Given that Saturn is nearly 100 times more massive than Earth, it seems like a joke to refer to an exoplanet of the same weight as "light."
But that's what NASA and the European Space Agency, one of its partners on the James Webb Space Telescope, have called a world their observatory just discovered. Found 111 light-years away in space, the young planet is only about 6 million years old — a mere babe in cosmic terms. A wide ring of dust surrounds it in TWA 7, its star system in the Air Pump constellation.
With the Webb telescope's powerful infrared camera, scientists spotted what was pushing around that debris: a faint object at least 10 times lighter than the previous planets discovered through direct imaging.
The detection, which still must be confirmed through additional observations, represents the lightest planet ever seen with this technique outside the solar system, and it marks a major milestone in the search for exoplanets obscured by debris disks — those wide, dusty belts left behind after planets begin to form. Researchers say Webb’s sharper vision and deeper sensitivity mean smaller, colder, and more distant planets are finally within reach.
"This observatory enables us to capture images of planets with masses similar to those in the solar system, which represents an exciting step forward in our understanding of planetary systems, including our own," said Mathilde Malin of Johns Hopkins University in Baltimore, in a statement.
This exoplanet, dubbed TWA 7b, sits about 52 times farther from its star than Earth is from the sun. That places it right in the middle of a gap in the dust — the kind of thing scientists expect when a planet sculpts the debris around it with its gravity.
Telescopes of the past weren’t sensitive enough to spot such a small, faint planet so close to a bright star, but Webb captured its thermal glow with its mid-infrared instrument. Scientists then checked old existing images and data to rule out other possible explanations, like a background star, galaxy, or even a distant solar system object like a dwarf planet that happened to be in the same part of the sky. Nothing else fit. The discovery team published their findings in the journal Nature.
Webb usually observes exoplanets through indirect methods, such as transmission spectroscopy, a technique for studying a planet's atmosphere by analyzing how starlight filters through it. What distinguishes this observation of TWA 7b is that the telescope captured light from the planet itself.
The discovery comes on the heels of Webb's direct image of two previously known larger gas giants, YSES-1b and YSES-1c, about 300 light-years from Earth. The research revealed one of the exoplanets has sand-like clouds while the other is surrounded by moon-making material.
Few distant worlds meet the criteria for direct imaging because planets are often millions of times fainter than the stars they circle. And if they are orbiting close, their own light usually gets washed out. But scientists want these images because they allow scientists to get much more information about an exoplanet's composition.
Molecules within a planet's atmosphere absorb certain colors of light, so when astronomers study a planet's spectrum, they can look for what's missing from the rainbow to determine which gases — like water, methane, and carbon dioxide — are present in the planet's air.
"TWA 7b is suited for direct spectroscopic investigations, providing the opportunity to study the interior and the atmosphere of a non-irradiated sub-Jupiter-mass, cold exoplanet, and start comparative studies with our much older and cooler solar system giants," the authors wrote.
Scientists overcame the challenge of the star, sometimes known as CE Antilae, by blocking its light with a special telescope instrument called a coronagraph. This device suppressed the red dwarf star's bright glare. The technique allows astronomers to see planets that would otherwise be swamped out. After subtracting excess starlight using advanced image processing, the faint infrared source from TWA 7b emerged.
Computer models showed that a Saturn-size planet with a temperature of about 120 degrees Fahrenheit would match what Webb saw. The simulations were also consistent with the way the dust ring is shaped, including the seemingly "empty" area around the candidate planet's location.
Ongoing studies of the distant world will aim to better nail down its properties and confirm it is indeed a planet.
Topics NASA
