Sitting in his "lab" in Chennai, Indian amateur space scientist Shanmuga Subramanian beat both NASA and ISRO in locating Chandrayaan-2's elusive Vikram lander by scouring through the images from the US space agency's Moon orbiting spacecraft.
Subramanian, 33, who was on Tuesday the toast of the astronomy world, managed what ISRO and NASA couldn't through his close examination of before and after images of the scheduled landing.
NASA, which released images showing the site of the Vikram lander's impact and the associated debris field, acknowledged the role of the mechanical engineer and app developer in locating the site of the debris.
"NASA has credited me for finding Vikram Lander on Moon's surface VikramLander Chandrayaan2," Subramanian said in a tweet.
The 33-year-old, who belongs to Madurai in Tamil Nadu, told reporters in Chennai where he is currently based, that he spent hours going through the images taken by NASA's Moon orbiting Lunar Reconnaissance Orbiter (LRO), monitoring them on two computers kept in his “lab”.
He said he had spent four to six hours a day over the last couple of month closely analysing the images.
“It appears that the initial searches looked at wrong locations and this discovery by Shan was serendipitous,” Dibyendu Nandi, a professor at Kolkata's Indian Institute of Science Education and Research (IISER), told PTI.
The debris, first located by Subramanian, is about 750 metres northwest of the main crash site, NASA said.
After receiving this tip, the LRO team confirmed the identification by comparing the before and after images.
"Thank you for your email informing us of your discovery of debris from the Vikram lander. The LROC team confirmed that the location does exhibit changes in images taken before and after the date of the landing," John Keller, deputy project scientist LRO mission, told Subramanian in an acknowledgment mail.
"Using this information, the LROC team did additional searches in the area and located the site of the primary impact as well as other debris around the impact location and has announced the sighting on the NASA and ASU pages where you have been given credit for your observation," Keller said.
On September 7, the Indian Space Research Organisation attempted a soft landing of Vikram on the Moon, before losing contact with the lander ahead of the scheduled touchdown.
NASA has since made several attempts to locate the Chandrayaan-2 lander with the help of LRO, which flew over Vikram's landing site once on September 17 and next on October 14.
However, after analysing the images, NASA and ISRO couldn't locate the lander.
“The image processing and feature recognition ability of the human brain is difficult to easily automate. So what could not be achieved by feature recognition software was achieved by a curious member of the general public,” Nandi said.
He said Subramanian's findings about Vikram's “kinematics”, the study of motion at the time of impact, made the discovery more interesting.
For example, the depth of the impact crater compared to the spread of Vikram's debris hold clues to deciphering the speed and angle of impact, Nandi said.
“This information would be useful in reconstructing what went wrong with the landing manoeuvre, and at what height above the lunar surface the anomaly set in,” he said.
On September 26, the US space agency released a mosaic image of the site taken on September 17, inviting people to compare it with the images of the same area before the crash to find signs of the lander.
The first person to come up with a positive identification was Subramanian, who confirmed the location of the crashing site of Vikram by comparing before and after images.
On October 3, Subramanian tagged the Twitter handles of NASA, LRO and ISRO in a tweet, asking, "Is this Vikram lander? (1 km from the landing spot) Lander might have been buried in Lunar sand?"
On November 17, he zeroed in on his observations and tweeted out the possible crash site of the lander in the images.
"This might be Vikram lander's crash site (Lat:-70.8552 Lon:21.71233 ) & the ejecta that was thrown out of it might have landed over here … (The one on the left side was taken on July 16th & one on the right side was from Sept 17)," he said in a tweet accompanying the images.
As it turns out, Subramanian was spot on with his inferences.
“I have no idea why this was not located earlier by scientists associated with either ISRO or NASA,” Nandi noted.
“Typically these observations are in the public domain and given the amount of data and images, it is sometimes not possible to search through everything and scientists confine search locations to intelligent guesses,” he explained.
"When the images for the first mosaic were acquired, the impact point was poorly illuminated and thus not easily identifiable," NASA said in a statement, adding that two subsequent image sequences were acquired on October 14 and 15, and November 11.
The LRO team scoured the surrounding area in these new mosaics and found the impact point about 2,500 feet to the southeast of the planned touchdown site, and a spray of debris emanating outwards.