一條巨大的液態鐵「噴射流」 在地球內部發現 – iFuun

一條巨大的液態鐵「噴射流」 在地球內部發現

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一條巨大的液態鐵「噴射流」 在地球內部發現

一條快速流動的鐵水(molten iron)河被發現在阿拉斯加和西伯利亞底下奔騰,大約在地底下3千公里(1,864英哩),而且看起來好像在加速中。

一條巨大的液態鐵「噴射流」 在地球內部發現

這條巨大的噴射流,估計大約420公里寬(260英哩),而且幾乎和太陽表面一樣熱,在不到二十年,速度增加了三倍,現在正朝向歐洲前進。
成員之一、來自丹麥技術大學(Technical University of Denmark)的克里斯?芬雷(Chris Finlay)說:「我們了解太陽比了解地球核心還多。對於更加了解地球內部的活動,這個噴射流的發現,是令人興奮的一步。」

一條巨大的液態鐵「噴射流」 在地球內部發現

芬雷和研究小組在分析來自歐洲太空總署(European Space Agency,ESA) 名為蜂群(Swarm)的三顆衛星數據時,發現到這個噴射流。
在2013年發射,用來測量地球磁場的波動,這些衛星允許研究人員創造出一種X射線的地球的內部結構,揭露我們過去甚至不知道已存在的巨大元件。
來自英國里茲大學(University of Leeds)的首席研究員菲爾?利福摩爾(Phil Livermore)說:「歐洲太空總署的蜂群衛星正在提供最清晰的X射線核心照片。」

「我們不僅僅是第一次清楚地看到這個噴射流,我們也明白為什麼它在那裡。」
地球磁場被認為是產生於地球核心深處進行的活動。
地球核心本身是一塊固體,大小是月球的3分之2,主要是由鐵組成。溫度大約是攝氏5,400度(華氏9,800度),幾乎和太陽表面一樣熱,達到強烈的攝氏5,505度(華氏9,941度)。

一條巨大的液態鐵「噴射流」 在地球內部發現

Earth s Core
圍繞實心內核的是一層2,000公里厚(1,242英哩)的地球外核,主要是由液態鐵和鎳組成。
溫度,壓力以及在這一層組成物的差異在液態金屬產生移動和渦流,並且和地球自轉一起,產生電流,然後產生磁場。
當研究人員檢視來自北半球外核心區域的衛星數據時,發現在阿拉斯加和西伯利亞底下有奇怪的磁流 波瓣(lobe) 。

一條巨大的液態鐵「噴射流」 在地球內部發現

但這些波瓣並沒有停留在那些地方,它們正在往歐洲大陸的方向移動,而且研究小組表示它們正被鐵水噴射流推擠。
安迪?柯格林(Andy Coghlan)為新科學人(New Scientist)雜誌寫報導:「因為它們的移動只可能來自於鐵水的物理運動,因此波瓣被當作標記,允許研究人員跟蹤鐵水的流動。」
研究小組發現,這個噴射流從2000年以來就在加快速度,目前正在推擠在阿拉斯加和西伯利亞底下的波瓣,速度是典型的外核速度的三倍,以及地殼板塊速度的幾十萬倍。
芬雷在英國廣播公司新聞(BBC News)表示:「這個鐵水噴射流以每年約50公里在移動。」

一條巨大的液態鐵「噴射流」 在地球內部發現

「對你來說,這聽起來可能在地球表面不是很多,但你必須要記住這是非常濃稠的液體金屬,需要很大的能量來移動,這可能是在實心地球內移動的最快的。」
現階段還不清楚為什麼噴射流正在加速,但研究人員懷疑這是地球內部循環的一個自然部分,而且已經持續了幾十億年。
如果能夠了解我們現在在周期的位置,我們就可以預測地球磁場如何隨著時間而改變,包括在未來幾個世紀可能發生的逆轉。
如同新科學人雜誌的解釋,由於地球磁場似乎以每百年約5%的速度在減弱,磁場預計會翻轉,到時候磁南北極會互換角色。
歐洲太空總署的群蜂任務經理魯尼?弗萊博哈根(Rune Floberghagen) 在一份新聞稿聲明中說:「更多的驚奇是有可能的。」
「磁場永遠都在變化,而且甚至可能造成噴射流切換方向。」
 請您繼續閱讀更多來自 科技訊 的精彩文章:

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一條快速流動的鐵水(molten iron)河被發現在阿拉斯加和西伯利亞底下奔騰,大約在地底下3千公里(1,8 …

Source: 一條巨大的液態鐵「噴射流」 在地球內部發現 – iFuun

 

Trevor NaceContributor

I cover geology, earth science, and natural disasters.

Opinions expressed by Forbes Contributors are their own.

SCIENCE 12/22/2016 @ 12:11下午 62,099 views

A Liquid Iron Jet Has Surrounded Earth’s Core And Is Accelerating

An illustration of Earth's magnetic field as studied by the Swarm satellite program (Credit: http://www.esa.int)

An illustration of Earth’s magnetic field as studied by the Swarm satellite program (Credit: http://www.esa.int)

A recent major discovery identified a massive liquid iron “jet stream” circling the Earth’s outer core that appears to be accelerating. This comparatively fast flowing liquid iron stream is currently moving westward under Alaska and Siberia as measured by the Swarm satellites and recently published in Nature Geoscience.

The iron jet is moving at about 50 km per year, orders of magnitude faster than plates move and much faster than anything scientists knew of within Earth’s interior. Traveling at 50 km per year doesn’t seem rather fast compared to speeds on the surface of the Earth. However, consider the tremendous amount of energy required to push aside dense liquid metal under very high pressures across hundreds of miles. In addition, it appears that this liquid jet stream is accelerating but scientists have not determined what is causing the acceleration.

