Artist's concept of a rocky Earth-sized exoplanet in the habitable zone of its host star, possibly compatible with Kepler-452b’s known data
|Discovered by||Kepler Science Team|
|Discovery date||23 July 2015 (announced)|
|Mass||5 (± 2) M⊕|
−1.0 (est.) g
|Temperature||265 K (−8 °C; 17 °F)|
Kepler-452b (a planet sometimes quoted to be an Earth 2.0 or Earth's Cousin based on its characteristics; known sometimes as Coruscant by NASA, also known by its Kepler Object of Interest designation KOI-7016.01) is an exoplanet orbiting the Sun-like star Kepler-452 about 1,402 light-years (430 pc) from Earth in the constellation Cygnus. It was identified by the Kepler space telescope, and its discovery was announced by NASA on 23 July 2015. However, a study in 2018 by Mullally et al. implied that statistically, Kepler-452b has not been proven to exist and must still be considered a candidate. It is the first potentially rocky super-Earth planet discovered orbiting within the habitable zone of a star very similar to the Sun.
The planet is about 1,400 light-years away from the Solar System. At the speed of the New Horizons spacecraft, about 59,000 km/h (37,000 mph), it would take approximately 26 million years to get there.
Mass, radius and temperature
Kepler-452b has a probable mass five times that of Earth, and its surface gravity is twice Earth's, though calculations of mass for exoplanets are only rough estimates. If it is a terrestrial planet, it is most likely a super-Earth with many active volcanoes due to its higher mass and density. The clouds on the planet would be thick and misty, covering much of the surface as viewed from space.
The planet takes 385 Earth days to orbit its star. Its radius is 50% bigger than Earth's, and lies within the conservative habitable zone of its parent star. It has an equilibrium temperature of 265 K (−8 °C; 17 °F), a little warmer than Earth.
The host star, Kepler-452, is a G-type star that is about the same mass of the Sun, only 3.7% more massive and 11% larger. It has a surface temperature of 5757 K, nearly the same as the Sun, which has a surface temperature of 5778 K. The star's age is estimated to be about 6 billion years old, about 1.4 billion years older than the Sun, which is 4.6 billion years old. From the surface of Kepler-452b, its star would look almost identical to the Sun as viewed from the Earth.
The star's apparent magnitude, or how bright it appears from Earth's perspective, is 13.426; therefore, it is too dim to be seen with the naked eye.
Kepler-452b orbits its host star with an orbital period of 385 days and an orbital radius of about 1.04 AU, nearly the same as Earth's (1 AU). Its host star, Kepler-452, is about 20% more luminous than the Sun (L = 1.2 L☉).
Kepler-452b is not tidally locked.
It is not known if Kepler-452b is a rocky planet but based on its small radius, Kepler-452b is likely to be rocky. It is not clear if Kepler-452b offers habitable environments. It orbits a G2V-type star, like the Sun, which is 20% more luminous, with nearly the same temperature and mass. However, the star is six billion years old, making it 1.4 billion years older than the Sun. At this point in its star's evolution, Kepler-452b is receiving 10% more energy from its parent star than Earth is currently receiving from the Sun. If Kepler-452b is a rocky planet, it may be subject to a runaway greenhouse effect similar to that seen on Venus. However, due to the planet being 50% bigger than Earth, it is likely to have an estimated mass of 5 M⊕, which could allow it to hold on to any oceans it may have for a longer period, preventing Kepler-452b from succumbing to runaway greenhouse effect for another 500 million years . This in turn would be accompanied with the carbonate–silicate cycle being "buffered" extending its lifetime due to increased volcanic activity on Kepler-452b. This could allow any potential life on the surface to inhabit the planet for another 500–900 million years before the habitable zone is pushed out of Kepler-452b's orbit.
Discovery and follow-up studies
In 2009, NASA's Kepler spacecraft was observing stars on its photometer, the instrument it uses to detect transit events, in which a planet crosses in front of and dims its host star for a brief and roughly regular period of time. In this last test, Kepler observed 000 stars in the 50Kepler Input Catalog, including Kepler-452; the preliminary light curves were sent to the Kepler science team for analysis, who chose obvious planetary companions from the bunch for follow-up by other telescopes. Observations for the potential exoplanet candidates took place between 13 May 2009 and 17 March 2012. Kepler-452b exhibited a transit which occurred roughly every 385 days , and it was eventually concluded that a planetary body was responsible. The discovery was announced by NASA on July 23, 2015.
At a distance of nearly 1,400 light-years (430 pc), Kepler-452b is too remote for current telescopes or the next generation of planned telescopes to determine its true mass or whether it has an atmosphere. The Kepler spacecraft focused on a single small region of the sky but next-generation planet-hunting space telescopes, such as TESS and CHEOPS, will examine nearby stars throughout the sky with follow up studies planned for these closer exoplanets by the upcoming James Webb Space Telescope and future large ground-based telescopes to analyze their atmospheres, determine masses and infer compositions.
