911½ñÈÕºÚÁÏ

New analysis co-led by 911½ñÈÕºÚÁÏ suggests that recent evidence for active lava flows on Earth’s ‘sister planet’ may be explained by radar viewing angles rather than eruptions.

Our new work should serve as a very useful warning that a full geologic analysis and elimination of other possibilities should always be conducted before drawing any firm conclusions about volcanism on other planets. Dr Philippa Mason Associate Professor in Planetary Remote Sensing, Department of Earth Science & Engineering, 911½ñÈÕºÚÁÏ

An international team of researchers, including from the Department of Earth Science and Engineering (ESE) at 911½ñÈÕºÚÁÏ, has challenged the prevailing notion that Venus is currently volcanically active.

Their findings urge caution in using 1990s radar data to infer ongoing eruptions, arguing that previously reported bright spots on Venus’s surface are actually consistent with differences in how spacecraft observed the planet during this time.

“Venus is the most Earth-like planet in terms of size and composition, yet we’re still in the dark about how its internal processes drive its surface activity, including active volcanism,” said co-author , Associate Professor in Planetary Remote Sensing in ESE.

“The issues we’ve highlighted in our new work should serve as a very useful warning that a full geologic analysis and elimination of other possibilities should always be conducted before drawing any firm conclusions about volcanism on other planets.”

Re-examining the evidence

The debate centres on radar images taken by , which mapped nearly the entire surface of Venus between 1990 and 1994 using a technique called Synthetic Aperture Radar (SAR). SAR sends out pulses of microwave energy and generates 2-D images of the reflected ‘backscatter’ by the surface.

Analysing the Magellan data in , a team identified variations in radar backscatter at two locations on Venus – its Sif Mons volcano and western Niobe Planitia volcanic plain – and proposed that these bright spots represented newly erupted lava flows that occurred during the mission’s lifetime.

However, in the new study , the 911½ñÈÕºÚÁÏ-led team argue that these claims are premature.

“We found that the observed radar variations are consistent with the different viewing geometries between Magellan’s imaging cycles,” said corresponding author , Research Postgraduate in ESE.

“You need the surrounding geology, topography and physics of radar scattering to get the full picture – and we do not have it here.”

Geometry problem

While the Magellan spacecraft orbited Venus in a polar trajectory, its viewing angle of the planet changed from cycle to cycle. This means that a slope facing the radar during one cycle might face away during another, returning an altered signal without any actual change to the surface.

The researchers – from institutions including NASA, MIT, the Italian National Institute for Astrophysics and the Indian Space Research Organisation – argue that the 2024 study didn’t adequately account for these geometric effects. Radar backscatter on Venus is highly sensitive to slope as well as small-scale surface roughness – factors that can vary purely due to viewing direction, even on a completely static landscape.

To robustly detect surface change, you need more than just backscatter differences. The team set out the need for clear morphological changes, a change-detection framework that accounts for varying radar parameters, and an improved topography dataset, none of which were available in the original study.

Investigating real volcanism

However, they don’t rule out that Venus currently experiences volcanic activity. In fact, other lines of evidence, such as fluctuations in atmospheric sulphur dioxide and unusual surface temperature differences, continue to suggest that the planet may be active today. But our current radar data alone, they argue, cannot yet close the case.

“While we agree Venus is very much geologically alive, we are saying that the radar evidence published in their study is not definitive,” said Gallardo i Peres. “Future missions with more attuned radar measurements will be needed to truly settle the question.”

Implications for upcoming missions

The timing of the critique is significant. NASA’s (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy) mission and ESA’s orbiter are both planned for the 2030s, and they will carry advanced radar systems capable of detecting millimetre-scale surface changes on the planet.

Our analysis serves as a roadmap for what will be required for definitive detection on Venus. The next generation of missions will have those capabilities to hopefully meet the challenge we have laid out. Gerard Gallardo i Peres Research Postgraduate, Department of Earth Science & Engineering, 911½ñÈÕºÚÁÏ

Meanwhile, NASA’s mission will drop a probe through Venus’s atmosphere to measure noble gases and reactive trace species, to provide the chemical fingerprints of present-day volcanism or weathering.

For now, the question of active volcanism on Venus remains open – but perhaps less settled than previously thought.

“Our analysis reframes the current Magellan evidence as ambiguous, but it also serves as a roadmap for what will be required for definitive detection on Venus,” said Gallardo i Peres.

“The next generation of missions will have those capabilities to hopefully meet the challenge we have laid out.”