VOA慢速英语--天文学家首次在遥远的系外行星周围看到“月球形成盘”

Scientists say they have clearly identified for the first time a moon-forming area around a planet beyond our solar system.

The ring-shaped area surrounds an exoplanet called PDS 70c. An exoplanet is a planet that orbits a star outside our solar system.

The identified region is known as a circumplanetary disk. This is an area surrounding a planet where moons and other satellite objects can form. The disk is made up of gas and dust.

Researchers from the ALMA observatory¹, which operates from Chile's Atacama desert, made the discovery. ALMA is the largest radio telescope in the world.

Astronomers² had previously³ found signs of moon-forming disks around this exoplanet and others. They say, however, that in the past they were not able to clearly differentiate⁴ the disk from the surrounding environment.

The team says the new finding may help scientists better understand how moons and planets form in young star systems. The results were recently published in a study in The Astrophysical Journal Letters.

Myriam Benisty is a researcher who helped lead the study for the University of Grenoble in France and the University of Chile. "Our work presents a clear detection of a disk in which satellites could be forming," she said in a statement. Benisty added that the ALMA observations provided results of such high quality "that we could clearly identify that the disk is associated with the planet."

PDS 70c is a gas giant discovered in 2019, the U.S. space agency NASA says. It is one of two exoplanets orbiting the orange-colored star PDS 70. The exoplanets sit about 370 light years from Earth. A light year is the distance light travels in a year, about 9.5 trillion kilometers.

Both planets are similar to Jupiter, a gas giant and the biggest planet in our solar system.

The disk's diameter is comparable to the sun-to-Earth distance and has enough mass to form up to three satellites the size of the moon that orbits Earth, the researchers said in a statement.

Scientists say stars are born within clouds of interstellar gas and dust spread throughout galaxies⁵. Leftover⁶ material circling a new star can then form a planet. Circumplanetary disks surrounding some planets can similarly form moons.

Scientists have discovered more than 4,400 exoplanets. But no circumplanetary disks had been clearly identified until now because all known exoplanets were contained in "mature," or fully⁷ developed, solar systems.

The PDS 70 star -- which has about the same mass as our sun -- is about 5 million years old. The researchers say that is considered very young in cosmic terms. The two exoplanets orbiting the star are even younger.

Both exoplanets are "still in their youth," said study co-writer Stefano Facchini of the European Southern Observatory. He added that the planets were going through a period where their atmospheres are still being built. The researchers said there could be other planets in the system that have not yet been discovered.

Benisty said the long-awaited discovery is important "in order to test the theory of planet formation and directly observe the birth of planets and of their satellites."

Words in This Story

disk – n. a flat, round shape or object

detect – v. to discover or notice something

associate – v. to relate two things, people, etc. together

diameter – n. the distance through the center of something from one side to the other

interstellar – adj. between the stars

cosmic – adj. relating to the whole universe

1 observatory   

n.天文台，气象台，瞭望台，观测台

参考例句：

• Guy's house was close to the observatory.盖伊的房子离天文台很近。
• Officials from Greenwich Observatory have the clock checked twice a day.格林威治天文台的职员们每天对大钟检查两次。

2 astronomers   

n.天文学者，天文学家( astronomer的名词复数 )

参考例句：

• Astronomers can accurately foretell the date,time,and length of future eclipses. 天文学家能精确地预告未来日食月食的日期、时刻和时长。 来自《简明英汉词典》
• Astronomers used to ask why only Saturn has rings. 天文学家们过去一直感到奇怪，为什么只有土星有光环。 来自《简明英汉词典》

3 previously   

adv.以前，先前（地）

参考例句：

• The bicycle tyre blew out at a previously damaged point.自行车胎在以前损坏过的地方又爆开了。
• Let me digress for a moment and explain what had happened previously.让我岔开一会儿，解释原先发生了什么。

4 differentiate   

vi.(between)区分；vt.区别；使不同

参考例句：

• You can differentiate between the houses by the shape of their chimneys.你可以凭借烟囱形状的不同来区分这两幢房子。
• He never learned to differentiate between good and evil.他从未学会分辨善恶。

5 galaxies   

星系( galaxy的名词复数 )； 银河系； 一群（杰出或著名的人物）

参考例句：

• Quasars are the highly energetic cores of distant galaxies. 类星体是遥远星系的极为活跃的核心体。
• We still don't know how many galaxies there are in the universe. 我们还不知道宇宙中有多少个星系。

6 leftover   

n.剩货，残留物，剩饭；adj.残余的

参考例句：

• These narrow roads are a leftover from the days of horse-drawn carriages.这些小道是从马车时代沿用下来的。
• Wonder if that bakery lets us take leftover home.不知道那家糕饼店会不会让我们把卖剩的带回家。

7 fully   

adv.完全地，全部地，彻底地；充分地

参考例句：

• The doctor asked me to breathe in,then to breathe out fully.医生让我先吸气，然后全部呼出。
• They soon became fully integrated into the local community.他们很快就完全融入了当地人的圈子。