Extraterrestrial liquid water extrasolar planetary systems appear to have very different compositions to the Solar System, though there is probably sample bias arising from the detection methods. Liquid water has a distinct absorption spectroscopy signature compared to other states of water due to the state of its hydrogen bonds. Despite the confirmation of extraterrestrial water vapor and ice, however, the spectral signature of liquid water is yet to be confirmed outside of Earth. The signatures of surface water on terrestrial planets may be undetectable through thick atmospheres across the vast distances of space using current technology. Seasonal flows on warm Martian slopes, though
Gas giant Hot Jupiters are class IV or V. A cold hydrogen-rich gas giant more massive than Jupiter but less than about () will only be slightly larger in volume than Jupiter. For masses above , gravity will cause the planet to shrink (see degenerate matter). Kelvin–Helmholtz heating can cause a gas giant to radiate more energy than it receives from its host star. Although the words "gas" and "giant" are often combined, hydrogen planets need not be as large as the familiar gas giants from the Solar System. However, smaller gas planets and planets closer to their star will lose atmospheric