Exoplanets and Habitable Zones

• Since 1995, over 5,000 exoplanets have been discovered.
• NASA's Kepler space telescope, launched in 2009, discovered more than half of these exoplanets.
• The Kepler space telescope was retired in 2018, having discovered over 2,600 exoplanets.
• Astronomers dream of discovering the first true "alien Earth".
• Recent exoplanet discoveries indicate that small, rocky worlds are abundant in our galaxy.
• A potentially life-friendly planet must be small, rocky, and within the habitable/ "Goldilocks" zone of its star.
• The "Goldilocks" zone is a region where water can exist in liquid form on a planet's surface.
• Advancing telescope technology considers factors like atmospheric composition and the parent star's activity level.

Gliese 667Cc

• Lies 22 light-years from Earth.
• It is at least 4.5 times as massive as Earth.
• Completes one orbit in 28 days around its red dwarf star, which is cooler than the sun.
• Located in the habitable zone but could be scorched by flares from its red dwarf star.
• Discovered using the European Southern Observatory's 3.6-meter telescope in Chile.

Kepler-22b

• Lies 600 light-years away.
• First Kepler planet found in the habitable zone.
• About 2.4 times larger than Earth.
• Unclear if it is rocky, liquid, or gaseous.
• Orbit of 290 days is similar to Earth's 365 days.
• Orbits a G-class star like our sun, but smaller and colder.

Kepler-69c

• About 2,700 light-years away.
• About 70 percent larger than Earth.
• Composition is unknown.
• Completes an orbit every 242 days, similar to Venus.
• Host star is about 80 percent as luminous as the sun, placing it in the habitable zone.

Kepler-62f

• About 1,200 light-years away.
• About 40 percent larger than Earth.
• Orbits a star much cooler than our sun.
• 267-day orbit puts it in the habitable zone.
• Large size suggests it could be a rocky planet with oceans.

Kepler-186f

• About 500 light-years from Earth.
• At most 10 percent larger than Earth.
• Appears to reside on the outer edge of the habitable zone.
• Receives only one-third of the energy Earth gets from the sun.
• Parent star is a red dwarf, so not a true Earth twin.

Kepler-442b

• Situated 1,194 light-years away from Earth.
• 33 percent larger than Earth.
• Completes an orbit every 112 days.
• Discovered in 2015.
• May receive enough light to sustain a large biosphere.
• Receives sufficient radiation for photosynthesis.

Kepler-452b

• Situated 1,400 light-years from Earth.
• Discovered in 2015.
• First near-Earth-size planet orbiting a sun-sized star.
• 60 percent larger than Earth.
• Parent star (Kepler-452) is 10 percent larger than the sun.
• Orbits in the habitable zone.
• Has a "better than even chance" of being rocky.
• Orbit is only 20 days longer than Earth's.

Kepler-1649c

• Located 300 light-years from Earth.
• 1.06 times larger than Earth.
• Discovered in 2020 after reanalysis of Kepler data.
• Orbits in its star's habitable zone.
• Receives 75 percent of the light Earth receives from the sun.

Proxima Centauri b

• Located just four light-years away from Earth, making it Earth's closest known exoplanet.
• Discovered in 2016.
• Has a mass 1.27 times that of Earth's.
• Found in the habitable zone of Proxima Centauri.
• Exposed to extreme ultraviolet radiation due to close proximity to its star.
• Has an orbital period of only 11.2 days.
• Water on the planet likely evaporated early in the system's formation.
• A 2018 study found that some exoplanets could hold more water than Earth's oceans.
• TRAPPIST-1e is potentially the most likely to support life as we know it.