A vintage set of space probe data may help planetary scientists and astronomers make sense of the recent discovery of phosphine in Venus’ clouds.
When astronomers recently announced that they’d spotted evidence of a chemical compound called phosphine in Venus’ atmosphere, it stirred up a flurry of speculation about microbes drifting among the noxious clouds, somehow surviving and pumping out phosphine as part of their metabolism. On Earth, we don’t know of any other way to get phosphine, except with a lot of high-tech human intervention.
On Venus, phosphine is probably the product of a chemical process we just haven’t figured out yet. That’s not as exciting as alien farts, but it’s still pretty interesting. To understand exactly what’s happening in our hellish neighbor’s atmosphere, we’re going to need a lot more information about the chemistry and geology of Venus.
The phosphine discovery has sparked a new surge of interest in sending a new science mission to Venus – but even if a mission to Venus gets funding (never guaranteed), and even if everything goes perfectly (which doesn’t always happen), launch still would be years away. But we may already have some clues, stored away in NASA’s archives since 1978, when the Pioneer Venus probes dropped into Venus’ toxic atmosphere.
Chemist Rakesh Mogul (of California Polytechnic University, Pomona) and his colleagues recently turned to the Pioneer Venus data to see whether it could help confirm that radio telescopes on Earth had really detected phosphine in the planet’s atmosphere.
Message From A Doomed Space Probe
A spacecraft carrying four probes, each packed with scientific instruments, blasted off for Venus in August 1978. A few months later, the largest of the probes – appropriately if uncreatively named the Pioneer Venus Large Probe – left the mothership and dove toward the churning alien clouds below.
It was local night when the probe plunged into the upper layers of Venus’ atmosphere at 11 km/second (24,600 MPH). After free-falling about 50 km through the darkness, it deployed a parachute and drifted the rest of the way to the ground. Along the way, the Large Probe sent home about an hour’s worth of data from its mass spectrometer, gas chromatograph, and other instruments.
Although the probe didn’t survive its impact with the Venusian surface – not that it would have survived the heat and crushing atmospheric pressure anyway – the data it recorded lives on.
Mogul and his colleagues wondered what that 42-year-old data could tell them about phosphine on Venus. The probe’s mass spectrometer had sorted chemicals in Venus’ clouds according to their masses, which allowed scientists to compare those masses to known compounds and determine what chemicals were present in the clouds. And that data turned out to be detailed enough for Mogul and his colleagues to look for traces of phosphine and phosphorus, among other chemicals.
Their findings, which haven’t yet been published, appeared to confirm the presence of phosphine in Venus’ high clouds. Mogul and his colleagues also noticed that a handful of other chemicals seemed to show up in the clouds in greater quantities than it seems like they should, based on what we know about the chemistry of Venus’ atmosphere.
“We believe this to be an indication of chemistries not yet discovered, and/or chemistries potentially favorable for life,” they wrote. (For what it’s worth, my money is on the former option.) And all of that came from data collected several decades ago.
The Gift That Keeps On Giving
The recent study by Mogul and his colleagues hasn’t been peer-reviewed, so it’s best not to make too much of the results yet. However, it suggests that taking a second look at old data may help us better understand exactly what kind of weird chemistry is happening on Venus.
It also illustrates that most spacecraft are useful long after they’ve crashed, drifted away, or just fallen silent. Archived data is a resource that scientists can keep returning to in order to test new hypotheses or to take a look with new tools or methods. And sometimes they find things they missed the first time around – including really cool things like fast radio bursts.
Astronomers still aren’t sure exactly what causes the short, high-energy pulses of waves. Most of the ones we know about so far seem to come from outside our galaxy, and with a few exceptions, they don’t seem to repeat on any regular schedule. The unanswered questions aren’t too surprising, since astronomers have only known about fast radio bursts since 2007, when astronomers Duncan Lorimer and David Narkevic noticed one in some pulsar survey data that the Parkes Observatory had collected 6 years earlier, in 2001.
And 34-year-old data from the Voyager 2 spacecraft is still one of our best sources of information about the enigmatic ice giants, Uranus and Neptune, because we haven’t sent a spacecraft to even fly past either planet since. (Technically New Horizons flew past Uranus but didn’t take any pictures; stop laughing.)
Back in March 2020, space physicists Gina DiBraccio and Dan Gershman combed through Voyager 2’s old data to learn more about Uranus’ wobbly, sideways magnetosphere. They found evidence of a phenomenon called a plasmoid, a giant bubble of plasma hanging off part of the planet’s magnetic field “downwind” from the Sun, basically funneling particles from the planet’s atmosphere out into space.
Of course, old data can’t tell us everything; Venus and the ice giants all still deserve new missions to ask new questions and gather data with more modern instruments. And in terms of figuring out what Venus’ deal is, Earth-based telescopes can also collect a lot of new data to help answer questions and start building models. Meanwhile, however, turning to old data can help direct those observations and the science case for a future mission.