40 Exoplanets-High

Exoplanets FOCUS Question How do we find planets outside of our solar system?

系外行星焦点问题我们如何找到太阳系外的行星?

What Is an Exoplanet? People who lived long ago could look up at night and see Mercury, Venus, Mars, Jupiter, and Saturn— planets of our solar system. After telescopes were invented, astronomers discovered Uranus, Neptune, dwarf planets like Pluto, and many moons. Then people wondered: Are there more planets beyond our solar system? We now know that the answer is yes! A planet is a large object, made of rock or gas, that orbits a star. An exoplanet is any planet outside our solar system. Exoplanets do not orbit the Sun.

什么是系外行星?生活在很久以前的人们可以在晚上抬头看到水星、金星、火星、木星和土星——我们太阳系的行星。 望远镜发明后，天文学家发现了天王星、海王星、像冥王星这样的矮行星和许多卫星。 然后人们想知道:在我们的太阳系之外还有更多的行星吗? 现在我们知道答案是肯定的!行星是围绕恒星运行的由岩石或气体构成的大天体。 系外行星是太阳系以外的任何行星。 系外行星不围绕太阳运行。

Astronomers look for exoplanets because they want to know what the universe is made of and how it works. There is another reason people are interested in exoplanets. They want to know: Are we alone? It would be amazing to discover planets in other solar systems with kinds of life different from those that exist on Earth. Astronomers have discovered thousands of exoplanets. Some of them are small and rocky, like Mercury, Venus, Earth, and Mars. Others are large and made of gas, like Jupiter, Saturn, Neptune, and Uranus. Some seem to have watery atmospheres like Earth's. Others appear black, with atmospheres full of dark particles that are rich in carbon.

天文学家寻找系外行星是因为他们想知道宇宙是由什么组成的以及它是如何运作的。 人们对系外行星感兴趣还有另一个原因。 他们想知道:我们是孤独的吗? 如果能在其他太阳系的行星上发现与地球上不同的生命，那将是一件令人惊奇的事情。 天文学家已经发现了数千颗系外行星。 其中一些行星很小，多岩石，比如水星、金星、地球和火星。 其他的行星很大，由气体组成，比如木星、土星、海王星和天王星。 有些星球的大气层似乎和地球一样有水。 另一些则呈黑色，大气中充满了富含碳的黑色粒子。

How We Find Exoplanets There are billions of stars in the Milky Way galaxy, and billions of galaxies in the universe. With so many stars in the universe, it seemed certain that there must be other planets out there. Until the 1990s, however, there was no evidence. Exoplanets are hard to see. They are relatively small and they are very far away. Planets do not give off their own light. In order to see them, we must see starlight that they reflect. If we look toward a star to see a planet, the light from the star usually hides it. Scientists have come up with ways to search for exoplanets. One way is known as the transit method. As astronomers observe a star, it dims slightly when a planet passes between the star and the telescope. The planet blocks some of the starlight. Astronomers look for stars that dim and brighten in a regular, repeating pattern. This tells them that a planet is orbiting the star.

银河系中有数十亿颗恒星，宇宙中也有数十亿个星系。 宇宙中有这么多恒星，似乎可以肯定宇宙中一定有其他行星。 然而，直到20世纪90年代，还没有证据。 系外行星很难看到。 它们相对较小，而且距离很远。 行星本身不发光。 为了看到它们，我们必须看到它们反射的星光。 如果我们朝一颗恒星看行星，恒星发出的光通常会把行星隐藏起来。 科学家们已经想出了寻找系外行星的方法。 一种方法被称为凌日法。 当天文学家观测恒星时，当行星从恒星和望远镜之间经过时，它会略微变暗。 这颗行星挡住了部分星光。 天文学家寻找的是那些有规律的、重复的变暗变亮的恒星。 这告诉他们有一颗行星在绕着恒星运行。

As a planet orbits a star, the gravitational pull of the planet causes the star to move as well. In the astrometric method, astronomers measure the exact position of the star in space and how it wobbles in a repeating pattern over time. The Doppler method observes this wobble by recording the color of light from the star. Stars moving toward Earth appear bluer, and those moving away appear redder. A star with a nearby planet may appear bluer as it wobbles toward us and redder as it wobbles away. It is sometimes possible to observe an exoplanet directly. Astronomers block the light from the planet's star so that they can see objects around it. They can also observe planets directly by looking through more than one telescope at the same time, and combining information from the telescopes.

当行星围绕恒星运行时，行星的引力也会导致恒星运动。 在天体测量法中，天文学家测量恒星在空间中的确切位置，以及它如何随着时间的推移以重复的模式摆动。 多普勒方法通过记录恒星发出的光的颜色来观察这种摆动。 向地球移动的恒星看起来更蓝，远离地球的恒星看起来更红。 一颗恒星附近有一颗行星，当它向我们晃来晃去时，可能会显得更蓝，而当它晃去晃去时，可能会显得更红。 有时直接观测系外行星是可能的。 天文学家挡住了这颗行星的恒星发出的光，这样他们就能看到它周围的物体。 他们还可以通过同时使用多个望远镜观测行星，并结合来自望远镜的信息来直接观测行星。

Scientists are not satisfied with simply detecting planets, however. For each planet they discover, they want to know: How big is it? How far from its star is it? What is it made of? Does it have an atmosphere? What is the surface like? Knowing these things about planets increases our understanding of the universe. To answer these questions, scientists observe different forms of light coming from the planets, using many different ground-based telescopes and space telescopes. They watch carefully to see how the planets move in space. Astronomers used the Keck and Gemini telescopes in Hawaii to find four giant, red planets that orbit a star called HR 8799. The planets were found by blocking the starlight coming from HR 8799. Observers found planet HD 189733b when it made a transit in front of its star. Astronomers used the Spitzer Space Telescope to study the infrared light coming from the planet. They discovered that there is water vapor in its atmosphere.

然而，科学家们并不满足于仅仅探测行星。 对于他们发现的每一颗行星，他们都想知道:它有多大? 它离它的恒星有多远? 它是用什么做的?它有大气吗? 表面是什么样子的?了解这些关于行星的事情可以增加我们对宇宙的理解。 为了回答这些问题，科学家们使用许多不同的地面望远镜和太空望远镜观察来自行星的不同形式的光。 他们仔细观察行星如何在太空中运动。 天文学家使用夏威夷的凯克望远镜和双子座望远镜发现了四颗巨大的红色行星，它们围绕着一颗名为HR 8799的恒星运行。 这些行星是通过挡住来自HR 8799的星光发现的。 观测者发现了HD 189733b行星，当时它正在它的恒星前面凌日。 天文学家使用斯皮策太空望远镜来研究来自这颗行星的红外光。 他们发现它的大气中有水蒸气。