Spaceflight Insider

NASA’s Kepler mission discovers Earth’s larger, older cousin

The Kepler-452 system compared in size and scale alongside the Kepler-186 system and the Solar System.

Kepler-452 system compared in size and scale alongside the Kepler-186 system and the Solar System. Kepler-186 is a miniature stellar system that would fit entirely inside the orbit of Mercury. Image Credits: NASA/JPL-CalTech/R. Hurt

Scientists with NASA’s Kepler mission announced on Thursday, July 23, the confirmation of the first near-Earth-size planet in the “habitable zone” around a Sun-like star. The newly discovered planet, Kepler-452b, is the smallest planet found to date that orbits a Sun-like star in the habitable zone, the area around a star where liquid water could pool on the planet’s surface. The confirmation of Kepler-452b brings the number of confirmed planets to 1,030.

“On the 20th anniversary year of the discovery that proved other suns host planets, the Kepler exoplanet explorer has discovered a planet and star which most closely resemble the Earth and our Sun,” said John Grunsfeld, associate administrator of NASA’s Science Mission Directorate at the agency’s headquarters in Washington. “This exciting result brings us one step closer to finding an Earth 2.0.”

On Launch Pad 17-B at Cape Canaveral Air Force Station in Florida, United Launch Alliance's Delta II rocket carrying NASA's Kepler spacecraft rises through the exhaust cloud created by the firing of the rocket's engines. Liftoff was on time at 10:49 p.m. EST on March 6, 2009. Photo Credit: Carleton Bailie / SpaceFlight Insider

On Launch Pad 17-B at Cape Canaveral Air Force Station in Florida, United Launch Alliance’s Delta II rocket carrying NASA’s Kepler spacecraft rises through the exhaust cloud created by the firing of the rocket’s engines. Liftoff was on time at 10:49 p.m. EST on March 6, 2009. Photo Credit: Carleton Bailie / SpaceFlight Insider

Kepler-452b is about 60 percent larger than Earth in diameter, which puts it into the category of a super-Earth-size planet.

While previous research indicated that planets of Kepler-452b’s general size have a good chance of being rocky, its mass and composition have yet to be determined.

As is the case with all exoplanets, scientists from different points across the globe will study this newly-discovered world and work to validate or disprove these initial findings.

Kepler-452b’s 385-day long orbit is approximately 5 percent longer than Earth’s. The planet is also 5 percent farther from Kepler-452, the star that it orbits, than the Earth is from the Sun.

Kepler-452 is 6 billion years old, 1.5 billion years old than the Sun and has the same temperature. The star has a 10 percent larger diameter than the Sun and is 20 percent brighter.

“We can think of Kepler-452b as an older, bigger cousin to Earth, providing an opportunity to understand and reflect upon Earth’s evolving environment,” said Jon Jenkins, Kepler data analysis lead at NASA’s Ames Research Center in Moffett Field, California, who led the team that discovered Kepler-452b. “It’s awe-inspiring to consider that this planet has spent 6 billion years in the habitable zone of its star; longer than Earth. That’s substantial opportunity for life to arise, should all the necessary ingredients and conditions for life exist on this planet.”

In order to confirm the finding and learn more about the Kepler-452 system, the team conducted ground-based observations at the University of Texas at Austin’s McDonald Observatory, the Fred Lawrence Whipple Observatory on Mt. Hopkins in Arizona, and the W. M. Keck Observatory atop Mauna Kea in Hawaii.

These observations were important in terms of confirming that Kepler-452b was actually a planet. They helped researchers to establish the planet’s size as well as its orbit, and to refine the size and brightness of its parent star.

The Kepler-452 system is 1,400 light-years from Earth, in the constellation Cygnus. The paper documenting this discovery will be published in The Astronomical Journal.

In addition to Kepler-452b, there are 11 other habitable zone candidate planets that are between one and two times the diameter of the Earth in size. These potential planets are part of a group of 521 candidates that resulted from analysis of observations conducted from May 2009 to May 2013. Further observations and analysis will be required to confirm that the candidates are actual planets.

The Kepler spacecraft was launched on March 7, 2009, atop a United Launch Alliance Delta II rocket from Cape Canaveral Air Force Station’s Space Launch Complex 17-B (SLC-17B) located in Florida. On April 7, 2009, the cover of the telescope was jettisoned into space and the first images were captured on the following day.

