In Planetary Science Circles, Venus Is Now All The Rage

Extrasolar planets continually steal the scientific thunder from some of our nearest planetary neighbors. But if there’s any sort of trend at this year’s Europlanet Society Congress (EPSC), it’s the unmistakable groundswell of resources directed toward future missions to Venus, our hellish planetary companion.

A series of new surface and orbital missions slated for launch by NASA, the European Space Agency (ESA), India, and China is creating a level of new excitement about Venus exploration that hasn’t been seen since NASA’s Magellan radar mapper visited the planet in 1990 and ESA’s Venus Express began orbiting the planet in 2006.

There are two major drivers for all this activity. One is that we need to understand our infernal neighbor with extraordinarily high surface temperatures and pressures, if we are to ever understand extrasolar planetary systems like ours. And secondly, a better understanding of the ravages of climate change here on Earth. We need to understand what went wrong on Venus in order to help improve our own long-term atmospheric models.

Equipped with instruments that include radar imaging, radio science, and gravity sensing, NASA will launch its VERITAS (Venus Emissivity, Radio Science, InSAR, Topography & Spectroscopy) orbiter mission in November 2027. It’s due to arrive at the planet nine months later.

Scientists will use VERITAS’ data to make the first global, high-resolution maps of radar imagery and topography, says NASA. Surprisingly, planetary scientists are still using Magellan data. But veritas will take radar imaging of Venus’ surface to the next level.

The VERITAS spacecraft is first injected into the very elliptical orbit of about 30,000 km and then will perform an aerobraking maneuver for about a year. It will then settle into a final science orbit of between 180 to 250 km by 2031. Thus, its nominal two years of full science operations will only begin some 2.5 years after launch.

VERITAS will produce the first maps of surface rock composition and constrain surface weathering by peering through the planet’s dense atmosphere via infrared spectral windows, says NASA. The mission will also search for the thermal and chemical signatures of both recent and active volcanism.

NASA notes that three of VERITAS’ science drivers include: What geological processes are currently active on Venus? What are the size and state of the core? And if there is water deep in the interior of Venus, does it reach the atmosphere via volcanism?

In order to maximize its surface mapping of Venus’ topography to a very high accuracy, VERITAS will use a different radar wavelength than Magellan. In contrast to the Magellan mission, which used an s-band radar, veritas will use an X-band radar, Scott Hensley, a radar scientist NASA’s Jet Propulsion Laboratory and the VERITAS Mission project scientist, told me here in Granada. Magellan’s S-band radar had a wavelength of about 12 centimeters, he says. We’re X-band, so we have a wavelength of around four centimeters, says Hensley.

Why does that matter?

Generally speaking, people don’t want to use X-band at Venus because you lose so much power in the atmosphere, says Hensley. but we paid for the atmospheric loss by making sure that we were able to do X-band so we could get a very accurate topographic map, he says.

To that end, in terms of its resolution, VERITAS will be quite a bit better than Magellan.

There are two types of resolution you might care about, says Hensley. The obvious one is spatial resolution; how well you’re able to separate things on the surface. The other is radiometric resolution, a measure of how fine the grayscale is on the surface, says Hensley. That gives you more contrast and substance in the data, he says.

To illustrate the difference between Magellan’s radar resolution and what is predicted with VERITAS, Hensley presented a simulation of the big island of Hawaii as if seen by Magellan at 20 kilometers resolution. It looked a bit like a fuzzy blob. Veritas, by contrast, will image down to 250-meters spatial resolution. That’s two orders of magnitude better than Magellan, says Hensley.

On repeat orbital passes of the planet, VERITAS will be able to combine the data from two passes to measure if the surface has moved, says Hensley. we’ll be able to determine if a volcano expanding beneath the surface is causing the terrain to bulge, he says.

As for whether Venus was ever habitable?

We want to know if there was water present in the past, says Hensley, but determining the timing of the water is much more difficult. However, we hope to be able to determine if water was involved in the formation of continent-like features on Venus, called tesserae, he says.

Rising steeply some two to four km above the planet’s surrounding plains, these highly-deformed parts of the surface are believed to be the planet’s oldest geologic units. They manifest as highland circular plateaus that range up to 2500 km in diameter. These so-called ‘tesserae terrains’ dominate Venus’ high plateaus; covering some 8 percent of the planet’s surface.

Because these terrains are thought to be among the oldest on Venus, researchers think that deciphering their early geodynamics could fill in many of the remaining gaps about the evolution of both Venus’ surface and atmosphere.

As for the major VERITAS takeaways at mission’s end?

We’d like to understand why Venus and Earth which were once so similar in terms of their size and composition evolved to be so very different from each other, says Hensley. That has implications for Rocky planet evolution for all the discovered exoplanets, he says.

We only have one laboratory where we can get direct measurements of planets at the surface and that’s our solar system, says Hensley. So, these Venus observations provide us with a key place to generically test hypotheses for how rocky planets evolved, he says.


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