3 . The universe is expanding faster than it used to, meaning it’s about a billion years younger than we thought, a new study by a Nobel Prize winner says.

At issue is a number called the Hubble constant, a calculation for how fast the universe is expanding. Some scientists call it the most important number in cosmology, the study of the origin and development of the universe.

Using NASAS Hubble Space Telescope, lohns Hopkings University astronomer Adam Riess concluded in this week’s Astrophysical Journal that the figure is 9% higher than the previous calculation, which was based on studying leftovers from the Big Bang.

The trouble is， Riess and others think both calculations are correct. Confused? That’s OK, so are the experts. They find the conflict so confusing that they are talking about coming up with “new physics”, incorporating (合作) perhaps some yet-to-be-discovered particle or other cosmic (宇宙) “fudge factors” like dark energy or dark matter

“Its looking more and more like were going to need something new to explain this,” said Reiss, who won the 2011 Nobel in physics.

NASA astrophysicist John Mather, another Nobel winner, said this leaves two obvious options, “1. We’re making mistakes we can’t find yet. 2. Nature has something we can’t find yet.”

Even with the discovery, life continues on Earth the way it always has. But to astrophysicists trying to get a handle on our place in this expanding universe, this is a cosmic concern. In fact, the universe is really mystical (神秘的). Scientists have done lots of study about it but there is still much they haven’t discovered.

4 . A study confirmed that the cracks found on Mars’s surface last year by the Curiosity Rover are evidence of ancient lakes that likely dried up about 3.5 billion years ago. The new study provides further evidence of what the climate on the Red Planet may have been like in its ancient past.

The study, published online in Geology, proved that cracks on Mars’s surface previously photographed by Curiosity are dry mud cracks which could have only been formed when wet ground was exposed to the air. This conclusion was based on an analysis of a single area of rock known as “Old Soaker.”

Researchers used the Curiosity rover and information from its many tools including the Mars Hand Lens Imager, ChemCam Laser-Induced Breakdown Spectrometer (LIBS) and the Alpha Particle X-Ray Spectrometer (APXS) to study both the physical appearance and the chemistry of the rock, which is described as no bigger than a coffee table.

The analysis showed that cracks on the rocks were formed by exposure to air, rather than heat or the flow of water. In addition, the shape of the cracks suggests it experienced a single drying event on the planet, rather than getting wet and drying over repeatedly. The position of the cracks, closer to the center of the ancient lake rather than alongside it, also suggests that the lake levels changed often, rising and falling over time.

“The mud cracks are exciting because they help us to understand this ancient lake system,” lead study author Nathaniel Stein, a geologist at the California Institute of Technology in Pasadena, said, referring to the ancient lake system on the planet.

Scientists have known of the existence of ancient water on Mars for years. A 2015 NASA study that measured water in Mars’s atmosphere suggested that ancient oceans may once have had more water than our own Arctic Ocean. However, because the planet has less gravity and a thinner atmosphere than Earth, this water evaporated(蒸发) into space over the course of several billion years.

5 . How big is space? That is a question man has been asking since the beginning of time. When your grandparents were in school, it was ________that the universe was very________perhaps only 5, 000 light years________. 500 years ago people considered that the universe was only a little bit________than the earth. In modern times with the________of technology we are finally starting to________the immense（无边的）size of the universe, and it is much bigger than anyone________have ever imagined.

Scientists cannot stretch（伸展）a measuring tape from the earth to a nearby star, so________do they know how far away they are? Scientists use something________parallax（视差）. Parallax means________that they look at how much the stars move in the sky________throughout the year as the earth circles the sun. This is not something________to you. In fact if you stretch out your hand in front of you and________your thumb, while________one eye, and then the other, your thumb will________to move back and forth. Stars do the________thing, but our eyes are too close to see the________. However, if we take a picture while on one side of the earth's orbit, and then take another when we get to the________side of the orbit, then we have a large enough________that we can see the stars' parallax, and________how far away they really are.

6 . Many scientists today are convinced that life exists elsewhere in the universe---life probably much like that on our own planet. They reason in the following way.

As far as astronomers can determine, the entire universe is built of the same matter. They have no reason to doubt that matter obeys the same laws in every part of the universe. Therefore, it is reasonable to guess that other stars, with their own planets, were born in the same way as our own solar system. What we know of life on earth suggests that life will arise wherever the proper conditions exist.

Life requires the right amount and kind of atmosphere. This eliminates(除去) all those planets in the universe that are not about the same size and weight as the earth. A smaller planet would lose its atmosphere; a larger one would hold too much of it.

Life also requires a steady supply of heat and light. This eliminates double stars, or stars that flare up suddenly. Only single stars that are steady sources of heat and light like our sun would qualify.

Finally, life could evolve(进化) only if the planet is just the right distance from its sun. With a weaker sun than our own, the planet would have to be closer to it. With a stronger sun, it would have to be farther away.

If we suppose that every star in the universe has a family of planets, then how many planets might support life? First, eliminate those stars that are not like our sun. Next eliminate most of their planets; they are either too far from or too close to their suns. Then eliminate all those planets which are not the same size and weight as the earth. Finally, remember that the proper conditions do not necessarily mean that life actually does exist on a planet. It may not have begun yet, or it may have already died out.

This process of elimination seems to leave very few planets on which earthlike life might be found. However, even if life could exist on only one planet in a million, there are so many billions of planets that this would still leave a vast number on which life could exist.

8 . In the first days of space exploration, one concern was the possibility that astronauts or spacecraft might be hit by meteoroids. Scientists calculated that this possibility was extremely small because meteoroids are rare. Astronauts and spacecraft, on the other hand, would almost certainly encounter space debris, which poses a greater threat.

However, in the 60 years since the beginning of space exploration, large quantities of human-made orbital debris have accumulated. Much of the debris consists of satellites that have stopped functioning or rocket booster sections that separated from the main spacecraft. Some of the debris consists of items lost by astronauts. Still more of the debris is the result of collisions. such as when one satellite collides with another or with a large piece of debris.

NASA estimates there are millions of debris particles that are too small to be tracked. These circle Earth at a speed of up to 17, 500 miles per hour, making even the smallest particles dangerous. One scientist calculated that a chip of paint hitting the window of a spacecraft at orbital speeds will hit with the same amount of force as a bowling ball traveling at 60 mph. Such an impact occurred on the space shuttle Challenger's second flight.

Larger objects are even more dangerous, but they can be monitored and avoided. Many satellites have the ability to adjust their course slightly and can be remotely directed to avoid collisions with larger objects that would damage or destroy the satellites. NASA and the European Space Agency (ESA) have departments dedicated to cataloging, modeling, and predicting the movements of space debris.

To avoid adding to the amount of debris, obsolete satellites may need to be able to take themselves out of orbit as their usefulness comes to an end. Until a way to remove these remains is implemented. however. those 500, 000 pieces of large fragments, along with the millions of smaller pieces, will continue to orbit Earth.