We Might Finally Know Why Pluto Is So Much Colder Than It Should Be

Back in 2015 when New Horizons arrived on planet Pluto, the spacecraft revealed that the dwarf planet was a frozen lump. With a heart-shaped icecap that in theory could hide an ocean, this planet spits out X-rays for no obvious reason, and it has a very low temperature – lower than anyone had ever predicted before.

Scientists previously believed that Pluto’s temperature is -280 degrees Fahrenheit (-173 Celsius), but New Horizons showed that the dwarf planet is incredibly cold, or 330 degrees below Fahrenheit (-201 Celsius).

In comparison to Earth, in 2013 researchers announced that a NASA satellite observed a record Antarctic chill at minus 135.8 (-93.2 degrees Celsius), a temperature humans could survive for just three minutes.

It’s not unexpected for Pluto to be a cold planed, especially because the dwarf planet drifts through the Solar System at an average distance of 3.67 billion miles (5.9 billion kilometers) from the Sun. If we compare it to our planet, it’s 40 times further away than Earth is. Also, as it’s a very small planet the gravity is very weak and its atmosphere leaks into space.

According to Xi Zhang, a planetary scientist from the University of California, it’s very difficult to correctly estimate Pluto’s temperature because of its thin atmosphere.

“The sun’s ultraviolet rays break down nitrogen, methane and other gases in Pluto’s atmosphere, creating a haze of solid particles. New Horizons’ images basically showed a lot of these particles”, Zhang said.

In a report published in the journal “Nature”, Zhang and his colleagues argue that the planet’s hazy coat explains why Pluto is extra-cold.

“Pluto’s haze is so abundant that it can absorb a lot of solar radiation, though there’s a good deal of uncertainty about this complex atmospheric chemistry. We really don’t know the detailed composition of the haze particles,” he said.

High in Pluto’s atmosphere, smog begins to form and then the particles fall downward and chain together, like a formation of skydivers, except the chemical clusters won’t break away before landing.

The spacecraft detected a thick layer of these hydrocarbon particles, called tholins, that give Pluto the reddish color. Tholins are larger than gas molecules. This means that their ability to heat up and cool down is greater.

Zhang and his colleagues found out that the haze absorbs solar energy and radiates it into space, although previous hypotheses suggested that gaseous hydrogen cyanide was the coolant. However, recent probes of Pluto discovered too little of this gas.

“Water vapor could also be chilling Pluto but the sheer amount of vapor that would be needed made this a dubious prospect”, said Zhang.

Despite this discovery, the case on the scientists understanding of Pluto’s atmospheric temperature is not yet closed, and researchers may have their answer within two years.

The observatory will launch the James Webb Telescope in 2019, which will have the right instruments and once aimed at Pluto, the telescope will shows us whether the dwarf planet indeed sweats in infrared.


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