15. January 2021
Laboratory experiments demonstrate promising new approach

Back to Venus armed with lab­o­ra­to­ry find­ings

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Space
Venus – the 'opaque neighbour'
Venus – the 'opaque neigh­bour'
Image 1/9, Credit: JAXA/ISAS/DARTS/Damia Bouic

Venus – the 'opaque neighbour'

Venus, Earth's neigh­bour in space, hides its sur­face un­der a dense at­mo­sphere. Venus's clouds of sul­phuric acid pre­vent tele­scopes and in­stru­ments on board space­craft hav­ing a di­rect view of the plan­et’s sur­face in vis­i­ble wave­lengths of light. These im­ages of Venus were ac­quired in 2019 by the Japanese Venus or­biter Akat­su­ki from dif­fer­ent dis­tances in ul­tra­vi­o­let wave­lengths. The ex­traor­di­nary dy­nam­ics of the plan­et's at­mo­spher­ic pro­cess­es are clear­er in ul­tra­vi­o­let light than in vis­i­ble light. Bands of cloud ex­hib­it 'su­per-ro­ta­tion' as they move around Venus faster than the plan­et turns around its ax­is of ro­ta­tion.
Inhospitable environment
In­hos­pitable en­vi­ron­ment
Image 2/9, Credit: Russian Academy of Sciences

Inhospitable environment

In the di­rec­tion of the Sun, Venus is the clos­est plan­et to Earth. It or­bits on av­er­age 40 mil­lion kilo­me­tres clos­er to the Sun. The clos­er prox­im­i­ty is on­ly one rea­son why Venus's sur­face is hot­ter than Earth's. A much greater in­flu­ence on the tem­per­a­ture is an ex­treme green­house ef­fect that heats the plan­et to a con­sis­tent 470 de­grees Cel­sius at its sur­face. The high tem­per­a­tures and the high at­mo­spher­ic pres­sure of 90 bar make land­ing on Venus with space­craft ex­treme­ly dif­fi­cult. The So­vi­et Union suc­ceed­ed in land­ing on Venus eight times be­tween 1970 and 1983 with lan­ders from its Ven­era pro­gramme. Many of these lan­ders trans­mit­ted da­ta and im­ages for up to two hours. These im­ages show the land­scape at the land­ing sites of Ven­era 9 and Ven­era 13, in a field of vol­canic basalt rocks.
Venus – Earth's mysterious sister
Venus – Earth's mys­te­ri­ous sis­ter
Image 3/9, Credit: JAXA/ISAS/DARTS/Damia Bouic

Venus – Earth's mysterious sister

Venus is con­sid­ered Earth's sis­ter plan­et. It is al­most ex­act­ly the same size and or­bits on av­er­age on­ly 40 mil­lion kilo­me­tres clos­er to the Sun. How­ev­er, the two plan­ets de­vel­oped very dif­fer­ent­ly. The at­mo­sphere of Venus is a hun­dred times denser than that of Earth. With­in it, the ex­treme green­house ef­fect re­sults in a con­stant sur­face tem­per­a­ture of 470 de­grees Cel­sius – a tem­per­a­ture at which wa­ter would in­stant­ly evap­o­rate and even lead would melt.
EnVision Venus orbiter
En­Vi­sion Venus or­biter
Image 4/9, Credit: VR2Planets

EnVision Venus orbiter

En­Vi­sion is a can­di­date for an ESA Venus or­biter that would use radar to study fea­tures on and be­low the plan­et’s sur­face. An­oth­er goal of the mis­sion would be to look for ac­tive vol­ca­noes.
NASA proposal for Venus mission
NASA pro­pos­al for Venus mis­sion
Image 5/9, Credit: NASA/JPL-Caltech

