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EnVision
An illustration of the proposed EnVision spacecraft orbiting Venus. (credit: VR2Planets - François Civet)

EnVision and the Cosmic Vision decision


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In 2016, the European Space Agency announced a call for medium-size missions within their Cosmic Vision Program. In layman’s terms, “medium-size” means moderate-cost (less than 550 million euros, or $610 million) and low-risk, and this is achieved by keeping payloads small and by using proven, heritage technology for both spacecraft and payload. Alongside these common-sense conditions is a third and less tangible quality, that the project be scientifically robust. But when comparing excellent cases from vastly different fields, the merits of one scientific mission over another can seem subjective. It’s not enough to lament the dearth of data in said field, or to establish how a project will discover this or that, or even to show exactly how said “groundbreaking technology” will work. ESA wants a mission that will stir up an unprecedented level of excitement, support, and interest within the scientific community. Here is how they attempt to measure a project’s relevance.

At this stage, it is a given that all three proposals are affordable, feasible, and innovative, with the potential to shed new light on the universe. With three projects of seemingly equal caliber and gravitas, the decision may come down to more ephemeral concerns.

“Each member state has a representative in the Science Programme Committee, and it's their duty to define the content of the program,” said Luigi Colangeli, head of ESA’s Science Coordination Office. “Study groups work with the various proposals to arrive at something that is compatible with the boundary conditions, in this case, of a M-5, or medium-class mission. Right now, we are studying the evolution of the three missions. And then next year we will put together a peer review panel, who will analyze the three candidates and recommend the best selection to our Director of Science.”

Since the call went out four years ago, ESA have been whittling down proposals, from 25 at the beginning to only three now: Envision, Theseus, or SPICA. In February the EnVision conference took place at the National Centre for Space Studies (CNES) in Paris. EnVision is a low-altitude polar orbiter that is meant to perform high-resolution radar mapping, surface composition, and atmospheric studies of Venus. The purpose of the meeting was to call the Venus community to attention, because the clock is ticking. Consortium members, ESA representatives, and interested scientists from all over the world were in attendance.

“We need to hear from the community,” said Séverine Robert, one of the science leads for the mission. “People who will enrich the project, and give us new ideas on what to do with the data.”

There’s a particular strategy that missions have used to win over decisionmakers in the past. First, build a worldwide network of interested and involved scientists. Then, publish theoretical predictions and constraints, white papers, groundbased observations, and lab experiments that support the case. A pre-existing framework lends visibility and credibility to arguments for a space mission, and makes more persuasive the claim that a given mission will inspire a renaissance in the field. After all, a wealth of new data is nothing if no one back on Earth cares or knows what to do with it.

“To clarify, we're not selling this mission to the general public,” said Richard Ghail, principal investigator for EnVision. “ESA will do that part later. We’re selling it to scientists. The other two missions are strong competitors and we’re not taking them lightly. We’re all trying to answer fundamental questions, and competing with the best science case. In that sense, any of the missions is a good mission.”

EnVision meeting
Scientists discuss the EnVision mission at a conference in Paris in February. (credit: Arwen Rimmer)

In the summer of 2021, an independent board of scientists appointed by ESA will give their advice as to which proposal to select from among the finalists. By tradition, the director always approves their selection. All three groups are currently in high gear to prove they are the best choice. The lucky one will launch in 2032. At this stage, it is a given that all three proposals are affordable, feasible, and innovative, with the potential to shed new light on the universe. But they are all very different, which begs the question of how the ESA will choose among them. It seems an impossible choice, like asking which Star Trek series is best. With three projects of seemingly equal caliber and gravitas, the decision may come down to more ephemeral concerns.

“At the end of the day, the science program is built based on excellence,” Colangeli said. “That's our first goal. We must be sure that the mission we select is scientifically compelling, but also for it to be compatible with our technical and the programmatic boundary conditions. So, we have to guarantee that all the risks in terms of the possible implementation are taken on board and clearly identified and mitigated. Our evaluation thinks in terms of the science that the mission can return, and also in terms of the positioning of this mission in an international context. So, the truth is somewhere between a pure scientific assessment and a programmatic assessment.”

Practically speaking, this means that ESA study members are weighing various matters. Should we focus on new missions that complement current and future projects, or on broadening coverage? What will put ESA in the best position: innovation or refinement? Which field is really suffering for new data? What project has the most potential for interdisciplinary collaborations? What discipline is currently growing and attracting the most talented young researchers? Which mission is the most likely to jumpstart a string of successful missions going into the future? To give satisfactory answers to these questions, project scientists must somehow find the perfect balance of cost, feasibility, and importance; an arduous and constantly evolving task.

Venus is unique in the solar system, but as it turns out, maybe not so unique in the universe at large.

On Monday and Tuesday before the formal start of the meeting, members of the consortium attended a workshop where they discussed scientific, technical, and administrative priorities moving forward. The conference then officially opened on Wednesday, February 12 to a packed house attended by ESA representatives. Team leaders gave overview presentations and status reports on the instrumentation suite. Thursday and Friday were dedicated to further talks by consortium members on technical goals and challenges, and presentations by unaffiliated scientists whose current work would be enriched by collaboration with the EnVision project. There were lively and important discussions after each talk; some encouraging and some critical. The latter asides were usually focused on whether this molecule or that feature would really be detectable with a given instrument.

