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Astronomers reveal the most extreme planets

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Published: 13:48, 13 June 2017   Update: 15:18, 26 July 2020
Astronomers reveal the most extreme planets

Risingbd Desk: Scientists recently discovered the hottest planet ever found – with a surface temperature greater than some stars.

As the hunt for planets outside our own solar system continues, we have discovered many other worlds with extreme features.

And the ongoing exploration of our own solar system has revealed some pretty weird contenders, too.

How hot a planet gets depends primarily on how close it is to its host star – and on how hot that star burns.

In our own solar system, Mercury is the closest planet to the sun at a mean distance of 57,910,000km.

Temperatures on its dayside reach about 430°C, while the sun itself has a surface temperature of 5,500°C.

But stars more massive than the sun burn hotter.

The star HD 195689 – also known as KELT-9 – is 2.5 times more massive than the sun and has a surface temperature of almost 10,000°C.

Its planet, KELT-9b, is much closer to its host star than Mercury is to the sun.

Though we cannot measure the exact distance from afar, it circles its host star every 1.5 days (Mercury’s orbit takes 88 days).

This results in a whopping 4300°C – which is hotter than many of the stars with a lower mass than our sun.

The rocky planet Mercury would be a molten droplet of lava at this temperature.

KELT-9b, however, is a Jupiter-type gas giant.

It is shrivelling away as the molecules in its atmosphere are breaking down to their constituent atoms – and burning off.

At a temperature of just 50 degrees above absolute zero – -223°C – OGLE-2005-BLG-390Lb snatches the title of the coldest planet.

At about 5.5 times the Earth’s mass it is likely to be a rocky planet too.

Though not too distant from its host star at an orbit that would put it somewhere between Mars and Jupiter in our solar system, its host star is a low mass, cool star known as a red dwarf.

The planet is popularly referred to as Hoth in reference to an icy planet in the Star Wars franchise.

Contrary to its fictional counterpart, however, it won’t be able to sustain much of an atmosphere (nor life, for that matter).

This because most of its gases will be frozen solid – adding to the snow on the surface.
If a planet can be as hot as a star, what then makes the difference between stars and planets?

Stars are so much more massive than planets that they are ignited by fusion processes as a result of the huge gravitational forces in their cores.

Common stars like our sun burn by fusing hydrogen into helium.

But there is a form of star called a brown dwarf, which are big enough to start some fusion processes but not large enough to sustain them.

Planet DENIS-P J082303.1-491201 b with the equally unpronounceable alias 2MASS J08230313-4912012 b has 28.5 times the mass of Jupiter – making it the most massive planet listed in NASA’s exoplanet archive.

Source: The Mail



Risingbd/June 13, 2017/Mukul

 

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