NASA scientists are preparing to paint the most detailed picture to date of the atmosphere of Venus when the aptly named DAVINCI — or Deep Atmosphere Venus Investigation of Noble Gases, Chemistry, and Imaging — mission drops a probe to the planet's surface.
When the 3-foot-wide (0.9 meters) descent sphere of the DAVINCI mission takes its one-way parachute trip to Venus' surface in the early 2030s, it will be carrying the VASI (Venus Atmospheric Structure Investigation) instrument along with five other instruments. VASI will collect data regarding the temperature, pressure and winds of Venus' atmosphere as it makes its hellish descent and enters the planet's crushing lower atmosphere.
"There are actually some big puzzles about the deep atmosphere of Venus," Ralph Lorenz, the science lead for the VASI instrument and a planetary scientist at the Johns Hopkins Applied Physics Laboratory (APL) in Maryland, said in a statement. "We don't have all the pieces of that puzzle and DAVINCI will give us those pieces by measuring the composition at the same time as the pressure and temperature as we get near the surface."
The dense atmosphere of Venus hides several mysteries, including how it is structured, as well as how the planet's many volcanoes have interacted with it over the eons. One of scientists' key goals in plunging a probe through the atmosphere of the second planet from the sun is to determine whether that world is still volcanically active. The probe could sniff this out through measurements of atmospheric temperatures, winds and composition.
Solving these puzzles could give scientists an idea of what continued volcanic activity could mean for our own planet's atmosphere.
"The long-term habitability of our planet, as we understand it, rests on the coupling of the interior and atmosphere," Lorenz said. "The long-term abundance of carbon dioxide in our atmosphere, which we really rely on to have kept Earth's surface warm enough to be habitable over geologic time, relies on volcanoes."
A one-way trip to Venus
One of the main challenges associated with investigating Venus has been the extreme conditions of the planet, which boasts surface pressures up to 90 times greater than that of Earth and surface temperatures around 900 degrees Fahrenheit (460 degrees Celsius).
Additionally, before any probe can reach the planet's surface from orbit it must first pass through clouds of sulfuric acid in the upper atmosphere of Venus. (These clouds also happen to make Venus tough to observe from Earth; reflective and shiny, they obscure our view of the planet's surface.)
These threats mean that DAVINCI's descent sphere systems and sensors will be enclosed within a hardy, submarine-like structure. But while the sphere is built to withstand intense atmospheric pressures and is insulated to shield sensors from the intense heat near Venus' surface, VASI's sensors must be somewhat exposed to the harsh conditions in order to do their job.
"Venus is hard. The conditions, especially low in the atmosphere, make it very challenging to engineer the instrumentation and the systems to support the instrumentation," Lorenz said. "All that has to be either protected from the environment or somehow built to tolerate it."
As the sphere drops through the atmosphere of Venus, VASI will measure the temperature with a sensor within a thin, straw-like metal tube. As the atmosphere heats the tube, the sensor measures and records the expansion and thus the temperature without directly being exposed to the corrosive environment.
VASI will collect atmospheric pressure readings using a silicon membrane encased within it. One side of the membrane is exposed to a vacuum while the other side faces Venus' atmosphere. The atmosphere pushes on the membrane, stretching it, and the extent of this stretching reveals the strength of the atmospheric pressure.
The instrument will measure Venusian winds with a combination of accelerometers that test for changes in speed and direction and gyroscopes that measure orientation. The mission will also track changes in wind speed and direction by monitoring shifts in the frequency and wavelength of radio waves.
Named for Italian Renaissance polymath Leonardo da Vinci, DAVINCI is currently set for launch in 2029. If it stays on schedule, the descent sphere will plunge through the thick atmosphere of Venus in 2031.
The drop will take around an hour. The probe is not expected to survive the fall, but if it does, NASA scientists are prepared to get around 17 minutes of bonus science at the surface with the doomed device.
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Robert Lea is a science journalist in the U.K. whose articles have been published in Physics World, New Scientist, Astronomy Magazine, All About Space, Newsweek and ZME Science. He also writes about science communication for Elsevier and the European Journal of Physics. Rob holds a bachelor of science degree in physics and astronomy from the U.K.’s Open University. Follow him on Twitter @sciencef1rst.