Abstract
The family of planets grew for the first time in written history when, in 1781, William Herschel discovered a new celestial body which Anders Lexell subsequently proved to be a planet. In the next century Neptune was found, as well as many minor planets. With the discovery of new planets in our Solar System, the notion of planets around other stars was also more acceptable. The search for such extrasolar planetary systems is now a part of astronomy. In spite of the difficult task requiring special observational methods, thousands of so-called exoplanets have been discovered.
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Notes
- 1.
Some early claims involved the binary star 70 Ophiuchi. In 1855, Capt. W. S. Jacob at the East India Company’s Madras Observatory reported that anomalies in the motion of the pair around each other made a planet “highly probable” in this system. In the 1890s, Thomas See (US Naval Observatory) stated that the orbital anomalies proved the presence of a dark body with a 36-year period around one of the stars in 70 Ophiuchi. These are now viewed as erroneous detections.
- 2.
Planets around pulsars probably suffered much from the supernova. They may represent the surviving cores of Jupiter-like planets. Stars that explode as supernovae do so quickly compared to the time required for life to evolve on Earth. They leave behind a neutron star which continues to threaten life on any nearby planet. All three planets around the mentioned pulsar seem to share roughly the same orbit plane (like the Solar System), but the orbits are smaller than Mercury’s orbit.
- 3.
Based on resolution alone, a planet on an Earth-like orbit could be detected from 18 pc. Planets close to the star will be hidden in its glare. Planets further out from the host star are easier to see, especially if they are big and reflect well light.
- 4.
Eclipses provide another important bit of information. If one compares the spectrum of the star during the eclipse to a spectrum obtained outside the eclipse one can see two differences. First, there is a small decrease in the total flux. In addition, if absorption of light takes place in the planet’s atmosphere , then some specific lines can have extra absorption. The effect is minuscule, but when detected, will tell about the scale height, temperature, and density in the atmosphere of the planet. About 30 atmospheres have been detected. There is no clear indication for the presence of life yet as most of these planets are gas giants. Several of them have signs water though.
- 5.
An accretion disk is a disk a gas which is slowly creeping toward the center of the disk, in a stable and controlled manner. The accretion rate depends on the viscous properties of the gas: the more viscosity, the faster is inward flow of gas.
- 6.
Tidal locking means that the planet’s rotational period is equal to its orbital period around the star. For example, our Moon is tidally locked to the Earth, and therefore it always portrays the same side to us.
- 7.
Thermal equilibrium means that there is no net flow of energy from the system, i.e., its temperature is not rising or decreasing.
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Teerikorpi, P., Valtonen, M., Lehto, K., Lehto, H., Byrd, G., Chernin, A. (2019). Extrasolar Planetary Systems and Life in Other Solar Systems. In: The Evolving Universe and the Origin of Life. Springer, Cham. https://doi.org/10.1007/978-3-030-17921-2_32
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DOI: https://doi.org/10.1007/978-3-030-17921-2_32
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