Out There

The Earth-Twin Planet That Nobody Talks About

By Corey S. Powell | September 30, 2015 10:59 pm

Venus, as imaged more than two decades ago by the Magellan spacecraft. (Credit: NASA/JPL)

A colorized radar map of the Maat Mons volcano on Venus, shows lava flows of unknown age, along with an apparent impact crater in the foreground. This image, created more than two decades ago by NASA’s Magellan spacecraft, still represented the state of the art in our knowledge of Earth’s near-twin. (Credit: NASA/JPL)

NASA scientists were conferring today about a nearby planet that is shockingly similar to Earth. It is just 5% smaller in radius and 15% smaller in mass. It is almost the exact same age as our planet, and gets its warmth from an identical star. The only thing that’s a bit off is that it orbits a bit closer to its star than Earth does, so it receives nearly twice as much radiation. On the other, it also reflects away a lot of that radiation. Its theoretical (equilibrium) temperature is just below freezing, so with a little natural greenhouse warming it would be quite an inviting place.

If we found it orbiting another star, this world would surely be hailed as the most Earthlike exoplanet known: the best place yet to search for alien life.

No doubt you sense there is a catch, and indeed there is. The world I’m talking about is Venus. It is not orbiting another star; it is the planet closest to home right here in our own solar system. But I’m not just being coy. Despite its proximity, Venus is a profound enigma. It really should be a hospitable world, but the truth is that it is more like hell on almost-Earth. Understanding why that is–why our planet went right while Venus went terribly wrong–is crucial for finding out whether habitable planets are common or rare throughout the universe.

The ways in which Venus diverged from Earth are as dramatic as they are perplexing. Venus has a crushing atmosphere tinged with sulfuric acid clouds and dominated by carbon dioxide. It has a year-round surface temperature of about 450 degrees Celsius (850 degrees Fahrenheit), far hotter than an oven set to “broil.” It has no appreciable magnetic field to protect it from charged particles that blow out from the sun. It has no plate tectonics to renew its geology. It rotates so slowly that one “day” takes 243 Earth days, and its rotation is backwards compared to that of almost all the other planets. It has no moon.

Some of these traits may be connected. Perhaps Venus’s lack of a moon has something to do with its slow rotation. Its slow rotation, in turn, might be related to its lack of magnetic field…which in turn might be related to its thick, dry atmosphere…which in turn might be related to its lack of dynamic geology. There might be a chain reaction at work.

I’m saying “might” a lot because there is still a tremendous amount that scientists do not know about Venus. The perpetual cloud cover presents a huge challenge in studying its surface features. Even worse, landing a probe on its surface is exceedingly difficult. Atmospheric pressure on the ground is more than 90 times that at sea level on Earth, and then there are those searing temperatures, which quickly fry electronics and melt mechanical components. There is also a sense of gloom hanging over Venus, since the odds of finding anything alive there are just about zero. For these reasons, Venus has attracted a tiny fraction of the attention lavished on Mars.

Surface of Venus as seen by the Soviet Venera 14 lander, which touched down in 1982. It survived 57 minutes on the surface; no other probe has been there since. (Credit: Russian Academy of Sciences, processing by Ted Stryk)

Surface of Venus as seen by the Soviet Venera 14 lander, which touched down in 1982. The thick, cloudy atmosphere lends a ruddy cast to the scene. No other probe has been there since. (Credit: Russian Academy of Sciences, processing by Ted Stryk)

The last serious effort to map the surface of Venus was the work of NASA’s Magellan spacecraft, which circled the planet while scanning it with imaging radar. That mission concluded in 1994. The view from the ground is even more limited. The most recent Venus lander was Venera 14, which arrived in 1982. It was sent by the Soviet Union. That’s right: The last time we touched down on Venus, there was a Soviet Union.

