Mars! Mars! Mars! Over the last two decades, the red planet has played host to an even dozen orbiters, landers, rovers, and crashers. Meanwhile, the planet right next door, the one that’s the brightest object in the sky after the sun and moon, the one that in many ways is the most similar to the Earth, has received just two visitors since the 1980s. But Venus’ time as the Jan Brady of the Solar System is nearing an end, as new probes are on the way from the United States, Europe, India, and possibly Russia.
There’s a reason, of course, why an object as tantalizing as the “evening star” should receive such a relatively few visitors. Despite a diameter of 7,500 miles that’s just 400 shy of Earth, and its location in what’s considered the Sun’s “Goldilocks zone,” Venus has its problems—like surface temperatures that are hot enough to melt lead and a blanketing atmosphere so thick it’s equivalent to pressures found more than half a mile under the ocean. Then there’s the little matter of sulfuric acid rain and 185 mph winds. It all makes Venus a little hard to love. Or visit.
Venus did receive the first probe launched to any planet when Venera 1 passed by in 1961. It was the first in a string of probes sent to Earth’s hot sister by the Soviet Union. Venera 3 became the first human-made object to impact another world. Venera 4 the first to sample Venus’ atmosphere. And in 1970, five years before America landed Viking 1 on Mars, the Soviets brought Venera 7 to a soft landing on Venus. Unfortunately for Venera 7, conditions on the surface were so not-soft that the probe died within half an hour. In 1975, Venera 9 finally managed to return an image from Venus’ heat-rippled surface.
The final Soviet mission to Venus came in June of 1985 with the do-it-all mission of Vega 2. That mission included a balloon deployed into Venus’ atmosphere, a lander that survived for an hour in the region known as Aphrodite Terra, and a “mothership” that arced around Venus and went on to intersect Haley’s Comet. That is an impressive mission. The lander even managed to sample and analyze the surface before succumbing to the heat and pressure.
Since then, there’s been a real drought for the water-free world. But as Nature reports, a new generation of probes could not just peal back Venus’ smothering clouds, but tell us how they got there.
Venus suffers from a runaway greenhouse effect in which its thick, CO2 rich atmosphere swaddles it like a heat-trapping blanket. But radar maps of the surface have located features that contribute to the idea that Earth’s sister planet was once very much a sibling, with similar geology and water-filled oceans. A visitor to the Solar System a billion years ago might really have seen two worlds that looked like twins.
So how did Venus go from Earth-like to hell-scape? It probably wasn’t a Venusian Trump dropping out of their equivalent of the Paris agreement. Though Venus is similar to Earth in size and composition, it’s quite different in other ways. It has no moon, its axis is much less tilted meaning that it has no seasons, and it has a supremely weird 243-Earth-day-long “reverse day” in which the Sun rises in the west and sets in the east … 122 days later. A day on Venus is actually longer than its year.
As planetary geologists have built up a picture of the early Solar System, it’s become clear that while there are now a neat handful of planets following nearly circular orbits, it wasn’t always that way. The early system was a place of titanic collisions and mergers as the planets cleared their “lanes.” Earth was involved in a collision with an object roughly the size of Mars some four billion years ago. That collision created the Moon, resurfaced the Earth, changed the planet’s tilt, and may have stripped away most of an originally thicker atmosphere. Venus also seems to have been on the receiving end of a major blow. That punch left it with that odd spin in the opposite direction of every other planet, but didn’t gift it with a satellite.
The long day, negligible tilt, and slow build up of greenhouse gases from vulcanism could have sealed Venus’ fate, even if no one ever opened an Aphrodite Terra Hummer dealership. But it doesn’t seem to have happened in a hurry. Venus may have very well been very Earthlike for three billion years. That’s not just more than long enough for life to appear and evolve, it’s almost ten times as long as liquid water is believed to have been present on the surface of Mars. And then the air turned sour, the temperatures rose, the seas boiled and … it was bad.
Over the next two decades, scientists should get a much better look at Venus’ current state and much better clues about its history.
The first to arrive will be an orbiting probe from India’s ISRO. The Indian space agency has shrouded their first interplanetary mission in clouds of secrecy almost as thick as Venus’ atmosphere, but a list of instruments being packed for the trip shows that the orbiter will carry sensors to provide high quality radar maps of the surface, a follow-up to a mapping NASA began with the Magellan probe 30 years ago. The ISRO orbiter is expected to arrive at Venus in 2023.
Soon after, NASA could return to the scene with a pair of probes: VERITAS and DAVINCI. VERITAS is one of the five planetary missions NASA has selected for the next decade. Like the Indian probe, it’s aimed primarily at looking at mapping Venus’ surface and doing analysis from orbit. Scientists behind the mission are particularly interested in features on Venus that appear to be indicate it may have plate tectonics similar to those on Earth. Plate tectonics are thought to have a big impact on helping to regulate the atmosphere and temperature of Earth, and it may be that when these processes shut down on Venus, that was the point where the greenhouse effect took over. DAVINCI is an atmospheric probe. It’s designed to penetrate Venus’ cloudscape, sample atmospheric chemistry, and return data and imagery all the way to the ground. However, it’s not really a lander in the sense that surviving impact and continuing to broadcast from the surface is not in the plan. Both of these Venus probes face a challenge of a non-engineering variety when they come up for review in July and compete against other proposals for NASA’s budget dollars. If they make it over that hurdle, look for them to reach Venus sometime around 2025.
Europe’s ESA has it’s own Venus mapper in the works under the name EnVision. It also faces a potential knock-out in a funding competition, but could fly by 2032 is the euros remain in place. Its mission wouldn’t overlap that of VERITAS so much as supplement it. The ESA probe would map the whole planet at resolution of about 15-30 meters. The American probe is designed to target specific areas of Venus’ surface and map them at 1 meter (3 foot) resolution — a resolution fine enough to spot the acid-etched, pressure-crushed Soviet landers from the 1980s.
Those old landers may not be lonely forever. A NASA team from Glenn Research Center in Ohio is testing a probe designed to join those Veneras and Vegas on the Venusian surface. The probe they’re designing is both light enough to hitch a ride with some other mission, and tough enough for a prolonged stay on the surface. It wouldn’t try to hold off the heat or the pressure. Instead it would simply be made from electronics designed to operate in that environment.
But there’s a chance that technology will go back to Venus on a launch from the same cosmodrome that delivered the planet’s first visitor. Russian agency Roscosmos is said to be “eager to use this new technology.” They’ve produced a proposal for a joint mission with NASA for “Venera-D” where the D means long duration. That mission would harken back to Vega, delivering both an orbiter and a lander that might survive on the surface for months rather than minutes. It might even include another balloon. Unfortunately, unlike the other probes on the list, Venera-D doesn’t seem to be working its way through the funding process either in the U.S. or Russia.
These aren’t the only Venus probes in the works. Both in the U.S. and in Europe groups are looking to create probes that can take advantage of lower costs for launches and increased access to space. Not all of them will fly, but it seems unlikely that Venus won’t get a little more of the attention it deserves in the near future.
Volcanoes on Venus, from radar mapping conducted by Magellan probe.
