Strong signs of water seen on 'warm Neptune'; NASA detects using telescopes

US space agency NASA has detected signs of water on a distant Neptune-like planet called the HAT-P-26b. NASA’s Hubble and Spitzer space telescopes helped scientists find “a strong water signature” in the atmosphere of ‘warm Neptune’. The new findings may help scientists understand more about the birth and development of planetary systems.

The study reveals that the HAT-P-26b, which has been located about 437 light-years away, has a primitive atmosphere, which has been made of almost entirely of hydrogen and helium. The planet orbits a star roughly twice as old as the Sun.

The recent analysis is one of the most detailed studies till date of a ‘warm Neptune’ or a Neptune-sized planet and close to its star.
The study found that the atmosphere of the HAT-P-26b is relatively clear of clouds and has a strong water signature, however, the planet is not a water world. Till date, this is the best measurement of water on an exoplanet of this size.

Compared to Neptune and Uranus, the planets in our solar system with about the same mass, HAT-P-26b likely formed either closer to its host star or later in the development of its planetary system, or both.

“Astronomers have just begun to investigate the atmospheres of these distant Neptune-mass planets, and almost right away, we found an example that goes against the trend in our solar system,” said Hannah Wakeford, a postdoctoral researcher at NASA’s Goddard Space Flight Centre in the US.

Data from transits – occasions when the planet passed in front of its host star – was used by the researchers to study HAT-P-26b.

When the transit takes place, a fraction of the starlight gets filtered through the atmosphere of the planet. The atmosphere absorbs some wavelengths of light but not others.

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By looking at how the signatures of the starlight change as a result of this filtering, researchers can work backward to figure out the chemical composition of the atmosphere.

Researchers pooled data from four transits measured by Hubble and two seen by Spitzer. Together, those observations covered a wide range of wavelengths from yellow light through the near-infrared region.

“To have so much information about a warm Neptune is still rare, so analysing these data sets simultaneously is an achievement in and of itself,” said Tiffany Kataria of NASA’s Jet Propulsion Laboratory in the US.

To estimate HAT-P-26b’s metallicity, researchers were also able to use the water signature. It is an indication of how rich the planet is in all elements heavier than hydrogen and helium. It gives more clues about how a planet formed.

The researchers discovered that its metallicity is only about 4.8 times that of the Sun.

“This analysis shows that there is a lot more diversity in the atmospheres of these exoplanets than we were expecting, which is providing insight into how planets can form and evolve differently than in our solar system,” said David K Sing of the University of Exeter in the UK.

The research appears in the journal Science. 

(With inputs from PTI)