Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

’Heavy metal’ snow on blazing Venus is lead sulfide

10.02.2004


Lead sulfide — also known by its mineral name, galena — is a naturally occurring mineral found in Missouri, other parts of the world, and now ... other parts of the solar system.


Bruce Fegley, Jr., Ph.D., professor of earth and planetary sciences in Arts & Sciences, and Laura Schaefer, resarch assistant in the Planetary Chemistry Laboratory, with a chunk of galena, or lead sulfide. The researchers have determined that the feature on Venus that looks like snow is composed of both lead and bismuth sulfides, settling a long-time controversy in the planetary community.
David Kilper/WUSTL Photo



That’s because recent thermodynamic calculations by researchers at Washington University in St. Louis provide plausible evidence that "heavy metal snow," which blankets the surface of upper altitude Venusian rocks, is composed of both lead and bismuth sulfides.

The findings — by Laura Schaefer, research assistant in the Planetary Chemistry Laboratory, and M. Bruce Fegley, Jr., Ph.D., professor of Earth & Planetary Sciences in Arts & Sciences — discount previous hypotheses that the snow was made of elemental tellurium. They are important also because lead sulfide "snow" could allow the dating of Venus by lead isotopes, provided a soil sample can be obtained in a future mission.


Schaefer and Fegley’s work was presented at the 35th Division of Planetary Sciences (DPS) of the American Astronomical Society, held Sept.1-6, 2003, in Monterey, CA, and is published in the current issue of Icarus, the official journal of the DPS.

"We calculated the equilibrium compositions for 20 trace metals in Venus’ lower atmosphere, looking for something that condenses at this altitude of 2.6 kilometers," Schaefer said. Previous analyses, she added, simply "didn’t consider any chemistry. When we looked at the chemistry, we found that the best candidates were actually lead and bismuth sulfides."

Discovery of the metallic snow dates back to 1995, when Raymond E. Arvidson, Ph.D., chair of the Washington University Department of Earth and Planetary Sciences, and other researchers were analyzing the vast archives of data taken from NASA’s Magellan Mission to Venus in 1989. Magellan’s primary objective was to map the surface of Venus using a technique known as synthetic aperture radar (SAR). SAR images taken of Aphrodite Terra and other mountainous regions in Venus’ highlands revealed a mysterious brightening effect in the radar imaging maps

Using computers to factor in physical parameters such as elemental abundances —what elements are present and in what amounts, altitudes, temperatures, and pressures — researchers surmised that the brightening effect was due to a metal-containing "snow" only a few millimeters in thickness frosting the mountains’ rugged surfaces.

But even as the hypothesis of metallic snow was circulating throughout the planetary community, its chemical composition remained largely an educated guess, - one among many on the short-list of 98 possible metal-containing compounds that commonly exist around volcanic vents on Earth.

"An old idea we had was that you have compounds of these trace metals being erupted and condensing around volcanoes on Earth," Fegley explained. "Now on Venus, which is much hotter than Earth, you’d have a similar process: You’d be erupting these trace metals, which would then stay in the gas phase until they reached a high enough atmospheric level where they’d condense. Because you have a decrease in temperature with altitude, places like the Maxwell Montes on Venus — similar to Mauna Loa in Hawaii — get cold enough that some of these things would start to condense out."

The group took the list of possibilities and used their expertise in chemical thermodynamics to help them narrow the pool of suspects. In this case, whether a particular compound remained a plausible candidate was governed by two factors: thermodynamics — the rules that predict chemical stability based on environment — and the chemical profile of Venus, which was obtained from earlier American and Russian data-gathering missions.

"One of my old professors from MIT [Gordon Pettengill, the principal investigator for the Magellan SAR project,] did an experiment that proved our model for the [existence of] metallic snow, but he suggested tellurium," Fegley noted. " I decided to re-examine the issue in early 2003."

Schaefer and Fegley carefully considered what could happen to tellurium after it was introduced into the Venusian atmosphere by a volcanic event. But they went a step further by allowing it to undergo reactions with other volatile species present in the atmosphere.

