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Review unit 3

Fluency Practice

review reading 5: Changes in the Solar System

Page 167

Changes in Our Solar System

It’s reassuring to imagine that our solar system remains constant and unchanging. However, there has, in fact, been countless changes in our solar system during its 4.6 billion year history, some of them very dramatic.

It’s only relatively recently that scientists have understood why and how our solar system is changing.

At the heart of our solar system is its most enormous body − the sun − with the planets held into orbit by its powerful grasp. Scientists believe that the sun is about halfway through its long life.

At its birth, it shone with about only 40 percent of its current strength. As the sun gradually increased in power, it had a huge impact on the planets close to it. Only Mercury has scarcely changed, since it is the nearest planet to the sun and hence subject to its constant heat from the very beginning.

The second planet from the sun is Venus. Beneath its constant cover of clouds is an atmosphere of poisonous elements. With temperatures of 460 degree Celsius, the heat is intense.

Air pressure is 90 times that of Earth. These have all acted as severe impediments to life on the planet. However, scientists now think that it might not always have been that way.

Venus might once have been covered in oceans, and may even have supported life.

As the young son surged in strength, it could have heeded Venus up, causing more and more water vapor to be released into the atmosphere. This could have accelerated the warming process through the “greenhouse effect.”

The greenhouse effect can warm up a planet in the same way that the glass roof and walls of a greenhouse make the inside warmer than the outside. Water vapor and other gases act as windows of glass around the planet, causing it to heat up.

According to this theory, the heat had caused all the water on Venus to disappear.

Earth, the third planet from the sun, has also undergone changes over the course of the life of the solar system. Up until 650 million years ago, there were long periods of time when the water on the surface of the Earth was frozen into a sheet or ice, with few openings to the oceans below.

At other times, because of the placement of the continents, there was almost no ice, not even at the north or south poles.

As the sun continues to get hotter over the long term, the Earth will continue to heat up as well.

As temperatures rise, more water vapor will be released into the atmosphere. This will create a more potent greenhouse effect that will make our home planet highly vulnerable.

Its effects will be catastrophic. In about 500 million years, scientists expect temperatures to be so high that Earth will follow the same path as Venus. No humans will be able to reside in such a place.

Mars, the fourth planet from the sun, is naturally cooler than Earth. Night time temperatures drop to well below 100 degrees Celsius. Robots sent to Mars have sent back images that suggest there could be water on Mars.

Some scientists believe that there were once oceans on Mars. They think that Mars was once warmed by the greenhouse effect, thanks to gases from its volcanoes.

Scientists have suggested releasing greenhouse gases into the atmosphere of Mars in order to warm it up. Some have estimated that such a transformation of Mars could be achieved in just several hundred years.

Because of the great distances involved, we know less about the remaining planets in our solar system: Jupiter, Saturn, Uranus, and Neptune.

Various space probes have been deployed to these distant planets, which have sent back incredible images that have opened scientists’ eyes to some new facts.

For example, when the probe Voyager II encounter Jupiter’s moon lo, it sent back images of seven active volcanoes. These were the first active volcanoes found anywhere other than on Earth.

An additional ring was discovered around Saturn, and a new ring was discovered around the planet Uranus.

At least one new moon was discovered orbiting Saturn as well. Schoolchildren have long been taught that Pluto, discovered in 1930, was the ninth and final planet of the solar system.

In 2007, scientists decided to relabel Pluto a “dwarf planet,” since it was discovered that Pluto is actually much smaller than previously thought.

Other objects that are Pluto’s size have never been called planets. Additionally, Pluto’s strange orbit differs greatly from that of the other eight planets.

It seems that physical changes to our solar system take place gradually, over millions of years. However, in the realm of human perception, we have seen volcanoes on Io and a moon of Saturn “appear” and watched a planet “disappear” in our own lifetime.

This is not only given us new insight into our “big home” but confirms that human beings will still see many changes to come.