【 明 報 專 訊 】 美 國 天 文 學 家 周 一 宣 布 發 現 太 陽 系 新 巨 型 行 星 。 這 顆 冰 封 星 體 就 在 冥 王 星 以 外 約 16 億 公 里 ， 直 徑 為 1287 公 里 。 美 聯 社 形 容 ， 這 是 七 十 二 年 前 發 現 第 九 大 行 星 冥 王 星 以 來 ， 天 文 學 界 對 於 太 陽 系 的 最 重 大 發 現 ， 勢 將 衝 擊 人 類 對 太 陽 系 九 大 行 星 的 觀 念 。
【 明 報 專 訊 】 本 身 研 究 超 新 星 、 曾 在 美 國 太 空 總 署 做 研 究 的 香 港 天 文 學 家 潘 振 聲 博 士 表 示 ， 今 次 加 州 理 工 的 發 現 十 分 可 信 ， 因 為 那 是 有 真 正 科 學 證 據 、 可 以 驗 證 的 觀 測 發 現 。 他 告 訴 記 者 ﹕ 「 太 陽 系 的 行 星 數 目 將 從 此 修 正 ， 這 個 發 現 實 在 令 人 興 奮 ﹗ 」
【 明 報 專 訊 】 美 國 天 文 學 會 （ AAS ） 於 1899 成 立 ， 至 今 有 逾 100 年 歷 史 ， 是 北 美 洲 一 個 具 權 威 的 天 文 組 織 ， 成 員 包 括 天 文 學 家 、 科 學 家 及 熱 愛 天 文 學 的 人 士 。 學 會 成 立 的 宗 旨 是 要 加 強 天 文 學 界 的 專 業 和 自 律 ， 並 成 為 一 把 強 大 的 聲 音 為 天 文 學 者 謀 福 利 。 截 至 2001 年 6 月 30 日 ， AAS 會 員 總 人 數 約 達 6500 人 ﹔ 而 台 灣 清 華 大 學 新 任 校 長 徐 遐 生 ， 亦 曾 擔 當 AAS 會 長 。 註：該發現在這個學會中發表。
【 明 報 專 訊 】 冥 王 星 雖 於 七 十 二 年 前 發 現 並 被 定 為 第 九 大 行 星 ， 惟 其 行 星 的 地 位 卻 屢 受 質 疑 。 有 天 文 學 家 稱 ， 隨 着 在 「 柯 伊 伯 帶 」 陸 續 發 現 體 積 較 大 的 小 星 體 ， 位 處 這 些 小 行 星 群 當 中 的 冥 王 星 應 否 繼 續 被 當 為 行 星 ， 已 愈 來 愈 有 問 題 ， 有 論 者 便 認 為 ， 只 能 將 冥 王 星 說 成 是 較 大 的 小 行 星 ， 卻 不 是 行 星 。 布 朗 說 ﹕ 「 如 果 我 們 今 天 才 發 現 冥 王 星 ， 又 知 道 『 柯 伊 伯 帶 』 是 什 麼 一 回 事 下 ， 我 們 未 必 會 把 它 視 之 為 行 星 了 。 」
[註: 以下資料來自天文小站: ]
事實上，自從1930年2月18日，美國羅維爾天文台的湯堡，利用攝影比對法發現了第九行星－冥王星後，當時天文台內的工作人員都深信，冥王星就是當初羅維爾所認為，在海王星軌道外，一顆能影響海王星運行所謂的χ行星，但經過一段長時間觀測其運行後，發現冥王星可說是個「不正常的怪胎」。
全球最大的天文組織「國際天文聯合會」，開會期間就有人提議，要將冥王星由行星級重新定位為「海王星外星體」，還準備賦予「第一萬號」的榮譽編號，但此舉招致了包括美國天文學會在內的許多團體一致堅決反對，認為不尊重歷史傳統，整個提議因而作罷，冥王星方得以「苟存」於第九行星的寶座。由此可知，冥王星是如何地「先天不足」了！因此它絕非是羅威爾所追尋的χ行星，那麼「冥王星之外是否真的有第十行星存在？」，這，就成了個很有趣的問題。
〔另外參看 Is Pluto a giant comet?〕
CNN中以此為題：Biggest object since Pluto found in solar system
(CNN) -- A newly discovered body in the outer reaches of the solar system is larger than all the objects in the asteroid belt combined, astronomers announced Monday.