But Venus actually has a tremendous amount to tell us about life in the universe. If researchers knew more about Venus, they could judge how likely it is that Earth-size planets around other stars would follow the same disastrous course. They would have a point of comparison for evaluating which aspects of Earth’s development were crucial to the emergence of biology. They could also investigate the great questions hanging over Earth’s wayward twin: Was it always this nasty, or did it start out hospitable before devolving to its present state? Could life have started here billions of years ago, only to get snuffed out by a relentless environmental catastrophe?

Simulated Venus radar map from the VERITAS probe shows how much it would improve on the images from Magellan. (Credit: NASA-JPL/Caltech)

Simulated Venus radar map from the VERITAS probe shows how much it would improve on the imagery from Magellan. (Credit: NASA-JPL/Caltech)

At long last, we may start to get some new answers. Today, NASA announced five finalists for its next midsize, Discovery-class mission. Two of them target Venus. Next year the agency will pick on winner from the group, with the intent of launching it by 2021. One of the contenders, called VERITAS [PDF link], would revisit the radar-mapping concept of Magellan, but using modern technology to yield vastly sharper images. Such views would allow a much deeper examination of Venus’s geological evolution and its current state of activity. The other concept, DAVINCI, would send a probe drifting down through the Venusian atmosphere to study its composition, sniff out signs of volcanic eruptions, and study how the thick atmosphere interacts with the super-heated surface.

There are three other intriguing and highly worthy proposals in the latest set of Discovery candidates. In a perfect world we would do them all. In our imperfect world (though still a much more pleasant world than Venus), I’d vote for VERITAS. It would mark a huge step forward in making sense of Earth’s wayward twin, and learning whether Venus or Earth is more likely to be typical of the superficially Earthlike planets now being discovered around other stars.

Follow me on Twitter for more space and astronomy news: @coreyspowell

CATEGORIZED UNDER: exoplanets, extraterrestrial life, NASA, planets, select, solar system, space, Top Posts, Uncategorized

MORE ABOUT: Discovery, Mars, Venus

TheBrett

It’s about time they potentially sent some more probes to Venus. Venus is the true sister world to Earth, not like the small planet Mars. We need to have a floating probe in its atmosphere as well as orbiters, and we need to be trying to land something on its surface (that should be an easy one to sell in terms of tech spin-offs – highly temperature and pressure resistant machinery).

. . . I wouldn’t entirely rule out the possibility of life, either. Like you said, we don’t know if Venus ever had a good period where it had liquid water and hospitable temperatures that might have created conditions for life. That life is almost certainly absent on Venus’ surface today (although maybe not its interior), but then there’s the cloud deck of Venus, which is definitely a place where life might potentially be able to survive.

Also, didn’t they find some evidence that Venus’ atmosphere is out of chemical equilibrium? Something is generating compounds that should be quickly destroyed.
http://bastionofliberty.blogspot.com/ Francis W. Porretto

Given the high chemical reactivity of the Venerian atmosphere, there could be some sweet possibilities for terraforming it by “remote control.” Not that it would be cheap, of course; sending missiles heavily laden with reagents that far is more than a petty-cash project. But I can dream.
MMinCC

Why do you call what has evolved on Venus and an “environmental disaster”?

Why do you warmists want to lump the natural evolutional climate of a planet as an environmental disaster? Were untold numbers of rocks killed? Was it too many SUVs? Too many AlGore Mansions? Too many Venisians keeping their A/C at 68?

