LESSONS 48, 49

Script of the text for listening (VOA)

The picture that astronomers are creating of our universe has gotten a little more detailed. Last month, three teams of astronomers reported making direct images of planets orbiting other stars. Their observations are changing the way space scientists look at the universe.

Technological progress has made finding planets far from our own solar system common. The first discovery was confirmed in nineteen ninety-four. Today, more than three hundred twenty planets have been discovered beyond our solar system.

To make these discoveries, scientists looked for small movements in nearby stars. The movements show the gravitational influence of another object on the star.

Some planets have been found because they pass in front of the stars they orbit. This limits the amount of light seen on Earth for a short time.

What is new about the recent observations is that they are direct images of distant planets. That is something astronomers once thought would never be possible.

One team was led by Christian Marois, an astronomer at the Herzberg Institute of Astrophysics in Victoria, Canada. His group found three planets orbiting a star called HR Eight Seven Nine Nine. The star is about one hundred thirty light years from Earth in the constellation, or group of stars, known as Pegasus.

The team used the Keck Two and Gemini telescopes in Hawaii to produce the image showing the planets. The scientists also used a special technology called adaptive optics.

It changes the shape of a telescope's mirror to cancel the effects of the Earth's atmosphere. This permits clearer, higher quality images to be made.

The planets are huge. Two of them are ten times the mass of Jupiter - the largest planet in our solar system. This puts them near the mass, not of planets, but of failed stars called brown dwarfs. However, there is evidence that supports the idea that they are planets.

Bruce Macintosh of Lawrence Livermore National Laboratory helped make the discoveries. He says all three objects orbit their star in the same direction and plane -- the way planets do.

A second team announced the discovery of one planet orbiting the star Fomalhaut. Fomalhaut is the eighteenth brightest star in the sky. Paul Kalas of the University of California led a team that used the Hubble Space Telescope to find the planet now called Fomalhaut b. It took several years of observations to confirm its existence.

The planet is so distant from its star that it takes eight hundred seventy-two years to orbit Fomalhaut once.

Mister Kalas says Fomalhaut b orbits its star at the inside edge of a huge flattened ring of ice and dust. This disk is similar to the Kuiper Belt, which surrounds our own solar system.

A week after the announcements by the two teams, a French team announced that it had directly imaged a planet.

Ann-Marie Lagrange of the University of Grenoble led a team that used the Very Large Telescope operated by the European Southern Observatory in Chile. The astronomers found the planet orbiting Beta Pictoris, a star sixty-three light years away.

The planet has not been seen long enough for astronomers to know its orbital period. But the researchers believe they have confirmed its planetary nature. They believe it is about eight times the mass of Jupiter.

Дата добавления: 2015-11-16