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抱歉来晚了哇~~~这是周五的作业哈~~
【speed】
A home from home: Five planets that could host life 【free】 It's one of the big questions: Are we alone on this blue marble or is there life elsewhere in the cosmos? To shed light on this, astronomers are searching for habitable worlds circling far-off stars. A team has now published updated evidence for a planet that could be the most Earth-like yet. According to a project based at the US Arecibo Observatory, it would be the fifth potentially habitable world known outside our Solar System. So what do we know about these five Earth-like planets, and how likely is it that they could support life? 【98 words】
【time 1】 Earth "twin"
Gliese 581g
 ? Similarity to Earth (ESI): 0.92 ? Minimum mass: 2.2 times that of Earth ? Distance: 20.3 light-years
The discovery of Gliese 581g was announced in September 2010 by a US-led team. But as soon as they made the announcement, doubts began to surface. The team at the Geneva observatory which had discovered all four other planets around the star Gliese 581 failed to detect it in their own data. But the original discoverers of 581g have now published an analysis using more data to provide more promising evidence for its existence.
This would be significant because the Earth Similarity Index (ESI), devised by a team including Dirk Schulze-Makuch from Washington State University and Abel Mendez from the Arecibo Observatory, shows that Gliese 581g is the most Earth-like planet discovered to date. The ESI measures characteristics of exoplanets on a scale from zero to one, with one being identical to Earth. Accordingly, the online Habitable Exoplanets Catalog has decided to include it in their list of the most promising worlds to support life.
Like the other worlds in the catalogue, Gliese 581g orbits in a "sweet spot" around its star - the habitable zone, or Goldilocks zone - that is neither too hot nor too cold to allow for liquid water. It is just over twice the mass of Earth and, although the planet is closer to its parent star than is Earth, it receives about the same light flux (a measure of the star's apparent brightness) as our planet because Gliese 581 is a red dwarf star and therefore dimmer than our own Sun. Steven Vogt, from University of Santa Cruz, US, one of original discoverers, said Gliese 581g orbits "squarely in the star's Habitable Zone at 0.13 AU, where liquid water on planetary surfaces is a distinct possibility". Nevertheless, the planet's existence remains controversial. 【288 words】
【time 2】 New kid on the block
Gliese 667Cc
 ? Similarity to Earth (ESI): 0.85 ? Minimum mass: 4.5 times that of Earth ? Distance: 22 light-years
Announced in February 2012 by a team from the US Carnegie Insitution and Germany's Goettingen University, Gliese 667Cc belongs to a class of planets known as Super Earths - a class of planet with a size in between that of rocky worlds like Earth and Mars and the gas giants like Jupiter and Saturn.
Roughly 4.5 times the mass of Earth, Gliese 667Cc takes 28 days to complete a single orbit of its star, which is located just 22 light-years away.
The exoplanet absorbs about as much energy from its star as Earth does from the Sun, which means surface temperatures could be similar to Earth's. This would allow for the presence on the planet's surface of liquid water - one of the pre-requisites for life. However, astronomers say this cannot be confirmed without further information on the planet's atmosphere. Nevertheless, co-discoverer Guillem Anglada-Escude has said of 667Cc: "This planet is the new best candidate to support liquid water and, perhaps, life as we know it." 【184 words】
【time 3】 Big beast
Kepler 22b
 ? Similarity to Earth (ESI): 0.81 ? Minimum mass: 40 times that of Earth ? Distance: 620 light-years
Since it was launched in March 2009, Nasa's Kepler Space Telescope has detected more than 2,300 candidate exoplanets. Of these, Kepler 22b is the only confirmed world in the habitable zone around its parent star, which is the same class - a G-type - as our Sun (though slightly cooler and smaller).
With a radius 2.4 times that of Earth, Kepler 22b is the most massive of the five habitable planets. But its orbit of 290 days around a Sun-like star resembles that of our own planet. Astronomers do not yet know for sure whether it has a predominantly gaseous, rocky or liquid composition. But to some, its size suggests a composition closer to the gaseous Neptune than to Earth. At the time of its discovery, exoplanet hunter Geoff Marcy, from the University of California, Berkeley, told the AP news agency that he would "bet my telescope that there is no hard, rocky surface to walk on".
But this is not necessarily bad for its prospects for hosting biology: mission scientist Natalie Batalha said that if Kepler 22b were mostly ocean with a small rocky core, "it's not beyond the realm of possibility that life could exist in such an ocean". 【219 words】
【time 4】 Steam bath
HD85512b
 ? Similarity to Earth (ESI): 0.77 ? Minimum mass: 3.6 times that of Earth ? Distance: 35 light-years
Another Super-Earth, with a mass 3.6 times that of our planet, HD85512b orbits on the inner margins of its habitable zone. This means it is closer to Venus than Earth in the amount of energy it absorbs from its star. However, that would not necessarily preclude the possibility of life.
How hospitable the planet is may depend on how much cloud cover it has, since clouds reflect solar radiation. Its discoverers calculate that if HD85512b were to have more than 50% cloud cover (on the same order as Earth), it could offset the planet's proximity to its star enough for water to stay liquid at the surface.
However, any life forms on HD85512b will have to be suited to very balmy conditions, "It's going to be really muggy, just think about the muggiest day you can think of," co-discoverer Lisa Kaltenegger, from the Max Planck Institute in Germany, said at the time of its discovery. "We're not saying it's habitable for you and me." 【182 words】
【time 5】 Water world?
