Researchers have discovered a diamond planet 40 light years away from our solar system.
Led by postdoctoral fellow Nikku Madhusudhan of the Yale Physics Department, the research team has proposed that the planet 55 Cancri e has a carbon-based composition containing an outer layer of diamond that composes roughly a third of the planet’s mass. The planet revolves around a sun-like star called 55 Cancri A. The team’s research paper, which showed that the planet’s observed radius and mass could be best explained by a carbon-rich composition, will be published in the Astrophysical Journal Letters in a few weeks.
First detected in 2004, 55 Cancri e’s radius was measured in 2011 and its mass was calculated to be roughly eight times that of Earth. Yale geology and geophysics professor Kanani Lee, another author of the study, said 55 Cancri e’s mass classifies it as a “Super-Earth” — a planet with a mass larger than that of Earth but much smaller than that of large gaseous planets such as Neptune. To determine the planet’s composition, the research team generated a model of 55 Cancri e using a computer program that predicts a different hypothetical planetary mass and radius for each proposed chemical composition, Madhusudhan said. They then tried to find a composition with resulting mass and radius values closest to those of 55 Cancri e.
Having tried multiple Earth-like models in which iron, water and oxygen were abundant, the team found their desired result when they made carbon the dominant element on the planet. Madhusudhan said. Abundant traces of carbon were also found in the planet’s star, 55 Cancri A, and the model of the protoplanetary disk, which further supports the hypothesis, he added.
“The idea that rocky planets elsewhere could have completely different chemical compositions from Earth — it was very hard to get over that mental block,” Madhusudhan said. “We had to get rid of that bias and start looking at other compositions.”
Lee said the size similarity between 55 Cancri e and Earth makes their compositional difference even more significant.
The carbon-rich composition of 55 Cancri e’s suggests the presence of large amounts of diamond on the planet, Lee said. Since the planet’s orbiting period is 18 days as opposed to Earth’s 365 days, the surface temperature of the planet is approximately 4000 degrees Farenheit, she added. These high temperature and high pressure conditions favor diamond formation, she added.
“You could have a planet completely composed of diamond,” Lee said.
Madhusudhan and Lee both said further research on 55 Cancri e’s atmosphere should be conducted to confirm the accuracy of the proposed model. Adam Burrows, professor of astrophysical sciences at Princeton University, said the atmospheric thickness and composition of the planet must be determined before any definitive conclusion regarding the planet’s core can be drawn.
The Yale Center of Astronomy and Astrophysics, or the YCAA, awarded its postdoctoral prize fellowship to Madhusudhan in January. His project proposal was chosen from a pool of over 300 applicants, said YCAA director and astronomy professor Meg Urry. She added that the center viewed his research as instrumental in “creating synergies” between different disciplines, as exemplified by his collaboration with Lee.
Lee said the discovery of 55 Cancri e “helps us forget our biases of Earth-like planets.”
55 Cancri e and its star can be observed as part of the Cancer constellation.