Laura Kreidberg, who is researching exoplanet atmospheres at the Max Planck Institute, would like to see an independent analysis of the data before jumping to conclusions. “There are very small decisions in data processing that can cause unexpected bumps and bouncing noises,” says Kreidberg. “I would like to see the spectrum represented by a different team, using independent methods to see if they get the same.”
In fact, that process is already underway. Last week, another research team led by Lorenzo Mugnai, an astrophysicist at the Sapienza University of Rome, released a separate paper that independently analyzed the same Hubble data on GJ 1132 b. But when Mugnai’s team cracked the data, they found that the planet’s spectrum was relatively flat – in other words, it had no observable atmosphere. “It’s very difficult to be sure of the cause of the differences because it’s a very difficult analysis,” Mugnai said. “We know the devil is in the details.”
The two teams have regular meetings to find out what led to such a dramatic difference in their results, but Mugnai and Swain both think the problem may lie in how they explain the variation in sunlight as the planet moves in front of its star. a parameter known as darkening of the limb. “A star is not uniform in brightness from center to edge,” says Swain. “When the planet is near some edge, it seems to block less light, because a part of the star it covers is, on average, dimmer 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 obscuration and illumination of the star. Both teams used the same model, but with different coefficients. They are now planning to swap methods to see if they can repeat the results of the other team.
Nevertheless, Darius Modirrousta-Galian, the co-author of Mugnai’s newspaper, thinks that it is highly unlikely that GJ 1132 b could retain enough hydrogen to produce a second atmosphere because it is so close to its host. Exoplanet researchers are still unsure about how influential stellar radiation can be in shaping the atmosphere. “The approach we follow is that stellar radiation is actually so strong and that winds on the planet have supersonic velocities and extreme particle velocities, that the atmosphere is basically boiling down,” he says.
Modirrousta-Galian says the amount of hydrogen in the primordial shell needed to overcome this loss and create a second atmosphere will be several times the mass of the planet. “We have no problem within our model that the planet could be born with a hydrogen atmosphere,” he says. “The conclusion we’ve come to is that we just don’t have one right now.”
Still, more research – and ideally new observations by the James Webb Space Telescope, which launches on October 31 – is needed to verify or further complicate one of the teams’ results. If GJ 1132 b does have a hydrogen atmosphere, it could open new avenues of exploration for planetary scientists. First, this atmosphere will be much easier to analyze than that of small planets with denser envelopes of heavier elements. Hydrogen’s low molecular weight contributes to a wider, weaker atmosphere for light to shine through. And it provides a stronger spectrographic signature that is easier to read from the earth.
Both teams push the boundaries of what is possible with the Hubble Space Telescope, launched in 2000, two years before astronomers discovered the first known exoplanet. GJ 1132 b is 1.16 times larger than Earth and is the smallest planet that has ever had a published transmission spectrum. “I think the exciting thing here is to get a better understanding of the details that are really important for studying small planets,” he says.
More great wired stories