[ti:Study: Moon’s Thin Atmosphere Likely Formed by Meteorite Strikes]
[by:www.21voa.com]
[00:00.00]更多听力请访问21VOA.COM
[00:00.04]Scientists say new examinations of soil
[00:04.88]collected on the moon suggest its atmosphere
[00:09.64]might have been created by repeated meteorite strikes.
[00:15.24]Researchers studying the moon
[00:18.60]first used instruments
[00:20.96]to confirm it had an atmosphere
[00:23.60]in the early 1970s.
[00:26.60]The American space agency NASA
[00:30.16]explains the moon's atmosphere
[00:33.56]is "very thin and weak."
[00:35.92]It is technically considered an "exosphere."
[00:40.76]The newly examined soil
[00:43.60]was collected by NASA astronauts
[00:46.84]during America's Apollo program
[00:50.08]from 1969 to 1972.
[00:54.56]The trips resulted in astronauts
[00:58.24]capturing about 382 kilograms
[01:02.80]of rocks and soil, called samples.
[01:06.84]Instead of attempting
[01:09.16]to measure the moon's atmosphere in a direct way,
[01:12.96]investigators looked to the old soil material.
[01:17.32]They theorized that the soil should contain
[01:21.88]residue material from atoms
[01:24.64]released into the lunar atmosphere
[01:28.00]over billions of years.
[01:30.40]The research was led by scientists
[01:33.80]at the University of Chicago
[01:36.28]and Massachusetts Institute of Technology (MIT).
[01:42.88]Their results recently appeared in a study
[01:47.12]in the publication Science Advances.
[01:51.12]Nicole Nie was the lead writer of the study.
[01:55.84]She is a planetary scientist at MIT.
[02:00.84]Nie said that when meteorites impact,
[02:05.20]or hit, an object like the moon,
[02:08.16]they create very high temperatures.
[02:11.28]Such strikes can heat up the surface
[02:14.92]by 2,000 to 6,000 degrees Celsius.
[02:20.28]These extreme temperatures melt
[02:23.56]and vaporize rocks at the surface
[02:27.16]and release atoms contained in dust
[02:30.04]and soil into the atmosphere.
[02:33.48]Some of the atoms end up being pushed into space,
[02:37.96]while others remain just above the surface.
[02:41.68]The researchers said the soil examinations
[02:46.00]led to the discovery that the moon's atmosphere
[02:49.96]was formed through a process
[02:52.48]known as "impact vaporization."
[02:56.12]Nie and her team centered their examinations
[03:00.72]on two main elements – potassium and rubidium.
[03:06.12]These substances were chosen
[03:09.32]because they can easily be vaporized
[03:12.32]by meteorite hits.
[03:14.56]The process involved
[03:16.68]studying the behaviors
[03:18.68]of different kinds of isotopes
[03:21.20]found in potassium and rubidium.
[03:25.04]That study persuaded the team that repeated
[03:29.60]meteorite strikes formed the atmosphere.
[03:33.72]In the past, studies have shown the moon's atmosphere
[03:38.32]might have been created by either
[03:41.36]meteor activity or the solar wind.
[03:45.24]Solar wind describes a continuous
[03:48.88]flow of charged particles from the sun
[03:52.68]that spreads across the solar system.
[03:56.20]The researchers said the latest study
[04:00.32]provides new evidence
[04:02.24]that most of the lunar atmosphere
[04:05.00]was likely formed by repeated
[04:07.92]meteorite hits over billions of years.
[04:11.52]After testing 10 samples of lunar soil,
[04:15.92]the team concluded that much more of the atmosphere
[04:20.12]is due to meteor activity than to the solar wind.
[04:24.96]"At least 70 percent of the lunar atmosphere
[04:29.32]is created by these meteorite impacts,"
[04:33.36]Nie said in a statement.
[04:36.28]"A much smaller percentage
[04:38.72]is created by the solar wind a
[04:41.48]brasion of the surface," she added.
[04:45.16]Nicolas Dauphas is a professor of geophysical sciences
[04:50.72]at the University of Chicago.
[04:53.36]He helped lead the research.
[04:56.08]Dauphas said, "It turns out the answer
[05:00.44]to this longstanding question
[05:03.00]was right in front of us
[05:04.92]– preserved in lunar soil
[05:07.64]brought back to Earth by the Apollo missions."
[05:11.48]Nie said understanding such processes
[05:15.48]can be extremely valuable
[05:17.92]to planning future missions to the moon,
[05:21.08]Mars and beyond.
[05:23.40]"If humans want to move
[05:25.68]to different planetary bodies someday,
[05:29.20]we will have to understand what's going on
[05:32.48]at the surface to be able to prepare."
[05:36.12]She added, "Each planetary body is different,
[05:40.68]and the more we understand about these processes,
[05:45.16]the more complete picture we'll have."
[05:49.00]I'm Bryan Lynn. 更多听力请访问21VOA.COM
END OF TRACK. "END OF TRACK." The two men bowed. "Whoever was that person you were talking to?" she enquired, as soon as they stood together. The took of triumph faded from her eyes, she had grown worn and weary. The roses were wilting on the walls, the lights were mostly down now. Hetty, looking in to see if anything was wanted, found herself driven away almost fiercely. I only saw Master Jervie once when he called at tea time, The year 1747 was opened by measures of restriction. The House of Lords, offended at the publication of the proceedings of the trial of Lord Lovat, summoned the parties to their bar, committed them to prison, and refused to liberate them till they had pledged themselves not to repeat the offence, and had paid very heavy fees. The consequence of this was that the transactions of the Peers were almost entirely suppressed for nearly thirty years from this time, and we draw our knowledge of them chiefly from notes taken by Horace Walpole and Lord Chancellor Hardwicke. What is still more remarkable, the reports of the House of Commons, being taken by stealth, and on the merest sufferance, are of the most meagre kind, sometimes altogether wanting, and the speeches are given uniformly under fictitious names; for to have attributed to Pitt or Pelham their[112] speeches by name would have brought down on the printers the summary vengeance of the House. Many of the members complained bitterly of this breach of the privileges of Parliament, and of "being put into print by low fellows"; but Pelham had the sense to tolerate them, saying, "Let them alone; they make better speeches for us than we can make for ourselves." Altogether, the House of Commons exhibited the most deplorable aspect that can be conceived. The Ministry had pursued Walpole's system of buying up opponents by place, or pension, or secret service money, till there was no life left in the House. Ministers passed their measures without troubling themselves to say much in their behalf; and the opposition dwindled to Sir John Hinde Cotton, now dismissed from office, and a feeble remnant of Jacobites raised but miserable resistance. In vain the Prince of Wales and the secret instigations of Bolingbroke and Doddington stimulated the spirit of discontent; both Houses had degenerated into most silent and insignificant arenas of very commonplace business. "It certainly will be. Miss Widgeon," answered Maria, with strictly "company manners." "One who has never had a brother exposed to the constant dangers of army life can hardly understand how glad we all feel to have Si snatched from the very jaws of death and brung back to us." "Just plug at 'em as you would at a crow, and then go on your way whistlin'?" persisted Harry. "Hurroo!" echoed Hennessey; "that's the ticket." "Come forward, keeper," continued the baron, "and state how these arrows came into your hands!" "Yes." HoMEJULIA京香2018下载
ENTER NUMBET 0015dishule.com.cn
www.ynocqu.com.cn
hsmedia.net.cn
www.gemingba.com.cn
xztsnm.com.cn
www.xynimz.com.cn
centmen.net.cn
artren.com.cn
ssshaolin.net.cn
lyjobs.com.cn