Exoplanet
Introduction
An exoplanet, also known as an extrasolar planet, is a planet that orbits a star outside the solar system. The first scientific detection of an exoplanet was in 1988. However, the first confirmed detection came in 1992, with the discovery of several terrestrial-mass planets orbiting the pulsar PSR B1257+12. The first confirmation of an exoplanet orbiting a main-sequence star was made in 1995, when a giant planet was found in a four-day orbit around the nearby star 51 Pegasi.
Detection and Discovery
The study of exoplanets has been brought to the fore with the help of various spectroscopic methods. The radial velocity method, also known as Doppler spectroscopy, is the most effective method for locating extrasolar planets with existing technology. The main disadvantage of the radial velocity method is that it can only estimate a planet's minimum mass (Template:M sin i). The radial-velocity method measures variations in the velocity of the central star, due to the changing direction of the gravitational pull from an (unseen) exoplanet as it orbits the star.
Characteristics of Exoplanets
Exoplanets are extremely diverse in their characteristics, with a wide range of masses, sizes, and orbits. They range from gas giants larger than Jupiter to small, rocky planets about the size of Earth or the Moon. Some exoplanets orbit extremely close to their stars, with periods of only a few hours, while others may be located at a distance greater than that of Neptune from the Sun.
Habitability
The potential habitability of exoplanets is a complex issue. While the discovery of Earth-like planets in the habitable zone has sparked interest, the habitability of these planets depends on a wide range of factors. These include the planet's distance from its star, its size, its geological activity, its atmosphere, and the nature of its star.
Future of Exoplanet Research
The future of exoplanet research is promising, with new technologies and missions planned for the coming decades. The James Webb Space Telescope, set to launch in 2021, will be capable of observing exoplanets in unprecedented detail. Other planned missions, such as the PLATO spacecraft, aim to detect and study Earth-like planets around Sun-like stars.