Diamond Planet Discovered

Scientists from Australia, Germany, Italy, the UK and the USA, have detected a companion planet for Pulsar J1719-1438 in our Milky Way, and they believe that this companion planet could be made of diamond. The planet is thought to be small, less than 60,000km in diameter, with a mass slightly greater than that of Jupiter, about 2 x 10²⁷kg.
P1719-1438 and its planet are so close together that the planet is most likely to be a 'stripped-down' white dwarf, that is, one that has lost its outer layers and over 99.9% of its original mass. Based on the planet's orbiting times, the scientists think that this remnant is likely to be made up mostly of carbon and oxygen, while its high density suggests that the material present is crystalline, which leads them to believe that the planet could contain a sizable proportion of diamond.

Graphite can be transformed into diamond under pressures of more than about 4GPa, as is shown in the simplified phase diagram on the right. On Earth, diamonds can be formed in the mantle where the pressure is great enough to transform carbon sources into diamonds. Diamonds can also form when a meteorite impacts on the Earth because the impact creates a zone of high pressure and temperature in which carbon can be transformed into diamond.

Reference
M. Bailes, S. D. Bates, V. Bhalerao, N. D. R. Bhat, M. Burgay, S. Burke-Spolaor, N. D'Amico, S. Johnston, M. J. Keith, M. Kramer, S. R. Kulkarni, L. Levin, A. G. Lyne, S. Milia, A. Possenti, L. Spitler, B. Stappers, W. van Straten. Transformation of a Star into a Planet in a Millisecond Pulsar Binary. Science, 2011; DOI: 10.1126/science.1208890

Further Reading
Mass Conversions
Density Calculations
Allotropes

Study Questions

1. Convert 60,000km to a distance in:
   • meters
   • centimeters
     
   • millimeters
     
2. Convert 2 x 10²⁷kg to a mass in
   • grams
   • megagrams
   • gigagrams
     
3. What is the approximate radius of of the planet in cm?
4. What is the volume of the planet in cm³ (assuming the planet is spherical)?
5. Calculate the approximate density of the newly discovered planet (in g/cm³).
6. Convert 4GPa to a pressure in:
   • kilopascals
   • pascals
   • megapascals
   • atmospheres
     
   
   
7. Using the phase diagram for carbon in the article above:
   • What is the minimum temperature and pressure required to produce liquid carbon from gaseous carbon?
   • What is the maximum pressure at which graphite can exist?
   • What is the maximum temperature at which graphite can exist?
     
   • How many phases of carbon are present at 4500K and 0.01GPa?
   • What is the triple point for diamond?