The exoplanet nicknamed 'Earth 2.0', announced by NASA in 2015 as a close cousin of the Earth, is:

In July 2015, NASA announced the discovery of Kepler-452b, a planet that orbits a Sun-like star in its habitable zone. Because of its similarities to the Earth, it was nicknamed "Earth 2.0" or "Earth's cousin".

Key facts about Kepler-452b:

• It orbits the star Kepler-452, a G-type star similar to the Sun, in the constellation Cygnus.
• It is about 1,400 light-years (some estimates say about 1,800) away from the Earth.
• It is about 60 percent larger than the Earth in diameter, so it is classed as a "super-Earth".
• It takes about 385 days to orbit its star, close to the Earth's 365 days.

Habitable zone:

It lies in the habitable zone, also called the "Goldilocks zone": the region around a star where temperatures could allow liquid water to exist on a planet's surface.

Uncertainty:

Its mass and composition are not known precisely, so scientists cannot be sure whether it is rocky like the Earth.

Some later studies questioned whether the original signal was strong enough to confirm the planet. So its status is still discussed.

The Kepler mission:

• NASA's Kepler Space Telescope was launched in 2009 to find Earth-sized planets around other stars.
• It used the transit method, detecting the slight dimming of a star when a planet passes in front of it.
• It discovered more than 2,600 confirmed exoplanets before it retired in 2018.

Exoplanets:

• An exoplanet is a planet that orbits a star other than the Sun.
• The first exoplanet around a Sun-like star, 51 Pegasi b, was discovered in 1995 by Michel Mayor and Didier Queloz, who later won the Nobel Prize in Physics in 2019.
• More than 5,000 exoplanets have now been confirmed.

Why not the other options?

• ✗Proxima Centauri b orbits the nearest star to the Sun, Proxima Centauri.
• ✗Gliese 581g was a claimed planet whose existence has been doubted.
• ✗TRAPPIST-1e is one of seven Earth-sized planets around the star TRAPPIST-1.