This migration left fingerprints all over the planets' atmospheres, as the two worlds picked up heavy-element-laden planetesimals — small, solid bodies present in the protoplanetary disks around young stars — that are only located closer to the Sun. Some of these bodies dissolved into the atmosphere of our gas giants, enriching them with heavy elements.
If WASP-39 b has a similar composition as Saturn, then that would suggest it also experienced such a migration before settling in its current orbit. “[Previously,] we haven’t had a lot of success because our instruments have not had the sensitivity, the wavelength coverage, the accuracy to really tell us this information,” says Bean. “And so, we’ve been kind of stumbling around in the dark about this.”
But JWST is finally ripping open the metaphorical blinds. While more data still needs to be analyzed, the new data seems to point to WASP-39 b being comparable to Saturn, according to Bean.
Migration isn’t the only explanation for how WASP-39 b’s atmosphere may have been seeded with a heavy element like CO2, however. It’s possible that, while it was still young, the world was assailed by comets and asteroids — an upbringing that is also comparable to Saturn.
More to come
Besides having implications for WASP-39 b’s origins, the JWST teases yet another mystery, too — another type of molecule whose presence can’t be as easily explained as the CO2.
Knowing the temperature, pressure, and elemental abundances of a planet’s atmosphere, scientists can usually compute a good estimate of the world's expected chemistry. But the unidentified spectral feature is beyond what the model suggested, indicating that some other atmospheric phenomena is creating the mystery molecule.
“It’s a subtle spectral feature,” says Bean, which is why the team is taking its time to analyze all the data before they share their findings. But ultimately, “we wouldn’t have put it in the paper if we didn’t have a lot of confidence in it.”
JWST isn’t only focused on the mysteries of WASP-39 b, either. Or even just giant planets, for that matter.
Now that JWST has proven its capability, researchers will be using the observatory to peer at more Earth-like worlds. Although the level of detail attainable for a rocky planet will be significantly less than that for a giant planet, the confidence built by observing planets like WASP-39 b will influence how much trust is given to the telescope and its instruments when looking at rocky worlds.
“I think most people, given a choice [between WASP-39 b and Trappist-1 c] they'd probably pick Trappist-1 c,” says Bean, referencing a rocky, Venus-like world located some 40 light-years away. But “It’s all tied together for me," he says. "We have to understand [WASP-39 b] at the same time we have to understand [Trappist-1 c], because the unifying factor is planets with atmospheres, our observational techniques, and how we go about interpreting that.”