NASA’s Spitzer Space Telescope has helped confirm the discovery of the closest rocky planet outside our solar system, just 21 light-years away.
The exoplanet dubbed as HD 219134b is larger than Earth and orbits too close to its star to sustain life. 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.
Michael Werner, the project scientist for the Spitzer mission said that transiting exoplanets were worth their weight in gold because they can be extensively characterised.
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.
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.
Rocky planets such as this one, with bigger-than-Earth proportions, belong to a growing class of planets termed super-Earths.
Lead scientist and co-author Michael Gillon of the University of Liege in Belgium, said that thanks to NASA’s Kepler mission, they knew super-Earths were ubiquitous in our galaxy, and now had a local specimen to study in greater detail.
It could be considered a kind of Rosetta Stone for the study of super-Earths, he added.
The research will be published in the journal Astronomy and Astrophysics.