Your constant attempts at semantic infiltration are pitiful.
- coreyspowell
  
  I honestly cannot tell if you are being satirical.
http://www.mazepath.com/uncleal/qz4.htm Uncle Al

“Understanding why” “It has no appreciable magnetic field to protect it from charged particles that blow out from the sun” With twice the insolation, Venus high atmosphere has twice the solar vacuum UV to ionize water. With no magnetic field, that high atmosphere is stripped off by solar wind. Venus’ very large deuterium/hydrogen ratio measures this stripping of a wet world to a dry world. Carbon and sulfur oxides from vulcanism, then positive feedback for thermal trapping.

http://www.lpi.usra.edu/books/MESSII/9038.pdf
Table 1, D/H (×10^6)
149 ± 3 Earth bulk
16,000 ± 200 Venus atmosphere
780 ± 80 Mars atmosphere

http://www.vanderbilt.edu/AnS/physics/astrocourses/AST101/readings/water_on_venus.html
“Venus lost at least 99.9% of the water it started out with”

Terraforming Venus absent water is futility. Crash a large wet comet or three, wait a few millennia for things to equilibrate, then add autotrophic photosynthesis. Mars admits to that solution, though there isn’t much sunlight to support photosynthesis.
- coreyspowell
  
  Good points, all, but they do not address the deeper questions. Why was Venus’s accretion history so much different than Earth’s? When and how did its climate heat up? What kind of volcanism and other geologic activity are occurring today? How do those geologic processes influence the atmosphere? Are there any limited forms of tectonics? Does slow rotation automatically eliminate the possibility of a substantial magnetic field?
  
  I could keep going, but you get the idea. We have a solid big-picture snapshot of Venus, but are woefully missing the details.
  - http://www.mazepath.com/uncleal/qz4.htm Uncle Al
    
    Same accretion history. Climate divergence is quantitatively explained above. Cytherean tectonics is internal radioactive decay heating absent most surface venting, then catastrophic planetary-scale resurfacing. Global meteor craters have a sharp old age cut off. Atmospheric composition less water and with carbon and sulfur oxides is explained above. A self-exciting dynamo requires planetary rotation.
    
    We are rich with details in 25-year old literature. Venus is fundamentally boring except for 1) volatile element harvesting (tellurium, bismuth, lead on mountain tops by chemical transport, plus shipping and handling), 2) periodic turnover of planetary crust all at once to vent accumulated internal heat.
    
    http://news.wustl.edu/news/Pages/3026.aspx
    http://www.space.com/28334-venus-heavy-metal-frost.html
    and doi:10.1126/science.271.5245.28
    
    Ceramics (rocks) are plasticized by trace water content, promoting plastic deformation. Look at cultured quartz’ vibrational Q-values versus ppm water content. (minimum electronic C-grade through AA-grade). Venus is extraordinarily dry. Its crust is extraordinarily rigid. Its tectonics are long term boring punctuated by horrifying. Spend NASA money somewhere productive. Visit asteroid 16 Psyche whose extraordinary density suggests a protoplanet’s stripped metal core. We have no idea what light elements dope Earth’s core, a Mar’s-sized limp of iron, nickel, and presumably primordial siderophilic heavy metals.
    
    If 16 Psyche is indeed a large differentiated protoplanet’s core, it is dripping with noble metals. That is worth harvesting.
Michael Allan Brenchley

Maybe focusing on own planet would be a better start
- coreyspowell
  
  Early studies of Venus were hugely influential in developing better climate models and an improved understanding of greenhouse warming. These are not either-or choices.
David Kaplan

Good story. There’s an under explored learning lab close to home.
OWilson

Perception versus reality.
I once asked my U.K. GEC grammar school science class to name the nearest planet to earth, and the farthest planet from the sun.
Nobody got the correct answers, Mars, they said was closest.
Pluto (then a planet) they said, was the farthest. (This was a trick question, because as any astronomer knew at the time, Pluto in its elongated orbit was inside the orbit of Neptune

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About Corey S. Powell

Corey S. Powell is DISCOVER's Editor at Large and former Editor in Chief. Previously he has sat on the board of editors of Scientific American, taught science journalism at NYU, and been fired from NASA. Corey is the author of "20 Ways the World Could End," one of the first doomsday manuals, and "God in the Equation," an examination of the spiritual impulse in modern cosmology. He lives in Brooklyn, under nearly starless skies.