Wednesday, March 27, 2019

Speaking of Science: The case for Venus

Speaking of Science
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Venus and the waning crescent moon rise above the Wasatch Mountains near Salt Lake City on Jan. 31. (NASA/Bill Dunford)

(Recommended listening as you read this: "Venus, the Bringer of Peace" from Gustav Holst's "The Planets.")

The first time humanity sent a piece of itself beyond Earth's orbit, it was to Venus. The Soviet spacecraft Venera 1 launched in February 1961 on a collision course with the second planet from the sun. The probe never made it: a communications failure two weeks after launch meant scientists couldn't perform necessary course adjustments for it to hit its target. It eventually ended up in orbit around the sun, where it circles silently still.

But Venus became the site of other firsts: It saw the first successful planetary encounter, by the American probe Mariner 2. Venera 3 was the first spacecraft to crash land on another planet, and Venera 4 was the first to conduct observations of an alien atmosphere. In December 1970, Venera 7 touched softly down on Venus and provided the first signals from the surface of a planet beyond our own. All three were Soviet spacecrafts.

But since the heyday of the 1960s and '70s, exploration of Earth's neighbor has been pretty sparse. There have been only two missions dedicated to Venus since 2000, and no landers since 1984. NASA hasn't explored the planet since the Magellan, an orbiter from 1990 to 1994, sent its last signal in 1994.

Last week, at the annual Lunar and Planetary Science Conference in Houston, North Carolina State planetary scientist Paul Byrne asked his colleagues, "why?"

Sure, Venus is basically "hell made real," Byrne admitted. Temperatures on its surface are about 900 degrees Fahrenheit — hot enough to melt lead — thanks to a thick atmosphere of more than 90 percent carbon dioxide. The pressure on the ground is roughly equivalent to that found 3,000 feet underwater on Earth. The entire world is shrouded in clouds of sulfuric acid that make it impossible to see the surface from space.

"But it is a fabulously interesting world," Byrne said in a presentation about the planet. "It really does deserve our attention."

In many ways, Venus advocates say, the planet is startlingly like Earth. The planets have similar sizes and structures; they are made of many of the same materials and are perched at similar distances from the sun. If there are any aliens looking at our solar system from billions of miles away, they'd perceive both worlds as potentially habitable. Indeed, some studies suggest that Venus was once covered in oceans and could have been home to life for as long as 2 billion years, before a runaway greenhouse effect roasted the surface and caused all water to boil away.

"Did they start off similarly?" Byrne wondered. "When did their paths diverge?" The answers to these questions are looking more and more relevant as Earthlings grapple with their own, human-caused warming problem.

Venus is also tremendously weird in its own right. It spins backward (!!!) on its axis so slowly that the sun rises and sets just once every 243 Earth days — in fact a day on Venus lasts longer than a Venusian year (224 Earth days). Many scientists believe that interactions between the sun's gravitational pull and tidal forces in the planet's very dense atmosphere are responsible for Venus's strange and slow spin.

Unlike the moon and Mars, which are pocked with craters accumulated during 4.6 billion years of bombardment by meteorites, Venus has a relatively smooth surface. This suggests that the rocks on Venus are geologically young, like those on Earth. Yet, while Earth's crust is continually refreshed by plate tectonics, scientists don't have evidence of tectonics on Venus. Are volcanoes spewing out fresh molten rock, resurfacing the alien planet over the course of millennia? Scientists will have to peer past the sulfur clouds to be sure.

But aspiring Venus explorers have had a tough time doing so. At least five potential missions to the planet were put forward during the most recent calls for proposals to NASA's New Frontiers and Discovery programs (which have funded projects like the New Horizons mission to Pluto and the InSight lander on Mars) but none were selected. Some scientists have said that that's because Venus is so inhospitable — even for people accustomed to navigating frozen desert worlds and dark, lifeless voids, the "self-cleaning oven" conditions (Byrne's words) on the planet are intimidating. Others worry that the lack of interest in Venus is a self-fulfilling prophecy: because young researchers have had no opportunities to work on Venus missions, they're less likely to want to devote their careers to the planet.

But a journey back to Earth's neighbor may still be on the cards: The European Space Agency is evaluating a mission called EnVision that would use radar to explore Venus's history, volcanic activity and atmosphere. Meanwhile, U.S. and Russian scientists have been collaborating on a proposal called Venera D, which would send an orbiter and lander to the planet.

"We are compelled to explore and understand the differences in the evolutionary path of these twin-planets," scientists said in a recent report about the mission concept.

— Sarah

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27 March 2019

The GRAVITY instrument on ESO's Very Large Telescope Interferometer (VLTI) has made the first direct observation of an exoplanet using optical interferometry. This method revealed a complex exoplanetary atmosphere with clouds of iron and silicates swirling in a planet-wide storm. The technique presents unique possibilities for characterising many of the exoplanets known today.

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27 March 2019

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