NASA’s Kepler space telescope has spotted two planets engaged in an odd dance with each other, say scientists, a finding that is a first for the U.S. space organization and astronomers everywhere.
The finding, which was first reported in the June 21st Science Express, notes the appearance of a pair of planets engaged in a tight orbit with one another. Kepler-36, which is located approximately 1200 light-years from Earth, has two planets with vastly different densities orbiting close to each other. Astronomers believe that Kepler-36c might appear more than twice the size of the moon in the night sky of Kepler-36b.
“These two worlds are having close encounters,” said Josh Carter, a Hubble Fellow at the Harvard-Smithsonian Center for Astrophysics, in statement.
“They are the closest to each other of any planetary system we’ve found,” said the report’s co-author Eric Agol of the University of Washington. “The bigger planet is pushing the smaller planet around more, so the smaller planet was harder to find.”
Scientists say that Kepler-36b is roughly 1.5 times the size of Earth and approximately 4.5 times heavier. Kepler-36b orbits Kepler-36 about every 14 days at an average distance of less than 11 million miles. Kepler-36c, on the other hand, orbits at a distance of approximately 12 million miles, about every 16 days. The neighboring planet is roughly 3.7 times the size of Earth.
The smaller planet, according to the report’s authors, is 30 percent iron, 15 percent water and less than 1 percent atmospheric hydrogen and helium. Kepler-36c, however, is more like a “hot Neptune.”
The research team notes that the planets come within 1.2 million miles of each other during their odd dance. The distance is five times the Earth-moon distance, but 20 times closer to one another than any two planets found in our solar system. By comparison, Mars’ orbit is about 49 million miles outside Earth’s path, while Venus’ orbital path lies roughly 27 million miles inside Earth’s.
Despite their closeness, researchers say they will never collide due to the timing of their orbits.
Individually, each planet falls into a class detected elsewhere. The smaller, inner planet, Kepler-36b, has about 4.5 times Earth’s mass and is about 1.5 times as large. The planet is thought to be a rocky orb with an estimated 30 percent of its mass in the form of iron. Its larger, outer companion Kepler-36c, boasts eight times Earth’s mass with a “substantial” atmosphere of hydrogen and helium, according to the team making the discovery.
“Here we have a pair of planets in nearby orbits but with very different densities,” said astronomer Steve Kawaler of Iowa State University, one of the co-authors of the report appearing in the journal Science. “How they both got there and survived is a mystery.”
Two planets of such dramatically different compositions and such tightly packed orbits represent “an exciting system,” noted Mr. Agol.
Kepler-36c was first discovered in data from NASA’s Kepler space telescope. Kepler utilizes a photometer to examine light from distant objects and it can identify a planet when it crosses in front of its parent star. The transit momentarily diminishes the light coming from the star.
Mr. Agol proposed using an algorithm called quasi-periodic pulse detection to look for a second planet around Kepler-36. Mr. Carter used the algorithm to comb through Kepler’s data.
“We found this one on a first quick look,” Mr. Carter said. “We’re now combing through the Kepler data to try to locate more.”
The algorithm discovered data that unearthed a tiny fainting of light coming from Kepler-36 every 16 days. “If you look at the transit time pattern for the large planet and the transit time pattern for the smaller planet, they are mirror images of one another,” Mr. Agol said.
The researchers were able to determine several facts about the planets because they come within 1.2 million miles of each other. The team calculated each planet’s characteristics because of changes in their orbits due to gravitational effects on each other. Researchers were also able to make several observations about the parent star, including the fact that Kepler-36 is 25 percent as dense as the sun.
This result was made possible with asteroseismology, the study of stars by observing their natural oscillations. Sunlike stars resonate like musical instruments, due to sound waves trapped in their interiors. And just like a musical instrument, the larger the star, the “deeper” are its resonances. This trapped sound makes the stars gently breathe in and out, or oscillate.
“Kepler-36 shows beautiful oscillations. By measuring the oscillations we were able to measure the size, mass and age of the star to exquisite precision,” said study co-author Bill Chaplin of the University of Birmingham in a press statement. “Without asteroseismology, it would not have been possible to place such tight constraints on the properties of the planets.”
Researchers are struggling to understand how these two very different worlds ended up in such close orbits. Within our solar system, rocky planets reside close to the Sun while the gas giants remain distant.
Although Kepler-36 is the first planetary system found to experience such close encounters, it undoubtedly will not be the last.
“We’re wondering how many more like this are out there,” said astronomers. “We found this one on a first quick look,” added Carter. “We’re now combing through the Kepler data to try to locate more.”
Co-author Bill Chaplin (University of Birmingham, UK) noted, “Kepler-36 shows beautiful oscillations. By measuring the oscillations we were able to measure the size, mass and age of the star to exquisite precision.”
He added, “Without asteroseismology, it would not have been possible to place such tight constraints on the properties of the planets.”
NASA, the Space Telescope Science Institute and the National Science Foundation funded the research.