New research this past December, led by Yale University scientists, suggests that a rocky planet twice
Earth's size orbiting a nearby star is a diamond planet. "This is our
first glimpse of a rocky world with a fundamentally different chemistry
from Earth," said lead researcher Nikku Madhusudhan, a Yale postdoctoral
researcher in physics and astronomy. "The surface of this planet is
likely covered in graphite and diamond rather than water and granite."
The study estimates that at least a third of the planet's mass—the
equivalent of about three Earth masses—could be diamond.
"By contrast, Earth's interior is rich in oxygen, but extremely poor in
carbon—less than a part in thousand by mass," says co-author and Yale
geophysicist Kanani Lee. The identification of a carbon-rich super-Earth means
that distant rocky planets can no longer be assumed to have chemical
constituents, interiors, atmospheres, or biologies similar to those of
Earth.
The paper reporting the findings has been accepted for publication in the journal Astrophysical Journal Letters. The planet—called 55 Cancri e—has
a radius twice Earth's, and a mass eight times greater, making it a
"super-Earth." It is one of five planets orbiting a sun-like star, 55
Cancri, that is located 40 light years from Earth yet visible to the
naked eye in the constellation of Cancer.
The planet orbits at hyper speed—its year lasts just 18 hours, in
contrast to Earth's 365 days. It is also blazingly hot, with a
temperature of about 3,900 degrees Fahrenheit, researchers said, a far
cry from a habitable world. The planet was first observed transiting its
star last year, allowing astronomers to measure its radius for the
first time. This new information, combined with the most recent estimate
of its mass, allowed Madhusudhan and colleagues to infer its chemical
composition using models of its interior and computing all possible
combinations of elements and compounds that would yield those specific
characteristics.
Astronomers had previously reported that the host star has more
carbon than oxygen, and Madhusudhan and colleagues confirmed that
substantial amounts of carbon and silicon carbide, and a negligible
amount of water ice, were available during the planet's formation.
Astronomers also thought 55 Cancri e contained a substantial amount of
super-heated water, based on the assumption that its chemical makeup was
similar to Earth's, Madhusudhan said. But the new research suggests the
planet has no water at all, and appears to be composed primarily of
carbon (as graphite and diamond), iron, silicon carbide, and, possibly,
some silicates.
The discovery also opens new avenues for the study of geochemistry
and geophysical processes in Earth-sized alien planets. A carbon-rich
composition could influence the planet's thermal evolution and plate
tectonics, for example, with implications for volcanism, seismic
activity, and mountain formation. "Stars are simple—given a star's mass
and age, you know its basic structure and history," said David Spergel, professor of astronomy and chair of astrophysical sciences atPrinceton University, who is not a co-author of the study. "Planets are much more complex.
This 'diamond-rich super-Earth' is likely just one example of the
rich sets of discoveries that await us as we begin to explore planets
around nearby stars." In 2011, Madhusudhan led the first discovery of a
carbon-rich atmosphere in a distant gas giant planet, opening the
possibility of long-theorized carbon-rich rocky planets (or "diamond
planets")
The new research represents the first time that astronomers have
identified a likely diamond planet around a sun-like star and specified
its chemical make-up. Follow-up observations of the planet's atmosphere
and additional estimates of the stellar composition would strengthen the
findings about the planet's chemical composition.
For more information: "A Possible Carbon-rich Interior in Super-Earth 55 Cancri e," Astrophysical Journal Letters. Journal reference: Astrophysical Journal Letters
Image credit: NASA
Source: The Daily Galaxy via Yale University
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