This artist's concept depicts one possible appearance of the planet Kepler-452b, the first near-Earth-size world to be found in the habitable zone of star that is similar to our sun. Image Credit: NASA/JPL-Caltech/T. Pyle

This artist’s concept depicts one possible appearance of the planet Kepler-452b, the first near-Earth-size world to be found in the habitable zone of star that is similar to our Sun. Image Credit: NASA / JPL-Caltech / T. Pyle


Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise.

While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004.

Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.

Reader Comments

While Kepler 452b appears to be inside the habitable zone of the star it orbits, with a radius 1.6 times that of Earth, it is actually a bit more likely to be a mini-Neptune with no prospects of being habitable in the conventional sense than a rocky Earth-like planet. Still, there are more promising “Earth twins” (i.e. Earth-size planets in Earth-like orbits around Sun-like stars) exoplanet candidates currently being studied by the Kepler science team:

It is only a matter of time before scientists find a confirmed “Earth twin”.

Andrew, How could it possibly be an ‘Ice Giant’ like Neptune?
Way to close to its sun.

Brian,there is a quickly growing list of hundreds of extrasolar planets categorized by astronomers as Neptune-like and mini-Neptunes (i.e. between Earth and Neptune in mass and radius) with effective stellar fluxes ranging up to several hundred times higher than Earth.In fact, the majority of the extrasolar planets discovered by Kepler are categorized as “warm” or even “hot Neptunes”. And while Uranus and Neptune are categorized as “ice giants”, the “ice” in their interiors are high pressure (i.e. tens of thousands of atmospheres) and high temperature (i.e. thousands of degrees) forms of water, ammonia and methane ice very unlike the ice cubes you might use to cool your favorite summer beverage.

Edit; Should have been ‘ice Gas Giant’

No edit required: Uranus and Neptune are typically categorized today as “ice giants”, but like I have mentioned, their interiors are composed of high pressure/temperature forms of water, ammonia and methane ice. And while the “ice giants” of our solar system exist in the colder outer regions, they can also form and exist under much higher temperature conditions in many other planetary systems just as gas giants like Jupiter.

I believe, according to the articles I’ve read, that the size of this planet gives it a > 50% chance of being rocky and not an ice giant.

Also, please check the original article on the NASA site:

The article states:

“In addition to confirming Kepler-452b, the Kepler team has increased the number of new exoplanet candidates by 521 from their analysis of observations conducted from May 2009 to May 2013, raising the number of planet candidates detected by the Kepler mission to 4,696. Candidates require follow-up observations and analysis to verify they are actual planets.

Twelve of the new planet candidates have diameters between one to two times that of Earth, and orbit in their star’s habitable zone. Of these, nine orbit stars that are similar to our sun in size and temperature.”

That would bring the total, if all are confirmed, to 10 planets like Earth, that we know of, so far, in that one small patch of sky being studied by the Kepler space telescope. All I can say is…wow. The implications are truly staggering.

With all the detections of “hot Jupiters” (gas giants orbiting very close to their parent star) and not finding any Earth-sized worlds in habitable zones, I was beginning to wonder, even though I knew the bias for early detections was for planets like hot Jupiters, if there really was a significant population of solar systems out there that would have worlds like ours. Given this one, let alone these 10, the answer is that our Milky Way Galaxy alone has at least millions, based on probability and the assumption that distributions will be similar if you look at other patches of sky in the galactic plane. That’s a pretty awesome realization. People have conjectured this before, but never has there been any evidence to go on – until now.

Because of that, this might truly be one of the greatest discoveries mankind has made to date. This has nothing to do with visiting it, with the problems on our planet, or the idea of trashing this planet and moving to a new one. This has to do with how common Earth-like worlds are and how likely it is we might find something like ourselves out there. And the odds just went way, way up. That’s huge. Let’s celebrate this for what it is and not lose sight of the importance of this discovery.

Joe, an independent assessment of the chances this world being a terrestrial or rocky planet puts the odds at no greater than 40% (not all that different than what NASA’s press release but still less than even odds). See the following and the cited peer reviewed references included:

This assessment is based largely on the work of Leslie Rogers (A Hubble Fellow at Caltech) to derive a mass/radius relationship for Earth to Neptune-size worlds using Kepler data and masses derived from radial velocity surveys.

Leslie A. Rogers, “Most 1.6 Earth-Radius Planets are not Rocky”, The Astrophysical Journal, Vol. 801, No. 1, Article id. 41, March 2015

In either case, the difference is really not all that large but I am looking forward to seeing a copy of the peer-reviewed discovery paper to see if it includes this oft-cited “>50%” figure and how it was derived.

Great information. Great access!!!

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