Pallas is 'Peter Pan' space rock 研究:智神星是“小飞侠”式
文章来源:未知 文章作者:meng 发布时间:2009-10-12 01:10 字体: [ ]  进入论坛
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The Hubble telescope has provided new insight on 2 Pallas, one of the largest asteroids2 in the Solar System.

哈勃望远镜提供了对2智神星——太阳系中最大的小行星之一——的最新观察资料。

Ceres and Vesta will be visited by the Dawn mission in the next few years
Ceres and Vesta will be visited by the Dawn mission in the next few years

The nearly 600km-wide rock is an example of an object that started out on the process of becoming a planet but never grew up into the real thing.

Researchers have published a 3D model of the grapefruit-shaped mini-world in Science magazine.

Hubble's data makes it possible to discern(辨别,看清楚) surface features, including what appears to be a big impact crater3(撞击坑).

The new information is expected to help scientists better understand how planets evolve in their earliest phases.

"Pallas is a unique piece of the puzzle of how our Solar System formed," said Britney Schmidt, of the University of California, Los Angeles, who led the observations.

Layering process

Pallas resides(居留,属于) some 400 million km from the Sun, in between the orbits of Mars and Jupiter.

It was the second object discovered in the main asteroid1 belt (hence the name, 2 Pallas), in 1802.

Only Ceres is wider (950km diameter). Another asteroid, Vesta, has a narrower girth(周围长度) but is more massive than Pallas.

All three can be considered "protoplanets(原行星)", an assessment4(估价,评估) reinforced(加强) in the case of Pallas by the latest Hubble observations.

Theory holds that planets grow from aggregations5 of the dust and rock found circling new-born stars.

Collisions between clumps6 of material produce progressively bigger objects.

Eventually, a few will become large enough, and hot enough, to start to undergo differentiation7 - a process of layering in which the densest8(密集的,浓厚的) materials move to the centre of the object to form a core.

In the case of Pallas, this process appears to have initiated9, but its slightly irregular shape suggests it never quite moved to completion.

"Whether you could form a core is something we can't really determine with these observations, but Pallas is big enough and round enough that it's very possible that its interior started to separate out," Ms Schmidt told BBC News.

"Ceres is perfectly10 round and so there's a really good chance that that happened. For Pallas, it may be just that this process got started but never finished."

Wet history

Dark features in the Hubble pictures indicate the presence of hydrated(含水的) minerals on the surface of the asteroid(小行星).

If Pallas formed early in the asteroid belt, it would probably have incorporated large quantities of water-ice.

As the rock heated up, this water would have melted. Not only would this have aided differentiation but it also would have altered the silicate11 rock(硅酸盐岩石) to produce the type of mineralogical signal obvious today.

It was highly unlikely, though, that Pallas got hot enough to melt silicate rock, said the California researcher.

The presence even now of a lot of water-ice in the asteroid might help to explain its relatively12 low density13 (2,400-2,800kg per cubic metre), she added.

The Science paper describing the Hubble observations includes a 3D representation of Pallas. This was built up from a series of snapshots of the asteroid's outline as it rotated in the view of the telescope.

It reveals an intriguing14(吸引人的,有趣的) depression in the southern hemisphere which Schmidt's team interprets as(把……理解为) a possible impact crater. It is large - about 240km across. It is also near dark terrain15(地带,地域) which could be material ejected or altered by a collision.

Pallas is known to share orbital characteristics with a group of rocks that could have been blown off the asteroid. The largest of this "family" is called Ioffe and has a diameter of 22km. It is entirely16 possible Ioffe originated in the assumed crater.

Nasa has sent a spacecraft to the asteroid belt to visit Ceres and Vesta. The Dawn probe will arrive first at the smaller of the two objects in 2011.

Pallas, unfortunately, is not on the itinerary(旅程,游记).

But Britney Schmidt believes interest in the asteroids and what they represent can only grow and is hopeful that her protoplanet could one day become a target for a space mission.

"We are really changing our perspective on these objects. When you say asteroid people don't tend to think of big, dynamic(动态的,有力的), evolved bodies; but that's probably what we have in the case of [Ceres, Vesta and Pallas].

"I'm trying to evolve people's thinking, taking them from 'big rocks to little planets'.

"It's also timely, with public discussion about Pluto17 and what makes - or doesn't make - a planet. The public are so interested in that."



