Planetary Sciences News

Scientists Find "Close Cousin" of Earth

The Kepler space telescope spots a planet in a solar system 1400 light years away that closely resembles Earth in its size, distance from its star, and the type of star it orbits.

By

NASA’s Kepler mission has discovered the first small planet orbiting a star other than our Sun that both occupies the “habitable zone”—where liquid water can exist—and circles a distant star similar to our own, scientists announced at a briefing today.

Although the new planet, Kepler-452b, measures about 60% larger in diameter than Earth, it has a 385-day orbit, just about the same as Earth’s. It orbits just 5% farther from its star than Earth does from the Sun, and it could have an Earth-like rocky composition based on previous research of other planets its size, according to scientists.

Because of the similar circumstances for Earth and Kepler-452b, conditions on the newfound planet—called an extrasolar planet, or exoplanet because it is in a remote solar system—are thought to be not too hot and not too cold for water on its surface to remain a liquid. Although many other extrasolar planets have previously been found that occupy that same “Goldilocks zone” or habitable zone, this one stands out as the first nearly as small as Earth.

A Star Like Our Sun

The newfound planet’s star, Kepler-452, resembles our Sun in that it is also a so-called G-type star; appears—based on its color—to have a similar temperature to our Sun; and seems to be only roughly 1.5 billion years older than our approximately 4.5 billion-year-old Sun, scientists at the briefing said. The planet, which looks to be the only one in orbit around its sun, lies about 1400 light years away from our solar system in the Cygnus constellation.

Kepler-452b “is the closest thing that we have to another place that somebody else might call home,” said Jon Jenkins, Kepler data analysis lead at NASA’s Ames Research Center in Moffett Field, Calif.

John Grunsfeld, associate administrator for NASA’s Science Mission Directorate, called Kepler-452b “a pretty close cousin” to Earth.

Finding Planets

The Kepler mission uses a space telescope of the same name to scrutinize distant stars for evidence of other bodies—possibly planets—passing across stellar faces. These transits are seen as tiny dips in the brightness of the background star.

If these blips recur with the same exact recorded decrease in brightness, it is likely that a planet is passing in front of the star. Once detected, the planet’s orbital size—and thus the distance between it and its host star—can be approximated from the recurrence period, and its size can be estimated by how much the planet’s bulk causes the star behind it to dim.

A scatter chart of extrasolar planet candidates by size and how long they take to orbit their stars show   previous discoveries through January 2015 as blue dots, while yellow dots depict more than 500 new candidates just added to the catalog. Credit: NASA Ames/W. Stenzel
A scatter chart of extrasolar planet candidates by size and how long they take to orbit their stars show previous discoveries through January 2015 as blue dots, while yellow dots depict more than 500 new candidates just added to the catalog. Credit: NASA Ames/W. Stenzel

The mission first observed Kepler-452b in 2012, but scientists did not have enough data to confirm that it was indeed a planet until now.

Catalog Grows

Based on the Kepler telescope’s most recent observations, the mission added 512 exoplanet candidates, including Kepler-452b, to its catalog today, increasing the total number of exoplanet candidates to 4696. Today’s announcement also puts the total number of confirmed extrasolar planets at 1030.

Twelve of the new additions to the catalog—including the new “cousin” planet—orbit in the habitable zone around their sun, and nine of those orbit sun-like stars, according to Jeff Coughlin, Kepler research scientist at the Search for Extraterrestrial Intelligence Institute in Mountain View, Calif.

—Randy Showstack, Staff Writer

Citation: Showstack, R. (2015), Scientists find “close cousin” of Earth, Eos, 96, doi:10.1029/2015EO033235. Published on 23 July 2015.

© 2015. The authors. CC BY-NC 3.0