Why future missions to Venus will not be as easy as they look
The recent discovery of phosphine in the planet’s atmosphere has given added impetus to future exploration missions
On 14 September, the entire world was waiting for the Royal Astronomical Society’s impending announcement on Venus. As it turned out, an international team of astronomers had used high-precision telescopes in Hawaii and Chile to discover a rare molecule—phosphine—floating in the clouds around the planet.
The discovery could be a hint of life, a biomarker, on a planet known for its hellish environment and volcanic surface. While a great deal of research will have to be conducted before anything can be confirmed, the announcement has come as an added bonus for the many missions that could explore one of Earth’s closest planetary neighbours in the near future.
But first, a look at the missions that have tried something similar in the past. Every country and agency, from the European Space Agency to those of the erstwhile Soviet Union and the US, has sent missions to Venus over the last few decades—there have been more than 40 such missions. In 1962, US space agency Nasa’s deep space probe Mariner 2 became the first spacecraft to conduct a successful planetary flyby. It also sent back temperature readings and other information about Venus.
The Soviet Union’s Venera programme saw a series of unmanned planetary probes to Venus being launched between 1961-84. While some of these probes never made it past Earth’s orbit, others crash-landed on Venus, like the Venera 3. Other missions analysed the chemical composition of the planet’s upper atmosphere. Venera 9 and 10 sent back the first black and white images of Venus’ surface in 1975; Venera 13 was the first lander to transmit colour images in 1982.
The Japanese Aerospace Exploration Agency’s (Jaxa’s) Akatsuki, launched in 2010, is currently orbiting the planet. It studies weather patterns and signs of active volcanism on the planet through high-speed imagery, radio science and camera instruments.
“Everything we learn about the atmosphere of Venus, and the chemical cycles there, broadens our knowledge of how Earth-like planets in the universe evolve, and how other planets have diverged from Earth’s path. Thus, if we really want to deeply understand climate change, geological history and the nature of planets in general, we need to understand how we should interpret these findings," says David Grinspoon, a senior scientist at the Planetary Science Institute, a US-based non-profit that focuses on planetary science and exploration of the solar system. Grinspoon, who studies surface-atmospheric interactions on terrestrial planets, atmospheric evolution and habitability, says the discovery of phosphine offers additional impetus for more missions to the planet and seek answers to some fundamental questions. “We already had a lot of important reasons to further explore Venus…. But now we have even more reason to go," he adds on email.
One proposed mission is India’s Shukrayaan-1—an Indian Space Research Organisation orbiter that will aim to study the planet’s surface and atmosphere. It has a tentative launch date of 2023, which could be extended to 2025, and will carry science instruments from India and other countries. One such instrument could come from the Swedish Institute of Space Physics, which announced in July that its Venusian Neutrals Analyzer (or VNA), which would be aboard Shukrayaan-1, would study how charged particles from the sun interact with the atmosphere and exosphere of the planet.
Nasa’s VERITAS (short for Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy) mission is under consideration for its Discovery programme, a series of missions to explore the Solar System that has been running since 1992. According to an official statement, the VERITAS spacecraft, proposed for a 2026 launch, would orbit Venus and peer through the planet’s obscuring clouds with the help of a powerful radar system to create 3D global maps and a near-infrared spectrometer to figure out what the surface is made of. “It would also measure the planet’s gravitational field to determine the structure of Venus’ interior. Together, the instruments would offer clues about the planet’s past and present geologic processes, from its core to its surface," the release explains. The last mission that studied Venus’ surface was Magellan, which ended in 1994.
Like VERITAS, the DAVINCI+ (Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging Plus) mission is another candidate for studying the planet’s atmosphere and trying to decode whether Venus ever had an ocean.
Studying our “sister planet" is one of the most important topics in modern-day comparative planetology but any future missions will not be without significant challenges, says Siddharth Pandey, head of the Centre of Excellence in Astrobiology, Amity University, Mumbai. “You need high-temperature electronics because when you are moving towards the sun, the energy levels are quite high. All the probes that normally go towards the sun—either Mercury or Venus—they tend to have very strong thermal protection systems, which take up a lot of space inside a spacecraft," says Pandey. “For anything that is going towards Venus, it will need a similar kind of thermal insulation as well as electronics, systems like cameras, communication units that can operate in that high-energy environment," he adds.
While the surface environment of Venus is extremely hot, dry and harsh, the clouds are made of concentrated sulphuric acid. “So any vehicle we send there has to be made to withstand the acid environment," explains Grinspoon, describing the announcement on phosphine as “an exciting development". “It needs to be confirmed with follow-up observations," he adds. “But if it is really phosphine in the atmosphere of Venus, then it is telling us something we don’t know about the processes occurring in the atmosphere. Even if it is not a sign of biology, we stand to learn something from this, and it will be important to sort it out since we are hoping to use similar observations to test for the presence of life on exoplanets around other stars."
What is this molecule?
Phosphine is a colourless, toxic gas made of phosphorous and hydrogen.
What makes the discovery so interesting?
On Earth, phosphine is generated through natural processes—lightning and volcanic activity—but only in small amounts. The only known processes that produce phosphine on Earth in similar quantities are biological in origin. The amount of phosphine detected in the Venusian clouds is relatively large.
To understand whether this is happening biologically— through the possible presence of micro-organisms—by taking measurements in the planet’s atmosphere and potentially bringing back samples to Earth for further analysis.
Source: Royal Astronomical Society