Estonia Building Instrument To Sample Venus’ Atmosphere

For decades, researchers have argued over whether the sulfuric acid-rich clouds of Venus could harbor microbial life. With extraordinarily high temperatures and pressures, the surface of the planet is a veritable hellhole. But Venus’ mid-level atmosphere between 40 to 60 km altitude is thought to be surprisingly earthlike.

Trouble is, there’s currently a dearth of in situ data from Venus’ thick atmosphere. But over the next decade, three privately funded, MIT-led Venus missions will aim to characterize Venus’s atmosphere for habitability and, ultimately, life.

Estonia’s Tartu Observatory is building an instrument which will fly as the second of three so-called ‘Morningstar’ Venus missions and is tentatively scheduled for launch by 2030. Upon arrival at Venus, the TOPS (Tartu Observatory pH Sensor) will descend into our sister planet’s atmosphere to measure the acidity of single Venusian cloud droplets.

Most of these cloud droplets will likely contain high concentrations of sulfuric acid, a compound that will destroy most of life’s building blocks here on Earth.

TOPS is the first instrument that is going to measure acidity of individual single cloud particles directly in situ in the clouds of Venus, MIT astrobiologist Janusz Petkowski, the Venus Morningstar Mission’s deputy principal investigator, told me via email. Previously the concentration of sulfuric acid had to be inferred from remote observations or from in situ measurements of other atmospheric components, like water vapor or sulfur dioxide gas, he says.

TOPS’ success or failure will hinge on how well it can measure these cloud layers’ pH values, in other words, the clouds’ acidity or basicity.

Here’s How It Will Work

TOPS works by capturing photos of a sensor film that changes its fluorescent properties depending on the acidity of the liquid in contact with its surface, Mihkel Pajusalu, a planetary scientist at Estonia’s Tartu Observatory, told me in his office. It’s expected to measure the acidities of around 1000 liquid droplets by processing the images obtained onboard the probe, he says.

Understanding Venus is key to understanding exo-earths.

Gathering data from these regions is critically important in understanding the nature and evolution of terrestrial atmospheres, Stephen Kane, a planetary astrophysicist at the University of California at Riverside, told me via email.

Why Is This Important?

Because Venus-like planets may be a common outcome of planetary evolution and form a large fraction of planets orbiting other stars, says Kane. But he says that demonstrating non-lethal pH and/or temperature ranges is far removed from demonstrating that life is, or was once present.

Even so, the hope is that TOPS will find atmospheric pockets high in Venus’ atmosphere where the planet’s lethal concentrations of sulfuric acid have somehow been neutralized by salts, or chemicals such as ammonia.

But constraining the pH in the clouds will be important for more than just the acidity, Paul Rimmer, a planetary astrochemist at the University of Cambridge in the U.K., told me via email. It may indicate the presence of other chemistry involving salts or transition metals, which are important minor constituents of life as we know it, he says. Determining the pH will also help to better constrain the water activity of the droplets, which is another critical component for life as we know it, says Rimmer.

How Long Will TOPS Be Operational?

It’s expected that enough droplets will hit the sensor plate for the usable pigment film to be expended in a few seconds, says Pajusalu.

Relaying data from the CubeSat-sized instrument while inside Venus’ thick atmosphere will be difficult at best.

TOPS will be inside the probe that descends through the atmosphere and connected to the probe’s central computer, Pajusalu says. He expects TOPS will relay its data back to Earth using the same spacecraft that brought the descent probe to Venus.

Untangling Venus’ Atmosphere

The Venusian atmosphere remains an enigma wrapped in a mystery, where in this case it is wrapped in an opaque cloud layer, says Kane. Anything new that we learn regarding the atmospheric chemistry of our sister planet is a step in the right direction, he says.

As for Life?

Present constraints on Venus’ cloud composition make finding life there unlikely, says Rimmer.

Even if habitable pockets were found, he wonders how any life within them would keep from being exposed to the intolerably harsh conditions of acidity and dryness that plausibly characterize most —- maybe even all —- of Venus’ clouds?

One even more speculative possibility is that the clouds of Venus are inhabited by life as we don’t know it, says Rimmer. This very hypothetical life may still use some of the same chemistry as Earth life, but may be best suited for its own special environmental conditions, he says.

Such conditions may be extreme for us, but they could be moderate for the life that would inhabit these dry, acid droplets, says Rimmer.

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