California

Astronomers have discovered a planet roaming in the Milky Way, orbiting a white dwarf. Around 1.9 times the mass of Earth, this planet likely supported life during its lifetime and orbited a host star. However, all life must have ended when its star died a violent death. The event led the planet to drift away in the absence of a gravitational force.

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The discovery, made by a team led by astronomer Keming Zhang of the University of California, gives us a peek into how life might one day end on our own planet and the fate of Earth once the Sun dies and evolves into a white dwarf. Current research suggests that the Sun will meet its fate in about a billion years.

This planet is situated near the central bulge of our galaxy and is around 4,000 light-years away from us. The researchers studied the planet with the Keck 10-metre telescope in Hawaii.

They noticed that the planet was revolving around the dense, hot core of a star that had died. This core, known as the white dwarf, takes trillions of years to cool down completely. 

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Red Giant phase of a star

A star turns into a white dwarf once it runs out of hydrogen fuel to fuse in its core. It becomes less stable and puffs up to an enormous size, which is called the red giant phase. 

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During this phase, the star's outer atmosphere puffs up and it can expand to hundreds of times its initial size. When our Sun reaches this state, it is predicted to grow so large that it will gobble up Mercury, Venus, Earth and Mars in the process.

However, the newly discovered planet proves that this might not be the case after all. If that planet has managed to survive the red giant phase, then so can Earth and the other planets in the solar system.

In case, Earth is not eaten up by the sun, it might widen its orbit, thus improving its chances of survival.

"We do not currently have a consensus whether Earth could avoid being engulfed by the red giant sun," Zhang said in a statement.

"In any case, planet Earth will only be habitable for around another billion years, at which point Earth's oceans would be vaporized by runaway greenhouse effect—long before the risk of getting swallowed by the red giant," he added.

Zhang and his team found the planet using a phenomenon known as microlensing. It is used to locate other Earth-like worlds that might otherwise not be visible on telescope, in the galaxy. He says that this finding also shows the potential the technology has to discover more such planets.