EnVision, Europe’s mission to Venus

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Why is ESA launching a mission to Venus?

Venus is a hellscape. Its thick carbon dioxide atmosphere creates a runaway greenhouse effect causing average surface temperatures of 470 degrees Celsius (878 degrees Fahrenheit) — hot enough to melt lead. Venus’ inhospitable nature is further affirmed by its toxic clouds of sulphuric acid. But it wasn’t always this way.

Past missions to Venus have observed granite-like rocks that require abundant water to form. Scientists think the planet may have had liquid water on the surface for 2 billion years — far longer than Mars, which hosted surface water for a relatively brief 300 million years.

Due to its similar size and bulk composition, at some point, Venus seems to have been the most Earth-like planet in our solar system. And yet it experienced a mysterious, dramatic climate shift while Earth remained habitable. What did Venus experience that drove it from being habitable to hellish? Is its catastrophic natural greenhouse effect a cautionary tale to Earth’s fate?

These are some of the pressing questions that ESA’s mission to Venus, EnVision, aims to answer. EnVision, part of ESA’s Cosmic Vision program, will undertake a holistic study of Venus’ surface, subsurface and atmosphere to help scientists determine the mechanisms by which they interact and evolve. This will help us better understand the chain of events Venus experienced that made it so different from Earth.

The mission will also tell us how similar planets across the universe may evolve, how likely they are to host life, and how we should define habitable zones around stars.

How will EnVision study Venus?

After launching on an Ariane 6 rocket in 2031, EnVision will take about 15 months to reach Venus after which it will enter in an elliptical orbit around the planet. For the 16 months that follow, the spacecraft will use Venus’ upper atmosphere to slow down and circularize its orbit to less than 600 kilometers (373 miles) from the planet’s surface to closely observe Venus for years using its state-of-the-art instruments.

While most planetary orbiter missions can use typical spectrometers to identify the composition of an object’s surface and atmosphere, Venus’ thick clouds make it almost impossible to see its surface and lower atmosphere. However, there are a few wavelengths of light Venus’s thick atmosphere is transparent to, and EnVision will have tailor-made spectrometers to look in exactly such little windows of opportunity.

A medium-resolution infrared spectrometer will find out what comprises Venus’ surface and lower atmosphere while an ultraviolet spectrometer will study Venus’ sulphuric acid clouds and the atmosphere above them, the latter of which hosts mysterious dark patches that absorb half the solar energy the planet receives.

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