The spherical planetoid, half the size of Pluto, is the biggest found in the solar system since astronomers detected the ninth planet in 1930.
It orbits the sun from a distance of about 4 billion miles (6.4 billion kilometers) in a nether region known as the Kuiper Belt, a ring of thousands of primordial icy, rocky chunks beyond the planets that date back to the origins of the solar system.
The object, dubbed Quaoar, further strengthens the theory that Pluto is not a conventional planet but rather a Kuiper Belt object.
"Quaoar definitely hurts the case for Pluto being a planet," said planetary scientist Mike Brown, co-discover of the new object. "If Pluto were discovered today, no one would even consider calling it a planet because it's clearly a Kuiper Belt object."
The Kuiper Belt is home to many of the comets that periodically swing into the inner solar system. They and larger objects in the belt are pristine vestiges of the infant solar system, which could help explain how our space neighborhood formed.
The new object is about 800 miles (1,300 kilometers) in diameter and circles the sun once every 288 years. Its orbit is stable and circular in comparison to Pluto.
Pluto, usually the most distant planet, takes 248 years to complete a trip around the sun and orbits at an average distance of about 3.7 billion miles (5.8 billion kilometers).
But the eccentric ice planet follows an extremely elliptical orbit and goes inside the circular path of Neptune from time to time.
While traditionally classified as a planet, Pluto more likely is a Kuiper
Belt object that was pushed into an erratic, Neptune-crossing orbit billions
of years ago, according to astronomers.
Like other Kuiper Belt objects, Quaoar is thought to contain rock, water ice and frozen organic compounds such as methane, carbon dioxide and carbon monoxide.
The surface, slowly cooked over the eons by ultraviolet radiation from the sun, could be dark and similar in consistency to tar, Brown and co-discoverer Chad Trujillo said.
The California Institute of Technology researchers presented their findings Monday at an American Astronomical Society meeting in Birmingham, Alabama.
The scientific duo named the object Quaoar, pronounced KWAH-o-ar, after the creation god of the Tongva people, a Native American tribe in Southern California.
As telescopes and high-tech search techniques improve in the coming years, astronomers said they expect to find many more Kuiper Belt objects, including increasingly larger specimens.
"Right now, I'd say they get as big as Pluto," Brown said.
Astronomers have discovered the largest object in the solar system since Pluto was identified more than 70 years ago. The object, dubbed Quaoar (pronounced "kwa-whar") by its discoverers, is approximately half Pluto's size and nearly four billion miles away from Earth. Scientists announced its discovery on Monday at the meeting of the Division of Planetary Sciences of the American Astronomical Society.
Michael Brown and Chadwick Truillo of the California Institute of Technology first discovered Quaoar in June while they were surveying the Kuiper Belt, the field of comet-like bodies stretching seven billion miles beyond Neptune's orbit, using a 1.2-meter telescope. It appeared as a point of light creeping across the constellation Ophiuchus. The researchers then used the Hubble Space Telescope to measure the object's 1,300-kilometer diameter. The icy rock reflects just 10 percent of the light that hits it and moves around the sun in a circular path once every 288 years. Brown and Truillo chose the name Quaoar from creation mythology of the Native American Tongva tribe, early inhabitants of the Los Angeles area, but the object has not yet been officially christened. Until the International Astronomical Union (IAU) votes on the moniker, the body's designation is the somewhat less flashy 2002 LM60.Discovering Quaoar, the scientists say, fuels hope that more large-scale bodies will be found in the Kuiper Belt--perhaps even some larger than Pluto. As it stands, several hundred so-called Kuiper Belt Objects (KBO) have been identified since 1992. According to Brown, Pluto is also a KBO. "Quaoar definitely hurts the case for Pluto being a planet," he says. "If Pluto were discovered today, no one would even consider calling it a planet because it's clearly a Kuiper Belt Object." --Sarah Graham
簡介：太陽系：
從太陽開始數：
| 大小 | 行星距離太陽 | ||
| 系內行星： | 水星－＞金星－＞地球－－＞火星－－＞流星帶( asteroid belt) | 這些皆是較小行星，直徑少於13000公里(km)．固體 | 0.39-1.6 AU |
| 系外行星： | 木星－＞土星－＞天王星－＞海王星－＞柯伊伯帶 (Kupier Belt) | 巨型行星．氣體 | 5-30 AU |
| 外海王星物体： | 冥王星－＞創世者(Quaoar) | 外海王星物体： |
(AU是一個天文單位, 指由地球到太陽的距離.)
