Super-terrestials, super-terrestial planets, super-Earths. They go by a lot of names.
Basically, super- worlds are moderately sized, intermediate in mass between Earth and the Gas Giants. Unfortunately, there are a plethora of planetary classification schemes, so no one really has a good idea of what to really call all these new planets. I like the Star Trek planetary classification scheme, but I am biased. It suffers from be Science Fiction and doesn’t have a lot of scientific basis. However, this is probably due to the fact that it was developed about 40 years before we actual found any other planets.
Thanks to the Kepler mission, scientists are starting to get some idea of the size and types of planets roaming the Universe, at least the small part we have looked at, and are working on new theories to account for what is out there.
For example, the planet Gliese 436b (we have GOT to start naming planets something else) has a lot of water. But it isn’t just any water, because Gliese 436b is almost 15 times closer to its sun than Mercury is to our sun. Needless to say it is very hot. So how does all this water not evaporate into space?
|Amorphous ice||Amorphous ice is an ice lacking crystal structure. Amorphous ice exists in three forms: low-density (LDA) formed at atmospheric pressure, or below, high density (HDA) and very high density amorphous ice (VHDA), forming at higher pressures. LDA forms by extremely quick cooling of liquid water (“hyperquenched glassy water”, HGW), by depositing water vapour on very cold substrates (“amorphous solid water”, ASW) or by heating high density forms of ice at ambient pressure (“LDA”).|
|Ice Ih||Normal hexagonal crystalline ice. Virtually all ice in the biosphere is ice Ih, with the exception only of a small amount of ice Ic.|
|Ice Ic||A metastable cubic crystalline variant of ice. The oxygen atoms are arranged in a diamond structure. It is produced at temperatures between 130 and 220 K, and can exist up to 240 K, when it transforms into ice Ih. It may occasionally be present in the upper atmosphere.|
|Ice II||A rhombohedral crystalline form with highly ordered structure. Formed from ice Ih by compressing it at temperature of 190–210 K. When heated, it undergoes transformation to ice III.|
|Ice III||A tetragonal crystalline ice, formed by cooling water down to 250 K at 300 MPa. Least dense of the high-pressure phases. Denser than water.|
|Ice IV||A metastable rhombohedral phase. It can be formed by heating high-density amorphous ice slowly at a pressure of 810 MPa. It doesn’t form easily without a nucleating agent.|
|Ice V||A monoclinic crystalline phase. Formed by cooling water to 253 K at 500 MPa. Most complicated structure of all the phases.|
|Ice VI||A tetragonal crystalline phase. Formed by cooling water to 270 K at 1.1 GPa. Exhibits Debye relaxation.|
|Ice VII||A cubic phase. The hydrogen atoms’ positions are disordered. Exhibits Debye relaxation. The hydrogen bonds form two interpenetrating lattices.|
|Ice VIII||A more ordered version of ice VII, where the hydrogen atoms assume fixed positions. It is formed from ice VII, by cooling it below 5 °C (278 K).|
|Ice IX||A tetragonal phase. Formed gradually from ice III by cooling it from 208 K to 165 K, stable below 140 K and pressures between 200 MPa and 400 MPa. It has density of 1.16 g/cm3, slightly higher than ordinary ice.|
|Ice X||Proton-ordered symmetric ice. Forms at about 70 GPa.|
|Ice XI||An orthorhombic, low-temperature equilibrium form of hexagonal ice. It is ferroelectric. Ice XI is considered the most stable configuration of ice Ih. The natural transformation process is very slow and ice XI has been found in Antarctic ice 100 to 10,000 years old. That study indicated that the temperature below which ice XI forms is −36 °C (240 K).|
|Ice XII||A tetragonal, metastable, dense crystalline phase. It is observed in the phase space of ice V and ice VI. It can be prepared by heating high-density amorphous ice from 77 K to about 183 K at 810 MPa. It has a density of 1.3 g cm−3 at 127 K (i.e., approximately 1.3 times more dense than water).|
|Ice XIII||A monoclinic crystalline phase. Formed by cooling water to below 130 K at 500 MPa. The proton-ordered form of ice V.|
|Ice XIV||An orthorhombic crystalline phase. Formed below 118 K at 1.2 GPa. The proton-ordered form of ice XII.|
|Ice XV||The proton-ordered form of ice VI formed by cooling water to around 80–108 K at 1.1 GPa.|
Water has this interesting property that ice will form at different temperatures, as long as there is enough pressure. My favorite example is from Kurt Vonnegut’s book Cat’s Craddle where ice 9 played an important part of the plot. So Gliese 436b is a “hot ice” planet. That means it is big enough and has enough atmosphere and gravity to form ice at the planets surface temperature of 822 °F (439 °C) which is just slightly over the boiling point. As a matter of fact, the hottest planet in our solar system, Venus, is about this hot, but doesn’t have any water that we have found (yet).
It will be very interesting to see how scientists attempt to catalogue everything into nice neat piles and then watch as the Universe throws a curve ball so nothing fits in those categories anymore. Oh, well. Just another day in the incredibly complex Universe.
– Ex astris, scientia –
I am and avid amateur astronomer and intellectual property attorney in Pasadena, California and I am a Rising Star as rated by Super Lawyers Magazine. As a former Chief Petty Officer in the U.S. Navy, I am a proud member of the Armed Service Committee of the Los Angeles County Bar Association working to aid all active duty and veterans in our communities. Connect with me on Google +