'Morning' and 'evening' detected on an exoplanet, WASP-39b, for the first time

Today, we explore another fascinating discovery about WASP-39b and its atmosphere, which has recently been exciting astronomers worldwide. This distant planet, 700 light-years from Earth, is unlike anything astronomers have seen before.

Dr. James Kirk from the Department of Physics at Imperial College London has been pivotal in this discovery. 

“There is no planet like this in our Solar System. Now, we have been able to directly measure an exoplanet’s morning and evening side over a wide wavelength range,” he states.

WASP-39b’s atmosphere

WASP-39b has a radius larger than Jupiter. However, its mass is similar to Saturn. The planet orbits its star so closely that it experiences a surface temperature of over 1000°C (1832°F).

A day on this planet, due to its proximity to the star, is as swift as its orbit. Fascinatingly, this planet is ‘tidally locked.’

This implies that the same side of the planet always faces its star, similar to our Moon’s relationship with the Earth.

This synchronization creates a constant ‘day’ side always exposed to the star’s heat and a ‘night’ side in perpetual darkness.

But here’s where things get tricky. There’s also a ‘morning’ and ‘evening’ side to the planet.

Morning and evening side of WASP-39b

This remarkable analysis led by the Space Telescope Science Institute and Dr. James Kirk revealed unusual atmospheric conditions on WASP-39b. The ‘morning’ side was much cloudier than the ‘evening’ side. 

Notably, astronomers examine the atmospheres of exoplanets by analyzing the light that filters through the planet’s atmosphere as it passes in front of its star.

This analysis generally assumes a uniform atmosphere across the planet. But WASP-39b begs to differ.

“This analysis is also particularly interesting because you’re getting 3D information on the planet that you weren’t getting before,” explained Néstor Espinoza, an exoplanet researcher at the Space Telescope Science Institute and lead author on the study.

“Because we can tell that the evening edge is hotter, that means it’s a little puffier. So, theoretically, there is a small swell at the terminator approaching the nightside of the planet.” 

WASP-39b atmospheres

On WASP-39b, the day side, always basking in the star’s warmth, is much hotter than the night side. This extreme temperature difference generates a powerful wind at the equator. 

Now, picture this — the ‘morning’ side is where the cooler night wind moves into the scorching day side, while the ‘evening’ side is where the sizzling day wind carries over to the night side. It creates a tantalizing duality.

This unique atmospheric condition reveals a distinct change in temperature from the morning to the evening side, with the evening registering as a blistering 800°C (1472°F), while the morning remains relatively cooler at 600°C (1112°F).

Clouds, data, and theories

This temperature difference also impacts the way clouds form, leading the team to hypothesize different amounts of cloud cover on the morning and evening sides.

The data aligned with their hypothesis, revealing a cloudier morning side than the evening.

Dr. Kirk’s analysis technique focused on the light received as the planet began and ended its pass across the star’s surface.

The results matched well with the analyses completed by other team members, lending credibility to the finding.

Future study of WASP-39b

With the efficacy of the method and the precision of JWST demonstrated, the team now plans to analyze more data from the JWST, which could reveal more about the differences in WASP-39b atmospheres.

“Now we’ve demonstrated the feasibility of this method with JWST, and the precision of JWST is so immense, it really opens up a new avenue into understanding and measuring atmospheric circulation for exoplanets that we were previously largely insensitive to,” Dr Kirk said. 

“It’s really stunning that we are able to parse this small difference out, and it’s only possible due Webb’s sensitivity across near-infrared wavelengths and its extremely stable photometric sensors,” added Espinoza.

“Any tiny movement in the instrument or with the observatory while collecting data would have severely limited our ability to make this detection. It must be extraordinarily precise, and Webb is just that.”

As we delve deeper into the mysteries of these distant worlds and continue to push the boundaries of our knowledge, who knows what other secrets the universe holds?

Will discoveries like these change our understanding of the universe? Time will certainly tell.

The study is recently published in the journal Nature.

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