India's Shukrayaan-1 Mission to Venus: What ISRO's Spacecraft Will Hunt for in the Planet's Atmosphere

The Soviet Venera 13 lander touched down on Venus in March 1982 and survived for 127 minutes. That was a record. The surface temperature on Venus runs at around 465 degrees Celsius, hot enough to melt lead, and the atmospheric pressure at ground level is roughly 90 times what you'd feel standing at sea level on Earth. Every probe that has ever landed on Venus has been crushed or cooked within two hours. No mission has lasted longer.

This is the planet ISRO wants to send Shukrayaan-1 to study.

The spacecraft won't land. It will orbit. But the questions it is being designed to answer are not simple ones, and the fact that Venus is so hostile is precisely what makes those questions so urgent.

Venus is almost exactly the same size as Earth. Its mass is 81 percent of Earth's. Early in the solar system's history, it may have had liquid water oceans. Models suggest it was potentially habitable for up to two billion years before something, volcanic outgassing, a runaway greenhouse effect, or both, turned it into the pressure-cooker it is today. Understanding what triggered that transformation is one of the most consequential questions in planetary science, because Earth sits inside the same neighbourhood and shares the same basic architecture.

ISRO has confirmed Shukrayaan-1 as a planned mission, with the spacecraft intended to carry a suite of scientific instruments to study the Venusian atmosphere, surface geology beneath the cloud cover, and the interaction between the solar wind and the planet's ionosphere. Venus has no magnetic field of its own, which means the solar wind hits its upper atmosphere directly, a stripping process that may have helped drive its water away over geological time.

The mission follows the pattern ISRO established with Mangalyaan, the Mars Orbiter Mission that reached Mars orbit in 2014 on its first attempt, and with Chandrayaan-3, which landed near the lunar south pole in August 2023. Shukrayaan-1 represents the next step in that sequence: a deeper solar system target with a more complex scientific payload.

In September 2020, a team led by astronomer Jane Greaves at Cardiff University published a paper in Nature Astronomy reporting the detection of phosphine gas in Venus's cloud layer, at altitudes between 48 and 60 kilometres. Phosphine on Earth is produced by industrial processes and by anaerobic bacteria. The researchers found no known abiotic chemical pathway that could explain the concentrations they detected. The paper was contested almost immediately, subsequent reanalysis suggested the signal might have been weaker than initially reported, and the debate over calibration errors ran for months, but the core question it raised has not gone away.

At cloud-deck altitudes on Venus, temperatures drop to between 30 and 70 degrees Celsius and pressure approaches Earth-normal. If any environment on Venus could theoretically support microbial chemistry, it is this zone. No one is claiming life exists there. The scientific position is more careful: we do not yet have the data to rule it out, and we do not have an instrument in orbit right now capable of settling the question.

Shukrayaan-1's proposed payload includes a high-resolution synthetic aperture radar to map the surface through the opaque cloud cover, and atmospheric spectrometers capable of analysing the chemical composition of those cloud layers. If the mission launches and reaches Venus, it will be one of the first spacecraft specifically equipped to look at this question with modern instrumentation.

The Shukrayaan-1 science objectives, as published by ISRO, cover three broad areas. First: the structure, composition, and dynamics of the Venusian atmosphere, including the sulphuric acid cloud layers that make the planet permanently overcast. Second: the surface geology, volcanic features, tectonic structures, and highland regions, using radar that can penetrate cloud cover the way Magellan did in the early 1990s, but with higher resolution. Third: the solar wind interaction with the ionosphere, which has implications for understanding how planets lose their atmospheres over time.

That third objective connects directly to a question with implications beyond Venus. Mars also lost most of its atmosphere, and NASA's MAVEN mission has been studying that process at Mars since 2014. Venus lost its water. Earth kept both. The difference may come down to magnetic fields, volcanic history, and orbital distance, but the data from a single planet can only tell you so much. Shukrayaan-1 would give planetary scientists a second detailed data set from a planet at a different point in the same cautionary story.

Venus launch windows are determined by orbital mechanics: Earth and Venus align favourably roughly every 19 months. ISRO has discussed a launch window in the late 2020s, though no fixed date has been publicly confirmed as of the most recent official statements. The spacecraft's design is still being finalised, and the payload selection process has involved collaboration with international scientific teams.

Two other Venus missions are also in development. NASA's DAVINCI mission is designed to drop a probe through the atmosphere, sampling gases on the way down. NASA's VERITAS mission will use radar to map the surface in detail. The European Space Agency's EnVision mission will orbit Venus with its own radar and spectrometer suite. All three are planned for the late 2020s to early 2030s. After decades of neglect, the last dedicated Venus orbiter before these was ESA's Venus Express, which ended its mission in 2015, the planet is suddenly receiving serious attention from multiple space agencies simultaneously.

ISRO entering this cluster of missions is significant. Shukrayaan-1 would give India a presence at every major planetary body in the inner solar system: the Moon via Chandrayaan, Mars via Mangalyaan, and Venus via Shukrayaan. The scientific return compounds across missions, data from one informs the interpretation of data from another.

The planet that destroys everything sent to its surface is, from orbit, one of the most scientifically productive targets left in the solar system. The answers it holds about runaway atmospheres, lost oceans, and the narrow conditions that separate a living planet from a dead one are answers that apply, in the end, to the planet we are already standing on.