The liquid iron jet is similar to the jet stream found within our atmosphere but at 3,000 km below the surface of the Earth. The jet appears to be 420 km wide and covers half way around the planet as it travels through Earth’s liquid outer core. This iron jet has likely been circling the Earth for hundreds of millions of years, yet we just discovered its existence. Despite a good understanding of the iron jet’s width and length, the depth to which it extends is far from known.

The liquid jet likely aligns between two different boundaries within Earth’s core. The boundary, which the research team calls a “tangent cylinder” is like a tube running along the solid inner core along Earth’s rotational axis. When molten iron travels toward the cylinder it is diverted sideways and forms a jet along the theoretical tube.

A superposition of the flow direction and magnitude of the liquid iron jet (Credit: Nature Geoscience)

A superposition of the flow direction and magnitude of the liquid iron jet (Credit: Nature Geoscience)

As part of the Swarm program, a trio of three spacecraft were launched in 2013 to circle and map the Earth’s magnetic field in 4 dimensions. Scientists are now able to measure spatial changes with time in Earth’s magnetic field from the European Space Agency’s Swarm satellite program. The three satellites allow unprecedented high resolution magnetic field measurements. This allows scientists to examine the structure of Earth’s interior and the dynamic behavior of its magnetic field through time.

The ultimate goal of Swarm is to measure and quantify why Earth’s magnetic field has continuously weakened in the past centuries. The fear is that Earth may be close to a magnetic reversal, whereby the magnetic north flips from its current position near the North Pole to the South Pole. Geologists can measure past pole reversals, which happen every couple hundred thousand years, and note the significant impact this has on climate and population dynamics.

Understanding and monitoring the movement of this liquid iron jet will hopefully shed light on the current state of the liquid core, how it behaves, and the likelihood of an imminent global magnetic reversal.

Trevor Nace is a geologist, Forbes contributor, and adventurer. Follow him on Twitter @trevornace

Iron ‘jet stream’ detected in Earth’s outer core

Artwork EarthImage copyrightESA
Image captionArtwork: A depiction of where the jet is moving – in the outer core. The Swarm satellites fly a few hundred km above the planet and sense its magnetic field

Scientists say they have identified a remarkable new feature in Earth’s molten outer core.

They describe it as a kind of “jet stream" – a fast-flowing river of liquid iron that is surging westwards under Alaska and Siberia.

The moving mass of metal has been inferred from measurements made by Europe’s Swarm satellites.

This trio of spacecraft are currently mapping Earth’s magnetic field to try to understand its fundamental workings.

The scientists say the jet is the best explanation for the patches of concentrated field strength that the satellites observe in the northern hemisphere.

“This jet of liquid iron is moving at about fifty kilometres per year," explained Dr Chris Finlay from the National Space Institute at the Technical University of Denmark (DTU Space).

“That might not sound like a lot to you on Earth’s surface, but you have to remember this a very dense liquid metal and it takes a huge amount of energy to move this thing around and that’s probably the fastest motion we have anywhere within the solid Earth,” he told BBC News.

Dr Finlay was speaking here at the American Geophysical Union (AGU) meeting in San Francisco, just ahead of the official publication of the research in the journal Nature Geoscience.

Artwork: The Swarm satellites were launched in 2013 to study Earth's magnetic fieldImage copyrightESA
Image captionArtwork: The Swarm satellites were launched in 2013 to study Earth’s magnetic field

Most people will be familiar with the atmospheric jet stream – the high-altitude, rapidly flowing belt of air on which aeroplanes ride to get to their destination more quickly.

Dr Finlay and colleagues want us to envision something similar but made of metal and 3,000km down, under our feet.

They assess the jet to be about 420km wide, and say it wraps half-way around the planet.

Its behaviour will be critical to the generation and maintenance of the global magnetic field, they add.

“It’s likely that the jet stream has been in play for hundreds of millions of years," said Dr Phil Livermore from Leeds University, UK, and the lead author on the journal paper.

In the paper, the team puts forward a model to explain the jet.

Artwork EarthImage copyrightESA
Image captionThe major part of Earth’s magnetic field is generated via convection of molten iron in the outer core. The field protects all life from damaging space radiation

The scientists say the feature probably aligns to a boundary between two different regions in the core.

They call this boundary the “tangent cylinder". They imagine this as a tube sitting around the solid inner core, running along Earth’s rotation axis.

When liquid iron approaches the boundary from both sides, it gets squeezed out sideways to form the jet, which then hugs the imaginary tube.

“Of course, you need a force to move fluid towards the tangent cylinder," said Prof Rainer Hollerbach, also from Leeds and another co-author on the paper.

“This could be provided by buoyancy, or perhaps more likely from changes in the magnetic field within the core."

Although the team believes it understands how wide and how long the jet is, the depth to which it descends is far from certain.

Dr Livermore told BBC News: “It currently wraps about 180 degrees around the tangent cylinder. Although observations only constrain the jet stream on the edge of the core, our theoretical understanding suggests that the jet could in principle go very deep indeed – possibly in fact all the way down to the edge of the core in the southern hemisphere (i.e. at the other end of the tangent cylinder)."

That the team can make such inferences speaks to the impressive capabilities of the Swarm constellation.

Launched in November 2013, the European Space Agency satellites are providing unparalleled insights into the structure and behaviour of Earth’s magnetic field.

With their highly sensitive instruments, they are gradually teasing apart the field’s various components – from the dominant signal coming from the movement of iron in the outer core to the almost imperceptible contribution made by ocean currents.

It is hoped the Swarm satellites’ data could ultimately tell us why Earth’s magnetic field has been weakening in recent centuries.

Scientists have speculated we could be on the cusp of a polarity reversal, which would see North become South, and South become North.

This occurs every few hundred thousand years.

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