Carbon planets are “oddball” worlds; strange beasts inhabiting the planetary zoo, that belong to the distant families of stars beyond our Sun. Extremely dark, bizarre, rocky, and very rich in the element carbon, some planetary scientists propose that at least one-third of a carbon planet’s mass is composed of diamond. While our own Earth is composed of silicate rocks, a core of iron, and a slender coating of water and life, worlds such as our own may not have been the first planets in the Universe to have hosted living creatures. In June 2016, astronomers suggested that the first potentially habitable alien worlds to form in the Cosmos might have been these strange, dark diamond planets. The new research suggests that planet-birth in the ancient Universe might have created carbon planets composed of graphite, carbides, and diamond–and that astronomers might discover these distant diamonds in the sky by searching for a rare class of stars.
“This work shows that even stars làm bằng đại học a tiny fraction of the carbon in our Solar System can host planets,” commented Natalie Mashian in a June 7, 2016 Harvard-Smithsonian Center for Astrophysics (CfA) Press Release. Mashian is the lead author of the study and a graduate student at Harvard University in Cambridge, Massachusetts.
The primordial Universe was composed primarily of hydrogen and helium. A pristine expanse, the ancient Cosmos was devoid of chemical elements like carbon and oxygen so necessary for the emergence and evolution of life as we know it. Only after the first stars were born, blasting the dark and dismal Universe with their brilliant flames of fabulous light, could life somehow mysteriously develop from strange cradles composed of non-living substances. When the first generation of stars blasted themselves to smithereens in violent supernovae explosions, they seeded the second stellar generation with the elements that could give rise to planet formation–making life as we know it possible.
Carbon planets are distant, weird worlds that contain more carbon than oxygen. Dr. Marc Kuchner ( NASA’s Goddard Space Flight Center) and Dr. Sara Seager (MIT) coined the term for these hypothetical exoplanets in 2005 on the basis of a suggestion made by Dr. Katherina Lodders (Washington University in St. Louis) that our Solar System’s behemoth Jupiter developed from a carbon-laden core. Earlier studies of exoplanets with high carbon-to-oxygen ratios were conducted by Dr. Bruce Fegley (Washington University in St. Louis) and the late Dr. Alastair G. W. Cameron (Harvard University) in 1987. Many planetary scientists think that carbon planets could be born if a baby star’s surrounding protoplanetary accretion disk is carbon-rich and oxygen-poor. These dark diamonds in the sky would not develop in the same way as Venus, Earth, and Mars, which are made up primarily of silicon-oxygen compounds. This theory is based on credible scientific ideas and has gained a great deal of support among scientists. Different planetary systems possess different carbon-to-oxygen ratios, with our own Solar System’s planets being best described as “oxygen planets”. There are currently two unconfirmed, potential carbon planet discoveries: PSR J1719-1438 b, detected on August 25, 2011, and 55 Cancri e. The exoplanet 55 Cancri e was detected while it was in the act of floating (transiting) across the brilliant, glaring face of its parent-star, 55 Cancri–a glittering inhabitant of the Cancer constellation that is approximately 40 light-years from our Solar System. 55 Cancri is a particularly brilliant star, and because of its dazzling light, astronomers were able to obtain information about its potentially carbon-rich planet. Transit events enabled astronomers to determine 55 Cancri e’s chemical composition.
Dark Diamonds In the Sky
The first batch of exoplanets were discovered back in 1992. Since then, literally thousands of planets belonging to the families of stars other than our Sun have been discovered by planet-hunting astronomers. The discoveries of distant wonder-worlds have rapidly come pouring in over the past generation, and many of these planets have proven to be so decidedly alien in their attributes that they are unlike anything astronomers had previously thought could exist–or even dreamed of ever seeing. From hot-Jupiter gas-giants, that cling very closely to their parent-stars in tight, broiling orbits, to other gas-giants that have roamed far from their place of birth, to carbon planets that display exotic chemistries, to a second generation of planets that have been born around a type of stellar ghost called a white dwarf star, astronomers have certainly learned to expect the unexpected. This is because their discoveries have over and over and over again confounded their expectations. So far, we have no evidence of life existing beyond Earth–but that doesn’t mean it isn’t there.
