Scientific American<\/em> 320\/2 (February 2019): 56-63. \u00a0I continue with those notes:<\/p>\n\u00a0<\/p>\n
Most of the exoplanets that scientists have discovered thus far were found by what is called \u201cthe transit method.\u201d \u00a0Astronomers watch distant stars for fluctuations in their brightness that seem to be caused when orbiting planets pass in front of them. \u00a0With careful observation, it\u2019s possible to measure the planet\u2019s size. \u00a0But it can\u2019t tell us much more: \u00a0Venus and Earth are very similar in size; a distant extraterrestrial observer would find it difficult to distinguish between them. \u00a0Venus and Earth formed under very similar conditions, and Venus may once even have had oceans, perhaps earlier than our planet. \u00a0But Earth has hosted life for roughly four billion years, whereas the conditions on Venus are lethal.<\/p>\n
\u00a0<\/p>\n
It\u2019s true that we can measure the distance of far away exoplanets from their stars, and we can guess whether or not they\u2019re in their star\u2019s \u201chabitable zone,\u201d the region near the star where a rocky planet might possibly have liquid water on its surface. \u00a0Manifestly, Earth is in this zone for our star, the Sun. \u00a0But Venus may once have been, as well, and maybe for a very long time. \u00a0Has it moved? \u00a0Not necessarily. \u00a0As the Sun\u2019s luminosity increases with age, the habitable zone moves outward. \u00a0So Venus is now inside the line where that zone begins. \u00a0A runaway \u201cgreenhouse\u201d effect long since burned its oceans away \u2014 probably at least a billion years ago \u2014 if it ever had them. \u00a0Surface temperatures on Venus are nearly 800 degrees hotter than on Earth, hot enough to make rocks glow.<\/p>\n
\u00a0<\/p>\n
What happened? \u00a0Why? \u00a0Does Venus represent the ultimate fate of all habitable planets?<\/p>\n
\u00a0<\/p>\n
The study of Venus is extremely difficult, because (among other reasons) of the difficulty of peering through its thick and toxic atmosphere, which is partly made of sulfuric acid. \u00a0Air pressure at the planet\u2019s surface is approximately the same as water pressure on Earth at 3000 feet below sea level.<\/p>\n
\u00a0<\/p>\n
Some scientists, however, think that Venus\u2019s atmosphere was once Earth-like. \u00a0But the planet now lacks a magnetic field to repel the solar wind \u2014 the stream of radiation that flows from the Sun \u2014 and that accordingly, that wind eliminated Venus\u2019s water, dissociating it into oxygen and hydrogen ions and blowing them off into space.<\/p>\n
\u00a0<\/p>\n
At this point, our only data from the actual Venusian surface were gathered by four Soviet Venera landers that survived for barely a few minutes each after touching down. \u00a0Other than that, we rely on decades-old information from the Magellan orbiter.<\/p>\n
\u00a0<\/p>\n
It\u2019s time for a new NASA mission to Venus.<\/p>\n
\u00a0<\/p>\n
(To be continued.)<\/p>\n
\u00a0<\/p>\n
\u00a0<\/p>\n<\/body><\/html>\n","protected":false},"excerpt":{"rendered":"
\u00a0 \u00a0 On Thursday, I posted some notes (\u201cThe Exoplanet Next Door\u201d) \u00a0from M. Darby Dyar, Suzanne E. Smrekar, and Stephen R. Kane, \u201cThe Exoplanet Next Door: What Venus can teach us about planets far beyond our solar system,\u201d Scientific American 320\/2 (February 2019): 56-63. \u00a0I continue with those notes: \u00a0 Most of the exoplanets […]<\/p>\n","protected":false},"author":1019,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[2869,1017,2872,2866,1531],"class_list":["post-69634","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-exobiology","tag-exoplanets","tag-nasa","tag-plate-tectonics","tag-venus"],"yoast_head":"\n
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<\/a>