Previewing EnVision: ESA’s newest mission to Venus

On June 10, the European Space Agency (ESA) announced that they had selected their next mission to Venus — EnVision. The mission, set to operate alongside NASA’s newly announced DAVINCI+ and VERITAS missions, will study Earth’s sister planet in extreme detail. 

Selected as the agency’s fifth medium-class mission in their Cosmic Vision program, EnVision will use a suite of specially designed radars and instruments to map the surface of Venus and understand how the planet evolved so much differently from Earth. Additionally, EnVision hopes to answer questions regarding Venus’ past, present, and future geologic and tectonic activity, and how it may effect Venus’ environment.

Led by Dr. Richard Ghail of the University of London, EnVision is currently set to launch in the early 2030s on an Ariane 6 rocket from Kourou, French Guiana. 

With the amount of interest in Venus increasing due to recent scientific discoveries and missions like EnVision, the question “why Venus?” can be asked. 

For Dr. Ghail, the interest in Venus started as a child.

“When I was six years old, Viking landed on Mars. I ran home from school to watch it on the TV, and it was really exciting. But something like nine months before that, the Russians had run Venera 9 on Venus. Which in many ways is even more remarkable, given the conditions on Venus,” said Dr. Ghail in an interview with NASASpaceflight. 

Venus, taken by the Venera 9 lander, the first Venusian lander to return images from the surface. (Credit: Soviet space program; enhanced by NASA)

“But growing up, the experience was that we were seeing ever more planets out in the solar system. We went to Jupiter, Saturn, etc. But Venus just remains a mystery. And then when I was doing my degree, towards the end of that Magellan arrived at Venus and kind of unveiled the planet, and we saw through the clouds to the surface and got our first real picture of this other world. And I got the chance to do a PhD studying it.”

However, the lack of missions and interest in studying the planet at the time, studying only Venus was not enough to get by for Dr. Ghail. 

“But Venus doesn’t pay the bills. And so I ended up in engineering geology. I applied my radar knowledge to something called interferometry, where we measure very small-scale ground movements for tunneling and other things like that. And I realized at some point, I think around the time that Venus Express got selected, that we could fly one of these radars to Venus, and we could look for actual ground movement changes on Venus,” Dr. Ghail said. 

“And that is where EnVision came from.”

As mentioned, one of the primary goals of EnVision’s mission is to answer how and why Venus developed so much differently than Earth. Earth and Venus are often looked at as sister planets, as they share many characteristics; such as their size, orbit, surface composition, surface features, and atmospheres. 

However, Venus, as we now know, houses a much more hostile environment underneath its incredibly thick atmosphere.

So, how will EnVision seek to answer how Venus became the hellish, hostile world it is today? For Dr. Ghail and the EnVision team, the philosophy behind using EnVision to solve this is similar to an Earth Observation philosophy.

“Our goal really was to try to do all that we could from orbit, to make the observations that are possible to be made from orbit, to understand the processes that are going on. So we’re really interested in Venus today, and how it got to be the way that it is today. Some of the other missions maybe are focused on Venus in the past, and while that’s a question that leads to today, we are very much focused on Venus today.” Dr. Ghail said. 

“To look for evidence for past oceans, so maybe we see ancient shorelines, maybe we see sedimentary rocks. And to look at the spectra in the infrared of the rock types. Some of which, like granite, form in the presence of water, or typically form in the presence of water. And so if we see large bodies of granite, we know that Venus once had oceans. So we can get a handle on the past, but the focus is very much on really, why is Venus different to the Earth? And how did the two planets evolve differently?”

“And the focus is very much on, where is Venus active today? And what does that tell us about how Venus works today? And the focus at the moment I guess, is on volcanism as the easiest kind of activity to detect. We should see it in imagery. We will see it in hot spots in the infrared. We’ll see the gasses that come out of the volcanoes and where they go.”