NASA proposal for Venus mission

VER­I­TAS is a fi­nal­ist for one of two new mis­sions in NASA's Dis­cov­ery Pro­gram. One fo­cus is the map­ping of sur­face min­er­al­o­gy, for which DLR’s VEM (Venus Emis­siv­i­ty Map­per) spec­trom­e­ter is a can­di­date in­stru­ment.
Venus in the laboratory
Venus in the lab­o­ra­to­ry
Image 6/9, Credit: © DLR. All rights reserved

Venus in the laboratory

At the DLR Plan­e­tary Spec­troscopy Lab­o­ra­to­ry (PSL), sci­en­tists are in­ves­ti­gat­ing how the re­flectance and emis­siv­i­ty of rocks change un­der ex­treme­ly high tem­per­a­tures. This al­lows the in­ter­pre­ta­tion of spec­tral mea­sure­ments of hot plan­e­tary sur­faces, such as those of Venus and Mer­cury, and to de­vel­op sen­sors and in­stru­ments for fu­ture space­craft that will de­ter­mine the min­er­alog­i­cal and geo­chem­i­cal com­po­si­tion of such hot sur­faces.
DLR high-temperature measurement chamber
DLR high-tem­per­a­ture mea­sure­ment cham­ber
Image 7/9, Credit: DLR (CC-BY 3.0)

DLR high-temperature measurement chamber

DLR's unique ex­per­i­men­tal fa­cil­i­ty, the Plan­e­tary Spec­troscopy Lab­o­ra­to­ry (PSL), is used to mea­sure the emit­ted ther­mal ra­di­a­tion from dif­fer­ent rock sam­ples heat­ed to ex­treme­ly high tem­per­a­tures typ­i­cal on Venus (470 de­grees Cel­sius) or Mer­cury (up to 430 de­grees Cel­sius). These spec­tra of emit­ted and re­flect­ed ra­di­a­tion dif­fer from that at the 'nor­mal', low­er tem­per­a­tures that ex­ist on Earth. The spec­tral pro­files can be ap­plied to fu­ture ex­per­i­ments on mis­sions to Venus and Mer­cury to iden­ti­fy rock types on the plan­e­tary sur­faces. For the anal­y­sis of Venu­sian rocks and their min­er­alog­i­cal and geo­chem­i­cal com­po­si­tion, knowl­edge of the spec­tral pro­files at wave­lengths around one mi­crome­tre is par­tic­u­lar­ly im­por­tant. At these wave­lengths, in­frared sen­sors can ob­serve the sur­face of the plan­et through the dense Venu­sian at­mo­sphere with­in so-called 'at­mo­spher­ic win­dows'.
Rock dust in the furnace
Rock dust in the fur­nace
Image 8/9, Credit: © DLR. All rights reserved

Rock dust in the furnace

At DLR's Plan­e­tary Spec­troscopy Lab­o­ra­to­ry (PSL), sam­ples of dif­fer­ent rocks are ex­posed to ex­treme­ly high tem­per­a­tures up to 500 de­grees Cel­sius. Their spec­tral be­haviour, re­flec­tion of vis­i­ble light and ther­mal ra­di­a­tion in in­frared wave­lengths, are record­ed. Sam­ples that have dif­fer­ent min­er­al com­po­si­tions and vari­able phys­i­cal prop­er­ties such as grain size, cav­i­ties and rough­ness are ex­am­ined to cre­ate a ‘spec­tral li­brary’. Fol­low­ing the ex­per­i­ment, the sam­ples are baked to­geth­er in their con­tain­ers and demon­strate that high tem­per­a­tures sig­nif­i­cant­ly al­ter the rock sub­stances. For com­par­i­son, gran­ite melts un­der cer­tain con­di­tions at tem­per­a­tures of 650 de­grees Cel­sius. Basalt, a typ­i­cal vol­canic rock that al­so oc­curs on Venus, melts at 900 de­grees Cel­sius.
Venus – the volcanic planet
Venus – the vol­canic plan­et
Image 9/9, Credit: NASA/JPL

