Even while human spaceflight goes through a period of uncertainty, robotic interplanetary spacecraft persevere. We have spacecraft at Saturn, Mars, and Mercury and others on their way to Jupiter, Pluto and the large asteroids Vesta and Ceres. And yet there is something missing. NASA has no spacecraft at Venus, and recent decisions mean that there is little chance of a new U.S. mission to Earth’s sister planet for at least a decade. This is unfortunate, especially now, when understanding climate has become so relevant.
Historically our knowledge of climate change is inextricably tied to growing awareness of our planetary twin and its overheated CO2-rich atmosphere. At some point Venus apparently suffered a “runaway greenhouse” where solar heating triggered irreversible ocean evaporation. Carl Sagan did his early research on the extreme greenhouse climate of Venus. When I was a student working with Sagan he had me read the PhD thesis of another scientist who cut his teeth on a Venus climate model: James Hansen – now the NASA scientist most identified with climate advocacy. Recently Hansen has warned of the “Venus Syndrome” a worst-case scenario where unchecked burning of fossil fuels might cause a runaway greenhouse on Earth. I am skeptical of the claim that we could trigger such a catastrophe. But neither he nor I really know the answer, because the detailed modeling required to test this cannot be done well with our current sketchy knowledge of the current and past climates of Venus. New spacecraft could go a long way toward filling in the gaps by revealing how sunlight is converted into heat and motion and solving the mystery of if, how, when and why our sister planet went through this transformation.
Whether or not the past of Venus portends the future of Earth, it is quite clear that what is being lost now is vital knowledge of how climate works on an Earthlike planet. What I fear is that this loss may be irretrievable. We may be on the edge of a runaway feedback that threatens to dry up support for Venus research for a generation.
NASA research support goes where the missions go. So NASA has been cutting support for basic research about the geology and climate of Venus, which results in fewer grad students pursuing Venus science. Consequently, the community within NASA advocating for new Venus missions has been shrinking, which makes it harder for new missions to compete against those with larger constituencies. In general, I think NASA does a good job at selecting missions. Yet these factors work against missions to a planet that has not recently been visited.
We have not had a Venus launch since 1989. NASA just selected its new round of competed missions and, of 7 serious Venus mission proposals, none made the cut. Venus research is in serious danger of a death spiral. Some of us have been advocating new Venus missions for decades only to get repeatedly shot down. Now we have to face the prospect of no missions to Venus within our careers. Perseverance can be admirable, but doing the same thing repeatedly and expecting different results is, well, you know.
The international community is aware of this gap, but nobody else has the resources and experience of NASA. The European Space Agency’s Venus Express mission, launched in 2005 and still in orbit, is humanity’s one remaining climate monitoring spacecraft at Venus, but even the best case scenarios show it dying before any other spacecraft shows up to join it. The Japanese space agency launched Akatsuki in May 2010 but, tragically a malfunction that December caused the spacecraft to miss Venus and spin helplessly around the sun.
There is no anti-Venus conspiracy at work within NASA – all the missions recently picked are worthy and there is not enough money to fund all of the good ones. But the worsening prospects for Venus research are unfortunate when considering the lessons that Venus has to offer about climate and the origin, survival and loss of life-supporting conditions on Earthlike planets.
One small ray of hope here is that in NASA’s recent Decadal Survey, an ambitious orbiter, the Venus Climate Mission is recommended for consideration if other more expensive plans fall through. Of course, as a Venus guy I’m not disinterested. I would love to participate in such a mission. I also think it would be good for our country and the world.