The James Webb Space Telescope has directly imaged the lowest-mass exoplanet outside the solar system to date. The planet is also the closest to its star and can be observed directly with a $10 billion space telescope.
The imaging was a “race against time” as the extrasolar planet, or “exoplanet,” was about to disappear behind the bright light of its parent star, perhaps for up to a decade.
Planet AF Leporis b (AF Lep b) is no stranger to setting records. In 2023, this exoplanet, or “exoplanet,” becomes the lowest-mass planet outside the solar system detected by direct observation. It then became a less massive world whose mass is measured by “astrometry”, a technique that monitors a star’s motion over many years to determine “oscillations” caused by the gravitational pull of an orbiting planet.
AF Lep b is a young exoplanet estimated to be only 23 million years old. If this sounds ancient, consider that the Earth is estimated to be about 4.6 billion years old. AF Lep b is about 3.2 times the mass of Jupiter and about 1.2 times the mass of the solar system’s gas giant.
“AF Lep b is on the inland side of detectability. Although it is very sensitive, the James Webb Space Telescope is smaller than the largest telescopes we have on Earth,” said Kyle Franson, a researcher at the University of Texas at Austin. He said in a statement. “We observe at longer wavelengths, which makes things appear blurrier. It becomes more difficult to separate one source from another when they appear so close together.”
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However, because it is located 88 light-years from Earth, AF Lep b still appears to the James Webb Space Telescope (JWST) as just a tiny dot. Fortunately, astronomers can learn a lot from such a “spot.”
Firefly on a lighthouse
Since the discovery of the first exoplanet in the 1990s, the number of exoplanets has grown to more than 6,000 entries, with thousands more confirmed. However, very few of them have been filmed directly.
Most exoplanets are detected through their impact on their host star, either when they block light as they cross the face of their star or through the gravitational forces they exert on that star.
This is because when viewed from a distance of several light-years, the angular separation between exoplanets and their host stars becomes very small, making them difficult to distinguish and drowning out the light of their stars. This can be thought of as standing on the deck of an offshore ship and trying to see the light of a firefly sitting on a lit lighthouse lamp.
The James Webb Space Telescope has the advantage of observing exoplanets around their stars, using an instrument called a coronagraph. This blocks the light from the star, making it easier to spot the planets orbiting it. AF Lep b is a good candidate for such an observation, because because it is a very small planet, its “firefly glow” is strong.
The team wanted to learn more about this exoplanet’s atmosphere because worlds like AF Lep b with masses similar to those of the solar system’s gas giants are rare. But to do this, the team had to move quickly.
This race against time appeared to these astronomers because the distant gas giant is currently about eight times the distance between the Earth and the Sun from its star, but its orbit is close to the star from our perspective.
At its current distance from its star, the coronagraph blocks 90% of AF Lep’s light, but as the planet gets closer to its star, more and more will be blocked until the James Webb Space Telescope can’t see the planet anymore, even then. tool.
The team could have waited for AF Lep b to appear from the other side of the star, but with a 25 Earth-year orbit, it could take more than a decade before this becomes possible.
“Conventional wisdom was that the James Webb Space Telescope was more sensitive to low-mass planets in wide orbits than ground-based facilities, but before its launch, it was not clear whether it would be able to compete at small separation distances,” said the team member and U.S. . “We’re really pushing the instruments to their limits here,” Texas astronomer Brendan Bowler said in the statement.
Through their observations, the team discovered that AF Lep b has a very active atmosphere, with convection currents mixing elements between its lower and upper levels. The team also discovered a much larger amount of carbon monoxide than they expected around AF Lep b. They assume that strong updrafts will be the only way to deliver this gas to the planet’s upper atmosphere.
It was exciting for the team to learn more about this exoplanet, but perhaps even more exciting was that these observations were possible at all. The research is further evidence that the James Webb Space Telescope is delivering results beyond expectations.
“In the big picture, these data were captured in the second year of operations for the James Webb Space Telescope,” Buller concluded. “It’s not just about the planets we know now. It’s also about the planets we know [will] Find out soon. This portends some exciting work we will see in the coming years.
“There’s a lot more to come.”
The team’s research is published in Astrophysical Journal.
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