In astrophysics and planetary science the term "ice" refers to volatile chemical compounds with freezing points above about 100 K (−280 °F; −173 °C), such as water, ammonia, or methane, with freezing points of 273, 195, and 91 K (31.7, −108.7, and −295.9 °F; −0.1, −78.1, and −182.2 °C), respectively.
In the 1990s, it was realized that Uranus and Neptune are a distinct class of giant planet, different from the other giant planets, Jupiter and Saturn. They have become known as ice giants. They were solids when the planets were stuck together during their formation. Today, little of the water in Uranus and Neptune is in the form of ice. Instead, the water is a supercritical fluid at the temperatures and pressures inside them.
Ice giants consist of only about 20% hydrogen and helium in mass, as opposed to the Solar System's gas giants, Jupiter and Saturn, which are both more than 90% hydrogen and helium in mass.
Questions and Answers
Q: What are ice giants?
A: Ice giants are huge planets made mostly of elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur.
Q: How many ice giants are in the Solar System?
A: There are two known ice giants in the Solar System - Uranus and Neptune.
Q: What is the definition of "ice" in astrophysics and planetary science?
A: In astrophysics and planetary science the term "ice" refers to volatile chemical compounds with freezing points above about 100 K (−280 °F; −173 °C), such as water, ammonia, or methane.
Q: How does the composition of ice giants compare to that of gas giants?
A: Ice giants consist of only about 20% hydrogen and helium in mass, whereas gas giants like Jupiter and Saturn are both more than 90% hydrogen and helium in mass.
Q: When were Uranus and Neptune discovered to be a distinct class from other giant planets?
A: It was realized that Uranus and Neptune were a distinct class of giant planet different from other giant planets like Jupiter and Saturn during the 1990s.
Q: What form is most of the water on Uranus & Neptune found in today?
A: Most of the water on Uranus & Neptune is found today as a supercritical fluid at temperatures & pressures inside them rather than being frozen into an icy form.
