Why is NASA going back to Venus?
Wladimir Lyra and Stephen Kane  Star News  Venus is for us the Shepperds Star. As it is never too far from the sun, we can only see it in the late afternoon or early in the morning. Thus, the ancients thought they were seeing two different objects, one east of the sun, Vesper (meaning evening, after sunset), and another west of the sun, Lucifer (meaning lightbringer, announcing the sunrise). It wasnt until the 6th century BC that the Greek philosopher Pythaghoras showed, following its motion along the year, that it was the same object. Because it is the third brightest object in the sky, after only the sun and the moon, they named it after Aphrodite, the goddess of love and beauty. In Latin, Venus  Venus is so bright because it is very close to us. It orbits our star at 72% of the distance the Earth does; its year counts 225 days, to Earths 365. Venus is also about the same size as the Earth: its diameter is about 95% the Earths. At this distance from the sun, and having roughly the same mass, Venus and Earth are often considered twin planets. Pre-space age, drawings of Venus imagined a balmy planet, with tropical swamps and megafauna. Reality couldnt be more different. Venus is a hellish planet. The temperature at its surface is 850 degrees Fahrenheit, so hot it can melt lead. The atmosphere is 100 times denser than Earths, and almost pure unbreathable carbon dioxide. The pressure on the surface is what you would experience on Earth a mile deep in the ocean. While the clouds on Earth are made of droplets of water, the clouds on Venus are made of droplets of sulfuric acid. The first spacecraft to land on Venus, the Soviet Venera, did not last one hour under these unforgiving conditions. The dense atmosphere is obviously responsible for the hot temperatures. From its distance to the sun, Venus' average temperature should actually be 8 degrees. Earths equilibrium temperature is not that different: minus-1 degree. Wait a minute. Sure, it can get that cold up north in the winter. Certainly not in Las Cruces, and definitely this is not Earths average temperature. Youre right. Earths surface temperature is in fact closer to 58 degrees, due to the greenhouse effect in our lower atmosphere. All this atmosphere that Venus has also generates a greenhouse, but far more intense, heating the planet to 850 degrees. This greenhouse is so extreme that Venus is hotter than Mercury, which is closer to the Sun but airless. Earths atmosphere is a lightweight summer blanket. Venus atmosphere is a thick duvet on fire. Venus is a cautionary tale. Its as if we lived in a small, beautiful town, teeming with life, right next to another town of about the same size that seems like it was once identical, but now it's burned to the ground with no sign of life. Worse, no one knows what happened to that town, or when it happened. Again, nobody knows. Thats one of the main reasons we study Venus. If we dont want to suffer the same fate as we keep warming our planet with greenhouse emissions, we should know exactly when, how, and why that nearby town was destroyed. We may be closer to solving that riddle. This year, an international fleet of spacecraft was announced to head to Venus later in the decade. NASA selected two missions: DAVINCI (Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging), and VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy). DAVINCI will analyze the brutal atmosphere of Venus, to understand how it formed and evolved, why it is a runaway hothouse, and also determine whether Venus had an ocean. VERITAS will characterize the geology of Venus, how it has evolved, what processes are operating today, and if water has been present near the surface. VERITAS will map Venus surface, checking whether processes such as plate tectonics and volcanism are still active. It will also study the types of minerals that exist on Venus, which are currently unknown. Ultimately, it will determine the conditions of Venus mantle, and how similar or different it is to Earths. The third mission is European, EnVision, designed to help us understand the relationships between Venus geological activity and its atmosphere. Together, these three missions will upend our understanding of Venus, and answer the question of what happened to our sibling planet, and why Venus and Earth took such different evolutionary paths from similar initial conditions. Venus has undergone a runaway greenhouse. If Venus was ever habitable in the past, it is now sterilized. It if had oceans, they boiled away. These three missions may help us prevent the same fate on Earth  Wladimir Lyra is a professor of astronomy at New Mexico State University. He can be reached at wlyra@nmsu.edu (email) or @DrRRLyrae (twitter). Stephen Kane is a professor of astronomy at the University of California, Riverside. He can be reached at skane@ucr.edu (email) or @ExoCytherean (twitter). More Star News: