July 30, 2015
Felicia Chou NASA Headquarters, Washington
Jet Propulsion Laboratory, Pasadena, Calif.
This artist’s conception shows the silhouette of a rocky planet, dubbed HD 219134b, as it passes in front of its star. At 21 light-years away, the planet is the closest outside of our solar system that can be seen crossing, or transiting, its star — a bonus for astronomers because transiting planets make ideal specimens for detailed studies of their atmospheres. It was discovered using the HARPS-North instrument on the Italian 3.6-meter National Galileo Telescope in the Canary Islands, and NASA’s Spitzer Space Telescope.
The planet, which is about 1.6 times the size of Earth, is also the nearest confirmed rocky planet outside our solar system. It orbits a star that is cooler and smaller than our sun, whipping closely around it in a mere three days. The proximity of the planet to the star means that it would be scorching hot and not habitable.
Transiting planets are ideal targets for astronomers wanting to know more about planetary compositions and atmospheres. As a planet passes in front of its star, it causes the starlight to dim, and telescopes can measure this effect. If molecules are present in the planet’s atmosphere, they can absorb certain wavelengths of light, leaving imprints in the starlight. This type of technique will be used in the future to investigate potentially habitable planets and search for signs of life.
This sky map shows the location of the star HD 219134 (circle), host to the nearest confirmed rocky planet found to date outside of our solar system. The star lies just off the “W” shape of the constellation Cassiopeia and can be seen with the naked eye in dark skies. It actually has multiple planets, none of which are habitable.
This artist’s rendition shows one possible appearance for the planet HD 219134b, the nearest confirmed rocky exoplanet found to date outside our solar system. The planet is 1.6 times the size of Earth, and whips around its star in just three days. Scientists predict that the scorching-hot planet — known to be rocky through measurements of its mass and size — would have a rocky, partially molten surface with geological activity, including possibly volcanoes.
Using NASA’s Spitzer Space Telescope, astronomers have confirmed the discovery of the nearest rocky planet outside our solar system, larger than Earth and a potential gold mine of science data.
Dubbed HD 219134b, this exoplanet, which orbits too close to its star to sustain life, is a mere 21 light-years away. While the planet itself can’t be seen directly, even by telescopes, the star it orbits is visible to the naked eye in dark skies in the Cassiopeia constellation, near the North Star.
HD 219134b is also the closest exoplanet to Earth to be detected transiting, or crossing in front of, its star and, therefore, perfect for extensive research.
“Transiting exoplanets are worth their weight in gold because they can be extensively characterized,” said Michael Werner, the project scientist for the Spitzer mission at NASA’s Jet Propulsion Laboratory in Pasadena, California. “This exoplanet will be one of the most studied for decades to come.”
The planet, initially discovered using the HARPS-North instrument on the Italian 3.6-meter Galileo National Telescope in the Canary Islands, is the subject of a study accepted for publication in the journal Astronomy & Astrophysics
Galileo National Telescope
Study lead author Ati Motalebi of the Geneva Observatory in Switzerland said she believes the planet is the ideal target for NASA’s James Webb Space Telescope in 2018.
“Webb and future large, ground-based observatories are sure to point at it and examine it in detail,” Motalebi said.
Only a small fraction of exoplanets can be detected transiting their stars due to their relative orientation to Earth. When the orientation is just right, the planet’s orbit places it between its star and Earth, dimming the detectable light of its star. It’s this dimming of the star that is actually captured by observatories such as Spitzer and can reveal not only the size of the planet but also clues about its composition.
“Most of the known planets are hundreds of light-years away. This one is practically a next-door neighbor,” said astronomer and study co-author Lars A. Buchhave of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. For reference, the closest known planet is GJ674b at 14.8 light-years away; its composition is unknown.
HD 219134b was first sighted by the HARPS-North instrument and a method called the radial velocity technique, in which a planet’s mass and orbit can be measured by the tug it exerts on its host star. The planet was determined to have a mass 4.5 times that of Earth, and a speedy three-day orbit around its star.
Spitzer followed up on the finding, discovering the planet transits its star. Infrared measurements from Spitzer revealed the planet’s size, about 1.6 times that of Earth. Combining the size and mass gives it a density of 3.5 ounces per cubic inch (six grams per cubic centimeter) — confirming HD 219134b is a rocky planet.
Now that astronomers know HD 219134b transits its star, scientists will be scrambling to observe it from the ground and space. The goal is to tease chemical information out of the dimming starlight as the planet passes before it. If the planet has an atmosphere, chemicals in it can imprint patterns in the observed starlight.
Rocky planets such as this one, with bigger-than-Earth proportions, belong to a growing class of planets termed super-Earths.
“Thanks to NASA’s Kepler mission, we know super-Earths are ubiquitous in our galaxy, but we still know very little about them,” said co-author Michael Gillon of the University of Liege in Belgium, lead scientist for the Spitzer detection of the transit.
“Now we have a local specimen to study in greater detail. It can be considered a kind of Rosetta Stone for the study of super-Earths.”
Further observations with HARPS-North also revealed three more planets in the same star system, farther than HD 219134b. Two are relatively small and not too far from the star. Small, tightly packed multi-planet systems are completely different from our own solar system, but, like super-Earths, are being found in increasing numbers.
JPL manages the Spitzer mission for NASA’s Science Mission Directorate in Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Co. in Littleton, Colorado. Data are archived at the Infrared Science Archive, housed at Caltech’s Infrared Processing and Analysis Center.
For more information about NASA’s Spitzer Space Telescope, visit:
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Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge, on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.