Radio waves

What echoing radio waves have taught us about Venus

In addition, the observation time with the Goldstone antenna was very limited. The dish is part of the Deep Space Network used to communicate with various space probes. Often times, the team’s scheduled time with the dish would be canceled instead of a higher priority request for installation.

The reward

The team started observing Venus in 2006. Originally, they requested 121 separate observing sessions and eventually got around 50. By 2020, they had managed to make 21 observations which produced usable data. “It is a difficult measure to take and it requires both great precision and patience,” Margot reaffirms with a smile.

The results of their patience and precision are remarkable. The team found that the average day on Venus (between 2006 and 2020) was 243.0226 Earth days. In addition, the length of the Venusian day varies up to 20 minutes. Margot believes this is in part due to the extremely dense atmosphere of Venus, which, unlike the solid surface below, has a rotation period of just four days. As the atmosphere “shakes” above Venus, it transfers a certain angular momentum to the planet itself.

The team also found that Venus’ axis is tilted 2.6392 °, an accuracy ten times better than previous estimates. The rate of precession – how fast the pole of Venus wobbles – is 44.58 “per year, which means that the pole traces a full circle in the sky every 29,000 years. A more accurate rate of precession yielded to the team a measure of the moment of inertia of the planet, which in turn, gave a rough estimate of the size of Venus’ core, which was previously unknown. Margot’s team discovered that it was about 3,500 km in diameter, roughly the same size as the Earth’s.

But do the similarities end there? Our planet’s core has a molten outer layer and a solid center, but what about the core of Venus? At this point, says Margot, we can’t be sure. Recent computer modeling suggests that it could be solid or melted, or perhaps solid in the center with a melted outer region, like that of Earth. Margot thinks it’s probably entirely liquid, but would like additional data from ongoing speckle sightings to confirm this. Alternatively, he says, direct observational evidence of the size of the nucleus could come from tracking the motion of an orbiter around Venus and measuring the tidal deformations induced on the planet by the Sun. “The best ultimate way [to learn about the core] is to have seismometers on the surface; but that will not happen anytime soon, ”he adds, due to the hellish conditions on the planet.

Work at home

While they continue their work on Venus, Margot’s team is also using radar spot tracking on the moons of Jupiter Europa and Ganymede. Astronomers firmly believe that Europe has a world ocean below its icy surface and Ganymede might have one as well. But using this technique to observe these moons is much more difficult than Mercury or Venus because of the distance involved, so the radar echoes received over this vast distance are thousands of times weaker. Early results from the team, however, already suggest that Europa “has an outer layer that is decoupled from the inside of the body,” says Margot, confirming that it does have an underground world ocean.

We have become accustomed to the remarkable discoveries made by robotic space probes circling or even circulating on our heavenly neighbors. And why not? But Margot and her team remind us that equally amazing new knowledge of the cosmos, including our sister planet, is being gained from here on Earth.