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STEVE EMBER: I'm Steve Ember.

DOUG JOHNSON: And I'm Doug Johnson with EXPLORATIONS in VOA Special English. Today we tell about an American space agency project to study salt levels in the Earth's oceans. We report on plans to collect rock particles from a nearby asteroid. And we tell about a discovery of huge magnetic bubbles in space.

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STEVE EMBER: On June 10th, the National Aeronautics and Space Administration, NASA, launched a satellite called Aquarius. The satellite will measure and study the saltiness of Earth's oceans from space. The aim of the project is to learn about our changing climate. The project is a joint effort between NASA and Argentina's space agency.

Some satellites orbiting the Earth provide information about sea temperatures and depths. Others gather information about the ocean's color and winds. But there has never before been a worldwide study of the salt levels of the sea surface.

Until now, this kind of information came only from ships and buoys floating in the ocean. Experts say Aquarius will gather as much information about sea surface salinity as has been collected by ships over the past 125 years.

DOUG JOHNSON: NASA officials say the project will give scientists a better understanding of Earth's changing climate. They say it should provide missing information about the water cycle and the circulation, or movement, of ocean waters. These two forces are a major influence on the ocean's climate. Experts say the salt measurements will provide the information that links these forces within the climate system.

The Earth's water cycle is the continuous movement of water as it changes from a liquid to a vapor or gas. Water from the sea rises up as vapor to form clouds before changing to rain or snow. Most of the planet's evaporation and precipitation take place over oceans. Understanding salt levels will help experts better understand how increases and decreases of fresh water from rain affect the ocean environment.

STEVE EMBER: When scientists study the circulation of ocean water, they are looking at how the water mass of the ocean forms layers and mixes together. This mixing is a product of the oceans' density and buoyancy. These, in turn, depend on the water's temperature and saltiness. Buoyancy is the upward force that a liquid places on an object that is less dense than itself. Knowing about salt levels helps tell scientists more about the ocean water movement.

Scientists will use salt water measurements to understand how the ocean's climate is changing. Gary Lagerloef works for the Earth and Space Research Institute in Seattle, Washington. He is the main investigator of the Aquarius project. He says information gathered by Aquarius will show how the ocean environment is changing.

GARY LAGERLOEF: "One of the big overarching questions in climate is, is the global water cycle changing? Many climate forecasting models suggest that it will change over time as the climate warms up. But measuring these changes in rainfall over the ocean is very, very difficult to do. But salinity is actually an important parameter that gives us an indication of what might be going on."

DOUG JOHNSON: Aquarius will also produce maps of saltwater movement around the world every month. The satellite is equipped with microwave radiometers. These measuring devices must be very exact and secure to provide detailed information.

Yi Chao is a scientist with the Aquarius project at NASA's Jet Propulsion Lab in California. He says different intensities of saltwater produce different energy. The radiometer measures microwaves from the water. Scientists use mathematic equations to estimate salt levels based on those microwaves.

The Aquarius project is expected to last three years.

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STEVE EMBER: NASA officials have announced plans to launch a spacecraft to a nearby asteroid in 2016. Asteroids are the rocky remains from the collapse of a solar nebula. This huge cloud of gas collapsed about 4,500 million years ago to form our sun and planets.

The goal of the project is to collect rock particles from an asteroid called 1999 RQ36. Scientists hope to study these particles to learn more about how our solar system was formed. NASA says they might also provide a better understanding of how life began.

DOUG JOHNSON: The operation is called OSIRIS-REx. That is short for Origins-Spectral Interpretation-Resource Identification-Security–Regolith Explorer. It will take OSIRIS-Rex four years to travel to the asteroid. Once they are close together, the unmanned spacecraft will spend months mapping 1999RQ36. Experts will then choose an area of the asteroid where the spacecraft will take a rock sample using its robotic arm.

NASA already has a collection of meteorites, small pieces of asteroids that broke away and fell to Earth. Organic molecules on meteorites may hold valuable information. But the intense heat of passing through the Earth's atmosphere likely damaged those molecules. After they land, meteorites can pick up small organisms and chemicals from Earth's environment.

DOUG JOHNSON: Material from the RQ36 asteroid will be sent back to Earth in a special protective device. This way, it will be unchanged when it arrives on our planet in 2023.

STEVE EMBER: Gathering material from the asteroid is not the only goal. Experts have identified RQ36 as a possibly dangerous asteroid. There is a small chance it might hit the Earth in the year 2182.

Experts say the OSIRIS-REx operation will help them learn more about asteroids by measuring the "Yarkovsky effect" for the first time. The "Yarkovsky effect" is a small push on an asteroid that happens when it takes in sunlight and produces heat. This small push adds up over time. Knowing more about how the Yarkovsky effect changes an asteroid's orbit will help scientists better predict whether RQ36 will come near Earth.

DOUG JOHNSON: Michael Drake is the Director of the Lunar and Planetary Laboratory at the University of Arizona. His group will lead the OSIRIS-REx team. He says engineers are already studying ways to move the asteroid out of Earth's path. One possible method is to create a large sail.

MICHAEL DRAKE: "There are strategies such as putting a large Mylar sail, maybe say half a mile across, attached to the surface, that in itself is an interesting engineering challenge, and using photons from the Sun to sail it away much like a sailboat works on the ocean."

DOUG JOHNSON: Professor Drake says another way to move the asteroid would be to paint one side of the dark rock white. This would change the amount of sunlight it reflects. Changing the amount of solar photon pressure on the asteroid would change its path.

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STEVE EMBER: NASA scientists say the agency's two Voyager spacecraft have provided some surprising news about the edge of the solar system. They say this area seems to be made of huge bubble-like structures.

The two Voyager spacecraft were launched in 1977. The two spacecraft have spent more than a third of a century traveling to the edges of our solar system. They are currently about 14 billion kilometers from Earth.

Scientists say computer estimates suggest the bubbles are about 160 million kilometers wide. They say it would take one of the Voyagers weeks to cross just one bubble. Voyager One entered this area around 2007. Voyager Two entered it about a year later. Scientists at first did not understand what the Voyagers were sensing, but now they believe they have a better idea.

DOUG JOHNSON: Merav Opher is an astronomer at Boston University. He explains that the sun's magnetic field extends all the way to the edge of the solar system. As the sun turns, its magnetic field twists and folds. As the lines of the magnetic force cross one another, they reorganize into magnetic bubbles.

Earlier theories predicted that the faraway magnetic folds of the sun were curved and folded back to rejoin the sun. But these bubbles seem to be disconnected from the sun's magnetic field. NASA says the structure of the sun's far away magnetic field is of huge importance because it tells how our solar system interacts with the rest of the galaxy.

Merav Opher says scientists are hoping to learn more about these bubble structures. She says this finding is just the beginning, and that he expects more surprises ahead.

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STEVE EMBER: This program was written and produced by Dana Demange, with reporting by Jessica Berman. I'm Steve Ember.

DOUG JOHNSON: And I'm Doug Johnson. Join us again next week for EXPLORATIONS in VOA Special English.

salinity: 鹽性；鹽度

photon: a unit of electromagnetic energy 光子；光量子

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（來源：VOA 編輯：崔旭燕）