Friendly Venus?

Modern-day Venus is a very unfriendly world. With a temperature close to 890 Fahrenheit (477 Celsius) and an atmospheric pressure ninety times that of Earth, it is hard to imagine the second planet from the sun being hospitable. To make it even more alien, the length of its day is 116.75 Earth days (it rotates slowly compared to Earth), and its year is 225 Earth days. Its atmosphere has much more nitrogen and carbon than Earth’s.
That, however, is modern-day Venus. What about a younger Venus? Could an ancient Venus have been kinder?
Venus' surface as revealed by radar. Image credit Magellan Project/JPL/NASA.
Venus’ surface as revealed by radar. Image credit Magellan Project/JPL/NASA. Astronomy Picture of the Day September 3rd, 2005.
This brings us to today’s featured article, “Was Venus the first habitable world of our solar system?” by M. J. Way, Anthony D. Del Genio, Nancy Y. Kiang, Linda E. Sohl, David H. Grinspoon, Igor Aleinov, Maxwell Kelley, and Thomas Clune. Published in American Geophysical Union’s Geophysical Research Letters in 2016, this work examines the possible climate of early Venus using a three-dimensional general circulation model, or GCM. 
This model included an atmosphere of nitrogen, with added components of carbon dioxide and methane in amounts similar to that of Earth (the amounts of these gases that are currently, or would have been previously in Venus’ atmosphere is not well known). The GCM also had an ocean, land, and allowed snow to accumulate. The ocean was about 310 meters (339 yards) deep, and covered about sixty percent of the surface (Earth’s ocean, for comparison, covers about seventy percent). Two times were looked at: Venus 2.9 billion years ago, and 0.715 billions years ago (which correlates to the time of the most recent signs of resurfacing of Venus).
Of the simulations, three used the current rotation rate of Venus, and the fourth was much faster (sixteen times Earth’s) to test the effect. In the first three, young Venus ended up with heavy clouds wherever it was daylight. On the nighttime side of the planet, it was cold enough for snow; it was only a thin coat, and melted by noon. Two of these simulations also showed part of Venus’ northern latitudes with a permanent five meter (16 feet) deep snow bank. The global average temperature came in at 11, 15, and 23 Celsius (approximately 52, 59, and 73 Fahrenheit, respectively). The simulation with faster rotation resulted in much warmer temperatures; global average jumped to 56 Celsius (133 Fahrenheit).
With the temperatures for the simulations with reasonable rotation rates, ancient Venus becomes quite temperate, However, it is unsure whether or not Venus ever had an ocean of any sort, or what its atmosphere was like in the past. Its geological history is not very well known either. Even if it was once a life-friendly planet, that does not mean that life would have magically arisen; it would have had to stay friendly for a long enough time period for life to arise. Whether or not all the requirements for life were met long-term requires further study.
Bibliography
Astronomy Picture of the Day. “APOD: 2005 September 3 – Venus Unveiled.” N.p., 3 Sept. 2005. Web.
The image used in today’s post.
Bennett, Jeffrey O., ed. The Cosmic Perspective:  The Solar System. 7th ed. Boston: Addison-Wesley, 2014. Print.
Textbook used for reference on what we know of Venus.
L. E. Sohl, D. H. Grinspoon, I. Aleino v, M. Kelley, and T. Clune (2016), Was Venus the rst habitable world of our solar system?, Geophys. Res. Lett., 43doi:10.1002/2016GL069790.
Today’s main article.
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