How do the two poles of Mars differ?
Recent discoveries made by the Mars Global Surveyor spacecraft show that the two poles of Mars are very different, indicating that the climate may have been different at the two poles for quite a long time. The south pole has a permanent cap of frozen carbon dioxide mixed with layers of other material. Since the carbon dioxide ice evaporates directly into the thin Martian air, rather than melting the way water ice does on Earth, the landscape shows features unlike anything on Earth. There are flat-bottomed circular depressions and round-walled plateaus, and complex fingerprint-like whorls of grooves. The north pole's ice cap, while about the same size, is simply a layer on top of the ground, with small pits probably caused by evaporation of the ice. Its structure seems simpler, and it may be composed mainly of water ice rather than frozen carbon dioxide. Why are the two poles of Mars so different? Scientists hope to discover the answer as exploration of the red planet continues.
How much junk is in orbit around the Earth?
Ever since we started going into space, we have been leaving behind bits of orbiting debris. Today, there are known to be about 9,000 pieces of orbiting junk larger than ten centimeters (4"), and it is estimated that there are more than 100,000 pieces between 1 cm (3/8") and 10 cm. There are probably tens of millions of particles smaller than one centimeter. Debris impacts are a serious problem for spacecraft in Earth orbit. With an average collision speed of around ten kilometers per second (22,000 mph), even a tiny particle can cause great damage. Current practices are aimed at limiting the amount of new debris, but existing space junk will remain in orbit for many years. Modern spacecraft like the International Space Station are heavily shielded against debris impacts.
How do we know the universe is expanding?
Astronomers see countless galaxies for billions of light years in every direction. The farther away a galaxy is, the faster it moves away from us. The whole universe is expanding. How do we know? When an object moves away from an observer, the light from that object changes color, similar to the way a train whistle changes pitch if the train is moving away. This "Doppler shift" causes the light of receding galaxies to stretch out, becoming more reddish. Measuring this "red shift," astronomers can tell how fast each galaxy is receding. If the universe is currently expanding, it makes sense that at one time it was much smaller. The "Big Bang" theory, which describes how the universe might have started in a stupendous explosion, is one possible explanation of how the universe began.
What asteroid is shaped like a bone?
An asteroid called 216 Kleopatra that orbits between Mars and Jupiter has been imaged by radar, creating a detailed model of its shape. It is shaped like a giant dog bone as big as New Jersey. Because of its optical color and because it reflects radar waves very well, astronomers believe that 216 Kleopatra is made mostly out of metals like nickel or iron. Large parts of it are composed of loose, metal-rich rubble, although there may be larger solid chunks in the center. How did 216 Kleopatra get to be so strangely shaped? It may have been sculpted by one or more tremendous collisions billions of years ago. With two lobes connected by a thin neck, 216 Kleopatra is the most unusually shaped object found in the Solar System so far.
What is the "green flash" of the sun?
You may have heard stories about the "green flash" that can sometimes be seen as the Sun sets, if conditions are just right. Is it real, or just a myth? As the Sun descends toward the horizon, its color changes from yellow- white at noon to deep shades of orange and red, because the blue and green colors are scattered by the air. But there's still some green light in the mixture, and that is the key to the green flash. If the air is very clear, there's a point when the topmost rays of the Sun's light can shine brilliant emerald green. This green flash, which lasts only a few seconds, happens when the Sun's light is split into its component colors, the same way that a prism creates a rainbow. The shortest wavelengths (green at sunset) appear at the top of the Sun just as it drops below the horizon.
What telescopes float on oil?
The Gemini North and Gemini South astronomical telescopes float on oil bearings so turning and aiming are very smooth and only require a tiny force. Even though each of these monster telescopes weighs 377 tons, a single person can turn it if the drive motors are not engaged. Gemini North (on Hawaii's Mauna Kea volcano) and Gemini South (on Chile's Cerro Pachon) are among the most advanced telescopes in the world, in some ways even outperforming the orbiting Hubble Telescope. Each has an 8.1-meter mirror (more than 26 feet) and is optimized for infrared observations, which will allow astronomers to observe very distant galaxies and penetrate clouds of dust in our own galaxy.
What robots will fly with the astronauts?
Astronauts on missions in the Space Shuttle and the International Space Station will soon be joined by softball-size flying robots called Personal Satellite Assistants (PSAs). These spherical machines, now being designed in a NASA project, will move around in the weightless crew cabin under their own air-jet propulsion. Each PSA will have a microphone, a camera, many sensors, and wireless data communications. A small flat-screen display will allow the PSA to serve as a self-positioning video conferencing tool, and it will be able to enter small spaces and send back a video feed of what it sees, hears, and senses. The PSA is the first generation of a whole line of robotic assistants for space workers. We may also see "outdoor" construction robots to build large structures in the weightless vacuum of orbit.
What are the oldest stars in the galaxy?
Our galaxy's oldest stars are also the smallest and the most abundant, numbering 70% of the galaxy's stars. They are red dwarfs, dim stars that are difficult to even see. Some of these stars formed more than ten billion years ago, and many of them are part of ancient globular clusters, spherical collections of stars that are found in a large halo around the galaxy. Red dwarfs live a long time because they burn slowly. Without a large mass of gas, they are not able to create a high temperature and pressure in their cores where the fusion reactions take place, so the hydrogen fuses very slowly. Objects that gather even less mass than a red dwarf do not generate enough internal pressure and heat to begin fusion. Unable to "light up," they become brown dwarfs, destined to fade into invisibility and become cold, dark balls of frozen gas.
What are the most common objects in the Solar System?
The most abundant, substantial objects in the Solar System are the comets of the Oort Cloud, a roughly spherical shell that begins at three times the distance of Pluto's orbit and extends about halfway to the nearest stars. According to current estimates, there are about six trillion comets in the Oort Cloud. From the distance of the Oort cloud, the sun is a bright star, about as bright as Venus looks from Earth. The temperature there is only four degrees Kelvin, which is about as cold as gets in the natural universe. Once in a while, an Oort comet falls into the inner solar system. These rare visitors are interesting to science because they represent a sample of conditions as they were in the earliest stages of formation of the solar system.
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