Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

June 26, 1998

A Planet For Gliese 876
Credit and Copyright: Digitized Sky Survey

Explanation: Centered in this unremarkable, 1/4 degree wide patch of sky in the constellation Aquarius is the star Gliese 876. Gliese 876 is smaller than the Sun, only about 1/3 as massive, and too faint to be seen without a telescope. But it is known to be one of the nearest stars, only 15 light-years distant. Astronomers have just announced findings that imply Gliese 876 has a planet at least 1.6 times as massive as Jupiter - making this now one of the closest suspected planetary systems. Like many recent discoveries, this planet's detection is is not based on direct imaging but on spectroscopic measurements of the periodic change in motion or "Doppler wobble" produced in the parent star as the planet orbits. The Doppler wobble of Gliese 876 indicates that its planet orbits once every 61 days at an average distance of about 1/5 the radius of the Earth's orbit.

格利澤876星(Gliese 876),位在寶瓶座這片不起眼、寬1/4度的天空的中心。 Gliese 876比太陽小,質量只有太陽的1/3,而且非常昏暗,沒借助望遠鏡不得見。 但它是已知的最鄰近恒星之一,距離我們只有15光年遠。 天文學家剛剛宣布,資料暗指Gliese 876有一顆質量至少是木星1.6倍的行星,讓它成為目前最鄰近的可能行星系統之一。 像最近的許多發現一樣,這顆行星的偵測不是基於直接成像,而是使用行星繞行母星時,母星發生週期性運動變化或 "都普勒晃動 "的光譜測量。 Gliese 876的都普勒晃動顯示,它的行星每61天繞行一次,平均軌道距離約為地球軌道半徑的1/5。

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