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Little Venus in the Middle of the Atlantic  

Uli Köhler (DLR, Germany) reports on an expedition to Iceland that is helping to prepare for NASA and ESA missions to Venus at the beginning of the next decade. 

Read article in the fully formatted PDF of the Europlanet Magazine.

Venus-like conditions do not exist anywhere on Earth. With temperatures hot enough to melt lead, a toxic atmosphere heavy with clouds of sulphuric acid and an atmospheric pressure 90 times higher, simulating a mission to Venus is no mean feat. However, Iceland comes closest as an analogue, mainly due to its volcanic origin. Last summer, this island in the North Atlantic was the destination of an expedition, involving researchers funded through Europlanet’s Transnational Access programme, in preparation for NASA’s VERITAS mission to Earth’s ‘evil twin’. 

Iceland is home to the largest glaciers in Europe and is one of the most volcanically active regions in the world. In summer 2023, again in December, and also after the turn of the new year, there were spectacular volcanic eruptions near Iceland’s capital, Reykjavik. The first of those was a real stroke of luck for the field campaign, which studied some of the most recently solidified lava flows in Iceland. 

The eruption of the small volcano, Litli-Hrútur, made it possible to carry out radar measurements from the air as well as acquiring multispectral images of the lava on the ground, which in places was still at a temperature of over 400 degrees Celsius. Some measurements were even conducted at night to avoid the possible influence of sunlight. The purpose of the expedition, led by the Jet Propulsion Laboratory in Pasadena, California, was to optimise experiments for NASA’s VERITAS mission to Venus. Both VERITAS and ESA’s EnVision mission are scheduled for launch after 2030. There, they will acquire data from orbit, in order to help answer the numerous questions that have puzzled Venus researchers for the past three decades. Why did Earth’s inner neighbour, which was probably physically similar when the two bodies formed, evolve so differently? Do these disparities stem solely from Venus orbiting the Sun 50 million kilometres closer than Earth, thereby receiving double the solar energy per square metre? 

The main reason for the extreme greenhouse effect on Venus is its atmosphere, which consists almost entirely of carbon dioxide. This maintains surface temperatures consistently above 460 degrees Celsius and renders the existence of water or life impossible today.

Hidden from view

Within this dense atmosphere of carbon dioxide, thick clouds of sulphuric acid prevent telescopes and cameras from observing Venus’s surface in visible light. However, radar signals from orbiting spacecraft can get through its atmosphere and reflect off its surface, revealing the roughness and even the topography of the landscape.

Venus has not experienced plate tectonics, at least not in its recent past. On Earth, plate tectonics are caused by the overturning of huge, only partially molten rock formations in the planet’s mantle, leading to volcanism. This allows the heat generated in the interior by the radioactive decay of elements to be dissipated in a ‘controlled’ manner. Under the crust of Venus, however, the heat builds up like a pressure cooker without a valve until the ‘cauldron’ explodes and erupts in the form of a global volcanic catastrophe.

Little is known about the types of volcanism involved when this happens or the composition of the lavas and minerals from which the solidified rock forms. Images and measurements from the Soviet-era Venera spacecraft suggest that the volcanic rock is basalt, which is found on all Earth-like planets. Of particular interest, however, are the minerals in the rocks, which could answer the question of whether water was actually present on Venus in earlier times and influenced its development.

Venus is back in fashion

Three new missions will be sent to Venus at the beginning of the next decade. ESA, in partnership with NASA, has selected EnVision. This mission will analyse Venus from its core to its upper atmosphere, as well as the interactions between the various ‘levels’. The aim is to gain a better understanding of the planet’s formation, evolution, activity and weather patterns. EnVision will also investigate whether Venus once supported water for long periods, and perhaps even had the conditions necessary for life.

NASA is planning two Venus missions – the Venus Emissivity, Radio Science, InSAR, Topography And Spectroscopy (VERITAS) orbiter, which will complement EnVision in its experimental instrumentation, and the Deep Atmosphere Venus Investigation of Noble gases, Chemistry and Imaging (DAVINCI) mission, which flies by Venus and drops an atmospheric probe.

Venus researchers are now fairly sure that water was present on the surface of the planet for long periods in its early history. This poses the question – could Venus once have harboured life? It is not yet possible to say if this can be answered with the new missions; the first step is to gain a better understanding of the planet. New and improved technologies will be used in the planned Venus missions from ESA and NASA – but they need to be tested first. This is where Iceland comes in as a ‘little Venus’, because the latest lava flows have not yet weathered and, most importantly, there is no vegetation yet.

Exploring Venus on Earth

The Icelandic field campaign saw nearly 20 VERITAS scientists from the USA, Italy and Germany target two main volcanic areas. The first was the almost 100-square-kilometre solidified lava flow from the 2014 Holuhraun eruption in central Iceland, near the famous Askja caldera, and the second was the still active eruption of Litli-Hrútur on the Reykjanes Peninsula on the south coast. It also included some lava flows from nearby volcanoes that erupted in 2021 and 2022.

DLR is involved, scientifically and experimentally, in ESA’s EnVision and NASA’s VERITAS missions. For both missions, the DLR Institute of Planetary Research (scientific lead) and the DLR Institute of Optical Sensor Systems (lead instrument developer) are jointly developing a spectrometer for near-infrared wavelengths, called the Venus Emissivity Mapper (VEM). VEM will map the mineralogical composition of rocks on the surface of Venus for the first time by measuring their thermal radiation. Ideally, the VEM data will be combined with mapping data from a high-resolution radar instrument so that precise topographical information can be acquired in addition to the mineralogical data. DLR is also contributing algorithms to the VERITAS radar experiment.

During the Iceland campaign, DLR was represented on the ground by a five-member team, including Solmaz Adeli, Stephen Patrick Garland, Nils Müller and Akin Domac, whose participation was supported through Europlanet. A DLR crew also used an F-SAR radar system installed on a Dornier 228-212 research aircraft to obtain high-resolution data from approximately 6000 metres above the lava flows. These high-resolution radar ‘images’ are in the same radar frequencies that will be obtained by the VERITAS and EnVision missions as the spacecraft orbit Venus. They can be acquired in all weather conditions and even at night, which will be invaluable for mapping the surface of Venus.

While the aircraft carried out precise radar measurements of the Holuhraun and Litli-Hrútur lava flows along defined routes, the crew on the ground simultaneously conducted laser measurements of the flows and the sandy areas next to them. The data sets will later be compared and harmonised.

While radar focuses on the topography, structure and roughness of the lava flows, spectroscopy deals with the composition of the volcanic rock. This is done by measuring the emissions from hot or cooled lava. DLR used its VEM Emulator (VEMulator) in Iceland for this purpose, which measures in six filtered wavelengths, modelled on the ‘spectral windows’ of the venusian atmosphere. The ‘ground segment’ of the field campaign sometimes had to cope with harsh working conditions, as some of the lava flows consisted of rock with razor sharp edges. Aerial support came in the form of drones, which acquired millimetre-accurate images from an altitude of just a few metres. The team collected 60 kilogrammes of samples at the VEMulator measurement points. These are now being analysed at the Planetary Spectroscopy Laboratory in Berlin (a facility developed through Europlanet funding).

The results will be used to finalise the design and calibration of the experiments that DLR has developed for NASA’s VERITAS and ESA’s EnVision missions, intended to map the global distribution of minerals on Earth’s somewhat overheated neighbour. 

Links

Find out more about the DLR Planetary Spectroscopy Laboratory’s Venus Chamber.

This article is adapted from a version first published in the DLR Magazine.

Issue 7 of Europlanet Magazine