New planet discovered orbiting nearby star	天文學(xué)家新發(fā)現(xiàn)一顆類地行星
Handout picture released June 14, 2005 shows an artist's conception of a newly discovered planet being shown as a hot, rocky, geologically active world glowing in the deep red light of its nearby parent star, the M dwarf Gliese 876. The heat and the reddish light are among the few things about the new planet that are certain (reuters) A planet that may be Earth-like - but too hot for life as we know it - has been discovered orbiting a nearby star. The discovery of the planet, with an estimated radius about twice that of Earth, was announced Monday at the National Science Foundation. "This is the smallest extrasolar planet yet detected and the first of a new class of rocky terrestrial planets," Paul Butler of the Carnegie Institution in Washington said in a statement. "It's like Earth's bigger cousin." Geoffrey Marcy, professor of astronomy at the University of California, Berkeley, added: "Over 2,000 years ago, the Greek philosophers Aristotle and Epicurus argued about whether there were other Earth-like planets. Now, for the first time, we have evidence for a rocky planet around a normal star." Though the researchers have no direct proof that the new planet is rocky, its mass means it is not a giant gas planet like Jupiter, they said. They estimated the planet's mass as 5.9 to 7.5 times that of Earth. It is orbiting a star called Gliese 876, 15 light years from Earth, with an orbit time of just 1.94 Earth days. They estimated the surface temperature on the new planet at between 400 degrees and 750 degrees Fahrenheit. Gliese 876 is a small, red star with about one-third the mass of the sun. The researchers said this is the smallest star around which planets have been discovered. In addition to the newly found planet the star has two large gas planets around it. Butler said the researchers think that the most probable composition of the planet is similar to inner planets of this solar system - a nickel/iron rock. Gregory Laughlin of the Lick Observatory at the University of California, Santa Cruz, said a planet of this mass could have enough gravity to hold onto an atmosphere. "It would still be considered a rocky planet, probably with an iron core and a silicon mantle. It could even have a dense steamy water layer." Three other extrasolar planets believed to be of rocky composition have been reported, but they orbit a pulsar - the flashing corpse of an exploded star - rather than a normal type of star. (Agencies)	最近，天文學(xué)家新發(fā)現(xiàn)了一顆類地行星，它圍繞著附近的一顆恒星運轉(zhuǎn)。但從已知情況來看，其表面溫度太高，不適合生命生存。 美國國家自然科學(xué)基金會本周一（6月13日）宣布了這一消息。據(jù)估計，這個行星的半徑約為地球的兩倍。 華盛頓卡耐基學(xué)院的保羅·巴特勒聲稱：“這顆行星是迄今為止人類所發(fā)現(xiàn)的最小的太陽系外行星，也是第一顆新型的巖狀類地行星。它就像是地球的堂兄?！? 加州大學(xué)伯克利分校的天文學(xué)教授杰弗里·馬西補(bǔ)充說：“大約2000多年前，古希臘哲學(xué)家亞里斯多德和伊壁鳩魯就曾經(jīng)對宇宙中是否存在類地行星展開過激烈辯論?，F(xiàn)在，我們第一次有證據(jù)表明，宇宙中存在一顆環(huán)繞常態(tài)恒星運轉(zhuǎn)的巖狀行星?！? 盡管目前研究人員還沒有直接證據(jù)證明這是一顆巖狀行星，但是他們宣稱，這顆行星的質(zhì)量表明，它并不是一顆類似木星的巨大氣體行星。他們估計這顆行星的質(zhì)量大約是地球的5.9到7.5倍。 這顆行星圍繞著一顆名為“格里斯876”的恒星運轉(zhuǎn)，該恒星距地球15光年，繞軌道運行一周的時間約為地球上的1.94天。據(jù)研究人員估計，這顆新發(fā)現(xiàn)的行星的表面溫度介于400至750華氏度之間。 “格里斯876”是一顆小型紅色恒星，其質(zhì)量約為太陽的三分之一。研究人員說，這是目前人類所發(fā)現(xiàn)的最小的有行星環(huán)繞的恒星。除新發(fā)現(xiàn)的這顆行星之外，還有兩顆巨大的氣體行星圍繞著它運轉(zhuǎn)。 巴特勒說，研究人員認(rèn)為這顆行星的成分極有可能與太陽系內(nèi)行星類似，由含有鎳和鐵成份的巖石組成。 格雷戈里·勞福琳在位于加州大學(xué)圣克魯斯分校的利克天文臺工作。他斷言，具有如此巨大質(zhì)量的行星必能產(chǎn)生足夠的引力，吸引住大氣。他說：“我們?nèi)钥烧J(rèn)為它是一顆巖狀行星，其內(nèi)核可能為鐵，表層覆蓋著鎳，其外層甚至可能籠罩著濃厚的蒸汽狀的水?！? 之前人們曾報道過另外三顆據(jù)信由巖石組成的太陽系外行星，但是，它們是圍繞著一顆脈沖星（恒星爆發(fā)后遺留的發(fā)光的殘存物）運轉(zhuǎn)的，而不是一顆常態(tài)的恒星。 （中國日報網(wǎng)站譯）