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. Because very large planets orbiting close to their stars are easier to spot with both methods, our haul of alien worlds is overloaded with these bloated giants.
For comparison, Jupiter contains enough mass to make Earths. The green triangles indicate planets in our solar system. At lower masses, notice that as the mass of these hypothetical planets increases, the radius also increases. That makes sense—if you were building a model of a planet out of clay, your toy planet would increase in size as you added more clay.
This occurs because increasing the mass also increases the gravity of the planet, so that compressible materials even rock is compressible will become more tightly packed, shrinking the size of the more massive planet. In reality, planets are not pure compositions like the hypothetical water or iron planet. Earth is composed of a solid iron core, an outer liquid-iron core, a rocky mantle and crust, and a relatively thin atmospheric layer.
Exoplanets are similarly likely to be differentiated into compositional layers. The theoretical lines in Figure 4 are simply guides that suggest a range of possible compositions.
Astronomers who work on the complex modeling of the interiors of rocky planets make the simplifying assumption that the planet consists of two or three layers. This is not perfect, but it is a reasonable approximation and another good example of how science works. Often, the first step in understanding something new is to narrow down the range of possibilities. This sets the stage for refining and deepening our knowledge. Notice that these planets fall between the models for a pure iron and a pure rock planet, consistent with what we would expect for the known mixed-chemical composition of Venus and Earth.
In the case of gaseous planets, the situation is more complex. Hydrogen is the lightest element in the periodic table, yet many of the detected exoplanets in Figure 4 with masses greater than M Earth have radii that suggest they are lower in density than a pure hydrogen planet.
Hydrogen is the lightest element, so what is happening here? Why do some gas giant planets have inflated radii that are larger than the fictitious pure hydrogen planet? Many of these planets reside in short-period orbits close to the host star where they intercept a significant amount of radiated energy.
If this energy is trapped deep in the planet atmosphere, it can cause the planet to expand. Planets that orbit close to their host stars in slightly eccentric orbits have another source of energy: the star will raise tides in these planets that tend to circularize the orbits. This process also results in tidal dissipation of energy that can inflate the atmosphere. 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 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.
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. This includes planets that have been confirmed or validated.
Note that some confirmed planets were never designated as candidates.
0コメント