Mangalyaan mission over, what MOM got for us from Mars

After eight years of spectacular performance, India’s iconic Mars Orbiter Mission (MOM), popularly known as Mangalyaan, lost communication with Earth in April this year, bringing an end to its life. Incidentally, it was designed to last for just six months but outperformed everyone’s expectations. ISRO announced on October 3, that its attempt to re-establish contact with the craft has failed, and India’s first interplanetary mission is officially terminated. “The spacecraft is non-recoverable and attained its end of life,” said ISRO in a press release on October 3.

“This was a pilot technology demonstration mission. Hence, we cannot claim big scientific achievements. Yet the craft functioning for nearly eight years has done reasonably good science and has been a learning ground for Chandrayaan-2 and other deep space missions,” Dr Mylswamy Annadurai, the then programme director of ISRO’s MOM mission, said.

Delicate dance

Launched on November 5, 2013, MOM was inserted into Mars orbit on September 24, 2014. Placed in a highly elliptical orbit, it took the craft as close as 421.7 km to the surface of Mars and as far away as 76,993.6 km. In this orbit, MOM took 72 hours, 51 minutes and 51 seconds to go around Mars once.

If the orbit was in the same plane as the planet’s trajectory around the Sun, then MOM would have slipped behind and been eclipsed by Mars in every orbit. Shielded by the planet during the eclipse, the craft would have entered the shadow of Mars.

MOM is solar-powered and, therefore, cannot function without the power of the Sun. During an eclipse by Mars, MOM would have become precariously powerless. The craft’s orbit was inclined at 150 degrees to avoid this hazardous scenario. Orbiting Mars in the inclined plane, the ship was either above or below the planet in direct view of the Sun.

Nevertheless, even in this inclined orbit, the craft would have been eclipsed by the planet once in a while, resulting in risky power out. The ship was designed to autonomously operate its rockets to steer itself away from danger and swiftly move out of the darkness.

On average, Mars is around 225 million km away from Earth. It can be as close as 54.6 million km and as high as 401 million km. Hence, the radio signal from Mars to reach Earth takes between 5 to 20 minutes, making the two-way communication delay 10 to 40 minutes.

Hence, it is impossible to manoeuvre the spacecraft like a remote car from the control station on Earth. “MOM is enabled with autonomous functions,” says Mylswamy Annadurai. On board, rockets are fired to make the orbital correction, spin the craft, and point the antenna towards the Earth. “Out of the 852 kg of fuel at launch, we hoped enough fuel would be left for its operation for six months. However, more than 40 kg was left over after the Mars orbital insertion, permitting the craft to survive for years,” says Mylswamy Annadurai.

In 2017, MOM was computed to go into an eclipse for longer than it could manage. Little more than 20 kg of the fuel had to be used up to perform the critical manoeuvre to drive the orbiter to safety. That left the craft with just around 13 kg of fuel. Routine orbital maintenance requires about 2.5 kg of fuel per year. The ship had to cease functioning with the depleting fuel. The fatal eclipse in April 2022 was but the final nail.

As had occurred many times in the past, the Mars Orbiter Mission entered the dark shadow of Mars in April 2022, only this time, it was seven long hours of darkness. The autonomous function should have taken over and steered the craft to sunlight. The backup satellite battery was designed to power for only 1 hour and 40 minutes.

The prolonged eclipse drained the battery beyond its limit. Without adequate fuel and battery power, the ship could not orient the antenna towards the Earth. The craft could not come out of this ruinous power outage, and the communication instruments stopped working. ISRO could not revive the spacecraft.

After eight incredible years of service, MOM was declared dead. Its current whereabouts are unknown. With no fuel to maintain its orbit, and the ground controllers helpless, the craft will slowly drift towards Mars surface.

The legacy

The scientific objective of the mission was to explore the Martian surface features, morphology, mineralogy and Mars atmosphere using five indigenous scientific instruments – Lyman-Alpha Photometer (LAP), Methane Sensor for Mars (MSM); Mars Exospheric Neutral Composition Analyser (MENCA); Thermal Infrared Imaging Spectrometer (TIS) and Mars Colour Camera (MCC). “These science instruments were realised indigenously with a total mass budget of less than 15 kg in a stringent time schedule. What we have achieved with these modest instruments is commendable,” Mylswamy Annadurai told The Federal. “We could come out with a Mars atlas from the images obtained by the Mars Colour Camera (MCC),” he added.

One of the notable discoveries of MOM is the unusually ‘hot’ Argon molecules in the upper atmosphere of Mars. The average motion of the molecules in a gas depends upon the system’s temperature. The hotter it is, the higher the average speed of the molecules. However, the Mars Exospheric Neutral Composition Analyser (MENCA) detected an anomaly. The Argon in the exosphere, around 220 km from the planet’s surface, was moving much faster than the temperature of that layer would warrant.

MOM made this observation when Mars was at its closest point to the Sun in its elliptical orbit. ‘Hot’ molecules can easily escape from the atmosphere’s surface to outer space. Thus, the data from MOM could explain how the once thick Martian atmosphere became as thin as it is today. Further, the composition of the upper atmosphere showed that the abundance of oxygen exceeds that of carbon dioxide at an altitude of 270 during the evening hours when the planet is closer to the Sun.