A sense of hope and anticipation was palpable in the meeting room. During breaks and meals, the scientists talked shop with focus and exuberance. Not even the shadow of Brexit could dampen the occasion, and in fact, it seemed practically inconsequential to those in attendance. When asked whether Brexit would affect ESA operations, Ghail had this to say:

ESA pre-dates the EU. It's not an EU venture. Often it partners with the EU for missions. For example, satellites are procured by the EU from ESA. The UK is one of the three big funders of the European Space Agency and it will continue to do so. There will be changes in how the UK and EU do space missions together. But ESA is not an arm of the EU. The EU funds instruments or missions in the same way that France or America does. The day of the Brexit vote the ESA came out with a statement saying, “Brexit has no effect.” But what we (British scientists) have noticed, is that when we've gone to the government, or the UK Space Agency for funding, the response is always, “We don't have time to deal with this. We're dealing with Brexit.” But long term, once we're sorted out, and we know where we stand, I don't expect any essential changes.

In the meantime, the consortium is focused on building the best science case they can. Ghail summed up their rationale as follows:

We used to think it was a simple story. Mars is cold and dead because it's too far from the Sun. Venus is hot and dead because it's too close to the Sun. But it's not as simple as that. Our understanding of Venus has changed massively in the last five or ten years. Magellan data has been re-examined, and Venus Express and Akatsuki have both given us surprising information about the atmosphere and the surface. Venus is much more active than we thought. So what's driving that activity? That's the question.

EnVision’s payload will have a surface radar from NASA and subsurface radar from ASI (Italian Space Agency), three different kinds of spectrometers, and a radio science experiment. The whole suite will, in theory, be able to examine Venus from its inner core to its atmosphere in high resolution, characterizing core and mantle structure, look for signs of active and past geologic processes, and seek evidence of a liquid water history. The team believes that the information they gather will help planetary scientists uncover why Venus and Earth took such different evolutionary paths, when everything about our original composition was apparently so similar.

“They are so radically different environmentally, physically, and geologically,” Ghail said. “Yet they’re both rocky, and similar in distance from the Sun. So the goal of our mission is to really try and understand why.”

EnVision has been in the works for more than a decade. The first version of the proposal was rejected five years ago, as it was too expensive, but this time around NASA is considering providing the surface radar. They have not made a formal commitment, nor does ESA require one at the present phase of the study. But this tentative offer was vital to getting through the initial winnowing stages of the call, because it brought costs down.

“The synthetic-aperture radar is an expensive piece of equipment,” Ghail said. “Britain didn't have the resources to fund it in the original proposal. So we were not selected initially. Then NASA said, actually, we could put up the money and supply the radae, because they want the mission to go. So, there are senior Americans on the team giving science input, and they will do the first step of the radar processing.”

The plan is for EnVision to be launched on an Ariane 6 rocket, cruise for about five months, then enter a circular orbit around Venus after a six-month aerobraking period. If everything goes to plan, it will have enough fuel left to maintain orbit for four years, and cover at least six full cycles (1 Cycle = 1 Venus sidereal day of 243 Earth days).

“When we look at other solar systems, you see a lot of planets that are basically in the Venus range,” said Helbert. “And what the newspapers label as a ‘second Earth,’ if we look closely, they are more like Venus. So, then the question becomes even more interesting. Could Venus have been habitable?”

EnVision is a “worldly” mission, concerned with atmospheric science, geology, surface mapping, and monitoring volcanic activity. Space only comes into it in the sense of an impediment, the bridge that must be crossed so the real work can begin. It is perhaps indicative of how multi-faceted “space science” has become, that there was not a single astronomer at the conference. Attendees were either geologists, planetary scientists, atmospheric chemists, or engineers. But the team hopes to bring in astronomers as well, specifically, exoplanet researchers.

Venus is unique in the solar system, but as it turns out, maybe not so unique in the universe at large. The vast majority of the terrestrial exoplanets found thus far fall into a “Venus-zone,” which makes it a perfect laboratory for the study of exoplanets. A better understanding of how Venus evolved could help explain why we have found so many analogues.

Jörn Helbert, one of the instrument leads, believes that EnVision will help us to understand why the Earth is so life-friendly, while Venus is clearly not.

“The question is why?” Helbert said. “And the question is, what’s the accident? Are we just lucky to end up on a habitable planet? Or is Venus the accident? When we look at other solar systems, you see a lot of planets that are basically in the Venus range. And what the newspapers label as a ‘second Earth,’ if we look closely, they are more like Venus. So, then the question becomes even more interesting. Could Venus have been habitable?”

Perhaps our nearest neighbor is the blueprint and Earth the outlier. These are fundamental questions that can only be answered by in-depth comparative studies. The fields of planetary and exoplanet science have a competitive and sometimes contentious relationship. Perhaps a new era of exploration on Venus might finally bring them together? Planet formation models could certainly use another data point.

