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28th March 2022

5,000th exoplanet is confirmed

The number of known planets beyond our Solar System has crossed the 5,000 milestone, following the addition of 65 newly confirmed worlds to NASA's Exoplanet Archive.



The first suspected detection of an exoplanet occurred in 1988. Researchers announced the first confirmation of detection in 1992, with the discovery of three terrestrial-mass planets orbiting a pulsar about 2,500 light years from Earth. Confirmation of an exoplanet in a main sequence star system followed a few years later in 1995, with a gas giant found orbiting the nearby Sun-like star 51 Pegasi.

Over the next decade and a half, new methods aided the discovery of exoplanets, as their numbers gradually increased. Then in 2009, NASA launched the Kepler Space Telescope, a revolutionary tool for monitoring 150,000 stars and their changes in brightness. During its mission lifetime, Kepler found many Earth-sized exoplanets in or near habitable zones, while characterising other planet types and providing estimates for the galaxy as a whole.

NASA retired the Kepler Space Telescope in 2018. But astronomers have continued to pore over the data it generated, as well as discovering new planets through subsequent observatories like the Transiting Exoplanet Survey Satellite (TESS) and ground-based telescopes.

Last week, NASA announced that the cumulative total number of confirmed exoplanets has passed 5,000. They are divided into a variety of types – some that are similar to the planets in our Solar System, others vastly different and unique. Among them are a mysterious category known as "super-Earths" because they are larger than our home world and possibly rocky. The most common exoplanets appear to be Neptune-like, although this may change in the future as our observational capabilities improve and much larger numbers of exoplanets are spotted, revealing a more accurate picture.


exoplanets future timeline
Credit: NASA/JPL-Caltech


In addition to the more common types, astronomers have found all manner of weird and wonderful planetary systems. WASP-76b, for example, is so hellishly hot that it rains molten iron, blown by winds of 10,000 mph (16,100 km/h). TRAPPIST-1, meanwhile, contains an entire solar system of seven Earth-sized planets, four of which lie within the habitable zone and thus may be suitable for life. Then there is TOI-178, a rare system of six exoplanets, five of which are locked in a complex "chain of resonance".

Even more unusual discoveries have been made. Last year, astronomers led by MIT reported evidence of a giant impact between an Earth-sized exoplanet and a smaller body, which stripped off part of one planet's atmosphere in HD 172555, a system 95 light years from Earth. The first candidate outside the Milky Way has also been reported, based on the eclipsing of a bright X-ray source in the Whirlpool Galaxy.

The 5,000th confirmed exoplanet is K2-367 b (pictured below), a Neptune-like world about one-fifth the size of Jupiter with a mass of 6.4 Earths. Found by the transit method, it orbits a small K-type star every 20.6 days and is believed to have a surface temperature of 450 K (177°C). The system is 577 light years away.

Although a significant milestone, the current tally is of course a drop in the ocean when compared with the estimated 100 billion or more planets in our galaxy. Future telescopes will have much greater capabilities than Kepler, however. This could enable the creation of yet another exponential trend in progress like we see in other areas of science and technology. The PLATO observatory, for example, will scan up to a million stars when operational from 2026-2030. Telescopes by the mid-21st century will be even larger and more powerful, perhaps by orders of magnitude. The majority of exoplanets in our galaxy might be detected and categorised within the next hundred years, with many of these alien worlds directly imaged in exquisite detail.


exoplanets future timeline
Computer-generated image of K2-367 b. Credit: NASA


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