Despite no go-ahead for missions, scientists are still trying to get to Earth’s evil twin
There’s a planet just next door that could explain the origins of life in the universe. It was probably once covered in oceans. It may have been habitable for billions of years. Astronomers are desperate to land spacecraft there.
No, not Mars. That tantalizing planet is Venus. But despite all its appeal, Venus is one of the hardest places in the solar system to get to know. That’s partly because modern Venus is famously hellish, with temperatures hot enough to melt lead and choking clouds of sulfuric acid.
“If you wanted sinners to fry in their own juice, Venus would be the place to send them,” V. S. Avduevsky, deputy director of the Soviet Union’s spaceflight control center, said in 1976 after his country’s Venera 9 and 10 landers returned their dismal view of the planet’s landscape.
Today, would-be Venus explorers say they have the technology to master those damning conditions. “There’s a perception that Venus is a very difficult place to have a mission,” says planetary scientist Darby Dyar of Mount Holyoke College in South Hadley, Mass. “Everybody knows about the high pressures and temperatures on Venus, so people think we don’t have technology to survive that. The answer is that we do.”
And researchers are actively developing more Venus-defying technology while vying for the financial support needed to get a mission off the ground.
In 2017, five Venus projects — including a mapping orbiter, a probe that would taste the atmosphere as it fell through it, and landers that would zap rocks with lasers — failed to get NASA’s green light for flight. But all were considered technologically ready to go, and the laser team got funding for technology development.
“NASA’s mission selection process is highly competitive,” says Thomas Zurbuchen, associate administrator for NASA’s science mission programs in Washington, D.C. “Earth’s so-called ‘twin’ planet Venus is a fascinating body, and of tremendous interest to our science community… the Venus community should continue to compete for future missions.”
From afar, Venus and Earth would look like equally promising targets in the search for alien life. Both are roughly the same size and mass, and Venus lies close to the sun’s habitable zone, where temperatures enable stable liquid water on a planet’s surface.
“We need to understand what made a planet go down the Venus path rather than the Earth path,” says astrobiologist David Grinspoon of the Planetary Science Institute, who is based in Washington, D.C.
A few orbiters have visited Venus in the past decade, including the European Space Agency’s Venus Express from 2006 to 2014, and the Japanese space agency’s Akatsuki, in orbit since December 2015. But despite dozens of proposed missions spanning almost 30 years, no NASA spacecraft has visited Earth’s twin since the Magellan craft ended its mission by plunging into Venus’ atmosphere in 1994 and burning up. And no spacecraft at all have landed on the Venusian surface since 1985.
One obvious barrier is Venus’ thick atmosphere which, in recent images from Akatsuki, makes the planet look like a smooth, milky marble. The atmosphere is 96.5 percent carbon dioxide, which blocks scientists’ view of the surface in almost all wavelengths of light. As recently as 2011, astronomers thought it was impossible to use spectroscopy — a technique that splits light from an object into different wavelengths to tell an object’s composition — from orbit to reveal what Venus’ surface is made of.
But it turns out that Venus’ atmosphere is transparent to at least five wavelengths of light that can help identify different minerals. Venus Express proved it would work: Looking at one infrared wavelength allowed astronomers to see hot spots that might be signs of active volcanism. An orbiter that used the other four wavelengths, too, could do even more, Dyar says.
To really understand the surface, scientists want to go there. But a lander would have to contend with the opaque atmosphere while looking for a safe place to touch down. The best map of Venus’ surface, based on radar data from Magellan, is too low-resolution to show rocks or slopes that could topple a lander, says James Garvin of NASA’s Goddard Space Flight Center in Greenbelt, Md.
Garvin and his colleagues are testing a computer vision technique called Structure from Motion that could help a lander map its own landing site on the way down. Quickly analyzing many images of stationary objects taken from different angles as the spacecraft descends can create a 3-D rendering of the ground.
A tryout in a helicopter over a quarry in Maryland showed that the technology could plot boulders less than half a meter across, about the size of a basketball hoop. “With a handful of GoPro pictures, we made beautiful little topographic maps,” Garvin says. “We can do it at Venus even with this crappy atmosphere that is so murky you wouldn’t think it works.” He plans to present the experiment in March in The Woodlands, Texas, at the Lunar and Planetary Science Conference.
Once a lander has made it to Venus’ surface, it faces its next challenge: surviving.