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1 asteroid uo1yD     
n.小行星;海盘车(动物)
参考例句:
  • Astronomers have yet to witness an asteroid impact with another planet.天文学家还没有目击过小行星撞击其它行星。
  • It's very unlikely that an asteroid will crash into Earth but the danger exists.小行星撞地球的可能性很小,但这样的危险还是存在的。
2 asteroids d02ebba086eb60b6155b94e12649ff84     
n.小行星( asteroid的名词复数 );海盘车,海星
参考例句:
  • Asteroids,also known as "minor planets",are numerous in the outer space. 小行星,亦称为“小型行星”,在外太空中不计其数。
  • Most stars probably have their quota of planets, meteorids, comets, and asteroids. 多数恒星也许还拥有若干行星、流星、彗星和小行星。
3 crater WofzH     
n.火山口,弹坑
参考例句:
  • With a telescope you can see the huge crater of Ve-suvius.用望远镜你能看到巨大的维苏威火山口。
  • They came to the lip of a dead crater.他们来到了一个死火山口。
4 assessment vO7yu     
n.评价;评估;对财产的估价,被估定的金额
参考例句:
  • This is a very perceptive assessment of the situation.这是一个对该情况的极富洞察力的评价。
  • What is your assessment of the situation?你对时局的看法如何?
5 aggregations 4c4f91ef635e1dd162c5cdd100d293aa     
n.聚集( aggregation的名词复数 );集成;集结;聚集体
参考例句:
  • A pattern of overlapping aggregations is usually found. 通常可发现一种叠聚集现象。 来自辞典例句
  • The atoms of the different chemical elements are different aggregations of atoms of the same kind. 不同化学元素的原子是同类原子的不同聚合物。 来自辞典例句
6 clumps a9a186997b6161c6394b07405cf2f2aa     
n.(树、灌木、植物等的)丛、簇( clump的名词复数 );(土、泥等)团;块;笨重的脚步声v.(树、灌木、植物等的)丛、簇( clump的第三人称单数 );(土、泥等)团;块;笨重的脚步声
参考例句:
  • These plants quickly form dense clumps. 这些植物很快形成了浓密的树丛。 来自《简明英汉词典》
  • The bulbs were over. All that remained of them were clumps of brown leaves. 这些鳞茎死了,剩下的只是一丛丛的黃叶子。 来自《简明英汉词典》
7 differentiation wuozfs     
n.区别,区分
参考例句:
  • There can be no differentiation without contrast. 有比较才有差别。
  • The operation that is the inverse of differentiation is called integration. 与微分相反的运算叫做积分。
8 densest 196f3886c6c5dffe98d26ccca5d0e045     
密集的( dense的最高级 ); 密度大的; 愚笨的; (信息量大得)难理解的
参考例句:
  • Past Botoi some of the densest jungle forests on Anopopei grew virtually into the water. 过了坊远湾,岛上的莽莽丛林便几乎直长到水中。
  • Earth is the densest of all of these remaining planets. 地球是所剩下行星中最致密的星球。
9 initiated 9cd5622f36ab9090359c3cf3ca4ddda3     
n. 创始人 adj. 新加入的 vt. 开始,创始,启蒙,介绍加入
参考例句:
  • He has not yet been thoroughly initiated into the mysteries of computers. 他对计算机的奥秘尚未入门。
  • The artist initiated the girl into the art world in France. 这个艺术家介绍这个女孩加入巴黎艺术界。
10 perfectly 8Mzxb     
adv.完美地,无可非议地,彻底地
参考例句:
  • The witnesses were each perfectly certain of what they said.证人们个个对自己所说的话十分肯定。
  • Everything that we're doing is all perfectly above board.我们做的每件事情都是光明正大的。
11 silicate 4EXy2     
n.硅酸盐
参考例句:
  • There are large amounts of aluminum silicate in the area.这个地区有大量的硅酸铝。
  • Silicate minerals are characteristically refractory and difficult to break down.硅酸盐矿物的特点是耐熔和难以分离。
12 relatively bkqzS3     
adv.比较...地,相对地
参考例句:
  • The rabbit is a relatively recent introduction in Australia.兔子是相对较新引入澳大利亚的物种。
  • The operation was relatively painless.手术相对来说不痛。
13 density rOdzZ     
n.密集,密度,浓度
参考例句:
  • The population density of that country is 685 per square mile.那个国家的人口密度为每平方英里685人。
  • The region has a very high population density.该地区的人口密度很高。
14 intriguing vqyzM1     
adj.有趣的;迷人的v.搞阴谋诡计(intrigue的现在分词);激起…的好奇心
参考例句:
  • These discoveries raise intriguing questions. 这些发现带来了非常有趣的问题。
  • It all sounds very intriguing. 这些听起来都很有趣。 来自《简明英汉词典》
15 terrain sgeyk     
n.地面,地形,地图
参考例句:
  • He had made a detailed study of the terrain.他对地形作了缜密的研究。
  • He knows the terrain of this locality like the back of his hand.他对这一带的地形了如指掌。
16 entirely entirely     
ad.全部地,完整地;完全地,彻底地
参考例句:
  • The fire was entirely caused by their neglect of duty. 那场火灾完全是由于他们失职而引起的。
  • His life was entirely given up to the educational work. 他的一生统统献给了教育工作。
17 Pluto wu0yF     
n.冥王星
参考例句:
  • Pluto is the furthest planet from the sun.冥王星是离太阳最远的行星。
  • Pluto has an elliptic orbit.冥王星的轨道是椭圆形的。
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