Gliese 581d
 ? Similarity to Earth (ESI): 0.72 ? Minimum mass: 5.6 times that of Earth ? Distance: 20.3 light-years
Discovered in 2007 by a team at the Geneva Observatory using the HARPS planet-finding instrument in Chile, Gliese 581d is probably too large to be formed entirely of rocky material. Instead, it is a serious candidate for an ocean planet, according to one of its discoverers, Stephane Udry.
One of a system of five planets, it is the immediate neighbour of Gliese 581g. However, Gliese 581d orbits at a greater distance from its parent star, on the colder, outer fringe of the habitable zone. As a result, sunlight on Gliese 581d has about 35% the intensity that is does on Mars.
But computer simulations of the exoplanet's atmosphere suggest that under some scenarios, greenhouse gases would allow surface temperatures to remain above 0C, allowing water to stay liquid. Indeed, says Dr Udry, the planet "could even be covered by a large and deep ocean".
Since it is located only 20.3 light-years away - in the Constellation Libra - astronomers should be able to resolve some of these questions in the future, with direct spectroscopic observations of the planet's atmosphere. 【197 words】
【obstacle】
Spain and the markets The Spanish patient A full bail-out of the euro area’s fourth-largest economy is looming

IF SPAIN were a patient, the mood in the hospital ward would be tense. Every attempt by local specialists advised by renowned European consultants to treat the sickness brings no more than temporary relief. Even more worrying, the relapses after each dose are happening sooner and sooner. Spain’s chances of avoiding intensive care—a full bail-out—are receding to near vanishing-point.
The symptoms of Spanish sickness are manifest in ten-year government bond yields touching 7.75% on July 25th; previous bail-outs of Greece, Ireland and Portugal occurred not long after rates had surpassed 7%. Even more perturbing, two-year yields also briefly went above 7%, in effect foreclosing the government’s ability to borrow at anything but short maturities.
No isolation ward is possible in the financially integrated euro area and Spain’s sickness quickly infected other countries. The Italian ten-year bond yield went above 6.5%, its highest since January. European stockmarkets retreated and Italy’s fell to a euro-era low. Sentiment was further soured by a report from Moody’s, a ratings agency, saying that Germany, Luxembourg and the Netherlands might lose their cherished triple-A status. The prognosis was based in part on fears about the public-debt burden that northern countries might have to assume if bail-outs spread.
The market funk was the more troubling since a Spanish government with a lot going for it had appeared to be getting a grip. Public debt is rising fast, but at 69% of GDP last year was far lower than Italy’s 120%—and less even than Germany’s 81%. The budget deficit is high (8.9% of GDP in 2011), but only a week before the market panic Mariano Rajoy, the prime minister, announced more tough austerity measures. And on July 20th European finance ministers sanctioned the first tranche of a partial bail-out worth up to ?00 billion ($121 billion) for Spanish banks.
So why are investors in such a cold sweat about Spain? One reason is that Mr Rajoy flunked hard choices at the outset, notably the cleansing of the banks. Despite a low starting-point for public debt, deficit overshoots have revealed insufficient central control over the 17 regions that are responsible for a big chunk of spending. Investors fret that more regions may follow Valencia, which applied for aid on July 20th. They are in any case sceptical that Spain can meet its targets for cutting the deficit in the teeth of a recession that is harsher than expected.
The biggest worry is Spain’s external debt. Spain ran hefty current-account deficits in the first decade of the euro. As a result, its liabilities to foreign investors exceeded the assets that its residents own abroad by 92% of GDP last year, among the highest in the euro area. The problem for Spain is that foreign capital has been fleeing over the past year. That has weakened the banks and the economy and left the Spanish government shunned by foreign investors for its own financing needs.
The European summit in late June offered a flicker of hope but it is guttering. Euro-area leaders agreed that the European Stability Mechanism (ESM), their new permanent rescue fund, would be able to inject funds directly into banks rather than via loans to the government. That perked markets up since it promised to sever the link between weak banks and weak sovereigns. But before long the deal looked less solid: the ESM cannot come into force until September, when Germany’s constitutional court will rule on its legality. Assuming it passes that test, the ESM cannot be used for direct bank recapitalisation until a European supervisor is put in charge.
Spain may yet be able to fend off a bail-out for some time. It has some cash reserves and can still borrow at short maturities. The euro area also has its temporary rescue fund, which will lend the Spanish government the initial sum of money for the banks. But even if Spain survives a hot summer, the markets are signalling that it will need a full bail-out later this year.
That would be a nightmare, and not just for Spain. The Spanish government must borrow ?85 billion until the end of 2014 to cover its budget deficit and other needs such as bond redemptions, according to economists at Credit Suisse. Even if the IMF chips in a third as in previous bail-outs, European lenders would have to find ?50 billion or so. They have already committed ?00 billion to rescuing Spanish banks, so for other emergencies they would have only ?50 billion of the ?00 billion now in their rescue kitties.
The course of events is eerily similar to what happened a year ago. Then European leaders appeared to have secured their summer holidays with a “breakthrough” summit. But things soon fell apart. Nerves about Italy and Spain were calmed only when the European Central Bank (ECB) started buying their bonds. The central bank was never keen on this and it has not been buying bonds for several months. Even if the ECB were to resume purchases they might be less effective than before, because its refusal to share in the pain of the Greek debt restructuring in March frightened bondholders elsewhere.
The awkward truth is that the Spanish government is not alone in flunking hard choices. The plight of Spain and the danger of its sickness spreading to Italy call for a decisive countermove by Germany and the ECB. One being discussed would be to give the ESM a banking licence, which would magnify its resources by allowing it to borrow from the central bank. The graver the euro crisis gets, the bigger the response has to be—and the harder it is to sell to sceptical northern electorates.
【965 words】
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