The sky is a large place, and though it has been carefully examined for centuries, new features still turn up. Last March it was the rule of Uranus(天王星), and last week astronomers announced what may turn out to be a new planet, though a very small one, in the solar system.
The object was first sighted last month by Charles Kowal, an astronomer at the Hale Observatories in Pasadena, Calif. Mr Kowal observed a faint trail of light on photographic plates, indicating that something was moving in relation to the background of stars. Other observers have confirmed the discovery.
The "mini-planet", identified for the time being as "Object-Kowal", appears to be about 1. 5 billion miles away, between the orbit of Saturn(土星) and Uranus, and its diameter(直径) has been estimated at between 100 and 400 miles. Its orbit has not been determined yet, but if the orbit proves to be roughly circular, like that of the major planets, the new object would probably take 66 to 70 years to make a circuit of the sun.
Some astronomers have speculated that Mr Kowal's discovery may be the first indication of an asteroid(小行星) belt beyond Saturn.
A new study suggests that dark markings on the planet Mars represent sand—not water. The research in 2015 suggested that lines on some Martian hills were evidence of water. Yet American scientists now say these lines appear more like dry flows of sand. If water is present, it is likely to be a small amount. Water in liquid form would be necessary for microbial(微生物的) life.
NASA, the American space agency, said more research is needed. Michael Meyer is the lead scientist for NASA's Mars exploration programme. He noted that the latest study does not reject the presence of water. But he admitted," It just may not be as exciting as the idea of rivers going down the sides of cliffs(悬崖). "
The new findings come from a team led by Colin Dundas of the United States Geological Survey. His team measured 151 of these lines in 10 areas. Most of the lines end with slopes between 28 degrees and 35 degrees. These measurements are similar to active sand dunes(沙丘) on both Mars and Earth. A small covering of dust that moves and sometimes becomes lighter might help explain the markings. They usually appear in the Martian summer time, and then disappear until the next year. If these lines are dry, this suggests that recent Mars has not had large volumes of liquid water. Dundas and his research team say that many questions remain.
"I still think that Mars has a great potential for having had life early in its history," Meyer said." As long as that's true, we also have a reasonable possibility of life still being on Mars. It just happens to be cryptic or well hidden."
NASA currently has no robotic vehicle—either on Mars or in development—with the ability to climb steep slopes. The lack of such equipment has engineers coming up with ideas like Martian helicopters or planes without pilots.
Fancy your own satellite? Arizona State University is working towards making this a reality with its SunCube FemtoSat project. Smaller than a standard CubeSat, the low-cost student-designed spacecraft is aimed at providing greater access to space for scientists and hobbyists alike.
Assistant professor Jekan Thanga and a team of students have been developing the SunCube FemtoSat for the past two years. The small 3×3×3cm cube weighs just 35g and a longer (3×3×9cm, 100g) model has also been designed, which includes storage space.
Each SunCube FemtoSat has its own communication, data collection and propulsion (推进) systems and is powered by solar panels. It is made of off-the-shelf parts that are available in shops, and the energy-efficient solar panels are cut from scrap (碎片), which makes it save energy, sold at a discount by manufacturers. "With a spacecraft of this size, any university can do it," says Thanga. "That's part of our major goal—space discovery for everybody. "
The team says that while launching your own satellite would usually cost between US $ 60, 000-70, 000 per kilo, it would only cost $ 1, 000 to send a SunCube FemtoSat to the International Space Station, and $ 3, 000 to send it into low earth orbit. Leaving the earth's gravity would cost an estimated $ 27, 000.
The FemtoSat would be packed with a "jack in the box" style system that matches standard CubeSat sizes (around 10 cubic cm), simplifying the process of getting the tiny satellite into orbit. NASA has sent 30 CubeSats into space over the last years, with another 50 awaiting launch.
Thanga and his staff view the FemtoSat as a starting point for scientists and students, and even hope the device could be bought on the website like Amazon one day. Thanga imagines developing four main applications for the device, including hands-on testing experiences for students, and artificial gravity experiments. In addition, groups of SunCube FemtoSats could eventually be able to do the job of larger spacecraft at a vastly discounted cost.
Almost every day, we discuss the topic of health. (stay) healthy, we should eat well, work out regularly and have a healthy lifestyle.
Eat different kinds of food, (especial) fruit and vegetables. We all know that eating fruit and vegetables keeps us healthy, many of us only eat our favorite food. Remember that we can only get our body needs by eating a wide variety of food. When you are eating, notice how your body feels. When your stomach is full, stop (eat). If you always eat too much, most probably you 6. (become) out of shape.
Drink water and milk often. Everyone (know) that water is important to us. Besides water, kids also need plenty of calcium, and milk is rich in calcium. If you are 9 years old or older, you should drink least three cups of milk every day.
It is also of great (important) to lead a healthy lifestyle. Limit the amount of time you spend watching TV and playing computer games. Spend more time doing sports, and you'll be healthy and (energy).