Another question EnVision is hoping to investigate and answer is what the current state of Venus’ climate is like.

“One of the big questions, the third big question we’re trying to answer is, is the current climate of Venus stable in the long term? Has Venus been like this for a very long time? Or is this just how it is today, and tomorrow it will be different?” said Dr. Ghail.

(Video description: NASA’s Magellan spacecraft was launched to Venus on the STS-30 mission of Shuttle Atlantis on May 4, 1989 and began is four year, two month mission at the second planet in our solar system on August 10, 1990.)

Venus’ climate, as we currently know it, is extremely hostile and inhospitable. With a pressure of ~93 bar, temperatures of 740 K (467 °C, 872 °F), and extreme weather systems, the Venusian surface would not be a pleasant place to visit.

So why is it this way?

Many theories have been proposed throughout the decades suggesting when, how, and why Venus evolved more unpleasantly than Earth. However, with the lack of dedicated, advanced science missions to study the planet, we just don’t know how.

But volcanism, for Dr. Ghail and many other missions, is key to understanding what happened on Venus.

“All these questions are tied up together in the search for active volcanism. Where it takes place tells us how Venus works geologically. How much is taking place tells us how it’s working geologically but also how the atmosphere is maintained. And how much gas coming out tells about not just the long-term climate but also the interior. Is the interior fully degassed? Is there no water left? Or is it actually still quite wet inside, and maybe Venus has continually lost its water? And the history side really comes from looking at particularly the images very carefully.”

Suppose we understood the extent of past and present volcanism on the surface of Venus. In that case, it will help scientists understand environmental processes that are currently present in Venus’ atmosphere and on the surface. 

“Because we do know that for instance, the sulfuric acid droplets in the clouds would break down and disappear on a timescale of probably a million years or something like that without active vulcanism,” said Dr. Ghail. 

Beyond the two stated goals set by the EnVision team, Dr. Ghail and his team have their eyes on some other areas of interest that they hope to investigate.

(Video caption: ESA’s Venus Express mission spent April 2006 to January 2015 exploring Venus’s surface and atmosphere rom orbit.)

“I think that Venus has quite a significant sedimentary cycle,” said Dr. Ghail.

“Not significant when you compare it to Earth in a terrestrial sense. I mean, we aren’t seeing mountains disappearing in millions of years or things like that. But actually quite significant when you compare it to, say, the oceans, or Mars, where we see things that are billions of years old. And I’d like to understand that sedimentary cycle a lot better. And I think EnVision is going to give us lots of information that will help us do that, both in terms of imagery and dynamics within the atmosphere, and chemistry, and all those other things.”

Additionally, Dr. Ghail hopes to study Venus’ insanely thick atmosphere.

“And so I think we might get a very different picture of the environment of Venus in the lower atmosphere and how it works. I think almost, you know, I’ve said this to a few people, we should really start to think the atmosphere of Venus as being more like an ocean, in terms of a big, dense, massive body of fluid that moves around, than an atmosphere in the sense that we think of it. So that’s one of the big things I think for me.”

To investigate Venus in detail, EnVision will use a suite of radars and spectrometers to map out certain areas of Venus’ surface. Understanding what surface features are present in those areas will allow scientists to hypothesize what may have happened in the regions. 

Following this, EnVision, or another mission like VERITAS, can return to that area of interest to gain more context on what geologic processes led to the formation of that surface feature. 

“Our suite of observations are in the infrared, in the ultraviolet, in various radio spectra. The main imaging radar is at 3 GHz, but we also have a sounder at 10 MHz. So another frequency, and that allows us to get into the ground. And then, of course, we do tracking and radio science to probe both the clouds and the interior of the planet.” 

The first of EnVision’s instruments is the Venus Synthetic Aperture Radar (VenSAR), which will serve as the spacecraft’s main imaging radar. VenSAR will operate at 3 GHz in the S-band.