Dr. Alexander Wolszczan, an astronomer at Pennsylvania State University, made the historic first detection of planets beyond our own Sun. At the end of the 20th-century, Dr. Wolszczan observed the tattle-tale radio emissions coming from a compact millisecond pulsar located about 1,300 light-years from Earth. The parent-pulsar, dubbed PSR B1257+12, is a tiny, very dense denizen of the Virgo constellation, and like white dwarf stars–which are the relic cores of dead Sunlike stars–it is the ghostly remains of a once-living, hydrogen-burning, main-sequence star still on the Hertzsprung-Russell Diagram of stellar evolution. However, in the case of a pulsar, the progenitor star was much more massive than our Sun. A pulsar is a small ball of approximately 12 to 20 miles in diameter, that is all that is left of a once massive star that died in the fiery rage of a supernova blast that tore it to pieces. Pulsars harbor up to 1,000,000,000 tons of matter, pulled powerfully together into a sphere the size of a city like Dallas. A pulsar is a newborn, whirling neutron star, and these strange stellar corpses have densities that are equal to approximately 1,000,000 times that of water.
It was ultimately determined that PSR B1257+12 is circled by a family of several bizarre planets. The pulsar planets are believed to be rocky bodies like our own planet–but this is where all similarities come to a screeching halt. Pulsar planets, very much unlike our Earth, cannot hold on to an atmosphere. In fact, they are hostile, barren, dangerous worlds that are constantly showered by deadly radiation emanating from their parent stellar-ghost of a star.
Pulsars were about the last place astronomers once thought could host planets. However, such bizarre worlds proved to be the first tip of the proverbial iceberg, singing a siren’s song to astronomers that a vast number of other surprising “oddballs” were waiting to be discovered in the alien, exotic families of distant stars. Furthermore, the unfortunate, tormented planets circling PSR B1257+12 may be carbon planets with hard hearts of diamond.
Carbon planets are thought to harbor cores rich in iron or steel–just like the quartet of inner terrestrial planets inhabiting our Solar System: Mercury, Venus, Earth, and Mars. It is theorized that a layer of molten silicon carbide and titanium would surround the core of a carbon world and, above that, would be a layer of carbon in the form of graphite, that could potentially harbor a kilometers-thick substratum composed of diamond–that is, if there is enough pressure to produce it. It has been proposed that, during flaming volcanic eruptions, diamonds from the inner layers of a carbon planet could erupt up to the surface. This would result in mountains composed of diamonds and silicon carbides. The exotic surface of a carbon planet might be composed of liquid hydrocarbons (tar and methane) and carbon monoxide. It has also been suggested that, if a carbon world has an average surface temperature of below 77 degrees Celsius, it may also have a weather cycle if it has an atmosphere.
However, carbon planets probably have no water. This is because water would be unable to form on these arid worlds since any oxygen carried to them by crashing comets or asteroids would interact with the carbon on its surface. The atmosphere of a relatively cool carbon planet would probably be made up of carbon monoxide or carbon dioxide. This basically means that such a planet would be blanketed by carbon smog.
Geological features that are similar to those on our own planet may also be present on distant diamond worlds, but these features on the two different types of planets would have different compositions. For example, the rivers on these weird and exotic worlds would not be composed of rushing liquid water, but would instead consist of oils. If the temperature is adequately cool, then the gases would be able to photochemically synthesize into long-chain hydrocarbons. These hydrocarbons would pour down onto the carbon planet’s exotic surface.
The pulsar planets belonging to the family of PSR 1257+12 may have been born as a result of the ancient disruption of a carbon-producing star. It is also possible that carbon planets are located close to the Galactic Center, or within globular clusters orbiting our Milky Way, because this is where stars have a higher carbon-to-oxygen ratio than our Sun. When an elderly star has reached the end of that long stellar road, it emits huge quantities of carbon. As time goes by, and more and more generations of stars reach the end of the line, the concentration of carbon, and carbon planets, will increase.
There is also some evidence that the planets circling a type of small, relatively cool “failed star”, called a brown dwarf, are probably carbon planets depleted of water.
Did The First Life In The Universe Emerge On Diamond Planets?
Natalie Mashian and her doctoral thesis advisor, Dr. Avi Loeb of the CfA, studied a special class of elderly stars referred to as carbon-enhanced metal-poor stars, or CEMP stars. These iron-deficient stars harbor only about one hundred-thousandth as much iron as our Sun. This means that these anemic stars were born before interstellar space had been seeded with heavy atomic elements–those heavier than helium that are termed metals by astronomers. Only hydrogen, helium, and traces of beryllium were born in the Big Bang birth of the Universe almost 14 billion years ago–all of the metals were formed in the nuclear-fusing ovens within the searing-hot cores of stars, or else in the supernova blasts that heralded their demise. When stars perish, they toss their freshly-fused batch of metals into the space between stars, thus seeding the Cosmos with the stuff of life itself. The water that we drink, the sand beneath our feet, the iron in our blood, the calcium in our bones, are here because the stars are here. We are stardust.