Venus, often referred to as Earth's twin sister, has long intrigued scientists with its enigmatic atmosphere and extreme conditions. Numerous space agencies have already embarked on missions to study this neighbouring planet, shedding light on its mysteries and offering insights into the evolution of rocky planets.
The Indian Space Research Organisation (ISRO) has joined this quest with its Venus Orbiter Mission, colloquially known as Shukrayaan. Set to launch in December 2024, it is designed to study the surface and atmosphere of Venus. It is expected to be a significant milestone for ISRO and has garnered attention for its ambitious scientific objectives and innovative technology.
With a planned duration of four years, the spacecraft will weigh approximately 2,500 kg at launch and carry a science payload of around 100 kg.
Inspired by the success of previous missions like Chandrayaan and the Mars Orbiter Mission, ISRO initiated preliminary studies for interplanetary missions to Venus and Mars. An Announcement of Opportunity (AO) was released in 2017 to solicit science payload proposals, both from Indian academia and the international scientific community. ISRO has also explored collaborations with institutions from countries like France, Russia, Sweden, and Germany.
“The Venus Orbiter Mission aims to explore few major research areas such as Surface and Subsurface Stratigraphy that involves investigating Venus' surface and subsurface to understand its geological history and resurfacing processes. Besides this it will study the composition, dynamics, and chemistry of Venus' thick atmosphere, including the enigmatic phenomena like the greenhouse effect. The mission will also examine how Venus' ionosphere interacts with solar irradiance and solar wind, contributing to our knowledge of planetary atmospheres,” explained Srimathy Kesan, founder and CEO of Space Kidz India, which is into design, fabrication and launch of small satellites, spacecraft and ground systems.
Venus is a planet that is hard to classify easily. It is the second planet from the sun and also the second-brightest object in the night sky, just after the Moon. It is nearly the same size and mass as Earth, but it holds the title of being the hottest and most volcanically active planet in our solar system.
“Venus is situated in the Sun’s habitable zone, where conditions are just right for planets to potentially support life. But its dense atmosphere traps heat so effectively that it triggers a runaway greenhouse effect. This means that the planet becomes exceedingly hot and inhospitable due to the trapped heat, creating a harsh, corrosive environment.
"Venus has an average surface temperature of about 460°C, which is hot enough to melt lead. This temperature is maintained by a thick layer of carbon dioxide and sulphuric acid clouds that trap most of the incoming solar radiation and reflect it back to space. The atmosphere of Venus is about 90 times denser than that of Earth, which exerts a pressure equivalent to being 1 km underwater on Earth. The atmosphere also contains traces of other gases, such as nitrogen, water vapour, carbon monoxide and sulphur dioxide,” explained space expert Girish Linganna.
Venus has no moons and rotates very slowly in the opposite direction of most planets, making its day longer than its year. A day on Venus is for a duration of 243 Earth days, while a year is for a duration of 225 Earth days. This means that the Sun rises in the west and sets in the east on Venus and that one day-night cycle on Venus takes 117 Earth days. The ‘day-night cycle’ refers to the pattern of alternating day (when there is sunlight) and night (when it is dark) on a planet or celestial body. On Earth, this cycle is approximately 24 hours, meaning we have about 12 hours of daylight and 12 hours of darkness. However, on Venus, it takes 117 Earth days for this cycle to complete, so a day and a night on Venus are each much longer than on Earth.
The Venus Orbiter Mission's science payload comprises instruments from India and various international collaborators. Some notable Indian instruments include Venus L & S-Band SAR, VARTISS (HF radar), VSEAM (Surface Emissivity), and LIVE (Lightning Sensor). International contributions encompass terahertz devices for powerful radar pulses, proposed by NASA, and two Russian payloads for atmospheric studies.
“Venus may also have signs of life in its upper atmosphere, where some microbes could survive the harsh conditions. Some scientists have proposed that phosphine, a gas that is usually associated with biological processes, could be produced by living organisms in the clouds of Venus. However, this hypothesis is still controversial and requires further confirmation. Venus is a planet that challenges our understanding of planetary science and astrobiology. It is a world of contrasts and contradictions, but also of similarities and possibilities,” remarked Linganna.
In the past also there have been many missions to the moon, notably the Soviet Union (Venera Program): The Soviet Union conducted a series of missions under the Venera program in the 1960s and 1970s. Venera 7 was the first spacecraft to successfully land on Venus and transmit data back to Earth. These missions provided valuable data on Venus' surface conditions, including its extreme temperatures and atmospheric pressure.
Then there was NASA's Magellan spacecraft, launched in 1989, that used radar to map Venus' surface. It provided detailed topographic information and improved our understanding of Venus' geology and volcanic activity. Then there was ESA's Venus Express, launched in 2005, which studied Venus' atmosphere and climate.
It made significant contributions to our knowledge of the planet's atmospheric dynamics, including the discovery of a rotating vortex at its south pole. The Japan Aerospace Exploration Agency's (JAXA) Akatsuki mission was launched in 2010, and aimed to study Venus' atmosphere and climate. After a failed orbital insertion attempt, it successfully entered Venus' orbit in 2015, contributing to research on the planet's weather patterns and cloud formations.
“ISRO's Venus represents India's ambitious foray into planetary exploration and scientific research. By conducting a comparative analysis with other nations' missions, we can appreciate the significance of such endeavours in enhancing our understanding of Venus, Earth-like planets, and the broader universe. These international efforts collectively deepen our knowledge of this mysterious planet and its relevance to planetary science,” said Kesan.