Seasons watch

Like Earth, Mars also undergoes seasonal changes once in the Martian year of 687 days. Thus, each of the four seasons on Mars is nearly twice as long on Earth. Like on Earth, while it is winter in the southern hemisphere, it is summer in the northern hemisphere.

“Active for about eight years, MOM was able to observe nearly three to four seasonal changes on the surface of Mars,” says Mylswamy Annadurai. Seasonal changes in the terrain and atmosphere, both local and global, could be captured by MOM.

Moreover, due to its peculiar inclined orbit, MOM was designed to look closely at the polar regions of Mars. Observations of these regions were virgin, as no rovers have gone until now. These observations have yielded exciting data on the Martian weather systems.

The polar ice caps start to recede with the onset of spring and disappear entirely during summertime. The ice cap expands once again during autumn and, by winter, extends even up to mid-latitudes on Mars. The Martian polar ice caps are primarily made up of dry ice (carbon dioxide). Hence, when they melt, a large quantity of carbon dioxide is released, making the Martian atmosphere thick. Once again, the atmosphere becomes thin in winter when the ice cap grows.

The transformations in the polar terrain during the seasons give us a clue as to how clouds form on the surface of Mars. “The observations suggest that perhaps, like on Earth, rain precipitates on the surface of Mars. Nevertheless, only further research will be able to confirm it,” says Mylswamy Annadurai.

Dust storms

Like Earth’s orbit, the orbit of Mars is also elliptical. When Mars is closest to the Sun, its southern hemisphere is tilted towards it, making the southern summer comparatively hotter. The extra heat drives turbulence and stirs up planet-wide dust storms.

Driven by seasonal changes, numerous dust storms occur in a Martian year. Smaller storms, called dust devils, occur daily and last minutes to hours. Regional storms, lasting from days to weeks, often occur during the southern spring and summer. Planet-scale dust storms, that onset during the southern spring and summer, occur quasi-annually and can last for months.

“The highly elliptical orbit of MOM was intentionally designed to obtain closer, high-resolution images of spots, say, where a storm is brewing. We could also capture the large plant-wide images to see their wider impact. The mapping of the terrain during various seasons combined with high-resolution images is a treasure to understand Mars and its seasonal changes,” says Mylswamy Annadurai

MOM observed the gestation, formation and spread of such storms. For example, the Mars Colour Camera (MCC) observed the evolution of local-scale dust storms between October 11 and October 28, 2014. The storm became relatively larger on October 20 and nearly disappeared, leaving a haze on October 28, 2014.

Leaking gas

Heated by the sunlight, the molecules in the upper atmosphere may move fast enough to break free from the clutches of the planet’s gravity. This process, known as ‘Jean’s escape’ (named after James Jean, an English astronomer), accounts for much hydrogen leakage from Earth. At lower altitudes, in the dense atmosphere, a fast-moving gas molecule is likely to collide with another and remain confined in the atmosphere. However, in a region called ‘exobase’, the air is so thin that gas particles hardly collide. In this layer, unhindered gas molecules with great velocities fly into space.

Alternatively, the upper atmosphere can heat up and expand. The accelerating air, powered by the heat, could attain escape velocity and be blown away into interplanetary space.

“One of the key findings of MOM is the rate of atmospheric loss which is much greater than Earth due to the seasonal planet-wide dust storms,” says Mylswamy Annadurai.

A perfect dust storm, one of the most intense planet-wide dust storms observed, gathered during the first week of June 2018. It grew and engulfed the whole planet by the first week of July 2018. It was so severe that NASA’s Mars rover, solar-powered Opportunity, was forced into survival mode. At the same time, the nuclear-powered Curiosity made real-time observations of the darkening of the Martian sky.

During this period, the MOM craft flew down to an altitude of 155 km. NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) joined hands with MOM to simultaneously observe the impact of the dust storm on the Martian upper atmosphere. While MAVEN observed the morningside, MOM attended the evening side. From the data, scientists found that the upper atmosphere was warmer on the evening side as compared to the morning side. Also, the upper atmosphere was warming and expanding as the dust storm enveloped the planet.

Propelled by the heat generated by the dust storm, the expanding upper atmosphere reached the critical altitude of 220 km – Martian exobase. Once the warm gas reaches this height, the fast-moving molecules will likely escape into outer space. In addition to Jean’s escape mechanism, MOM revealed that the planet-wide dust storms triggered enhanced leakage of the Martian atmosphere.

Impressive fete

The data from MOM have been much sought-after. More than 7,200 legitimate research users, of which 400 are international users from 50 countries, have registered to download the data, says ISRO. The wealth of data derived from the instruments will undoubtedly expand our knowledge of Mars, which one day can become the second home to humanity.

Nevertheless, critics point out that just about 27 papers have come out of MOM data, indicating perhaps a lack of emphasis on nurturing academic scientific partners. Perceptively, Dr Vikram Sarabhai, founder of the Indian space programme, had pointed out that the ground segment, capacity building for using the space technology, must go hand in hand with the design and development of the space segment.

While there are 1,585 researchers per million in China, India is far behind with just 255 per million. The lack of adequate scientific human resources, as indicated by the paltry number of researchers per million population in India, is perhaps a constraint that prevents Indian institutions from being able to use the data. And it is this factor – expanding our scientific base – that we must focus on while celebrating MOM’s legacy.