Adapted from Is There Life On Mars?
by Dr. Marc Fries

This is an idea that many people have pondered and speculated about for hundreds of years, and it is one that I have wondered about for most of my own life.
Earth is the only place that we know of where there is life. Many people have studied Mars, and some have even said that they thought they saw signs of life. We now know they were fooled by what they were able to see because we do not have telescopes that are powerful enough. To really confirm the existence of life on Mars, we need a close-up look at the planet!
Robotic spacecraft have given us great views of the planet, providing us with more information about the planet than we ever thought possible. Still, no humans have ever tried to go to Mars, and no human missions to Mars will be tried for years. In fact, the first people on Mars may be your age today. When you are grown, maybe you will watch—or even be one of—the people who make the first trip to Mars!
NASA is working hard to find if there is life on Mars. The United States and other countries have been sending robot spacecraft there for years. Some have orbited Mars, and some have landed. Each mission provides new pieces of information, teaching us more about this interesting planet. One of the greatest things we have learned is that Mars is more like Earth than anywhere else in the solar system. So, it is a good place to look for life, but it is still different from Earth in many ways.
On Earth, a compass points to the North Pole because our whole planet acts like a giant magnet. A planet's magnetic field does more than turn a compass needle—it turns away dangerous small pieces of space radiation. However, Mars does not act this way, as it does not have a magnetic field. It has a lot less air covering it than Earth, so it gets more harmful space radiation, which would not help to support life. Some research confirms the existence of water on Mars. However, there is a lot less than on Earth, and it is so cold there that most of the water is probably not liquid. It is ice! Mars would be a pretty tough place to try to live for years, let alone a day!
In 1976, NASA achieved progress in its exploration of Mars when it landed two ships there. One of these landers worked almost 4 years, while the other lasted more than 6 years. Think of spending that much time studying another world! One of their jobs was to see if there was anything living in the soil. They looked for tiny microscopic things, even bacteria. So far, we have not found any signs of life.
The landers also had cameras, which they used to take pictures of Mars. The pictures were sent back to Earth and showed a variety of things. For one, they showed changing seasons. They also showed close ups of the rocks and dirt. The cameras were not really part of the experiments to search for life, but they did show that there weren't any large creatures moving around! Future landers will dig under the ground to try to find out if there is anything living there.
Where is the best place to look for life? Mars is smaller than Earth, but it is still a very, very big place. So where should scientists aim landers to give them the best chance of finding signs of life? Because all life on Earth depends upon water, the next spacecraft will look for more signs of water. This will help later landers find good places to search for life.
There may not be life on Mars, but it would still be exciting to know if there used to be life there. NASA will be looking for tiny fossils for evidence of the prior existence of life. The fossils might show that there used to be life on Mars but that it just did not last.
Because Mars is inhospitable to people, robots will do a lot of the work on Mars in the collecting of information about the planets and its various properties. Someday, samples from Mars may be brought back to Earth, and they will be studied in the best labs. With proper advances in technology, humans may go to Mars in the future. However, there are many problems that have to be worked out first.
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Select all the correct answers.
Which two sentences best explain the central ideas of the passage?