留意: 這些皆是較小行星，直徑少於13000公里(km)．
巨型行星：是其他那四個行星．
而水星(4900)及冥王星(3000)更被視為小伙子；少於5000公里．
Mercury and Pluto are sometimes referred to as lesser planets
(not to be confused with minor planets which is the official term for asteroids).
The giant planets are sometimes also referred to as gas giants.
以大小和距離太陽的情況分析：可以約簡為： 小－＞流星帶－＞巨－＞柯伊伯帶－＞小（小星也可以被包在帶中）．
 |
因為學者計算海王星(Neptune)的軌跡發現不對之地方，於事有人推測存在第九行星，以引力影響海王星． |
 |
在1929年湯布(Clyde Tombaugh)偶然發現了冥王星(Pluto)．但它實在太小，不可能有這大的影響，於是推測尚有第十顆行星．最後人們發現這地帶有很多的細小星間物質．由柯伊推測這是短期流星的來源地：故稱為「柯 伊伯帶」(Kupier Belt)．已發現的有七萬顆，但有人推測有十萬顆，但多數很小，少於100公里．今次發現的創世者(Quaoar)則是相對地十分大的(有1260公里(km))． |
因為對這個「 柯 伊 伯 帶 」(Kupier Belt)的認識加深，所以有人認為冥王星只是這個帶的大哥哥，不算是行星．按Michael E. Brown & Chad Trujillo在天文學刊的文章：他們推算這個新行星的直徑有1260公里(km)(誤差為190公里)，他們宣稱它是"the largest currently known minor planet". 他們稱為創世者(Quaoar)也暫時定名為2002 LM60．（他們視為流星？！）
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The Kuiper Belt is a disk-shaped region past the orbit of Neptune roughly 30 to 100 AU （天文單位：即太陽距離地球的里數= 149,597,870.691 km; the average distance from the Earth to the Sun. 1 AU is a long way -- at 100 miles per hour (160 kph) it would take over 100 years to go 1 AU.）from the Sun containing many small icy bodies. It is now considered to be the source of the short-period comets. 但創世者也是很小的．它只有冥王星(Pluto)一半左右．
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Classification
The classification of these objects is a matter of minor controversy.
Traditionally, the solar system has been divided into
-
planets (the big bodies orbiting the Sun),
-
their satellites (a.k.a. moons, variously sized objects orbiting the planets),
-
asteroids (small dense objects orbiting the Sun = An asteroid is a large rock in outer space. ) and
-
comets (small icy objects with highly eccentric orbits).
Unfortunately,
the solar system has been found to be more complicated than this would suggest:
-
there are several moons larger than Pluto and two larger than Mercury; [Pluto is smaller than 7 of the moons in the Solar System. Because it is so small many scientists don't consider it a planet at all. ]
-
there are several small moons that are probably captured asteroids;
-
comets sometimes fizzle out and become indistinguishable from asteroids;
-
the Kuiper Belt objects and others like Chiron don't fit this scheme well;
-
The Earth/Moon and Pluto/Charon systems are sometimes considered "double planets".
Trans-Neptunian objects (TNOs)
Trans-Neptunian objects (TNOs) in 2:3 resonance with Neptune (meaning that they orbit the sun twice for every three times that Neptune does); these appear to be relatively stable orbits over millions of years; Pluto is the largest known object in this group, which accounts for about a third or more of all of the hundreds of known TNOs, and the objects in this group are now called "plutinos"; orbits have moderate eccentricities (generally 0.1 > e > 0.4) with orbital inclinations that can take the orbits well away from the ecliptic plane
"Cubewano-belt" (or "Leonard/Edgeworth/Kuiper/Whipple-belt")
objects, which are perhaps best described as ``main-belt"
TNOs (which are not in 2:3 resonance with Neptune, but note that there are
probably other groups of objects beyond Neptune as well, just as their are
numerous groups of minor bodies near the main asteroid belt); these objects
are thought to be related to comets (as this population is thought to be
a source for many of the observable comets), and the objects in 2:3 resonance
with Neptune (such as Pluto) may be related to the cubewano-belt objects;
orbits have low eccentricities (generally e < 0.1) [NOTE: this belt is
perhaps improperly called the "Kuiper belt" by many; to see why
this might be improper, click
here.]