The scientists from Japan Aerospace Exploration Agency (JAXA) went jubilant on Sunday. They had been anxiously waiting for the moment, when Japan’s Moon lander—Slim would come back to life again on the lunar surface. It had been shut for a week after power supply issue had surfaced, following the smooth landing of the spacecraft.

On Monday, JAXA announced that it was successful in re-establishing contact with the ‘Slim’ lander on Sunday night. 

Japanese scientists were able to fix the glitch and bring back Slim to life. Last year in September, India faced a similar instance, when back home ISRO scientists were trying hard and anxiously waiting for their 'Vikram' Moon lander and 'Pragyan' rover to come back to life on the lunar surface. 

Both were part of India’s successful lunar mission—‘Chandrayaan 3’. 

However, the glitch in them couldn’t be fixed and ISRO couldn’t establish contact with them again.

So, why could Slim come back to life again while India’s Vikram and Pragyan went into sleep mode forever. Here is what made the difference:

The key between Japan’s Slim Moon lander and India’s—Pragyan and Vikram Moon landers was sunlight. 

Slim’s solar cells are working again after a shift in lighting conditions allowed it to catch sunlight, JAXA agency said.

Earlier, when it landed on Moon on January 20 this year, it could not generate power as the solar cells pointed away from the Sun. It had run on battery power for several hours before JAXA scientists decided to turn it off to allow for a possible recovery of electricity when the angle of sunlight changed.

Same was the case with India’s Vikram Moon lander and Pragyan rover. Both ran on solar power. Therefore, they needed sunlight to charge their batteries and operate again. 

Pragyan and Vikram Moon landers were also put into sleep mode like Slim. Both were put on sleep mode in early September and were supposed to wake up again on September 22, last year, since lunar sunrise is long compared to Earth’s sunrise. A lunar night lasts for about Earth’s 14 days.

The reason they couldn’t wake up or come back to life again is also that lunar nights are extremely cold. The temperatures can go down upto minus 200 degree Celsius. This means that the batteries might have been affected. 

Like Japan’s space agency, ISRO had also expected to waiting for the temperatures to rise as the lunar day progressed. However, ISRO could make Vikram Moon lander and Pragyan rover operational again.

Meanwhile, India is the fourth country after the US, Russia, and China to land on the moon. India is also the first to ever land near the lunar south pole. Japan became the fifth successful country to land on lunar surface.