Two NASA space telescopes have joined hands together to identify the detailed chemical “fingerprint” of a planet which, in terms of its size, falls somewhere between the Earth and Neptune. One of such planets, named Gliese 3470 b aka GJ 3470 b, has a large rocky core underneath a hydrogen-and-helium atmosphere.
The planet is larger than Earth but is less massive than Neptune, and the planet weighs the same amount of 12.6 Earth masses. By observing the planet Gj 3470 b’s atmosphere, scientists will be able to find new clues about the planet’s nature and origin.
This is a big discovery from the planet-formation perspective. The planet orbits very close to the star and is far less massive than Jupiter - 318 times Earth's mass - but has managed to accrete the primordial hydrogen/helium atmosphere that is largely 'unpolluted' by heavier elements. We don't have anything like this in the solar system, and that's what makes it striking - Björn Benneke of the University of Montreal in Canada
To accomplish this what first appeared to be a Herculean task, the scientists at NASA first enlisted the combined multi-wavelength capabilities of both the Hubble and Spitzer space telescopes. In order to conduct the study on the planet’s atmosphere, the scientists first had to measure the absorption of starlight as the planet passed in front of its star and the loss of reflected light from the planet as it passed behind the star.
In total, the telescopes observed 12 transits and 20 eclipses. Benneke is not sure yet as to how to classify the new planet as, according to Benneke, the spectroscopic signature of such a world is available to them for the first time.
We expected an atmosphere strongly enriched in heavier elements like oxygen and carbon which are forming abundant water vapor and methane gas, similar to what we see on Neptune. Instead, we found an atmosphere that is so poor in heavy elements that its composition resembles the hydrogen/helium-rich composition of the Sun - Benneke
He further added, “Other exoplanets, called "hot Jupiters," are thought to form far from their stars and over time migrate much closer. But this planet seems to have formed just where it is today.”
Benneke has a hypothetical explanation regarding the nature of the planet. According to his hypothesis, the planet was born close to its red dwarf star. In its initial stage, the planet was nothing but a dry rock and it accreted hydrogen from a primordial disk of gas when it was very young.
Regarding his explanation, he added, “We're seeing an object that was able to accrete hydrogen from the protoplanetary disk but didn't run away to become a hot Jupiter. This is an intriguing regime.” He also thinks that before the planet could bulk up further, the disk dissipated.
Hopefully, NASA’s next James Webb Telescope will be able to shed more light on GJ 3470 b’s atmosphere.