 |
| 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，天文學家新發現了一顆類地行星，它圍繞著附近的一顆恒星運轉。但從已知情況來看，其表面溫度太高，不適合生命生存。
美國國家自然科學基金會本周一（6月13日）宣布了這一消息。據估計，這個行星的半徑約為地球的兩倍。
華盛頓卡耐基學院的保羅·巴特勒聲稱：“這顆行星是迄今為止人類所發現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。”
加州大學伯克利分校的天文學教授杰弗里·馬西補充說：“大約2000多年前，古希臘哲學家亞里斯多德和伊壁鳩魯就曾經對宇宙中是否存在類地行星展開過激烈辯論。現在，我們第一次有證據表明，宇宙中存在一顆環繞常態恒星運轉的巖狀行星。”
盡管目前研究人員還沒有直接證據證明這是一顆巖狀行星，但是他們宣稱，這顆行星的質量表明，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，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。據研究人員估計，這顆新發現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，其質量約為太陽的三分之一。研究人員說，這是目前人類所發現的最小的有行星環繞的恒星。除新發現的這顆行星之外，還有兩顆巨大的氣體行星圍繞著它運轉。
巴特勒說，研究人員認為這顆行星的成分極有可能與太陽系內行星類似，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圣克魯斯分校的利克天文臺工作。他斷言，具有如此巨大質量的行星必能產生足夠的引力，吸引住大氣。他說：“我們仍可認為它是一顆巖狀行星，其內核可能為鐵，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（恒星爆發后遺留的發光的殘存物）運轉的，而不是一顆常態的恒星。
（中國日報網站譯） |
Updated: 2005-06-16 09:43