In 1989, NASA’s Magellan spacecraft set sail for Venus, Earth’s closest planetary neighbor, in what would become one of the United States’ most successful deep space missions. Magellan was the first to image the entire surface of our “twin” planet, and other countries and space agencies have since mapped and probed the Venusian surface. But the planet still remains poorly understood.
NASA plans to change that and end the nation’s 30-years-plus drought in Venus exploration with two new Venus missions, VERITAS and DAVINCI+, expected to launch between 2028 and 2030. Planetary scientists hope the new Venus missions will help answer fundamental questions about the shrouded planet’s atmosphere and geology.
Mapping the Past
According to NASA, the VERITAS (Venus Emissivity, Radio Science, InSAR, Topography and Spectroscopy) mission plans to map the surface of Venus to determine the geologic history and why the planet developed so differently from Earth. The mission will also study the emissivity of its surface rocks and determine whether active volcanoes are releasing water vapor into the atmosphere.
“Emissivity is a measure of the vibrational energy of minerals,” explains professor Tracy Gregg, an expert in planetary volcanology from the State University of New York (SUNY) at Buffalo. “The spacecraft’s Venus Emissivity Mapper (VEM), which operates in the infrared, will tell us the approximate iron content of rocks on the surface. That information will help us determine if the differences in terrain types that we see in earlier Magellan radar images correspond with differences in [terrain] composition.”
Gregg notes that knowing the composition of different parts of the planet’s surface will inform volcanologists’ understanding of how those features were formed and how they might behave. Measurements from VEM will also help scientists better understand the tectonic forces at work in the Plateau Highlands areas of Venus. One such Highland area, Alpha Regio, was mapped extensively by the European Space Agency’s Venus Express satellite, which orbited Venus from 2006 until 2014.
“Knowing if all the Highlands are made of the same material or different materials would really make me sit back and think hard about how planets evolve,” says Gregg.
Scouting for Volcanoes
Scientists are also curious about the geologic forces currently at work on Venus.
“We’ll be looking for changes on the surface of the Venus that have occurred since Magellan but also for changes that might be occurring now,” explains Gregg. “The VISAR [Venus Interferometric Synthetic Aperture Radar] instrument will be looking for small changes in the elevation of the surface, which would indicate that volcanic eruptions have occurred since Magellan.”
Gregg notes that, by flying over designated areas repeatedly, VISAR can look for minute changes that are occurring during the VERITAS mission, which would indicate the presence of volcanic forces actively changing the surface of Venus.
Exploring Differences
Gregg believes volcanic data gathered by VERITAS and other Venus missions will also help scientists better understand the evolution of Earth.
“If Venus and Earth are not twins, they’re at least siblings,” she says. “They’re about the same size, mass and density, and about the same distance from the sun, so they should have about the same stuff inside. Yet they are so different.”
What happened, and when, she wonders, to create those stark differences? VERITAS can help answer those questions and, by extension, help explain the evolution of Earth, Mercury, Mars and other planets with a rocky surface.
Asking Probing Questions
In contrast to VERITAS, which will image Venus remotely through the planet’s thick covering of sulfur dioxide clouds, the DAVINCI+ mission will gather detailed measurements of Venus’ atmosphere and high-resolution images of its surface features. NASA scientists hope to gain insights into the origin and evolution of the Venusian atmosphere, determine if the planet ever had an ocean, and improve their understanding of the tectonic and volcanic history of the unique Highland areas known as tesserae.
DAVINCI+ includes both an orbiter and a spherical atmospheric probe. A multi-spectral camera on the orbiter will image the planet in the UV and 1-micron near the IR band during two Venus flybys before the probe is deployed.
The probe will descend to the planet’s surface, taking measurements of noble gases and other elements in the planet’s dense, heat-trapping atmosphere, which is made up primarily of the now-famous greenhouse gas carbon dioxide. Once below Venus’s clouds, the probe’s Venus Descent Imager will produce high-contrast images of the tesserae.
Inspecting the Details
Imaging Venus in IR wavelengths from orbit will be challenging at best, says Sanjay Limaye, a Distinguished Scientist at the University of Wisconsin.
“Multiple scattering effects will likely reduce the spatial resolution (from orbit) to about 40 to 50 kilometers,” he predicts. “Imaging during the probe’s descent, however, particularly the last 10 kilometers, should produce images with spatial resolution as small as one kilometer or even hundreds of meters.”
Psyching Out the Past
Limaye also believes that analysis of noble gases and the ratios of different isotopes such as deuterium and hydrogen can provide insights into the atmosphere’s evolution and theories about whether Venus had an ocean at one time.
“The ratio of deuterium [heavy hydrogen] to hydrogen in Venus’s atmosphere is about 120 to 150 times higher than on Earth,” he explains. “The high presence of deuterium infers that there was once liquid water on Venus. As the planet warmed, either through tectonic activity or solar UV radiation, its surface water evaporated, breaking into hydrogen and oxygen or deuterium and oxygen. The lighter hydrogen molecules escaped the atmosphere, leaving deuterium behind.”
Feeling the Heat
Historically, the most challenging aspects of Venus exploration have been the extreme heat (approximately 750 degrees Kelvin, or around 890 degrees Fahrenheit) and high atmospheric pressure (about 95 times the pressure at sea level on Earth) on the planet’s surface. And while probes can be engineered to withstand extreme pressure, no modern electronics can survive long in extreme heat. For this reason, all the data and images collected by the DAVINCI+ probe will be relayed to its orbiter during the descent phase of its mission.
Dr. James B. Garvin, chief scientist for NASA’s Goddard Space Flight Center and DAVINCI+’s principal investigator, expects the descent sphere to carry sufficient power and thermal control to conduct science and data relay operations for maybe 15 to 20 minutes once the probe lands. Once the probe stops transmitting, the orbiting spacecraft will relay DAVINCI+’s data back to Earth.
Space.com reports that other Venus missions — including the Russian Venera 13 probe in 1982 — have fared slightly better than what Garvin predicts, transmitting data from Venus’ surface for more than two hours.
Rethinking Battery Power
Extreme heat and pressure aside, Limaye explains that the real limiting factor to the operational life of Venus probes is something familiar to every smartphone user: battery life. Currently, the size and weight of solar panels necessary to power a probe for an extended period would make the launch of the probe itself completely unaffordable. But there is hope.
“NASA Glenn Research Center is developing new types of chemical batteries designed to last for two to three months under Venus’s high temperature conditions,” he says. “The Center has also demonstrated new types of electronics that could support prolonged missions on the surface of Venus.”
Building Momentum
Limaye believes that VERITAS and DAVINCI+ are both adding momentum to an important new era of Venus exploration. Space News reports that the Indian Space Research Organization (ISRO) plans to launch the Shukrayaan-1 orbiter in 2024 as its first mission to Venus. Following VERITAS and DAVINCI+, the European Space Agency plans to launch its EnVision mission to Venus in the early 2030s.
However, Limaye is not convinced that any of these missions will tell us much more about Earth than we already know — unless, of course, we discover verifiable signs of life on Venus.
“If we found life on Venus, that would open up an entirely new dimension of exploration,” he says. “If life can exist in an environment like Venus, we can learn some significant lessons about survival not only on Earth but [on] other planets as well.”
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