Next is the Venus Subsurface Radar Sounder (SRS). SRS will study the surface composition and interior of Venus in great detail to give scientists an understanding of what materials are where. SRS will operate in the 9-30 MHz range.

Sounders work by looking for dialectic contrast. These sounders will look for bright materials in contrast to dark materials. 

“Where we see that contrast in the ground, we see a boundary and we can learn something. The two places where we think we will see that very clearly are the bottoms of craters, craters should be very rough and that’s bright, and many of them are filled with a dark material. We don’t know whether that’s lava or sediments or some other process that’s filling up crater floors, and the sounder will help us understand that, measure its thickness, look for the layering, and things like that.”

The SRS will also look for tesserae — which are continental-like regions across the surface of Venus. 

The Akatsuki Venus climate orbiter mission from Japan is currently at Venus. While instruments have failed given the craft is in its 11th year of a planned 2 year mission, Akatsuki has enough propellant to remain operational until November 2021. (Credit: JAXA/Akihiro Ikeshita)

“We don’t know whether they are literally like our continents and as soon as you get to the plains they stop dead — you know, there’s plains over here, and there’s tesserae over here, and there’s a sharp boundary — or whether they continue gradually under the plains and they’ve been flooded over many millions of years by lava flows and other materials that make up the plains. And the sounder will help us understand that because it will see that boundary dipping down into the subsurface, either very gently or very steeply at the boundaries of the tesserae.”

Lastly, EnVision will carry the Venus Spectroscopy Suite (VenSpec). VenSpec will house three main channels for observation: VenSpec-H, VenSpec-M and VenSpec-U. VenSpec-H will perform high-resolution observations on Venus’ atmosphere. VenSpec-M will provide compositional information on Venusian rocks. Lastly, VenSpec-U will observe and monitor sulfured minor species and the mysterious UV absorber in Venus’ atmospheric clouds. 

All three of these instruments will allow EnVision to study Venus’ surface in extreme detail and look for past and present geologic/tectonic activity.

“I think there’s two really important questions that we want answer with that radar, and then there are other things that we’re looking for if we can find them. It’s never been done before at Venus so we don’t know exactly what we’ll find,” Dr. Ghail said. 

Dr. Ghail compared Earth’s tectonic and geologic activity to that of Venus’ to give us a better sense of where exactly researchers are in understanding Venusian tectonic activity.

“if you looked at the Earth with the information we have about Venus, and you saw, let’s say, the Pacific sea floor, you would see thousands, literally thousands of volcanoes. And without of some kind of prior knowledge as to which ones are active, because they’re under the sea, they’re not weathered, they’re not eroded like they are on our continents, and so you wouldn’t know whether they’re active or not,” said Dr. Ghail.

“And you could have a dozen different models for how the Earth might make the Pacific ocean. And that’s where we are with Venus. When you know where the active volcanoes are, you can see the mid-ocean ridge, you can see the subduction zones and the island arcs around them. And suddenly you see the picture of plate tectonics. And that is how our oceans are made and destroyed. Now we know, I think morphologically, that Venus doesn’t have plate tectonics, at least not in the sense that the Earth has it in our oceans. In fact it looks a lot more like our continents in a tectonic sense.”

This is where EnVision’s instruments come in to play.

At Venus, EnVision’s three main instruments will study the surface in extreme detail, and look for certain surface features that indicate what may have been — or is — going on in that area. 

“But we still don’t know how it works, and I think when we get that information, when we know where that activity is taking place, and we see the pattern of it, particularly, we will get a much, much better understanding of how it works as a planet.” 

So, when you consider Venus’ current environmental state, and how extreme its tectonics and geologic activity could be, the question “does this activity have a connection with the atmosphere?” can be asked. 

On Earth, large scale tectonic activity like volcanic eruptions can influence weather patterns. However, Earth’s climate regulates these weather patterns, and the area surrounding the eruption is back to normal after a few months or years.

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