Morning Star Crosses Star
|Venus Transiting the Sun, June 8, as seen by TRACE Image Credit: NASA/TRACE
Looking through the Venus transit, instead of looking at it, illustrated the effects of its dense atmosphere.
The banner (logarithmically scaled) image of Venus on the eastern limb of the Sun shows a faint ring around the planet. That faint ring, with a brightness of only about 1% of the brightness of the Sun close to its edge, is a consequence of the scattering that occurs in the atmosphere of Venus, allowing some sunlight to show around the edge of the otherwise dark planetary disk, as imaged by the TRACE spacecraft's telescopic view.
|Moon occulting Venus, the morning star, taken by the lunar probe, Clementine.
While Venus shares with Earth a similar size (95%) and mass (80%), its thick greenhouse atmosphere has transformed a potential terrestrial twin into a hostile, burning acidic world.
In total, more than 20 spacecraft have now tried to visit Venus, most recently highlighted by the US Magellan mission to plot detailed radar maps. Unlike earlier portrayals in mythology or in science-fiction, Venus offers life-as-we-know-it a rather inhospitable place.
Underneath those luminous clouds that reflect back 80% of incoming sunlight, "the most important single quality distinguishing Venus from Earth", writes planetary scientist David Grinspoon, "is the near total lack of water there."
The details are foreboding. At its surface, the Venusian atmosphere is 90 times denser than Earth's, or about the same as being 1 km (0.6 miles) beneath terrestrial oceans. The average surface temperature (470 degrees C, or 870 F) is hot enough to melt lead. At night, amidst distant lightning strikes high in the clouds, the ground would glow a faint red. Venus' surface is the hottest in our solar system, despite being twice the distance of Mercury from the Sun. Or as Dr. Grinspoon illustrates: "You could fry an egg on the sidewalk, but you'd have to do it quickly, before the sidewalk melted."
Venus has no tilted axis, and thus no winter, summer, nor any seasonal change. A relatively gentle breeze of a few miles per hour at the surface builds to a cloud-top gale that swirls like perpetual hurricanes: 350 km/hr, or 210 mph. While rather quiet geologically for the last few hundred million years, today's Venus is still volcanically active. Its terrain is marked by several large shield volcanoes, and is covered with solidified lava flows. Because of its slow rotation, the Venusian day and night each last 59 Earth days, or about two Earth months.
|Ultraviolet image of Venus obtained by Pioneer-12.
Image Credit: BNSC
"The portrait of Venus, as a verdant, rainy, overgrown swamp planet--perhaps complete with tree ferns and jungle animals--", writes Dr. Grinspoon, "became widespread in the popular and scientific literature through the nineteenth and most of the twentieth centuries." When one considers that as recently as 1955 -just a few years before the dawn of the space-age, the famous British astrophysicist, Fred Hoyle, considered Venus to be covered planetwide in oil, apparently our nearest neighbor still has many secrets left to reveal. [Hoyle speculated upon what became known as 'Hoyle Oil': "Venus is probably endowed beyond the dreams of the richest Texas oil-king".]
"We know, for sure, that there are signs of life at a few places on Venus," writes Grinspoon. "We know because we left them there--the smashed, corroding remains of our inquisitive machines. The most recent addition to this smattering of Earth-junk is whatever is left of Magellan".
Related Web Pages
Soviet Exploration of Venus
Dr. David Grinspoon's FunkyScience.net
Magellan Image Server
Magellan Mission Home
Fact Sheet on Venus
Past Missions to Venus
Atmosphere and Weather on Venus
Chemical Weathering Reactions on Venus