What do planets outside
our solar system, or exoplanets, look like? A variety of possibilities are
shown in this illustration. Scientists discovered the first exoplanets in the
1990s. As of 2022, the tally stands at just over 5,000 confirmed exoplanets. Credits:
NASA/JPL-Caltech
The count of confirmed exoplanets just ticked past the 5,000 mark,
representing a 30-year journey of discovery led by NASA space telescopes.
Not so long ago, we lived in a universe with only a small number of known
planets, all of them orbiting our Sun. But a new raft of discoveries marks a
scientific high point: More than 5,000 planets are now confirmed to exist
beyond our solar system.
The planetary odometer turned on March 21, with the latest batch of 65
exoplanets – planets outside our immediate solar family – added to the NASA
Exoplanet Archive. The archive records exoplanet discoveries that appear in
peer-reviewed, scientific papers, and that have been confirmed using multiple
detection methods or by analytical techniques.
The 5,000-plus 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 bigger than our own, and “mini-Neptunes,” smaller versions of our
system’s Neptune. Add to the mix planets orbiting two stars at once and planets
stubbornly orbiting the collapsed remnants of dead stars.
Astronomers have now
confirmed more than 5,000 exoplanets, or planets beyond our solar system.
That’s just a fraction of the likely hundreds of billions in our galaxy. The
cones of exoplanet discovery radiate out from planet Earth, like spokes on a
wheel. Many more discoveries await. Credits: NASA/JPL-Caltech
“It’s not just a number,” said Jessie Christiansen, science lead for the
archive and a research scientist with the NASA Exoplanet Science Institute at
Caltech in Pasadena. “Each one of them is a new world, a brand-new planet. I
get excited about every one because we don’t know anything about them.”
We do know this: Our galaxy likely holds hundreds of billions of such
planets. The steady drumbeat 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 pulses 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, the lead author on the paper that, 30
years ago, unveiled the first planets to be confirmed outside our solar system.
“If you can find planets around a neutron star, planets have to be
basically everywhere,” Wolszczan said. “The planet production process has to be
very robust.”
Wolszczan, who still searches for exoplanets as a professor at Penn State,
says we’re opening an era of discovery that will go beyond simply adding new
planets to the list. The Transiting Exoplanet Survey Satellite (TESS), launched in 2018,
continues to make new exoplanet discoveries. But soon powerful next-generation
telescopes and their highly sensitive instruments, starting with the recently
launched James Webb Space Telescope, will capture light
from the atmospheres of exoplanets, reading which gases are present to
potentially identify tell-tale signs of habitable conditions.
The Nancy Grace Roman Space Telescope, expected to launch in 2027, will
make new exoplanet discoveries using a variety of methods. The ESA (European
Space Agency) mission ARIEL, launching in 2029, will observe exoplanet
atmospheres; a piece of NASA technology aboard, called CASE, will help zero in
on exoplanet clouds and hazes.
“To my thinking, it is inevitable that we’ll 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 chemistry found throughout the universe, as well as the detection of widespread organic molecules, suggests detection of life itself is only a matter of time, he added.
In this animation, exoplanets are represented by musical notes played across decades of discovery. Circles show location and size of orbit, while their color indicates the detection method. Lower notes mean longer orbits, higher notes shorter orbits. Credits: NASA/JPL-Caltech/SYSTEM Sounds (M. Russo and A. Santaguida)
How to Find Other Worlds
The picture didn’t always look so bright. 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 appeared in the data from ground-based telescopes 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 still, nothing
looked likely to be habitable.
Finding small, rocky worlds more like our own required the next big leap in
exoplanet-hunting technology: the “transit” method. Astronomer William Borucki
came up with the idea of attaching extremely sensitive light detectors to a
telescope, then launching it into space. The telescope would stare for years at
a field of more than 170,000 stars, searching for tiny dips in starlight when a
planet crossed a star’s face.
That idea was realized in the Kepler Space Telescope.
Borucki, principal investigator of the now-retired Kepler mission, says its
launch in 2009 opened a new window on the universe.
“I get a real feeling of satisfaction, and really of awe at what’s out
there,” he said. “None of us expected this enormous variety of planetary
systems and stars. It’s just amazing.”
The more than 5,000 exoplanets confirmed in our galaxy so far include a variety of types – some that are similar to planets in our solar system, others vastly different. Among these are a mysterious variety known as “super-Earths” because they are larger than our world and possibly rocky. Credits: NASA/JPL-Caltech
Written by Pat Brennan
Source: https://www.nasa.gov/feature/jpl/cosmic-milestone-nasa-confirms-5000-exoplanets
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