ESA approves Venus EnVision mission
DLR is contributing a multispectral camera to map the mineralogy and perform measurements in the venusian atmosphere
Venus, Earth's inner neighbouring planet, is a mysterious celestial body. Almost the same size as Earth, with only a slightly smaller mass and largely made up of the same materials as Earth, Venus has developed in a completely different way. A dense atmosphere of carbon dioxide ensures permanent, global temperatures of over 460 degrees Celsius during the day and at night. 2031 will see the launch of a European Space Agency (ESA) spacecraft that will investigate why there are such large differences. On January 25, 2024, ESA officially included the EnVision mission that was selected in 2021 in its science programme. This means that mission planning and development of the spacecraft can begin. The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) is developing an instrument for the orbiter with which the mineralogy of the rocks on Venus can be mapped.
EnVision will study Venus from its inner core to its upper atmosphere and provide important new insights into the planet's evolution, geological activity and climate. Approval of the programme means that the study phase is complete, and ESA is committed to carrying out the mission. In the course of 2024, it will select an industrial contractor in Europe so that work on finalising the design and constructing the spacecraft can begin. EnVision is scheduled to lift off on an Ariane 6 launcher in 2031. Following the selection of the mission in 2021, a detailed mission plan has been developed. EnVision is intended to address the many unanswered questions about Venus, in particular how and when Earth's twin became so inhospitable.
From the core of Venus to its upper atmosphere
EnVision will study the entire planet from orbit. The mission will analyse the surface, interior and atmosphere of Venus with unprecedented accuracy in order to understand how the planet has evolved, how the core, mantle, crust and atmosphere interact with each other, and how Venus functions as a 'system'. To this end, EnVision will use several different measurement techniques to detect, for example, signs of active volcanism on the surface and in the atmosphere. Previous missions have shown that Venus was resurfaced globally by the eruption of thousands of volcanoes just over half a billion years ago.
To enable this comprehensive investigation, EnVision will carry a range of scientific instruments. It will be the first mission to look directly beneath the surface of Venus with a radar instrument. A second radar instrument, VenSAR, will map the surface with a resolution of up to 10 metres and determine properties such as the surface texture. Three different spectrometers will analyse the composition of the surface and the atmosphere. In addition, a radio science experiment will use electromagnetic waves to study the planet's internal structure and its atmospheric properties.
DLR will map the mineralogical characteristics
Even if Venus atmosphere does not allow a direct view of the surface of the planet, there are still indirect ways of 'imaging' it. This is done on the one hand with radar, which penetrates the clouds as it does for aircraft on Earth, and on the other hand, at certain wavelengths, particularly in the near infrared, by observing through what are referred to as 'atmospheric windows'. However, it is not possible to understand the surface of Venus without also understanding its atmosphere. A spectrometer suite consisting of three sub-instruments is being developed for EnVision to achieve this. It is named VenSpec and has the components VenSpec-U for analysing the upper atmosphere, VenSpec-H for measurements in the near-surface atmosphere and VenSpec-M, being developed by DLR, for measuring the thermal radiation and spectral properties of the surface.
The entire VenSpec instrument suite is being managed and coordinated by the DLR Institute of Planetary Research. By combining the results from all three channels, deeper insights can be gained into the close 'coupling' between the surface and the atmosphere of Venus. For example, VenSpec-M would detect an active volcanic eruption by detecting the hot lava, while VenSpec-H would simultaneously measure how much water vapour the volcano was releasing into the atmosphere and VenSpec-U would record the distribution of sulphur dioxide from the volcanic eruption in the upper atmosphere.
VenSpec-M will measure more than just the thermal signature of a hot, active volcano; the instrument will also map the mineralogical composition of the surface globally for the first time. VenSpec-M is being developed and built under the leadership of the DLR Institute of Optical Sensor Systems, while the DLR Institute of Planetary Research is responsible for the scientific management of the experiment on EnVision. Both institutes are located at the DLR site in Berlin-Adlershof.
Earth and Venus, two very different 'siblings'
Venus is the second planet from the Sun and Earth’s closest neighbour. It orbits the Sun at a distance of 102 million kilometres, making its orbit approximately 48 million kilometres closer to the Sun than that of Earth. The two rocky planets are similar in mass and size. However, Venus is very unsuitable as a destination for a space mission with astronauts. The planet has an extremely dense atmosphere with a pressure at the surface that is 92 times higher than on Earth. In addition, the gaseous envelope consists of 95 percent carbon dioxide, which creates a very strong greenhouse effect and ensures an average surface temperature of 464 degrees Celsius – lead would melt in this 'planetary oven'. The entire planet is enveloped in clouds, which consist mainly of sulphuric acid and therefore do not allow optical telescopes or cameras to image the surface.
The measurements carried out by EnVision will help to unlock important secrets about Earth's nearest neighbour. For example, EnVision will reveal how volcanoes and asteroid impacts have shaped the surface of Venus and how geologically active the planet is today. Whether the planet ever had water in the early days of its 4.5-billion-year history, and therefore also moderate temperatures, is one of the questions that has been the subject of intense debate for decades. If this was the case, Venus could also have had plate tectonics over a longer period of time and perhaps even the conditions for the existence of life. Today's landscapes on Venus – vast volcanic plains from which kilometre-high highlands extend, vaguely reminiscent of Earth's continents – can only be tentatively interpreted in this respect.
The mission will also study the interior of the planet and collect data on the structure and thickness of Venus' core, its thick rocky mantle and crust. Finally, it will study the weather and climate on Venus, including how these are influenced by geological activity on the surface.
Strong heritage and successful collaboration
EnVision is an ESA-led mission in partnership with NASA. NASA will provide the VenSAR synthetic aperture radar instrument and support communications between Earth and EnVision using the large antennas of the Deep Space Network. The other experiments will be contributed by ESA member states.
EnVision will be the second European mission to Venus. ESA's Venus Express mission (2005-2014) focussed more on the planet's atmosphere, but also made significant discoveries that pointed to possible volcanic hotspots on the surface. Atmospheric exploration continued with JAXA's Akatsuki mission, which is still actively tracking atmospheric movements and weather on Venus. NASA will also be travelling to Venus in the 2030s with two missions: the VERITAS orbiter and the DAVINCI atmospheric laboratory and lander.
Some time ago, NASA's Mariner and Pioneer missions to Venus (1960s and 1970s), the Soviet Union's Venera and Vega missions (1960s to 1980s) and NASA's Magellan radar mapping mission (1990-1994) all painted a picture of a completely alien world in the immediate vicinity of Earth.
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Dr. Jörn Helbert
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Press release DLR, 25 January 2024