“We need to understand Venus to understand how other worlds form,” Helbert said. “If you listen to people that model exoplanets, they are using Earth as their normalization case for the model. Because honestly, they don't know enough about Venus to use that in their models. So yes, you might think you found habitable planets around another star. But that's partly because you started with a habitable planet as your normalization case.”

Our evil twin is at the center of an international awakening. Last year, an article in Nature called the 2020s the “Decade of Venus,” and detailed several proposed missions from NASA, ESA, JAXA, and Roscosmos.

A niche-field which crosses over neatly with exoplanet science, and which the EnVision team doesn’t appear to be fully exploring, is astrobiology. Astrobiologists are focused on understanding habitability and uncovering the conditions needed for life and how life formed. Some study “proxy-aliens” called extremophiles: bizarre microbial forms of life on Earth and the kinds of creatures that just might be floating around in the clouds of Venus. This idea was popularized by Carl Sagan, and has never really gone away. Recently, a few papers using data out of Akatsuki have been arguing with each other about the mysterious ultraviolet absorbers in Venus’s atmosphere. This debate has stirred the imagination of the public and inspired the scholarly writing of astronomers for decades. It’s possible that EnVision’s high-resolution data could help solve this old mystery, and maybe even discover biosignatures. But they won’t find answers to questions they don’t ask.

Our current knowledge of Venus is painfully insufficient. If everything goes to plan with EnVision, and the world starts receiving data in 2034, it will then be more than 40 years since we last received information on the surface if no other missions arrive before EnVision. Magellan gave us our first and, so far, last look below the clouds in the early 1990s. But radar, materials, and computation technology has advanced phenomenally since then. EnVision will be able to deliver high-resolution data of the sort that scientists on Earth currently use to study weather patterns, climatology, and plate tectonics.

Although the main mission itself will only last a couple years, the pure amount of data they hope to collect will be enough to sustain the careers of future scientists for decades. EnVision may provide more than 160 terabytes of surface and atmospheric data, worlds away from the mere tens of gigabytes Magellan gathered.

“Communications have changed enormously,” Ghail said. “The kind of data we're talking about now would have been unimaginable even ten years ago. So that's been transformative.”

Mars has eight missions currently operating and four upcoming. All of this on a world that is geologically dead, with a barely-there atmosphere. Venus is another story altogether, a churning, toxic mystery, with multi-layered, complex weather patterns, and a surface that many people think might have active volcanism. While technical challenges may have hampered funding for the past forty years, modern advancements and the well-established use of rovers make further avoidance of the planet nonsensical. Venus is closer than Mars, and has a lot more going on: underground, on the surface, and in the air. As for why the Mars program has been so successful regardless, Helbert says it’s down to a good narrative.

“They have been very good at spinning the story of water and life,” he said. “Even so, they haven't really found water. They haven't found life. But the story worked. They moved from single missions to a coordinated, sustained program. And then our whole view of Mars changed. I expect the same will happen for Venus.”

Our evil twin is at the center of an international awakening. In the past few years, scholarly articles on Venus have seen a major uptick, buoyed by Akatsuki, continuing analysis from Venus Express, anticipation over pending funding allocations, a certain amount of Mars fatigue, and a wealth of interesting papers inspired by research that hypothesized that Venus could have had liquid water for the first couple billion years of its history. Last year, an article in Nature called the 2020s the “Decade of Venus,” and detailed several proposed missions from NASA, ESA, JAXA, and Roscosmos. In fact, NASA’s announcement that two Venus missions, VERITAS and DAVINCI+, were finalists in the next round of its Discovery program broke on the last day of the conference, and was met with excitement by everyone.

“In the past people had their own pet missions that they were pushing,” Helbert said. “Groups felt they had to compete. Finally now, we have a community of people coming together and saying, there's so many unanswered questions and we actually need a whole range of missions, not just one.”

The consensus in the community is that an international Venus program is desperately needed so that a steady stream of data can continuously flow in the years to come for scientists who stand to gain from a return to that bright, baffling world next door.

There is a growing sense that what’s good for one team, is good for another. Mission leaders for both VERITAS and DAVINCI+ were at the EnVision conference, and it was clear from their presentations that all three proposals are investigating very different things, with unique scientific goals and instrument suites. In fact, VERITAS and EnVision were designed from the ground up to be complementary. Venusian enthusiasts are at a bit of a loss when faced with skeptics who feel three missions per decade is a bit much. Is there such a thing as learning too much about another world? Exploring too much? Discovering too much?

Even so, there was no sense of resentment or jealousy when it comes to the thriving Mars program, but rather a general feeling that Venus’s time has come. Forty years certainly seems like too long to wait for new information. The consensus in the community is that an international Venus program is desperately needed so that a steady stream of data can continuously flow in the years to come for atmospheric chemists, geologists, planetary scientists, exoplanet researchers, and astrobiologists, all of whom stand to gain from a return to that bright, baffling world next door.


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