Atmosphere of distant ‘warm Neptune’ fascinates astronomers

A mixture of images from NASA’s Hubble and Spitzer telescopes has resulted in fascinating observations of the exoplanet HAT-P-26b, which is classified as a ‘warm Neptune’.
Water vapor and exotic clouds have been spotted in the atmosphere of the distant alien planet, which is 430 light-years away from Earth.
The planet displayed a preponderance of hydrogen and helium on much higher levels than seen in Neptune or Uranus – the two most comparable entities in our solar system when it comes to mass.
“This exciting new discovery shows that there is a lot more diversity in the atmospheres of these exoplanets than we have previously thought,” said David Sing, an astrophysics professor at the University of Exeter in the UK.
“This ‘warm Neptune’ is a much smaller planet than those we have been able to characterize in depth, so this new discovery about its atmosphere feels like a big breakthrough in our pursuit to learn more about how solar systems are formed, and how it compares to our own,” added Sing, who is the co-leader of a new study about HAT-P-26b that was published in the journal Science.

Identifying molecules in an atmosphere hundreds of light years away

Hannah Wakeford, co-leader of the new study and a postdoctoral researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, explained that HAT-P-26b is likely tidally locked, meaning it constantly shows the same face to its host star.
It orbits very close to the host star, completing a cycle every 4.2 Earth days.
When HAT-P-26b crossed its parent star’s face, from the perspective of the NASA telescopes, the planet’s atmosphere filtered out certain wavelengths of starlight.
This enabled the researchers to identified certain molecules within the atmosphere, one of which was water.
“For this mass range, this is the strongest water-absorption feature that we have ever measured,” Wakeford told
It’s also believed that clouds, likely composed of disodium sulfide as opposed to water vapor as on Earth, will be present in the skies of HAT-P-26b.
“This would be a very alien sky that you would be looking at,” Wakeford said. “These clouds would cause scattering in all of the colors, so you’d get a kind of scattery, washed-out, gray sky, which is interesting, if you were looking through these clouds.”

More like Neptune of Jupiter?

During their study of the distant planet, the team also assessed its metallicity, that is to say the extent to which it is composed of elements other than hydrogen and helium – anything heavier than helium being considered a metal in astronomical terms.
The scientists found that although HAT-P-26b is roughly as massive as Neptune, its metallicity is more similar to that of Jupiter.
“It suggests that this smaller planet actually formed closer to its star, more like where Jupiter formed,” Wakeford said. “And we didn’t know before that you could form [such] planets in that region. We expected the smaller worlds to be formed further out, where they would accumulate clumps of icy debris and richer heavy elements during the formation in the [protoplanetary] disk.”
The team’s findings add to growing knowledge of distant, alien worlds, knowledge that is facilitated by incredibly powerful telescopes.
Image credit: NASA/GSFC