Observing The Atmosphere Of A Diamond In The Sky

Super-Earths are fascinating exoplanet “oddballs” that are unlike anything in our own Solar System. Smaller than the quartet of outer, giant, gaseous worlds in orbit around our Sun, super-Earths are more massive than our planet, and they are composed of gas or rock or both. The exoplanet dubbed 55 Cancri e is a super-Earth that has a radius about twice that of our Earth, and it also sports a mass that is eight times greater. Carbon-rich, rocky, and very, very dark, it is thought that at least one-third of this “oddball’s” mass is composed of diamond. In February 2016, a team of astronomers announced that they had accomplished the first successful detection of gases in the atmosphere of this faraway super-Earth–the exotic atmosphere is light in weight, dry, and possibly laced with a bit of carbon, as well.

55 Cancri e had already been dubbed the “diamond planet” prior to this study. That is because models based on its mass and radius strongly suggest that its interior is carbon-rich. The research that shows the presence of hydrogen and helium–but no water vapor–in this exotic planet’s atmosphere, clearly reveals that it is very dry.

The astronomers who conducted this research used new processing techniques on data derived from the NASA/European Space Agency (ESA) Hubble Space Telescope (HST). The research was led by a University College London (UCL) team of European researchers who were able to study the atmosphere of 55 Cancri e, alternatively known as “Janssen”, in unprecedented detail. The results of this research appear in the February 16, 2016 issue of the The Astrophysical Journal.

“This is a very exciting result because it’s the first time that we have been able to find the spectral fingerprints that show the gases present in the atmosphere of a super-Earth. Our observations of 55 Cancri e‘s atmosphere suggest that the planet has managed to cling on to a significant amount of hydrogen and helium from the nebula from which it formed,” explained Angelos Tsiaras, a doctoral student at UCL, in a February 16, 2016 Europlanet Press Release. Mr. Tsiaras developed the analysis technique along with colleagues, Dr. Ingo Waldmann and Dr. Marco Rocchetto, in UCL’s Department of Physics & Astronomy.

Astronomers think that super-Earths are probably the most common type of planet inhabiting our Milky Way Galaxy, and they were given this name because they have a mass larger than Earth. The Wide Field Camera 3 (WFC3) on HST had previously been used to investigate the intriguing atmosphere of two other super-Earths, but no spectral features were seen in these earlier studies.

55 Cancri e has an 18 hour long year, as well as an extremely toasty surface temperature of as much as 2000 degrees Celsius. The “oddball” planet inhabits a solar system that circles around a parent-star, named 55 Cancri, that is sometimes alternatively referred to as “Copernicus.” 55 Cancri is a sparkling denizen of the Cancer constellation that is about 40 light years from Earth, and it is an especially brilliant star. Because of this star’s dazzling light, the team of astronomers were able to use new analysis techniques to obtain information about its carbon-rich planetary companion.

55 Cancri e was first detected while it was in the process of transiting across the glaring face of its parent-star. That transit event allowed astronomers to measure its radius. This newly acquired information, when combined with an estimation of the planet’s mass, enabled astronomers to determine its chemical composition.

History Of The Hunt

Ever since the first exoplanets were discovered back in 1992, about 2,000 of these distant, alien worlds–the planetary children of a star beyond our Sun–have been detected to date, and the discoveries of these weird wonder-worlds rapidly come pouring in. From hot-Jupiter gas-giants, that hug their parent-stars in tight, close, roasting orbits; to other gas-giant planets that have wandered far from their birthplace; to carbon planets showing exotic chemistries; to a second generation of planets a’borning around white dwarf stars, which are the relic cores of dead Sun-like stars; planet-hunting astronomers have learned to expect the unexpected. This is because their discoveries have time and time again confounded their expectations. So far, we have no evidence of life existing beyond our own planet, but with this treasure-trove of new discoveries rapidly coming in, the rather self-conceited notion that we have the Universe all to ourselves could easily change tomorrow.

Dr. Alexander Wolszczan, an astronomer at Pennsylvania State University, was the first to find the exoplanet holy grail, after having observed tattle-tale radio emissions emanating from a compact millisecond pulsar situated approximately 1,300 light-years from our planet.

The parental pulsar, dubbed PSR B1257+12, is a small, dense inhabitant of the Virgo constellation. A pulsar is a relatively small sphere, perhaps 12 to 20 miles in diameter, that is the relic remains of a massive star that perished in the flames of a ferocious supernova explosion. Pulsars contain up to 1,000,000,000 tons of matter, squeezed mercilessly into the size of a city like Tokyo. A pulsar is actually a young, wildly whirling neutron star, and these exotic stellar corpses possess a density that is equal to about 1,000,000 times that of the density of water.