As it turns out, sulfur dioxide is the third most abundant gas on Venus and is a major contributor to the thick layer of sulfuric acid clouds that envelope the planet. According to thermodynamic equations, any significant concentration of volatile tellurium would react with these sulfur-containing compounds to make tellurium sulfide, a relatively stable gas.

"So it can’t just condense out because it’s undergoing chemical reactions instead," Fegley said.

Lead sulfide and bismuth sulfide were identified as front-runners thanks to a specific physical property called a dielectric constant — an intrinsic value describing a material’s electrical conductivity — that Magellan’s SAR measured back in 1991.

"Typical volcanic rocks have a dielectric constant of a few, maybe 4, but the stuff that

Magellan saw in the highlands of Venus was much higher, about 100," Fegley explained. "In order to have a dielectric constant that high you have to have something that’s either a semiconductor or a conductor, and actually, these minerals that we’ve proposed condensing, the galena [lead sulfide], and the bismuth sulfide, have dielectric constants that are basically - BANG - right on."

If Schaefer and Fegley are right, having "snow" made of lead sulfide could have implications beyond confirming their own work; it could be used as a means of dating the beginning of Venus’ existence.

So how exactly would that work? By the same process that scientists have used to date the age of the Earth — lead dating — using the ratios of different lead isotopes (which differ only in number of neutrons).

All of these lofty dreams rest on there being an actual sample of dirt to analyze; a dream that could become reality with one of NASA’s New Frontiers Missions, a competitive $650 million dollar endeavor to be selected for funding in the next year or two.

Venus aficionados like Fegley are pushing for a more comprehensive probe of the Earth’s nearest neighbor. Their mission would include a detachable landing module that could perform geochemical analyses in the highlands using techniques like x-ray fluorescence and x-ray diffraction.

"All these ideas — these calculations — can be tested by one of these New Frontiers spacecrafts, if the Venus mission is picked," Fegley concluded. "What makes this type of work exciting is the fact that these ideas could be tested by spacecrafts that are on the drawing boards today,"

Carolyn Jones Otten | WUSTL
Further information:
http://news-info.wustl.edu/news/page/normal/633.html

More articles from Physics and Astronomy:

nachricht When fluid flows almost as fast as light -- with quantum rotation
22.06.2018 | The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences

nachricht Thermal Radiation from Tiny Particles
22.06.2018 | Universität Greifswald

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Temperature-controlled fiber-optic light source with liquid core

In a recent publication in the renowned journal Optica, scientists of Leibniz-Institute of Photonic Technology (Leibniz IPHT) in Jena showed that they can accurately control the optical properties of liquid-core fiber lasers and therefore their spectral band width by temperature and pressure tuning.

Already last year, the researchers provided experimental proof of a new dynamic of hybrid solitons– temporally and spectrally stationary light waves resulting...

Im Focus: Overdosing on Calcium

Nano crystals impact stem cell fate during bone formation

Scientists from the University of Freiburg and the University of Basel identified a master regulator for bone regeneration. Prasad Shastri, Professor of...

Im Focus: AchemAsia 2019 will take place in Shanghai

Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.

Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...

Im Focus: First real-time test of Li-Fi utilization for the industrial Internet of Things

The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.

Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.

Im Focus: Sharp images with flexible fibers

An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.

Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Munich conference on asteroid detection, tracking and defense

13.06.2018 | Event News

2nd International Baltic Earth Conference in Denmark: “The Baltic Sea region in Transition”

08.06.2018 | Event News

ISEKI_Food 2018: Conference with Holistic View of Food Production

05.06.2018 | Event News

 
Latest News

Graphene assembled film shows higher thermal conductivity than graphite film

22.06.2018 | Materials Sciences

Fast rising bedrock below West Antarctica reveals an extremely fluid Earth mantle

22.06.2018 | Earth Sciences

Zebrafish's near 360 degree UV-vision knocks stripes off Google Street View

22.06.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>