Laura Kreidberg, who leads research on exoplanet atmospheres at the Max Planck Institute, would like to see an independent analysis of the data before jumping to conclusions. “There are many small data processing decisions that can cause unexpected bumps and wobbles,” says Kreidberg. “I would like to see the spectrum reproduced by another team using independent methods to see if they get the same thing.”
In fact, that process is already underway. Last week, another research team led by Lorenzo Mugnai, an astrophysicist at Sapienza University of Rome, released a separate paper independently analyzing the same Hubble data on GJ 1132 b. But when Mugnai’s team analyzed the data, they found that the planet’s spectrum was relatively flat – in other words, there was no detectable atmosphere. “It is very difficult to be sure of the cause of the differences because it is a very difficult analysis,” said 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 both think the problem could lie in how they explain the variation in sunlight while ahead of the planet. star moves. a parameter known as darkening of limbs. “A star is not uniform in brightness from center to rim,” says Swain. “When the planet is close to some edge, it seems to block less light because part of the star covering it is fainter on average than the rest of the star.”
To correct this effect, researchers need to process their data with a model that can account for the star’s dimming and lighting up. Both teams used the same model, but with different coefficients. They now plan to swap methods to see if they can replicate the other team’s results.
Still, Darius Modirrousta-Galian, the co-author of Mugnai’s paper, thinks it is highly unlikely that GJ 1132 b has been able to hold enough hydrogen to produce a second atmosphere because it is so close to its host star. state. Exoplanet researchers still don’t know how influential stellar radiation can be in the formation of atmospheres. “The approach we are taking is that the radiation from stars is actually so strong and it causes winds on the planet to have supersonic speeds and extreme particle speeds, that the atmosphere is actually vaporizing,” he says.
Modirrousta-Galian says that the amount of hydrogen in the original shell needed to overcome this loss and create a second atmosphere would be several times the mass of the planet. “We have no problem within our model that the planet could have been born with a hydrogen atmosphere,” he says. “The conclusion we came to is that we just don’t have one now.”
Still, more research is needed – and ideally new observations by the James Webb Space Telescope, which starts October 31 – to verify or further complicate the results of both teams. If GJ 1132 b does indeed turn out to have a hydrogen atmosphere, this could open new avenues of research for planetary scientists. For one thing, these atmospheres would be much easier to analyze than those of small planets with denser envelopes made of heavier elements. The low molecular weight of hydrogen contributes to a broader, more swollen atmosphere that light can shine through. And that makes for a stronger spectrographic signature that is easier to read from Earth.
Both teams are pushing the boundaries of what’s possible with the Hubble Space Telescope, which was launched in the year 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 exciting thing here is getting a better understanding of what details really matter when studying small planets,” he says.
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