Scientists with the SETI (Search for Extraterrestrial Intelligence) Institute have already begun targeting Kepler-452b, the first near-Earth-size world found in the habitable zone of a Sun-like star. SETI Institute researchers are using the Allen Telescope Array, a collection of 6-meter (20 feet) telescopes in the Cascade Mountains of California, to scan for radio transmissions from Kepler-452b. As of July 2015, the array has scanned the exoplanet on over 2 billion frequency bands, with no result. The telescopes will continue to scan over a total of 9 billion channels, searching for alien radio signals.
Observation and exploration
The fact that Kepler-452b is 1,400 light years from Earth, and light travels 9.56×1012 kilometres (6.39×104 AU; 1.010 ly; 5.94×1012 mi) in a year, means it would take the best part of a millennium-and-a-half to reach it if a spacecraft could travel at the speed of light. The fastest current space craft, the New Horizons unmanned probe that passed Pluto in July 2015, travels at just 56,628 km/h (35,187 mph; 0.00037853 AU/h). At this rate, it would take the craft about 26 million years before it reached Kepler-452b.
Ryan Weed from Positron Dynamics says that with a spacecraft accelerating at a constant 1 g up to a velocity of 0.9995 c and due to time dilation we could reach Kepler-452b in 12 years, although from Earth perspective 1,500 years would have passed. 
|Notable Exoplanets – Kepler Space Telescope|
- "NASA Exoplanet Archive – Confirmed Planet Overview – Kepler-452b". NASA Exoplanet Archive. 2015. Retrieved 23 July 2015.
- "NASA's Kepler Mission Discovers Bigger, Older Cousin to Earth". National Aeronautics and Space Administration. July 23, 2015. Retrieved June 10, 2016.
- Rincon, Paul (23 July 2015). "'Earth 2.0' found in Nasa Kepler telescope haul". BBC News. Retrieved 24 July 2015.
- Kepler-452b: How long would it take humans to reach 'Earth 2' and could we live there?
- Pat Brennan (15 December 2015). "8 planets that make you think Star Wars is real". NASA. Retrieved 26 July 2016.
- Jenkins, Jon M.; Twicken, Joseph D.; Batalha, Natalie M.; et al. (23 July 2015). "Discovery and Validation of Kepler-452b: A 1.6 R⨁ Super Earth Exoplanet in the Habitable Zone of a G2 Star" (PDF). The Astronomical Journal. 150 (2): 56. arXiv:1507.06723. Bibcode:2015AJ....150...56J. doi:10.1088/0004-6256/150/2/56. ISSN 1538-3881. Retrieved 24 July 2015.
- KEPLER’S EARTH-LIKE PLANETS SHOULD NOT BE CONFIRMED WITHOUT INDEPENDENT DETECTION: THE CASE OF KEPLER-452b Fergal Mullally, Susan E. Thompson, Jeffrey L. Coughlin, Christopher J. Burke, and Jason F. Rowe, 2nd of April, 2018. Available at https://arxiv.org/pdf/1803.11307.pdf, Accessed 3rd April 2018.
- "The Habitable Exoplanets Catalog – Planetary Habitability Laboratory @ UPR Arecibo". upr.edu.
- Chou, Felicia; Johnson, Michele (23 July 2015). "NASA's Kepler Mission Discovers Bigger, Older Cousin to Earth" (Press release). NASA. Retrieved 23 July 2015.
- "NASA telescope discovers Earth-like planet in star's 'habitable zone". BNO News. 23 July 2015. Retrieved 23 July 2015.
- Feltman, Rachel (23 July 2015). "Scientists discover 12 new potential Earth-like planets". The Washington Post. Retrieved 23 July 2015.
- Overbye, Dennis (23 July 2015). "Kepler Data Reveals What Might Be Best 'Goldilocks' Planet Yet". The New York Times. Retrieved 23 July 2015.
- Witze, Alexandra (23 July 2015). "NASA spies Earth-sized exoplanet orbiting Sun-like star". Nature. Retrieved 23 July 2015.
- Fraser Cain (15 September 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.
- "Planet HIP 11915". Retrieved 17 July 2015.
- NASA Kepler press conference. 23 July 2015.
- Lugmayr, Luigi (23 July 2015). "Kepler-452b details unveiled". I4U News. Retrieved 23 July 2015.
- "Is Earth's Closest Cousin A Dying Planet?". Gizmodo.com. July 30, 2015. Retrieved May 24, 2016.
- SETI Targets Kepler-452b, Earth's 'Cousin,' in Search for Alien Life
- https://www.youtube.com/watch?v=EBebWBjpWIQ?t=13m22s Have you ever imagined how interstellar travel could work? | Ryan Weed | TEDxDanubia
|Wikimedia Commons has media related to Kepler-452b.|
- NASA – Mission overview
- NASA – Kepler Discoveries – Summary Table
- Habitable Exolanets Catalog at UPR-Arecibo.
- Discovery and Validation of Kepler-452b: A 1.6 R⨁ Super Earth Exoplanet in the Habitable Zone of a G2 Star