在兩顆太陽系外行星上發現大氣層
Atmospheres Detected for Two Extrasolar Planets <br />
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影像版權: NASA/JPL-Caltech/T. Pyle (SSC) <br />
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<font color="navy">Explanation: </font><br />
<font color="dimgray">Do extrasolar planets have water? In an attempt to find out, the orbiting Spitzer Space Telescope made detailed observations of the atmospheres of two planets that orbit stars other than our Sun. Unfortunately, water vapor was not detected in either exoplanet. Spitzer watched star systems HD 209458b and HD 189733b closely in infrared light both before and after the parent stars eclipsed their known planets. By comparing eclipsed and uneclipsed spectra very closely, astronomers could deduce bright light-emitting atmospheric gasses that were being blocked during eclipse. Were water vapor one of these atmospheric gases, a new indication that life might exist outside of our Solar System would have been found. The planets being analyzed are known as hot Jupiters -- they have sizes close to Jupiter but orbits closer to the distance of Mercury. The above illustration shows an artist's depiction of one of these dry worlds. Although no water vapor was detected this time, the techniques of measuring exoplanet atmospheres are quite promising, and the search for distant water and other biomarkers is just beginning. </font><br />
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<font color="navy">說明:</font><br />
<font color="dimgray">太陽系外行星上有水嗎？為了尋找答案，史匹哲太空望遠鏡仔細地觀察了兩顆繞著別的恆星運行的行星大氣。很可惜，在這兩顆行星上並沒有觀測到水蒸氣。史匹哲這次的觀測目標是 HD 209458b<font size="2">(圖示#1)</font> 和 HD 189733b 這兩顆太陽系外行星，它利用母星遮掩行星的前後，以紅外線波段進行觀測。仔細比較掩星時和平常時的光譜，天文學家推論出在掩星時，較明亮且會發光的行星大氣氣體被遮住了。如果能在大氣中找到水蒸氣，這代表著在太陽系之外可能也有生命的存在。這兩顆行星是屬於 "熱木星"型的，意即它們的大小與木星相近，但是它們的軌道卻像水星一樣小。上面這張畫是藝術家筆下的乾旱世界。雖然這次沒有成功地找到水蒸氣，但這個探測太陽系外行星大氣的方法仍是大有可為的，這代表著尋找太陽系外遙遠的水氣以及其他生命現象的課題已經邁進了一大步。 </font><br />
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圖示#1: HD 209458b<br />
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<font size="2">資料來源: Scientific American<br />
Department of Physics, NCKU</font><font color="white"><font size="1"><br />
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