It was eventually determined that PSR B1257+12 is orbited by several weird planets. The pulsar planets are thought to be rocky bodies like our Earth, but this is where all resemblance ends. Pulsar planets, in marked contrast to our planet, cannot sport an atmosphere. They are, in fact, extremely hostile worlds, showered in a constant bath of deadly radiation coming from their parent-stellar-relic.

The vicinity of a pulsar was about the last place that astronomers expected to find planets. Such strange beasts inhabiting the planetary zoo were the first to promise that a myriad of other strange “oddballs” exist in the alien families of other stars beyond our Sun.

In fact, the unfortunate planets circling PSR B1257+12 may be carbon planets that were born as the result of the disruption of a carbon-producing star.

Carbon Planets

A carbon planet is one that contains more carbon than oxygen, and it is thought that these strange, distant worlds are born from nourishing protoplanetary accretion disks that are rich in carbon–but poor in oxygen. Therefore, these exotic worlds would not develop in the same way as the quartet of relatively small, rocky, inner terrestrial planets of our Sun’s family (Mercury, Venus, Earth, and Mars), which are made up primarily of silicon-oxygen compounds. This particular theory is now based on strong scientific evidence, and it has been gaining increasing acceptance in the planetary science community. Differing planetary systems possess differing carbon-to-oxygen ratios, with our own Solar System’s quartet of terrestrial planets closer to being designated “oxygen planets.”

A carbon planet would likely contain an iron-or steel-rich core like the four terrestrial planets of our Sun’s family. Encircling that core would be molten silicon carbide and titanium carbide. Above that, would probably be a layer of carbon in the form of graphite–possibly sporting a kilometers-thick substratum composed of diamond, if there is sufficient pressure to produce it. It has been suggested that, during fiery volcanic eruptions, diamonds from the interior could shoot up to the surface, resulting in mountains made of diamonds and silicon carbides. The alien surface of such a wonder-world would display frozen or liquid hydrocarbons (tar and methane) and carbon monoxide. There could also possibly be a weather cycle on carbon planets with an atmosphere–that is, if that strange world boasts an average surface temperature that is below 77 degrees Celsius.

But carbon planets will likely be bereft of water. Water cannot form on these very dry worlds because any oxygen carried to them by impacting comets or asteroids will react with the carbon on the “oddball’s” strange surface. The atmosphere on a relatively cool carbon planet would mostly be composed of carbon dioxide or carbon monoxide, which would produce an abundance of carbon smog.

Many planetary scientists predict that carbon planets will be of similar diameter to silicate and water planets of about the same mass, and this likeness between the two types potentially makes them difficult to distinguish from one another. Geological features that are analogous to those on Earth may also be present on these carbon worlds, but with different compositions. For example, the rivers on these exotic planets may not be composed of flowing liquid water, but would instead consist of oils. If the temperature is sufficiently cool, then gases may be able to photochemically synthesize into long-chain hydrocarbons. These hydrocarbons could rain down onto the carbon planet’s bizarre surface.

Distant Atmosphere Of A Diamond In The Sky

Observations were made of 55 Cancri by scanning WFC3 rapidly across its glaring stellar face in order to create a number of spectra. By putting these observations together, and then processing the information through a computer “pipeline” series of analysis, the scientists were able to retrieve the spectral fingerprints of 55 Cancri e embedded in the tattle-tale light of its brilliant star.

“This result gives a first insight into the atmosphere of a super-Earth. We now have clues as to what the planet is currently like, how it might have formed and evolved, and this has important implications for 55 Cancri e and other super-Earths,” explained Dr. Giovanna Tinetti in the February 16, 2016 Europlanet Press Release. Dr. Tinetti is of UCL.

It is very interesting that the data also show a tattle-tale signature for hydrogen cyanide. Hydrogen cynanide is a marker for carbon-rich atmospheres.

“Such an amount of hydrogen cyanide would indicate an atmosphere with a very high ratio of carbon to oxygen,” explained Dr. Olivia Venot in the same Press Release. Dr. Venot, of KU Leuven University, Belgium, developed an atmospheric chemical model of 55 Cancri e that strengthened the analysis of the observations.

“If the presence of hydrogen cyanide and other molecules is confirmed in a few years time by the next generation of infrared telescopes, it would support the theory that this planet is indeed carbon-rich and a very exotic place… hydrogen cynanide or prussic acid is highly poisonous, so it is perhaps not a planet I would like to live on!” commented Dr. Jonathan Tennyson of UCL in the February 16, 2016 Europlanet Press Release.

The results of this study are summarized by Angelos Tsiaras et al. in a paper titled Detection of an atmosphere around the super-Earth 55 Cancri e, published in The Astrophysical Journal.

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