The relationship between Earth and the Sun is pleasant, for the most part. It gives us all of the sustenance we need, and in return, we don’t disrupt the orbital dynamics it governs. Other planetary systems aren’t so lucky; many planets tend to orbit their stars from such close distances, they simply don’t stand a chance.

These dynamics manifest in an extreme way with red dwarfs. In addition to being the most prevalent type of star in the universe, they are smaller, cooler, and less luminous, but they undergo more turbulence than larger stars tend to. Such things do not bode well for planets that orbit close in.

Just ask Gliese 436 b (otherwise known as GJ 436b): a Neptune-sized exoplanet discovered back in 2004 by researchers from Carnegie Institute of Washington and the University of California. You may remember it as the planet believed to be coated in hot ice. It has made its fair share of headlines over the years, and now it gets another moment in the spotlight.

Rendering of  GJ 436 b (Image Credit: NASA/JPL-Caltech)

In a press release from the University of Warwick, a team of researchers reveal that this planet, which orbits a red dwarf within the constellation of Leo, is caving in to the pressures exerted on it by its parent star.

To understand what this means, we must go back to 2013, when spectral analysis of Gliese 436 b proved inconsistent with other observations, suggesting it may have clouds in its atmosphere. At the time, Dr Heather Knutson (the lead author) remarked: “Either this planet has a high cloud layer obscuring the view, or it has a cloud-free atmosphere that is deficient in hydrogen, which would make it very unlike Neptune. Instead of hydrogen, it could have relatively large amounts of heavier molecules such as water vapor, carbon monoxide, and carbon dioxide, which would compress the atmosphere and make it hard for us to detect any chemical signatures.”

By studying its transmission spectrum once more, the researchers from Warwick learned that a large cloud is situated between us and GJ 436b. This cloud is largely composed of hydrogen, and presumably escaped from its planet’s atmosphere—continuing to trail behind.

Explaining what they saw during a transit, Dr Peter Wheatley (one of the study’s authors) notes:

Ultimately, this planet supports the notion low mass planets are similar to hot-Jupiters in the sense that their atmosphere can be stripped away by solar winds, resulting in planets around dwarf stars losing large quantities of mass. Just how much mass is usually lost was pretty much unquantified until now, which makes Gliese 436 b rare.

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