Planet AF Lep b has become a focal point for astronomers due to its unique characteristics. In 2023, it was identified as the lowest-mass planet outside our solar system to be directly observed and have its mass measured using astrometry. This technique involves tracking the subtle movements of a host star over time to understand more about orbiting companions.
Recently, AF Lep b was directly observed by the James Webb Space Telescope (JWST), making it the lowest-mass planet with the smallest angular separation from its host star seen from Earth. The findings were published in The Astrophysical Journal Letters.
At 23 million years old, AF Lep b is a young gas giant compared to Jupiter's 4.6 billion years. Its brightness makes it an ideal subject for observation. However, capturing images of this planet poses challenges due to its proximity to its host star and movement within its orbit. Graduate students Kyle Franson from The University of Texas at Austin and William Balmer from Johns Hopkins University led efforts to observe the planet before it becomes too close to its star.
“AF Lep b is right at the inner edge of being detectable," said Franson. "Even though it is extraordinarily sensitive, JWST is smaller than our largest telescopes on the ground." He added that observing at longer wavelengths can make objects appear fuzzier, complicating efforts to distinguish them when they are close together.
The JWST uses a coronagraph, which blocks starlight so nearby objects can be seen. At AF Lep b's current distance from its star, over 90% of the planet’s light is blocked by this tool.
Brendan Bowler, an astronomer at UT and co-author of the study, noted that “the conventional wisdom has been that JWST is more sensitive to lower-mass planets on wide orbits than ground-based facilities.” He acknowledged that using JWST for small separations pushes instrumentation limits.
AF Lep b takes approximately 25 years to complete an orbit around its star. While future observations might capture images when it's visible again on the other side of its star, this could take over a decade.
To secure observation time on JWST before losing sight of AF Lep b, Franson and Balmer applied for Director’s Discretionary Time—a reserved allocation for critical observations—which they received. “This is the first Director’s Discretionary Time program led by graduate students,” said Bowler.
Laurent Pueyo from the Space Telescope Science Institute praised their work: “It’s quite something that two graduate students are able to harness all these incredible technological innovations.”
The team discovered an active atmosphere on AF Lep b with convection currents mixing elements between atmospheric layers. Balmer noted unexpected levels of carbon monoxide: “The only way to get gas of that type into the planet’s upper atmosphere is with strong updrafts.”
Bowler emphasized ongoing opportunities: “In the big picture... there’s a lot more to come.” He highlighted potential discoveries beyond known planets through future observations with JWST.
Research support came from organizations including NASA and NSF while data collection involved multiple observatories worldwide such as ESO telescopes at La Silla Paranal Observatory and W.M Keck Observatory among others mentioned in related archives or surveys conducted previously under various institutions' initiatives globally contributing towards understanding celestial phenomena better collectively benefiting humanity scientifically eventually potentially practically someday hopefully perhaps ideally ideally ideally ideally ideally