Laura Kreidberg, who conducts research on exoplanet atmospheres at the Max Planck Institute, would like to see an independent analysis of the data before drawing conclusions. “There are a lot of small decisions in data processing that can cause unexpected bumps,” says Kreidberg. “I’d like to see the spectrum played by another team using independent methods to see if they get the same thing.”
In fact, this process is already underway. Last week, another research team led by Lorenzo Mugnai, an astrophysicist at Sapienza University in Rome, released a separate paper that independently analyzes the same Hubble data about GJ 1132 b. But when Mugnai’s team analyzed the data, they found that the spectrum of the planet it is relatively flat – in other words, it did not have a detectable atmosphere. “It is very difficult to be sure of the differences, because it is a very difficult analysis,” says Mugnai. “We know the devil is in the details.”
The two teams have regular meetings to find out what led to such a dramatic discrepancy in their results, but Mugnai and Swain believe the issue could lie in how they explain the variation in sunlight as the planet moves in front of its star. , a parameter known as limb darkening. “A star doesn’t have a uniform brightness from the center to the edge,” says Swain. “When the planet is close to one edge or the other, it seems to block less light, because part of the star it covers is weaker on average than the rest of the star.”
To correct this effect, researchers need to process their data with a model that can take into account the fading and brightness of the star. Both teams used the same model, but with different coefficients. Now plan exchange methods to see if they can replicate the other team’s results.
Even so, Darius Modirrousta-Galian, co-author of Mugnai’s paper, believes that it is very unlikely that GJ 1132 b managed to retain enough hydrogen to produce a second atmosphere because it is so close to its host star. Exoplanet researchers are still uncertain about how influential stellar radiation can be in forming atmospheres. “The approach we take is that, in fact, stellar irradiation is so strong and makes the winds on the planet have supersonic speeds and extreme particle speeds that the atmosphere practically boils,” he says.
Modirrousta-Galian says that the amount of hydrogen in the primordial tire that would be needed to overcome this loss and create a second atmosphere would be several times greater than the mass of the planet. “We have no problem with our model that the planet could have been born with a hydrogen atmosphere,” he says. “The conclusion we have reached is that we simply do not have one now.”
However, more research is needed – and ideally new observations from the James Webb Space Telescope, to be launched on October 31 – to verify or further complicate either the team’s results. If GJ 1132 b turns out to have a hydrogen atmosphere, it could open up new avenues of exploration for planetary scientists. First, these atmospheres would be much easier to analyze than those of small planets, with denser tires made of heavier elements. The low molecular weight of hydrogen contributes to a wider and fluffier atmosphere, so that the light shines. And that makes a stronger spectrographic signature, which is easier to read on Earth.
Both teams go beyond what is possible with the Hubble Space Telescope, which was launched in 2000, two years before astronomers discovered the first known exoplanet. At 1.16 times the size of Earth, GJ 1132 b is the smallest planet to ever have a published transmission spectrum, Swain notes. “I think the interesting thing here is to better understand what details really matter for the study of small planets,” he says.
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