The first landers on Venus, the Soviet Venera spacecraft in the 1970s and ‘80s, lasted around an hour each. The longevity record set by Venera 13 in 1982 was two hours and seven minutes. The planet’s surface is about 460° Celsius and its pressure is about 90 times that of Earth’s sea level, so spacecraft don’t have long before some crucial component is melted, crushed or corroded by the acidic atmosphere.
Modern missions are not expected to do much better: one hour minimum, five hours optimistically and 24 hours “in your wildest dreams,” Dyar says.
But a team at NASA’s Glenn Research Center in Cleveland is designing a lander that could last months. “We’re going to try to live on the surface of Venus,” says engineer Tibor Kremic of NASA Glenn.
Instead of using bulk to absorb heat or countering it with refrigeration, the proposed lander, called LLISSE (Long-Lived In-Situ Solar System Explorer), would use simple electronics made of silicon carbide that can withstand Venusian temperatures.“They’re not Pentiums, but they’re able to provide a reasonable amount of functionality,” says NASA Glenn electronics engineer Gary Hunter.
The group has tested the circuits in a Venus simulation chamber called GEER (Glenn Extreme Environment Rig). “Think of a giant soup can,” but with 6-centimeter-thick walls, Kremic says. The circuits still worked after 21.7 days in a simulated Venus atmosphere, reported Philip Neudeck of NASA Glenn in AIP Advances in 2016. Scheduling issues put an end to the experiment, but the circuits could have lasted longer, Hunter says.
Ultimately, the team wants to build a prototype lander that can last for 60 days. On Venus, that would be long enough to act as a weather station, monitoring changes in the atmosphere over time. “That has never been done before,” Kremic says.
And that presents the next challenge: Planetary scientists have to figure out what the data are telling them.
Rocks interact with the Venusian atmosphere differently than with Earth’s or Mars’ atmospheres. Mineralogists identify rocks based on the light they reflect and emit, but high temperature and pressure can shift light in ways that depend on the mineral’s crystal structure. Even when scientists get data on Venusian rocks, interpretation could be tricky.
“We don’t even know what to look for,” Dyar says.
Ongoing experiments at GEER are helping set the baseline. Scientists can leave rocks and other materials in the chamber for months at a time just to see what happens to them. Dyar and her colleagues are doing similar experiments in a high-temperature chamber at the Institute of Planetary Research in Berlin.
“We try to understand the physics of how things happen on the Venus surface so we can be better prepared when we explore,” Kremic says.
By simulating Venus-like conditions, researchers in Germany are working on how best to collect and interpret data from a future mission to the planet. At left, a stainless steel cup holding a hockey puck‒sized disk of minerals glows as the heat inside a chamber gets cranked up to 480° Celsius. That glow muddies efforts to analyze the minerals based on the light they emit. At right, a new kind of ceramic is barely visible under the same conditions, so interferes less with the analysis.
Two of the mission concepts NASA didn’t green-light use different strategies. VISAGE (Venus In-Situ Atmospheric and Geochemical Explorer) proposed bringing powdered rocks into a chamber inside the lander that maintains Earthlike conditions and measuring them there.
VICI (Venus In-situ Composition Investigations) takes a hands-off approach: Shoot rocks with a laser and analyze the resulting puff of dust. The Mars Curiosity rover uses that technique, but the density of Venus’ atmosphere might make the results harder to understand. The team is testing the technique in a Venus simulation chamber at Los Alamos National Laboratory in New Mexico.
“We’re convinced it will work,” says VICI principal investigator Lori Glaze at NASA Goddard. “We just need to do some more work to convince the rest of the community.”
There’s hope on the horizon, if Venus explorers can shrink their ambitions. Last year, NASA established a program called Venus Bridge to see if any missions to Venus can fly for $200 million or less. That figure is less than half the cost — and in some cases much less than half — of recently proposed missions.
“I’m a strong believer that constraints breed innovation,” Zurbuchen says, adding that advances in technology mean there are ways to explore that didn’t exist a decade ago. “If you put a financial constraint on it, great missions can happen.”
It would be hard to make meaningful headway on science questions for that little, Dyar notes. “The Venus community is torn,” she adds. But it may take multiple piecemeal missions to understand Venus anyway. “We’ll get the frosting on one trip and the cake on a different trip.”
In the meantime, the Venus hopefuls soldier on.
“My new favorite saying for the Venus community is, ‘Never give up, never surrender,’” Glaze says. “We keep trying.”
Source: Science News