the lander.” NASA’s Lunar Reconnaissance Orbiter later photographed the impact site. On 2 December 2019 NASA said Shanmuga Subramanian’s first identification of debris lay about 750 metres northwest of the main crash site.

Planned for one year, managed for far longer

ISRO’s note on the orbiter’s first year says it had completed more than 4,400 orbits, with 17 orbit-maintenance manoeuvres since reaching 100 kilometres on 24 September 2019. It keeps the craft in a polar orbit of 100 kilometres, give or take 25. Onboard fuel, ISRO wrote in August 2020, was enough for about seven years.

Instruments take turns. When the Sun sits at a low angle to the orbital plane, the optical instruments work. When it sits at a high angle, the radar does. CLASS, XSM and CHACE-2 run in every season, and downloaded data go to the Indian Space Science Data Centre. In its first year the orbiter’s terrain camera imaged nearly 4 million square kilometres of the Moon over 220 orbits.

Hydroxyl and water on the surface

NASA’s spectrometer on Chandrayaan-1 saw a hydration feature near 3 micrometres, but its range stopped at 3.0, so ISRO’s compilation says the nature of the signal could not be settled. Chandrayaan-2’s Imaging Infra-Red Spectrometer (IIRS) reads up to 5.0 micrometres at about 80 metres per pixel, and ISRO calls its result the first unambiguous detection of hydration features on the Moon, with separate signatures of hydroxyl and water.

A paper by Prakash Chauhan and colleagues in Current Science, listed in ISRO’s compilation, reports hydration at every latitude and surface type between 29 and 62 degrees north. Rocks rich in plagioclase, a light-coloured mineral, showed more hydration than the dark plains known as mare. At the crater Aristarchus, ISRO’s compilation puts the water content at about 15 to 170 parts per million, averaging about 80, and says the spectrum looks more like adsorbed hydroxyl than water.

Radar for polar ice

The orbiter’s Dual Frequency Synthetic Aperture Radar (DFSAR) is, in ISRO’s description, the first fully polarimetric dual-frequency imaging radar in lunar orbit. Earlier radars on Chandrayaan-1 and NASA’s Lunar Reconnaissance Orbiter found bright, anomalous signals in polar craters that could come from ice or from rough, rocky ground. Those results were ambiguous, the compilation says, and DFSAR’s full polarisation allows the two to be separated.

It maps probable ice-bearing patches inside small craters on the floor of Peary crater near the north pole. At Cabeus, the south polar crater hit by the 2009 LCROSS experiment, the first analysis found no thick, pure ice in the top two to three metres of the part studied. It did flag a few patches of possible “dirty ice” mixed into the soil.

An announcement from ISRO and the Physical Research Laboratory (PRL) on 27 May 2026 goes further. A PRL team with lead author Sinha, writing in npj Space Exploration, reports radar signatures beneath the floors of four doubly shadowed craters near the south pole, meaning small craters inside larger permanently shadowed ones. Their criterion is a circular polarisation ratio above 1 with a degree of polarisation below 0.13. A 1.1 kilometre crater inside Faustini gives the strongest case. In ISRO’s description all four are consistent with possible subsurface ice, and none is confirmed.

Sodium, argon-40 and two metals

The orbiter’s X-ray spectrometer CLASS gave the first global-scale measurement of sodium on the lunar surface, in a paper led by S. Narendranath of ISRO’s U R Rao Satellite Centre, published on 26 September 2022. Its global average is 1.33 plus or minus 0.03 per cent by weight, higher than previously known, the paper says: soil samples brought back by Apollo, Luna and Chang’e-5 span 0.3 to 0.72 per cent. Trends in the data suggest, in the authors’ reading, a long-lived layer of sodium sticking to grain surfaces, which could keep the Moon’s sodium exosphere supplied.

CHACE-2, a mass spectrometer that samples the Moon’s near-vacuum atmosphere, measured argon-40 between 60 degrees south and 60 degrees north. Earlier measurements from Apollo 17 and NASA’s LADEE had covered only the equator. The gas is thought to come from the decay of radioactive potassium-40, ISRO says. Its density peaks near sunrise, shows a smaller peak near sunset and bottoms out at night. It also bulges over two regions, the South Pole-Aitken basin and a terrain called KREEP. Among the possible causes the authors list moonquakes. At its September 2021 workshop ISRO added that CLASS found trace chromium and manganese.

The Sun, seen from the Moon

The Solar X-ray Monitor (XSM) has observed the Sun since September 2019, during the deepest solar minimum of the past century. A paper led by Santosh Vadawale of PRL counted 98 microflares weaker than A-class on the GOES scale of flare strength, over 76 days, with thermal energies from 3 × 10^26 to 6 × 10^27 ergs. The authors call it the first full analysis of a large sample of such events in soft X-rays.

ISRO’s results page adds nine B-class flares, from B1.3 to B4.5, whose magnesium, aluminium, silicon and sulphur abundances fell toward photosphere values at the peak and returned to coronal values afterwards. Those are the first absolute abundance measurements for flares that small, in ISRO’s words. The work predates Aditya-L1, India’s dedicated Sun mission.

On 10 May 2024 a series of coronal mass ejections, huge clouds of plasma thrown from the Sun, reached the Moon. CHACE-2 saw the number density of the dayside exosphere rise by more than a factor of ten, ISRO reports, in what it calls the first direct observation of an effect that models had predicted. The paper, by M. B. Dhanya and colleagues, appeared in Geophysical Research Letters on 16 August 2025.

Maps, boulders and a young fault

The terrain camera found a small thrust fault scarp in the Mare Fecunditatis region on 15 October 2019, in low-angle sunlight that throws small relief into shadow. Its length is 1,416 metres, the one-year note says, with an average relief of 24 metres, and it may date from the Copernican period, which would make it geologically young. Signs of crustal shortening and volcanic domes are on the workshop summary’s list of the camera’s findings.

Another instrument, the Orbiter High Resolution Camera (OHRC), counted 1,969 boulders larger than 1.12 metres around a 340 metre crater near Boguslawsky E, and ISRO’s compilation estimates the crater at 65 to 87 million years old from the boulder spread. ISRO’s documents disagree on that camera’s resolution: the compilation says 0.25 metres at nadir, the one-year note about 30 centimetres, and the workshop summary 25 centimetres.

What the orbiter gave Chandrayaan-3

ISRO’s compilation says OHRC was also used to image potential Chandrayaan-3 landing sites. A paper by K. Durga Prasad and colleagues used OHRC elevation models to characterise Chandrayaan-3’s alternate site, about 450 kilometres west of the primary one at nearly the same latitude.

The orbiter was also a communication backup. A contingency link is how ISRO’s mission page describes it, and the launch brochure lists it among the lander’s communication paths. On 21 August 2023, two days before the landing, ISRO announced that two-way communication had been established between the orbiter and Vikram, adding a channel to the control centre in Bengaluru. ISRO’s post said, “Welcome, buddy!”

Two days after the landing, on 25 August 2023, ISRO posted a photograph of the Chandrayaan-3 lander on the surface, taken by the orbiter’s high-resolution camera, with the words “I spy you!” A paper by S. Vijayan and colleagues at PRL and ISRO, using OHRC images with the Pragyan rover’s cameras, found that the landing site sits on a buried impact crater. Per ISRO’s 30 September 2024 release, the crater is about 160 kilometres across and 4.4 kilometres deep.