A rainbow-like light phenomenon observed on Venus cloud tops helps to identify the components of the planet’s acidic cloud cover
When travelling above the clouds, airplane passengers sometimes witness a glorious moment: a light phenomenon similar to a ring-shaped rainbow. Droplets in the clouds back-scattering the sunlight are responsible for this appearance. A team of scientists led by the Max Planck Institute for Solar System Research (MPS) in Göttingen have now fully imaged a glory on Venus – and thus for the first time on a planet other than Earth. The data was obtained by ESA’s space probe Venus Express. The data imply that the sulfuric acid in Venus’ cloud tops could additionally contain pure sulfur or iron chloride.
Glory and the goddess of love: The center of the concentric coloured circles is the pale yellow patch in the left half of the image. The glory extends over at least 1200 km. Not only visible light, but all wavelengths contribute to the glory. In order to also make the ultraviolet and infrared contributions visible, in this false color representation each wavelength in the camera data is accounted for by a different colour.
The veil of clouds surrounding Venus is as beautiful as it is hostile to life. Sulfuric acid constitutes their main component. Together with the planet’s dense atmosphere composed mainly of carbon dioxide, this cloud cover causes Venus’ extreme greenhouse effect. Temperatures of more than 400 degrees Celsius are common on the planet’s surface. The exact composition of the creamy-yellow clouds is still unclear. Almost 90 years ago, ground-based observations had shown that these clouds “swallow” ultraviolet light of certain wavelengths. Sulfuric acid alone cannot be responsible for this effect.
The list of possible candidates for the unknown substance is long: for example hydrobromic acid, amorphous sulfur, gaseous chloride and even bacteria have been suggested. But no one substance could be identified with certainty. Now, the glory spotted in the data of Venus Express’s Venus Monitoring Camera may offer help. After all, the phenomenon occurs only under very special conditions: the droplets (or possibly solid crystals) in the clouds must be absolutely spherical and of uniform size. The width of the concentric rings and their relative intensities allow conclusion with regard to their size and refractive properties.
The most important precondition necessary to observe a glory is the observing position, explains Dr. Wojciech Markiewicz from the MPS, first author of the new study. This holds true both on Earth and Venus. The observer must be accurately located on a line between the clouds and the Sun. The droplets in the clouds scatter the sunlight back; the observer sees his own shadow on the cloud tops surrounded by colorful concentric circles.
Since April 2011, the Venus Express spacecraft, that has been orbiting Venus since 2006, has been maneuvered into a suitable observing position more than twelve times. “In principle, our image, too, would show the shadow of the observing spacecraft”, says Markiewicz. However, approximately 6000 kilometers lay between space probe and cloud tops. From this distance, the shadow of the spacecraft appears so small, that the camera cannot resolve it.
The resulting image is not only impressive, but also of high scientific value. In computer simulations the researchers re-enacted the optical processes leading to the glory and tried to reconstruct their image as closely as possible. To this end, they varied parameters such as size and refractive index of the droplets. “In our calculations we could not reconstruct the image with droplets consisting of sulfuric acid alone”, says Markiewicz. The scientists’ calculations show that an additional substance must be present. This may well be the long-sought unknown UV-absorber. Especially droplets of sulfuric acid with a core of iron chloride or an outer layer of pure sulfur proved to be promising candidates.
Dr. Birgit Krummheuer | Max-Planck-Institut
The Dawn of DUNE
30.03.2015 | Fermi National Accelerator Laboratory (Fermilab)
NASA's Hubble and Chandra Discover Dark Matter Is Not as Sticky as Once Thought
30.03.2015 | Space Telescope Science Institute (STScI)
In an experiment at the Department of Energy's SLAC National Accelerator Laboratory, scientists precisely measured the temperature and structure of aluminum as...
The IPH presents a solution at HANNOVER MESSE 2015 to make ship traffic more reliable while decreasing the maintenance costs at the same time. In cooperation with project partners, the research institute from Hannover, Germany, has developed a sensor system which continuously monitors the condition of the marine gearbox, thus preventing breakdowns. Special feature: the monitoring system works wirelessly and energy-autonomously. The required electrical power is generated where it is needed – directly at the sensor.
As well as cars need to be certified regularly (in Germany by the TÜV – Technical Inspection Association), ships need to be inspected – if the powertrain stops...
When an earthquake hits, the faster first responders can get to an impacted area, the more likely infrastructure--and lives--can be saved.
The Atlantic overturning is one of Earth’s most important heat transport systems, pumping warm water northwards and cold water southwards. Also known as the Gulf Stream system, it is responsible for the mild climate in northwestern Europe.
Scientists now found evidence for a slowdown of the overturning – multiple lines of observation suggest that in recent decades, the current system has been...
Because they are regularly subjected to heavy vehicle traffic, emissions, moisture and salt, above- and underground parking garages, as well as bridges, frequently experience large areas of corrosion. Most inspection systems to date have only been capable of inspecting smaller surface areas.
From April 13 to April 17 at the Hannover Messe (hall 2, exhibit booth C16), engineers from the Fraunhofer Institute for Nondestructive Testing IZFP will be...
25.03.2015 | Event News
19.03.2015 | Event News
17.03.2015 | Event News
30.03.2015 | Press release
30.03.2015 | Life Sciences
30.03.2015 | Earth Sciences