Venus – the volcanic planet

Venus is sim­i­lar to Earth in many ways. The plan­ets are al­most the same size, but they have de­vel­oped very dif­fer­ent­ly since their for­ma­tion 4.5 bil­lion years ago. Al­most noth­ing is known about the ear­ly days of Venus be­cause ob­ser­va­tions made by space­craft re­veal a sur­prise – about half a bil­lion years ago, there was a glob­al cat­a­clysm on the plan­et as tens of thou­sands of vol­ca­noes erupt­ed and re­shaped the en­tire plan­e­tary sur­face. Traces of any­thing that ex­ist­ed be­fore were al­most com­plete­ly erased. One tenth of the sur­face has struc­tures, rem­i­nis­cent of Earth's con­ti­nents, that may have sur­vived the glob­al vol­canic catas­tro­phe. This per­spec­tive im­age cre­at­ed us­ing radar da­ta from NASA's Mag­el­lan mis­sion shows the eight-kilo­me­tre-high Maat Mons vol­cano, with so­lid­i­fied la­va flows in the fore­ground.
  • Scientists are simulating the extreme surface conditions of Venus in a DLR furnace.
  • Emission spectra measured in the laboratory of ferrous rocks at temperatures of 440–480°C can be used to identify similar rocks on Venus.
  • Laboratory measurements provide new results from data acquired by Venus landers 46 years ago.
  • The mineralogy and geochemistry of Venusian rocks can now be mapped with new instruments.
  • Focus: Space, Solar System exploration, Venus

Venus's impenetrable atmosphere has long made it difficult to conduct a thorough investigation of our neighbouring planet. In a step forward, by conducting laboratory experiments scientists from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) have now developed a way of determining the nature of the planet's surface using new instruments from orbit. The entire surface of Venus can now be mapped mineralogically for the first time, addressing a large gap in planetary research.

Venus and Earth – two very different siblings

Venus is Earth's sister planet. It is almost exactly the same size and orbits on average only 40 million kilometres closer to the Sun. However, the two planets developed in very different ways. On Earth, continents formed, separated by oceans. Then some three and a half billion years ago, life emerged under its atmosphere and evolved into the vast variety of organisms that we know today. Things happened very differently on Venus, which is surrounded by an atmosphere of gas a hundred times thicker than that of Earth. Within it, the extreme greenhouse effect results in a constant surface temperature of 470 degrees Celsius – a temperature at which water would instantly evaporate and even lead would melt. The planet is permanently enveloped in thick clouds of sulphuric acid, making it impossible for telescopes on Earth or instruments on board spacecraft to acquire even a glimpse of the surface. Scientists have managed, however, to map its landscape using radar. And now, through a series of laboratory experiments, DLR researchers have developed a new method for determining the nature of the planet's surface from orbit.

"For a good ten years, we have been using a unique laboratory facility to measure the emission properties of various rocks of the kind we might expect to find on Venus under the same extreme conditions that prevail on the planet," says Jörn Helbert, Head of DLR's Planetary Spectroscopy Laboratory (PSL) and lead author of a research paper that has now been published in Science Advances magazine. "The reflectance and emissivity of rocks change when they are exposed to the high temperatures that you find on Venus. As a result, spectral profiles measured at terrestrial temperatures cannot simply be applied there. But now, we have a tool that we can use as the basis for new instruments on the next planned missions to Venus that will finally allow us to determine which types of rock exist there."

Concordance with existing surface measurements from Venus

The four-person research group made up of researchers from DLR, the Planetary Science Institute in Tucson, Arizona, and Mount Holyoke College in Massachusetts have used the results of their laboratory experiments to devise a new 'spectral library' for various types of rock. "Determining the emission spectra in this way has enabled us to reconstruct the iron oxide content at the landing site of the Soviet Union’s Venera 9 and Venera 10 landers for the very first time," says DLR Planetary Scientist Alessandro Maturilli. "In 1975, the two landers transmitted images from Venus and provided important measurements. However, they were not equipped with an instrument that could directly measure iron oxide content."

