Due to the fact that the first exoplanet was found a era ago, astronomers have learned to anticipate the unexpected. For over twenty years, a extraordinary treasure trove of bizarre Wonder Worlds have been discovered. Indeed, some of these very alien planets, in orbit around stars beyond our Sun, are so weird that astronomers never thought something like them could actually exist in the Cosmos--that is, until they have been discovered.

Strange far away worlds aside, the Holy Grail of planet-hunting astronomers has long been to discover worlds more like home. In January 2020, astronomers declared the discovery of just such a long-sought world--the first to be found by NASA's Transiting Exoplanet Survey Satellite (TESS). The far away Earth-size planet is conveniently positioned in its star's habitable area

The habitable region of a star is that "Goldilocks" range of distances where weather conditions are not too hot, not too cold, however "just right" for liquid water to pool on the surface. Where liquid water exists, life as we know it may also exist. The Earth-like world, named TOI-700 d, orbits a small red dwarf star dubbed TOI-700, that is only 101.4 light-years away in the Dorado constellation. That star is the brightest known stellar host of a transiting liveable zone, Earth-size world. The acronym "TOI" refers to stars and exoplanets studied by TESS.

The red dwarf star, TOI-700, is of spectral class M, and it is 40% the mass, 40% the radius, and 50% of the temperature of our Sun. The bright star also shows low ranges of stellar activity. Red dwarf stars are the smallest--as well as the most abundant--true nuclear-fusing stars in our Milky Way Galaxy. Because they are so small and cool, they can "live" for trillions of years. In contrast, our quite bigger Sun can only "live" for 10 billion years.

Very huge stars can only "live" for millions of years due to the fact their extreme heat causes them to burn their supply of nuclear gas more hastily than their smaller stellar kin. The bigger the star, the shorter its "life." The first scientific discovery of an exoplanet was made in 1988. After that, the first validated detection was made in 1992, with the discovery of various terrestrial-mass planets in orbit around the pulsar PSR B1257+12. A pulsar is the balance of a big star that has ended its "life" in a core-collapse (Type II) supernova blast. Pulsars are young neutron stars that are born spinning swiftly with a regularity often likened to a lighthouse beacon on Earth.

They are city-sized objects that are so dense that one teaspoon full of their material can weigh as much as a thundering herd of wild horses. In effect, these infant neutron stars are one massive atomic nucleus. A pulsar was one of the final stellar objects that astronomers thought would play host to a family of planets--that is, until they have been discovered. The pulsar planets were the first of a lengthy series of oddball exoplanet discoveries. They are hostile small worlds that are mercilessly showered with their parent-pulsar's lethal beams of radiation. The first affirmation of an exoplanet, orbiting a "normal" hydrogen-burning star like our Sun, was made in 1995.

This new discovery additionally proved to be a stunning oddball--a massive planet circling quickly and close to its searing-hot stellar parent. The planet, 51 Pegasi b, is in a roasting 4-day orbit around its star, 51 Pegasi. As it turned out, this massive planetary "roaster" was the first of a new and unforeseen class of exoplanet--hot Jupiters--to be discovered. Since 51 Peg b's discovery, many others of its weird sort have been located in orbit around stars apart from our Sun. Some exoplanets have been imaged directly with the aid of telescopes.

However, the great majority have been found by means of indirect methods, such as the transit method, whereby a planet is discovered floating in front of the glaring face of its parent-star. Another indirect method--the radial velocity method--depends on the detection of a tiny wobble that an orbiting planet induces on its star.

Both the transit method and the radial velocity method assist the discovery of huge planets that are located near to their searing-hot, fiery parent-star--rather than smaller Earth-like worlds that circle their star at a greater--and more comfortable--distance. As of January 1, 2020, there are 4,160 affirmed exoplanets inhabiting 3,090 systems, with 676 structures hosting more than one solitary planet.