Though there have been several instances of astronomers detecting water vapor in the atmospheres of massive, Jupiter-like exoplanets, HAT-P-11b is different: It’s about the size of Neptune, making it the smallest known alien planet with water vapor in its atmosphere, according to researchers at the University of Maryland.

“Water is the most cosmically abundant molecule that we can directly observe in exoplanets, and we expect it to be prevalent in the upper atmospheres of planets at these temperatures,” lead author Jonathan Fraine told Space.com.

HAT-P-11b is found in the constellation Cygnus, about 124 light-years from Earth. It’s roughly four times the size of Earth, and is much closer to its parent star – it orbits at only one twentieth the distance between Earth and the Sun, making the trip once every five days. Its proximity also makes it much hotter than Earth, reaching temperatures as high as 1,120 degrees Fahrenheit.

Because of the smaller size, identifying the atmospheres of planets the size of Neptune, or even smaller “super Earths” can be challenging. In this study, the scientists attempted to describe the atmosphere of four other planets, only to be stymied by cloud cover. When clouds block light from passing through the planet’s atmosphere as it transitions in between Earth and its parent star, scientists are unable to effectively analyze the atmospheric composition.

Bigger planets, with their wider atmospheres, are not nearly as difficult to study.

Thankfully, HAT-P-11b is similar to exoplanet GJ436b, whose atmosphere has already been studied. Though one has clouds while the other doesn’t, the two planets are useful for comparison purposes.

“I like to consider them the bigger version of the Earth-Venus twin pair,” Fraine said of the planets HAT-P-11b and GJ436b. “They are basically the same mass, radius and temperature, but small changes in the formation, or even these bulk properties, may be causing vast changes in the atmospheric composition.”