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NASA just explained why Moon dust is ‘levitating’ above the lunar surface

It’s floating with no air.

NASA 解釋了為何月球上的塵粒會在沒有空氣的情況下懸浮

 

NASA scientists have figured out why dust particles on the Moon are floating several centimetres above the surface, despite the fact that there’s no wind or flowing water to propel them up there.

The discovery could not only explain how these dust particles are transported across vast distances on the Moon – they could also describe processes that are occurring in many airless environments, including the rings of Saturn.

 

NASA 的科學家終於了解為何月球上的塵粒會飄浮在離地數公分處,在沒有風也沒有流水支持它們漂浮的情況下。這個發現不只能解釋月球上塵粒被大範圍運送的現象,同時也可以解釋這樣的情形在無空氣環境中形成的過程,包括土星環。

“This new … model resolved a fundamental mechanism of dust charging and transport, which has been puzzling scientists for decades,” said one of the team, Xu Wang, from NASA’s Ames Research Centre in California.

Scientists have known about these levitating particles for over five decades now, and they’ve been used to explain the Moon’s strange ‘horizon glow’– a phenomenon first observed by the Apollo astronauts and NASA’s Surveyor probesin the 1960s.

When the Apollo mission orbited the far side of the Moon, they saw an incredibly bright arc of light shining on the horizon just after sunset. 

In 1994, NASA’s Clementine spacecraftcaptured this amazing image of the phenomenon:

 

來自加州的NASA 艾姆斯研究中心(NASA’s Ames Research Centre)的王旭(Xu Wang )說:「這個新的模型解決了塵粒充電以及移動的基礎機制,解決了科學家困惑了幾十年的疑問。」

 

科學家知曉這些塵粒的存在已經有超過五十年了,它們被用來解釋月球上的奇怪現象「地平線閃光」( ’horizon glow’) ,這個現象在1960 年代被阿波羅號的太空人和NASA 的測量員探測器首次觀察到。

 

在執行阿波羅任務繞行月球較遠一側的軌道時,他們看到在日落後月球地平線上有一個極為閃亮的弧形。在1994 年,NASA 的克萊門特號太空船捕捉到了這個現象的出色影像。

 

The same thing that was first witnessed by the Apollo astronauts surrounding the Moon in the 1960s was later recorded over the rings of Saturn, and in craters on the asteroid Eros

 

“These are all the examples of dust transporting across vast regions without winds or flowing water,” says NASA.

“Scientists believed electrostatic dust processes could explain these space observations, but until now, there were no studies to support these explanations.”

To figure out if these particles are actually being held in suspension above the lunar surface by electrostatic forces, Wang and his team performed an experiment in the lab to see what micron-sized dust particles would do when exposed to ultraviolet (UV) radiation or electrically-charged gases known as plasmas.

 

1960 年代時被阿波羅號太空人首次目擊的現象之後在土星環中也被記錄到,也在小行星厄洛斯( Eros)的隕石坑中被記錄到。

 

NASA:「這些都是塵粒在沒有風或流水的情況下大範圍傳送的例子。科學家相信塵粒的帶電過程可以解釋這些太空觀察現象,但是直到現在尚未有研究支持這些解釋。」

 

為了找出答案,查出是否這些塵粒真的是因為靜電力所以懸浮在月球表面, Xu Wang和他的團隊在實驗室中做了一個實驗,看看微米級的塵粒暴露在紫外線輻射或是帶電氣體離子體Plasma)中時會有什麼反應。

 

In both cases, the dust particles would leap several centimetres above the surface, and the team says that on the Moon, light would scatter through these levitating particles to create the horizon glow.

“On Earth’s moon, these dust particles would have been lofted more than 4 inches (10 centimetres) above the lunar surface,” NASA reports.

“[T]he Moon’s horizon glow – seen in images taken by Surveyor 5, 6, and 7 five decades ago – may have been caused in part by sunlight scattering in a cloud of electrostatically lofted dust particles.

 

在兩種情況下,塵粒都會從表面上浮起來幾公分,實驗團隊說在月球上,光線分散穿過這些塵粒,所以有地平線閃光。

 

NASA:「在月球上,這些塵粒可以從月表浮起超過4 英寸(10 公分)。月亮的地平線閃光的圖片可以在探測員5、6、7 號五十年前拍到的照片中看到,這可能是因為陽光在帶電懸浮塵粒雲中被分散而引起的。」

 

The study foundthat the strange properties of Moon dust combined with UV radiation or plasma from the Sun can loft single particles – or sometimes even large clusters of dust – up above the surface.

This is due to the reaction causing an emission and re-absorption of electrons inside ‘micro-cavities’ formed between neighbouring particles, which can generate unexpectedly large electrical charges and intense repulsive forces.

These forces cause the dust particles or clusters to lift off the surface, or ‘levitate’.

Andit’s not just causing the ‘horizon glow’ effect – it’s maintaining a frustratingly hostile environment on the Moon, because of how ‘sharp’ those floating particles actually are.

As the Soil Science Society of America explained back in 2008, the powdery dirt found on the lunar surface was formed by micrometeorite impacts that pounded local Moon rocks into fine particles.

 

這份研究指出月球塵粒有奇怪的性質,和來自太陽的紫外線輻射或是離子體結合後可以浮起來,有時候甚至可以讓大的塵粒團從表面浮起。這個現象是因為相鄰塵粒間的微米空間的電子排放與吸收反應,這可以產生預期之外的大量電荷以及強烈的斥力。這些力量讓塵粒或塵粒團漂浮或懸浮在表面上。

 

這個現象不只是造成了地平線閃光,這讓月球保持了一個不友善的環境,因為這些飄浮塵粒很銳利。美國土壤協會(Soil Science Society of America在2008 年時解釋說,在月球表現發現的粉狀土壤是由於微小的隕石撞擊月球、使月球本地的石頭變為細小塵粒而形成的。

 

The energy from these impacts actually melted the lunar dirt into a vapour, and once that vapour cooled and condensed on the soil particles, it covered them in a glassy shell.

“The dust was so abrasive that it actually wore through three layers of Kevlar-like material on Jack’s boot,” Larry Taylor, director of the Planetary Geosciences Institute at the University of Tennessee, said ofApollo 17 crewmember Harrison ‘Jack’ Schmitt’s 1972 Moon walk.

The NASA team says that this phenomenon could theoretically occur in any airless environment, and could explain how dust particles can move across the rings of Saturn, or form ‘dust ponds’ on the Eros asteroid, without any winds to propel them. 

“We expect dust particles to mobilise and transport electrostatically over the entire lunar surface, as well as the surface of any other airless planetary body,” said Wang.

The study has been published in Geophysical Research Letters.

 

撞擊的能量讓月球的土壤汽化,一旦汽化的土讓冷卻並冷凝在土壤塵粒上,它們就有了一層玻璃殼。田納西大學的行星地球科學機構的主任Larry Taylor提到阿波羅十七號成員Harrison JackSchmitt在1972 年的月球漫步:「那些塵粒被研磨過,它們能穿過傑克三層克維拉(Kevlar)材質的靴子。」

 

NASA 團隊說這樣的現象理論上可以在任何沒有空氣的環境下出現,也可以解釋在沒有風推動的情況下,為何土星環上的塵粒可以大範圍橫越,或是在小行星厄洛斯上形成「塵粒池」。

 

Xu Wang 說:「我們認為塵粒是藉由靜電力在整個月球表面移動和運送,就像所有任何沒有空氣的行星表面。」

 

這份研究被刊登在地球物理研究通訊(Geophysical Research Letters.)上。

 

 

來源:sciencealert

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