The two landers provided the only direct spectral measurements of Venusian rocks. The emission profiles determined in the laboratory and the spectra determined by the Venera missions are in very good agreement. "As such, we have demonstrated the accuracy of our new method, which represents a big step forward," says Jörn Helbert. Although further Venus lander missions are currently under discussion, global mapping of the planet can only be conducted from orbit. However, the atmosphere of Venus is impenetrable to wavelengths of visible light – those that the human eye can see. To make mapping of the surface possible despite the planet's atmosphere, scientists are focusing on what are known as 'atmospheric windows'. These are narrow bands of wavelengths at which the atmosphere of Venus is transparent, and thus allow a view of the surface. Five such 'windows' exist at wavelengths close to 1000 nanometres (one micrometre). These wavelengths are in the near-infrared, which is adjacent to the visible portion of the electromagnetic spectrum (approximately 400–700 nanometres).

Venus returns to the focus of planetary research

Through their experiment, the researchers have shown that for rock types measured in the laboratory, the spectra and their characteristic profiles can be used to reliably identify them from orbit. "Our aim is now to create the first global map of rocks on Venus," says Helbert. "That would be a major achievement! After all, we know far too little about Venus. In its infancy, the planet may have had water, like Earth, and may also have been less hostile to life." The scientists are looking to use the Venus Emissivity Mapper (VEM) instrument to implement their plan, mapping emissions in the few atmospheric windows available at near-infrared wavelengths. VEM could be installed on the EnVision mission of the European Space Agency (ESA) and on NASA's VERITAS orbiter later this decade.

Venus, Earth's celestial neighbour and often described as its sister planet, was the first target for interplanetary spacecraft. The Soviet mission Venera 1 launched in 1961 and the American Mariner 2 in 1962. Despite a number of spectacular successes, particularly the Soviet space programme's initial orbiters and then eight landings between 1970 and 1983, the planet named after the Roman goddess of love later fell somewhat out of favour in planetary research. Between 1990 and 1994, NASA's Magellan orbiter mapped Venus using radar, revealing myriad details of its multifaceted surface in high-resolution. From 2006 to 2015, ESA's Venus Express mission investigated the planet across a series of seven experiments.

However, we still know little about the nature of the planet's surface. For Earth's other immediate neighbours, the Moon and Mars, determining rock types, mineralogical composition and the abundance of chemical elements was far easier. As a result, nowadays we have a fairly thorough understanding of them. The astronauts involved in the Apollo missions and the robotic missions of the Soviet Union returned 400 kilograms of sample material from the Moon to Earth. Half a dozen landers have been able to analyse the rocks on Mars. A landing on Venus would be a heroic feat, as the lander descends into an increasingly hot oven. The high temperatures and atmospheric pressure – which reaches 92 bar on the ground (equivalent to the pressure at 900 metres underwater on Earth) – would put the electronics under immense strain. The Venera 13 lander was able to withstand these conditions for the greatest amount of time so far and, on 30 October 1981, succeeded in transmitting data from the furnace-like surface of Venus for almost two hours. The new method developed in this laboratory study would allow the surface of Venus to be studied systematically from orbit over a period of many years, without having to run the risk of a landing.

Contact
  • Melanie-Konstanze Wiese
    Cor­po­rate Com­mu­ni­ca­tions, Berlin, Neustre­litz, Dres­den, Je­na and Cot­tbus/Zit­tau
    Ger­man Aerospace Cen­ter (DLR)

    Pub­lic Af­fairs and Com­mu­ni­ca­tions
    Telephone: +49 30 67055-639
    Fax: +49 30 67055-102
    Rutherfordstraße 2
    12489 Berlin-Adlershof
    Contact
  • Jörn Helbert
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Rutherfordstraße 2
    12489 Berlin
    Contact
  • Ulrich Köhler
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Rutherfordstraße 2
    12489 Berlin
    Contact

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