In addition to providing a trove of information about the early universe, the James Webb Space Telescope since its 2021 launch has obtained valuable data on various already-known planets beyond our solar system, called exoplanets. Now, for the first time, Webb has discovered an exoplanet not previously known.
Webb has directly imaged a young gas giant planet roughly the size of Saturn, our solar system's second-largest planet, orbiting a star smaller than the sun located about 110 light-years from Earth in the constellation Antlia, researchers said. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).
Most of the roughly 5,900 exoplanets discovered since the 1990s have been detected using indirect methods, such as through observation of the slight dimming of a star's light when a planet passes in front of it, called the transit method. Less than 2% of them have been directly imaged, as Webb did with the newly identified planet.
While this planet is large when considered in the context of our solar system, it is actually the least massive one ever discovered through direct imaging - 10 times less massive than the previous record holder. This speaks to the sensitivity of Webb's instruments.
This discovery was achieved using a French-produced coronagraph, a device that blocks out the bright light from a star, installed on Webb's Mid-Infrared Instrument, or MIRI.
"Webb opens a new window - in terms of mass and the distance of a planet to the star - of exoplanets that had not been accessible to observations so far. This is important to explore the diversity of exoplanetary systems and understand how they form and evolve," said astronomer Anne-Marie Lagrange of the French research agency CNRS and LIRA/Observatoire de Paris, lead author of the study published on Wednesday in the journal Nature.
The planet orbits its host star, called TWA 7, at a distance about 52 times greater than Earth's orbital distance from the sun. To put that in perspective, our solar system's outermost planet Neptune orbits about 30 times further from the sun than Earth. The transit method of discovering exoplanets is particularly useful for spotting those orbiting close to their host star rather than much further out like the newly identified one.
"Indirect methods provide incredible information for planets close to their stars. Imaging is needed to robustly detect and characterize planets further away, typically 10 times the Earth- to-sun distance," Lagrange said.
The birth of a planetary system begins with a large cloud of gas and dust - called a molecular cloud - that collapses under its own gravity to form a central star. Leftover material spinning around the star in what is called a protoplanetary disk forms planets.
The star and the planet in this research are practically newborns - about 6 million years old, compared to the age of the sun and our solar system of roughly 4.5 billion years.
Because of the angle at which this planetary system is being observed - essentially looking at it from above rather than from the side - the researchers were able to discern the structure of the remaining disk. It has two broad concentric ring-like structures made up of rocky and dusty material and one narrow ring in which the planet is sitting.
The researchers do not yet know the composition of the planet's atmosphere, though future Webb observations may provide an answer. They also are not certain whether the planet, being as young as it is, is still gaining mass by accumulating additional material surrounding it.
While this planet is the smallest ever directly imaged, it is still much more massive than rocky planets like Earth that might be good candidates in the search for life beyond our solar system. Even with its tremendous capabilities of observing the cosmos in near-infrared and mid-infrared wavelengths, Webb is still not able to directly image Earth-sized exoplanets.
"Looking forward, I do hope the projects of direct imaging of Earth-like planets and searches for possible signs of life will become a reality," Lagrange said.
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