Even the Voyager probes, which are flying out of our solar system at tens of thousands of miles per hour, would take around 75, years to get there, according to NASA. Scientists detect exoplanets using a variety of methods.
Many are found using the transit method, in which scientists look at a distant star and measure how much it dims when an exoplanet passes in front of it. Of particular interest are exoplanets that exist within the habitable zone of their stars—an area not too hot and not too cold for liquid water to exist on their surface.
Such planets could be potentially habitable and play a key part in the ongoing search for life elsewhere in the universe. Some exoplanets, such as Kb , which is located around light-years away, have been identified as more likely to be habitable than others. Our solar system has eight major planets, half a dozen dwarf planets, and millions of smaller objects orbiting the Sun. The evidence we have of planetary systems in formation also suggest that they are likely to produce multi-planet systems.
The first planetary system was found around the star Upsilon Andromedae in using the Doppler method, and many others have been found since then about as of If the planets in other systems do not have orbits in the same plane, we are unlikely to see multiple transiting objects. Also, as we have noted before, Kepler was sensitive only to planets with orbital periods less than about 4 years.
What we expect from Kepler data, then, is evidence of coplanar planetary systems confined to what would be the realm of the terrestrial planets in our solar system. In fact, today we have data on about such exoplanet systems. Many have only two known planets, but a few have as many as five. For the most part, these are very compact systems with most of their planets closer to their star than Mercury is to the Sun.
The figure below shows one of the largest exoplanet systems: that of the star called Kepler Figure 5. Our solar system is shown to the same scale, for comparison. All but one of the planets in the K system are larger than Earth. These are super-Earths, and one of them 62d is in the size range of a mini-Neptune, where it is likely to be largely gaseous.
The smallest planet in this system is about the size of Mars. The three inner planets orbit very close to their star, and only the outer two have orbits larger than Mercury in our system. The Kepler habitable zone is much smaller than that of the Sun because the star is intrinsically fainter.
With closely spaced systems like this, the planets can interact gravitationally with each other. The result is that the observed transits occur a few minutes earlier or later than would be predicted from simple orbits.
These gravitational interactions have allowed the Kepler scientists to calculate masses for the planets, providing another way to learn about exoplanets. Kepler has discovered some interesting and unusual planetary systems. For example, most astronomers expected planets to be limited to single stars. But we have found planets orbiting close double stars, so that the planet would see two suns in its sky, like those of the fictional planet Tatooine in the Star Wars films.
At the opposite extreme, planets can orbit one star of a wide, double-star system without major interference from the second star. Although the Kepler mission is finding thousands of new exoplanets, these are limited to orbital periods of less than days and sizes larger than Mars. Still, we can use the Kepler discoveries to extrapolate the distribution of planets in our Galaxy.
For more information about building your own custom search queries, see the Pre-filtering Tables help document. For a list of published, refereed papers that derive planet occurrence rates, please see our Planet Occurrence Rate Papers page.
This list is not exhaustive; to suggest a paper, please submit a Helpdesk ticket. Not all of these planets were detected or discovered by Kepler. Astronomers call them exoplanets , and the number they have found is in the thousands and rising fast. To detect them, astronomers use two main methods.
The first is called transit photometry and involves pointing a telescope at a star and looking for the regular, slight dimming in its light caused by a planet orbiting in front of it. The other is the radial velocity technique. This relies on the gravitational tug of an exoplanet making its host star wobble slightly. This wobble makes the wavelength of light we see coming from the star vary in a telltale pattern.
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