The more than five thousand exoplanets analyzed have characteristics similar to those of our Solar System.
The count of worlds outside the Solar System added to NASA ‘s Exoplanet Archive just passed the 5,000 mark, following a latest batch of 65 added on March 21.
The archive records exoplanet discoveries that appear in peer-reviewed scientific articles and that have been confirmed using multiple detection methods or through analytical techniques.
The more than 5,000 planets found so far include small, rocky worlds like Earth, gas giants many times larger than Jupiter, and “hot Jupiters” in scorchingly close orbits around their stars. There are “super-Earths”, which are possible rocky worlds larger than our own , and “mini-Neptunes”, smaller versions of our system’s Neptune . Also planets orbiting two stars at once and worlds stubbornly orbiting the collapsed remnants of dead stars.
“It’s not just a number,” Jessie Christiansen, chief science officer for the archive and a research scientist at NASA ‘s Exoplanet Science Institute at Caltech, said in a statement. “Each one of them is a new world, a new planet. I get excited about each one because we don’t know anything about them.”
A handful of exoplanets among the millions that could have
Our galaxy probably contains hundreds of billions of such planets. The steady pace of discovery began in 1992 with strange new worlds orbiting an even stranger star. It was a type of neutron star known as a pulsar , a rapidly spinning stellar corpse that pulsates with millisecond bursts of searing radiation. Measuring slight changes in the timing of the pulses allowed scientists to reveal planets in orbit around the pulsar.
Finding just three planets around this spinning star essentially opened the floodgates, said Alexander Wolszczan, lead author of the paper that, 30 years ago, revealed the first confirmed planets outside our solar system.
“If you can find planets around a neutron star, the planets have to be basically everywhere,” Wolszczan said. “The planet production process has to be very robust.”
Wolszczan, who is still searching for exoplanets as a professor at Penn State, says we’re opening an era of discovery that will go beyond just adding new planets to the list. The Transiting Exoplanet Survey Satellite (TESS), launched in 2018, continues to discover new exoplanets. But soon, powerful next-generation telescopes and their highly sensitive instruments, starting with the recently launched James Webb Space Telescope , will capture light from exoplanets’ atmospheres, reading what gases are present to identify potentially telltale signs of habitable conditions.
The Nancy Grace Roman Space Telescope, due to launch in 2027 , will make new exoplanet discoveries using a variety of methods . The ESA (European Space Agency) ARIEL mission, due to launch in 2029 , will observe exoplanet atmospheres ; a piece of NASA technology on board, called CASE, will help zero in on the clouds and haze of exoplanets.
“In my opinion, it is inevitable that we will find some kind of life somewhere, most likely of some primitive kind,” Wolszczan said. The close connection between the chemistry of life on Earth and the chemistry found throughout the universe, as well as the detection of widespread organic molecules, suggests that the detection of life itself is only a matter of time, he added.
The first planet detected around a Sun-like star, in 1995, turned out to be a hot Jupiter: a gas giant about half the mass of our own Jupiter in an extremely close four-day orbit around its star. A year on this planet, in other words, lasts only four days.
More such planets showed up in ground-based telescope data once astronomers learned to recognize them: first dozens, then hundreds. They were found using the “wobble” method: tracking slight back-and-forth motions of a star, caused by gravitational tugs from orbiting planets. But even so, nothing seemed likely to be habitable.
Finding small, rocky worlds more like our own required the next big leap in exoplanet search technology : the “transit” method. Astronomer William Borucki came up with the idea of attaching extremely sensitive light detectors to a telescope and then launching it into space. The telescope would watch a field of more than 170,000 stars for years, looking for small dips in starlight when a planet crossed the face of a star.
Borucki, principal investigator of the Kepler mission, now retired, says that its launch in 2009 opened a new window on the universe. “I have a real sense of satisfaction and really awe of what’s out there,” he said. “None of us expected this huge variety of planets and stars.” (EuropePress)