VOA科学技术2024--Small Stars Might Offer Best Environment for Earth-like Planets

Stars about the size of our sun are not the most common ones in the Milky¹ Way Galaxy². Much smaller stars are far more common. Of all the stars in our galaxy, these small stars host the most planets. Scientists are studying the planets of these small stars in the search for worlds that may support life.

New research is providing understanding about how planets form around these small stars, called very low mass stars, or VLMS. The chemistry of the planet-forming disks of gas and dust surrounding them is different from similar disks observed around stars like the sun.

The James Webb Space Telescope has gathered data on a planet-forming, or protoplanetary, disk around a newborn star called ISO-Chal 147. It is only about 11 percent of the sun's mass. Its diameter is about 43 percent of the sun's, and its luminosity is about two percent of the sun's. Luminosity is a measure of electromagnetic radiation.

ISO-Chal 147 is about 625 light years from Earth. A light year, the distance light travels in a year, is 9.5 trillion kilometers.

Webb's observations showed that the gas in this star's protoplanetary disk is rich in carbon with no evidence of water. This differs from new sun-like stars, which have oxygen-rich gas and a lot of water vapor³ in their disks.

Scientists wonder if this difference could influence the future habitability of rocky planets that form around these small stars.

"A planet mainly requires, among other things, water to be in liquid state and have a suitable atmosphere for it to be habitable," said astrophysicist Aditya Arabhavi of the University of Groningen in the Netherlands who was lead writer of the study published recently in Science.

"Although we can expect that the different environment of VLMS disks would have a strong influence on the planetary composition and thus the habitability, it is difficult to predict whether this makes it less likely to be habitable," Arabhavi said.

Stars form when dense⁴ areas of gas and dust collapse⁵ under their own gravitational pull. Once a star appears at the center of such a cloud, the remaining material forms into a turning disk around it. This activity feeds star growth and often leads to the formation of planets.

The disks around very young sun-sized stars contain much more material than those around smaller stars. This means the larger stars are more likely to have "gas giant" planets form around them. This is the case with the sun and its planets Jupiter and Saturn⁶.

VLMS are "the most common stars in our Milky Way," said astrophysicist and study co-writer Thomas Henning of the Max Planck Institute for Astronomy in Germany.

"These objects are presently the targets in the search for rocky planets because they are easier to find around such stars. In addition, the masses of their planet-forming disks are in general too small to form giant planets, but large enough to form rocky planets," Henning said.

Scientists already have identified rocky planets orbiting very low mass stars, including some that orbit at the right distance to support life.

"I would expect that the planets would remain habitable if they are located in the zone where liquid water can exist," Henning said.

Still very young, ISO-Chal 147 may become a kind of very low mass star called a red dwarf⁷. The star's diameter is only about four times greater than Jupiter's. Our sun's diameter is about 10 times larger than Jupiter's.

Webb, which began operating in 2022, also identified ethane in ISO-Chal 147's protoplanetary disk. The discovery marks the first time the gas has been found outside our star system. The research also found other carbon gases never before observed in such a disk.

"Webb is certainly helping⁸ us by providing invaluable⁹ data that was never possible before," Arabhavi said.

Words in This Story

galaxy - n. a huge group of stars and planets

host -v. to be a place where something can be found

disk -n. a round, flattened¹⁰ shape

vapor -n. a gas

habitability -n. the ability to support life

suitable -adj. something that is right for a certain situation

composition -n. what something is made of

zone -n. an area that is different from others for a specific reason

1 milky   

adj.牛奶的，多奶的；乳白色的

参考例句：

• Alexander always has milky coffee at lunchtime.亚历山大总是在午餐时喝掺奶的咖啡。
• I like a hot milky drink at bedtime.我喜欢睡前喝杯热奶饮料。

2 galaxy   

n.星系；银河系；一群(杰出或著名的人物)

参考例句：

• The earth is one of the planets in the Galaxy.地球是银河系中的星球之一。
• The company has a galaxy of talent.该公司拥有一批优秀的人才。

3 vapor   

n.蒸汽，雾气

参考例句：

• The cold wind condenses vapor into rain.冷风使水蒸气凝结成雨。
• This new machine sometimes transpires a lot of hot vapor.这部机器有时排出大量的热气。

4 dense   

a.密集的，稠密的，浓密的；密度大的

参考例句：

• The general ambushed his troops in the dense woods. 将军把部队埋伏在浓密的树林里。
• The path was completely covered by the dense foliage. 小路被树叶厚厚地盖了一层。

5 collapse   

vi.累倒；昏倒；倒塌；塌陷

参考例句：

• The country's economy is on the verge of collapse.国家的经济已到了崩溃的边缘。
• The engineer made a complete diagnosis of the bridge's collapse.工程师对桥的倒塌做了一次彻底的调查分析。

6 Saturn   

n.农神，土星

参考例句：

• 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。
• These comparisons suggested that Saturn is made of lighter materials.这些比较告诉我们，土星由较轻的物质构成。

7 dwarf   

n.矮子，侏儒，矮小的动植物；vt.使…矮小

参考例句：

• The dwarf's long arms were not proportional to his height.那侏儒的长臂与他的身高不成比例。
• The dwarf shrugged his shoulders and shook his head. 矮子耸耸肩膀，摇摇头。

8 helping   

n.食物的一份&adj.帮助人的，辅助的

参考例句：

• The poor children regularly pony up for a second helping of my hamburger. 那些可怜的孩子们总是要求我把我的汉堡包再给他们一份。
• By doing this, they may at times be helping to restore competition. 这样一来, 他在某些时候,有助于竞争的加强。

9 invaluable   

adj.无价的，非常宝贵的，极为贵重的

参考例句：

• A computer would have been invaluable for this job.一台计算机对这个工作的作用会是无法估计的。
• This information was invaluable to him.这个消息对他来说是非常宝贵的。

10 flattened   

[医]（水）平扁的，弄平的

参考例句：

• She flattened her nose and lips against the window. 她把鼻子和嘴唇紧贴着窗户。
• I flattened myself against the wall to let them pass. 我身体紧靠着墙让他们通过。