NASA announces the discovery of 5,000 exoplanets

TAt that time there were only nine known planets in the entire universe – the host of worlds orbiting our sun. That local number was reduced to eight in 2006 when the International Astronomical Union made Pluto a dwarf planet. But even before Pluto had pink-slipped, the planetary count began growing much deeper in space when a planet was discovered orbiting a rapidly spinning pulsar in 1992; and later, in 1995, a Jupiter-like planet orbiting a Sun-like star. Since then, the planet’s population has exploded, and as NASA’s Jet Propulsion Laboratory reported this week, the official total of known worlds beyond our own has now passed 5,000.

Most of the discoveries were made by the Kepler space telescope. Launched in 2009, it searches for planets using what it calls the transit method — looking for the slight dimming of light that occurs when an orbiting planet momentarily blocks the star’s light. The dimming is fantastically subtle — the equivalent of removing a single lightbulb from a board of 10,000 of them, as Natalie Batalha, former Kepler mission leader, told TIME. And Kepler examined only a tiny part of the sky, comprising only 150,000 stars. Nonetheless, in its 11 years of operation it has confirmed the existence of 2,709 exoplanets and provided data on a further 2,057 that are still being studied.

The newer Transiting Exoplanet Survey Satellite (TESS), launched in 2018, also uses the transit method, but is equipped with multiple telescopic eyes that allow it to scan the entire celestial shell. In just its short operational life, it has confirmed the existence of 203 other exoplanets and spotted another 5,459 possible ones that astronomers are now studying.

The transit method is not the only way to search for exoplanets. Other telescopes – both in space and on Earth – use what is called the radial velocity method. In this case, they’re examining a star, looking for the slight wobble caused by the gravity of a planet – or planets – pulling on it as they orbit. The most famous multiplanet system to date is just 39 light-years from Earth, where seven planets orbit the red dwarf known as Trappist-1.

The planets discovered so far vary in size and composition. There are so-called hot Jupiters – which, as their name suggests, are gaseous worlds orbiting near the fires of their mother planet. Others are smaller gas worlds, similar in size to Neptune. Still others — the most promising — are compact, rocky planets like Earth, some orbiting in their star’s habitable zone, a place where temperatures are neither too hot nor too cold for water indispensable requirement of life as we know it to exist in a liquid state.

The mere fact that astronomers can find planets pretty much everywhere has led them to conclude that virtually every star in the universe is orbited by at least one planet – leading to trillions and trillions of potential worlds. “Each of them is a brand new planet,” NASA astronomer Jessie Christiansen said in a statement. “I’m happy about everyone because we don’t know anything about them.”

This story originally appeared in TIME Space, our weekly space-themed newsletter. Here you can sign up.

write to Jeffrey Kluger at jeffrey.kluger@time.com.