Astronomers using the mighty James Webb Space Telescope have captured direct images of four planets in a star system 130 light years from Earth — an astonishingly eagle-eyed feat of cosmic photography.  

The planets, all young gas giants, were spotted in HR 8799, a system that's only around 30 million years old. Though already extensively probed, these latest observations, as detailed in a new study published in The Astrophysical Journal, provide compelling evidence that the nascent worlds are rich in carbon dioxide — a promising sign that they formed in a similar way to the gas giants of our solar system, Jupiter and Saturn.

"By spotting these strong carbon dioxide features, we have shown there is a sizable fraction of heavier elements, like carbon, oxygen, and iron, in these planets' atmospheres," lead author William Balmer, an astrophysicist at John Hopkins University, said in a NASA statement.

It's rare that astronomers capture a direct glimpse of exoplanets. Generally, they produce little to no light of their own, and are vastly outshone by the light of their host star, plus the untold number of luminous objects in the night sky. As such, even detecting an exoplanet is rare; so far, only 6,000 worlds outside our solar system have been discovered, and they're usually spotted by searching for dips in the light of a star they cause when they pass in front of one from our perspective.

In their work, Balmer and his team used a special instrument, known as a coronagraph, built into the James Webb's Near-Infrared Camera (NIRCam) specifically designed to blot out the light of stars while searching for exoplanets.

"It's like putting your thumb up in front of the sun when you're looking up at the sky," Balmer told Agence France-Presse. 

That allowed the astronomers to see the "light that is emitted from the planet itself, as opposed to the fingerprint of that light from the host star," Balmer added.

The incredible snapshots provided astronomers with a clear look at the presence of CO2 in the distant exoplanets, which could lead to key insights on gas giant formation throughout the cosmos.

It's widely believed that Jupiter and Saturn were born by first forming heavy, solid cores that pulled in lighter elements nearby — like carbon dioxide — slowly accreting mass over time. 

But another theory known as disk instability — which is pretty controversial — holds that gas giants can also spawn in the massive protoplanetary disk that surrounds a star shortly after it's born. Clumps of matter in this circumstellar cloud, the theory holds, could rapidly collapse into protoplanets. Balmer and his team's findings suggest that the traditional "core accretion" is the one in evidence in the young star system. It's too early to declare that this is the prevailing way that gas giants form throughout the universe, but it's a valuable clue.

"We have other lines of evidence that hint at these four HR 8799 planets forming using this bottom-up approach," said coauthor Laurent Pueyo, an astronomer at the Space Telescope Science Institute in Baltimore, in the NASA statement. "How common is this for planets we can directly image? We don't know yet, but we're proposing more Webb observations to answer that question." 

"We want to take pictures of other solar systems and see how they're similar or different when compared to ours," Balmer added. "From there, we can try to get a sense of how weird our solar system really is — or how normal."

More on astronomical quartets: Scientists Discover Four Intriguing Planets Around Closest Single-Star Solar System to Earth


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