書讀百遍其義自現？- SAT自然科學類文章的五大結構讓你少讀99遍

一說到自然科學，很多人會想到一類學科，一個群科學家，或者一個電視節目……但在出國留學考試圈兒，跟一個老師或者學生提到自然科學，大家會像做填空題一樣，直接接上「類文章」——是的，自然科學是一類文章，它更多是出現在閱讀考試當中。今天打算開門見山，說說閱讀學科中的自然科學類文章。

大家熟悉名字，未必熟悉內核。學生如此，一些老師也如此。比如，這麼一段對話：

同學們，其實這些對話都沒有結束，自然科學它是一個話題類別，再細分還會有具體的學科，什麼天文地質啊，物理化學啊等等，但是知道這些學科和分類並不能最好地指導你的閱讀考試。閱讀考試可不是茶餘飯後讀讀咪蒙那麼簡單，而是要求短時高效找到準確的信息點，並做以恰當的理解轉化。在這個背景下，訓練的時候把文章的話題內容（如花崗岩的分類和特質）解讀得再仔細，再具體，我們能做的，也只有期待下一次考試還是會出非常類似內容，如果換成別的內容，之前的解讀就基本用不到了。

那怎麼辦，不學了么？當然要學。就像寫作有格式，聽力有套路，其實啊，閱讀也是有固定模式的……在SAT閱讀當中，最有套路模式的就是自然科學類的文章。我們要幫助大家實現的，就是學會辨認自然科學類文章的脈絡走向，組織框架，而對於文章內容，我們就可以不挑了。

基本上，自然科學類文章在SAT中的結構走向可以分為這麼5種——

1. 開門見山類

2. 理論假設類

3. 先立後破類

4. 先破後立類

5. 信息介紹類

咱們今天先說開門見山類

我們對照一篇的真題文章看一下（本文屬於開門見山類中最複雜的模式）：

When exoplanet hunters announced in January of 2014 that they had found a tribe of 「mini-Neptunes」 and the lightest planet ever detected outside our solar system, they highlighted more than just the diversity of exoplanets. The results, announced at a meeting of the American Astronomical Society, also show the power of an up-and-coming method of calculating the masses of alien worlds from the way they eclipse their stars.

The new technique, called transit timing variation (TTV), is enabling astronomers to fill out their picture of dozens of exoplanets detected by NASA』s Kepler spacecraft. The eclipses, or 「transits,」 that Kepler detected reveal only a planet』s size and orbital period. To know whether it is rocky, gaseous, or some mixture of the two, astronomers also need its mass. Traditionally, they have resorted to ground-based telescopes to determine it, by measuring the wobble of the star as the planet tugs on it. But TTY can determine masses from transit data alone.

The technique was the brainchild of Matthew Holman, an astrophysicist at Harvard University, and others. If two or more planets happened to be orbiting a star in close proximity, they reasoned, their gravitational tugs on each other would alter their orbital periods. If one of them was a transiting planet— dimming the light of its parent star as it passed between the star and Earth—astronomers would see its transit timing vary over multiple orbits, betraying the presence of a companion planet. If both planets were transiting, astronomers could measure the perturbations in both their orbits and work out the planets masses.

Holman and a colleague published the idea in 2005, and Eric Agol of the University of Washington, Seattle, and colleagues put forward a similar scheme almost simultaneously. For years afterward, however, astronomers failed to detect transit timing variations because almost all known exoplanets were gas giants spinning around their stars in tight orbits. Theorists think such planets formed farther from the star and later barreled inward, clearing away any potential wobble-inducing companions.

The technique became practical thanks to the Kepler spacecraft, which until 2013 was monitoring the brightness of 160,000 nearby stars for the telltale dimming due to transiting planets. Kepler began delivering data on dozens of planetary systems, many of them consisting of multiple planets. In 2010, astronomers began making TTV detections. Their expertise has been growing ever since.

David Kipping, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and his colleagues came across KOI-314c while combing Kepler data for TTV signatures due to exomoons, which should cause transiting exoplanets to wobble and change their transit timing. But the transits seen around the star KOI-314, a red dwarf some 200 light-years from Earth, pointed instead to the presence of two planets. Their transit times were varying in lockstep: when one planet slowed down in its orbit around the star, the other would speed up, and vice versa. 「We saw the same TTV signature, just in opposite phase to each other,」 Kipping says. 「It was obvious that these two planets must be interacting."

By simulating the dance on a computer, the researchers worked out the masses of the two planets. They found that the outer, KOI-314c, which orbits the star every 23 days, has the same mass as Earth, although it is about 60% larger than Earth in radius. Kipping and his colleagues infer that the planet—the lightest exoplanet so far discovered—has a rocky core and a thick, gaseous atmosphere. The inner planet, KOI-314c, is similar in size but about four times as massive.

Meanwhile, researchers led by Yoram Lithwick, an astronomer at Northwestern University in Evanston, Illinois, were looking at the TTV signatures of 163 exoplanets found by Kepler. The team determined that about 60 of them occupy a mass range between Earth and Neptune and are larger than expected for a rocky planet of that mass, suggesting they are blanketed by thick, extended atmospheres. They also found a pattern: as the planets grew bigger in radius, their density declined. 「If you make something twice as big, it becomes four times less dense,」 Lithwick says. 「So from going from a less than two Earth radii to four Earth radii, the density goes from rock-like all the way to gas.」 Lithwick predicts the surprising finding 「will have big implications for understanding planet formation.」

這樣的文章還有好多，大家如果找到了符合這個框架的文章，可以在後台留言確認，答對有獎啊~~