Three decades after the first discovery of a planet beyond our solar system, astronomers have now confirmed the existence of more than 5,000, bringing closer the prospect of one day discovering life beyond Earth.
The Nasa Exoplanet Archive, an official registry of planetary discoveries that began in 1992, admitted a new batch of 65 this week, taking the tally past the cosmic milestone. Hundreds of billions more are believed to exist in the Milky Way and in galaxies further afield.
“New missions, instruments and detection techniques have proliferated and with them the discoveries of all sorts of alien worlds. This week’s milestone marks 30 years of discovery that shows no sign of ebbing,” announced the Nasa Exoplanet Science Institute (NExSci) at the California Institute of Technology, which maintains the archive.
The first such discovery was in 1992, when the US-based astronomers Aleksander Wolszczan and Dale Frail announced that they had detected two planets in orbit around a type of neutron star known as a pulsar — the spinning corpse of a collapsed star — 2,300 light years from Earth. Their method relied on measuring minute fluctuations in the bursts of radiation emanating from the pulsar, which indicated the presence of planets moving around it.
Their findings opened the floodgates for more discoveries.
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“If you can find planets around a neutron star, planets have to be basically everywhere. The planet production process has to be very robust,” Wolszczan, a professor at Pennsylvania State University, said.
He added: “To my thinking, it is inevitable that we’ll find some kind of life somewhere — most likely of some primitive kind.”
Among the 5,000-plus now identified, 35 per cent are akin to Neptune in size (most of them ice giants but some of them warmer), 31 per cent are “super-Earths”, or rocky worlds many times the size of our planet, 30 per cent are gas giants, some of them many times the size of Jupiter, and 4 per cent are known as “terrestrial” and are Earth-like in size and form.
The now-retired Kepler Space Telescope, launched in 2009, and the Transiting Exoplanet Survey Satellite, launched in 2018, helped build up a catalogue of planetary findings by monitoring stars in a fixed field of view and watching for tiny dips in the starlight that indicate when a planet has crossed in front of it, known as the transit method.
Powerful new technology such as the recently launched James Webb Space Telescope — which will begin its observations of the universe within weeks from its vantage point one million miles from Earth — will also advance understanding of the composition of planets.
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Nasa’s Nancy Grace Roman Telescope, due to launch in 2027, will also hunt for exoplanets and the European Space Agency’s Ariel mission, launching in 2028, will aim to study their atmospheres.
By capturing light from the atmospheres of exoplanets and identifying the gases that are present, scientists can pinpoint those that may have conditions conducive to hosting life.
William Borucki, the astronomer who served as principal investigator for the Kepler mission, said: “I get a real feeling of satisfaction, and really of awe at what’s out there. None of us expected this enormous variety of planetary systems and stars. It’s just amazing.”
