Word: orbital
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Dates: during 1990-1999
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...suddenly, everything has changed. Not only do these still unnamed planets triple the number of worlds known to orbit stars like the sun--the only other example having been found just four months ago--but they have an even more profound significance. Both of them are temperate enough to allow water to exist in liquid form. And whatever else is necessary for life as we know it, say biologists, liquid water is an absolute prerequisite...
...orbiting world's gravity should, for example, tug faintly on the star that is its sun, pulling it first this way, then that. If the plane of the planet's orbit is such that a star is being pulled first toward and then away from the Earth, the motion will cause light waves coming from the star to be squeezed together, then stretched apart--making the light look first a little bit bluer than it really is, then a little bit redder, then bluer again, and so on. These subtle color changes--examples of the so-called Doppler shift...
...these planets, astronomers must now revise their theories to fit the new facts. To begin with, theorists have to scramble to explain how the 51 Pegasi planet could have formed and survived intact so close to its parent star. The planet around 70 Virginis is also problematic: its orbit is egg-shaped rather than circular, which suggests to some astronomers that it formed more like a star than like a planet. Indeed, many experts think it is technically a brown dwarf--a star that never got big enough to ignite--rather than a planet. Only the third object matches what...
...summer's tours took them in an even wider orbit, west in their van. "We were staying in people's houses and $30 a night motels, cramming six people into a room...
That won't be easy. The newly discovered planets are much bigger than Earth, yet it is almost impossible to learn very much about them. The stars they orbit--70 Virginis in the constellation Virgo and 47 Ursae Majoris in the Great Bear--are each about 35 light-years away. The speediest space probe would take millions of years to reach them; even a radio signal, the fastest known thing in the universe, would need 35 years to get there, and it would take another 35 for any aliens, should they exist, to answer. The planets are so dim that...