There are a lot of places to explore in space, and there is only so much money and time, but when the Discovery finalists were announced last year, it just seemed like Venus’s turn. There were two missions to Earth’s neighbor out of five, and when NASA announced that it might choose two missions in this selection round, well, it just seemed like everything was coming up Milhouse. Then two asteroid missions were chosen, and the Venus community was left to lick its wounds and figure out what went wrong. And yet, there is hope for Venus.
Venus scientists gathered last week at the 48th Lunar and Planetary Science Conference in The Woodlands, Texas, for a Venus Exploration Analysis Group (VEXAG) town hall meeting. The mood, while not jubilant, was not as despondent as one might have expected. There’s something unflappable about the Venus community, and you talk to its members, and you quickly realize that, yeah, maybe we’ll get there after all. To be sure, NASA hasn’t taken the most direct route―the agency hasn’t launched a Venus mission in almost 28 years―and it’s passed on some extraordinary missions along the way, including VERITAS and DAVINCI, the two Discovery finalists. But the science rationale behind Venus exploration has taken renewed importance, with implications beyond the understanding of that world, and the implications of Venus research now exceed even the boundaries of the solar system.
Yeah, maybe we’ll get there after all.
“I think the main selling point for Venus is that it is the cornerstone of comparative planetology,” said Bob Grimm at the town hall meeting. He is the director of the Department of Space Studies at the Southwest Research Institute and chair of VEXAG. In terms of size, composition, gravity, and density, Venus is Earth’s twin. Its surface should be Earth-like. The first Soviet landers sent to Venus were designed to float in what should have been a gorgeous Venusian ocean. Instead, the surface of Venus is hot enough to melt lead, 850 degrees. The Greenhouse Effect has rendered the planet hotter even than Mercury, which is much closer to the Sun. “We know that the atmosphere evolved in a hugely different way [from Earth]. The geology is hugely different. Why did Venus turn out so different?”
In the early evening hours of the Space Shuttle Atlantis’ first day in space for the four-day STS-30 mission, the Magellan spacecraft is released into space to begin its long journey to the planet Venus for an extensive radar mapping mission. The scene was photographed through Atlantis’ aft flight deck windows with a handheld 70mm camera. Credit: NASA
This question is of the utmost importance as astronomers are now able to identify countless new worlds circling other stars, many of which in the same sort of habitable zone occupied by Venus and Earth. Which, then, are Earth-like, and which are not, and why? Which might have life, and which are hellscapes? The answers to these questions are found on the second planet. “Venus has an important part to play in the study of habitability,” said Grimm. “Ultimately, where in the universe does Earth-size mean Earth-like?” The Venus community has engaged with the exoplanet community to learn what they need to know, and how Venus might help them.
Four months ago, NASA issued a call for New Frontiers-class mission proposals, and a Venus mission was one of six options. New Frontiers is the medium-tier class of planetary science missions, with a cost cap of $1 billion, excluding launch expenses. Those proposals are due on April 28. Specifically, the announcement of opportunity keeps with the planetary science decadal survey (the ten-year roadmap for space science and exploration), and calls for a “Venus In-Situ Explorer”―a lander, basically, that studies the chemistry and behavior of the surface and the atmosphere, and the interaction between the two.
If that mission is chosen, it will likely launch in 2027. It will be the first Venus lander NASA has ever launched. (Intentionally, that is. NASA’s Pioneer Venus Multiprobe operated briefly on the Venusian surface in 1978 after unexpectedly surviving its landing―a happy accident, but an accident all the same.) The competition will be fierce, with ocean worlds Titan and Enceladus notably added to the list of eligible mission concepts, but Venus has been a runner-up in two previous New Frontiers selections. It’s only a matter of time.
Pioneer Venus Multiprobe Artwork by Paul Hudson. Credit: NASA
Vexing Venus scientists is this. Thomas Zurbuchen, the associate administrator for NASA’s Science Mission Directorate, recently asked them to consider what they might do with $200 million if such a sum were suddenly offered. The smallest mission class today is Discovery, with a cost cap of approximately $450 million. Following the Discovery disaster, and just as the New Frontiers opportunity presents itself, NASA is asking the community to think much, much smaller. (A mission at that price tag would look a lot like a CubeSat or specialized instrument, for launch in the the early to mid-2020s.) This is not the sort of thing you want to hear before the big game.
“My reaction was first excitement… but I am now more worried than excited about this,” said one scientist present at the Venus town hall event. “I don’t want [this smaller mission] to be used as an excuse to not select the missions that will actually do the deep science we need. We don’t have a flagship right now, and many of us, including me, invest a lot of money and time and people’s lives in these concepts which I worry are directly threatened by this admittedly very attractive shiny object that we’re all going to pursue instead of the meal we were supposed to be getting.”
This is, perhaps, not the best way of looking at it, though one can hardly blame him for skepticism or concern. If there is to be a sub-Discovery mission class, the Venus community has the chance to use it as a pathfinding mission to prove the case for a New Frontiers or flagship-class mission. It comes down, however, to the opacity of NASA headquarters, and one’s perspective on the neglect of Venus thus far. Clearly, there is a low-level hunger at NASA to return, and the rise of exoplanets makes the science case for studying Venus as compelling as ever, but launches speak louder than words.
Surface photographs from the Soviet Venera 9 and 10 spacecraft. The Soviet Venera 9 and 10 spacecraft were launched on 8 and 14 June 1975, respectively, to do the unprecedented: place a lander on the surface of Venus and return images. The two spacecraft successfully landed a descent craft on 16 and 23 October 1975. These images were obtained on 22 and 25 October 1975. Venera 9 landed on a slope inclined by about 30 degrees to the horizontal whereas Venera 10 was only inclined about 8 degrees. The two spacecraft were separated by about 2100 km. Most of the rocks in the images are between about 0.3 and 1 meter. Credit: NASA
In the worst case scenario that Venus gets nothing from NASA, there is still another option on the table. Dave Senske, a planetary scientist at Jet Propulsion Laboratory, is co-chair of a Venus mission science definition team with Ludmila Zasova, a Russian colleague at the Space Research Institute in Moscow. They have been working to refine the scientific objectives of a possible Soviet-led mission to Venus, called Verena-D. The team presented their findings in January, and cooperation between NASA and the Russian Space Agency continue. “In the general sense,” said Senske, “we are working on a continuation [of the SDT report]. We have been directed to continue studying the Venera-D concept for the next two years… to help refine the science and capabilities needed to investigate Venus.” The mission would launch in the mid- to late-2020s.
There is hope for Venus, yet.
And if that falls through, there are still ways of doing Venus science. In the coming years, three separate missions―ESA’s BepiColombo and Solar Orbiter, and NASA’s Solar Probe Plus―will have flybys of Venus on the way to their respective targets. Venus scientists are looking at ways to do opportunistic science on those flybys, and are honing questions and developing experiments to that effect. Still in orbit around Venus doing science is the Japanese Space Agency’s AKATSUKI spacecraft.
But until there’s a spacecraft on the surface of Venus doing the sort of intense science that cannot be achieved from orbit, gaping questions will remain about why Venus is the way it is, and why Earth isn’t equally punishing. The plucky Venus community continues toiling away in the halls of academia, but absent a spacecraft with a meatball on the side of it, it is slow work, and sometimes frustrating, and sometimes heartbreaking. And regardless of whether success down the road is a $200 million NASA mission, a flagship, or a ride with the Russians, toil they do. “We don’t want to terraform Venus,” said Grimm at the town hall. “We just want to do these missions, do this science.” There is hope for Venus, yet.