Dark, icy, mysterious: What we now know about dwarf planet Pluto

  • Simar Bhasin, Hindustan Times
  • Updated: Jul 15, 2015 07:52 IST
For the first time since its discovery in 1930, the spotlight is on the icy, mysterious world of our farthest neighbour (Photo: NASA website)

After a journey of three billion miles which took more than nine years to cover, Nasa's spacecraft New Horizons whizzed past Pluto on Tuesday clicking pictures that will give us a better understanding of the dwarf planet.

A detailed analysis of the pictures would take a while, but mission scientists already have some interesting updates -- like for instance, it's bigger than we thought.

For the first time since its discovery in 1930, the spotlight is on the icy, mysterious world of our farthest neighbour

We have here a rundown on Pluto, a 20th-century discovery about to become the 21st-century darling of astronomers.

Pluto is bigger than we thought

New Horizons mission scientists have found Pluto to be 1,473 miles (2,370 kilometers) in diameter, somewhat larger than many prior estimates. Images acquired with the Long Range Reconnaissance Imager (LORRI) were used to make this determination.

This result confirms what was already suspected: Pluto is larger than all other known solar system objects beyond the orbit of Neptune.

“The size of Pluto has been debated since its discovery in 1930. We are excited to finally lay this question to rest,” said mission scientist Bill McKinnon.

Measuring Pluto’s size has been a decades-long challenge due to complicating factors from its atmosphere.

One of the reasons why Pluto became a 'dwarf' planet is because of its size. Those who feel the new measurements should force a rethink on its status, hear this: even with a 2,370 km diameter it is only half the size of the smallest planet, Mercury.

First a planet, then a dwarf planet

When American astronomer Clyde Tombaugh first spotted it in 1930, it was enrolled as the ninth planet of our solar system

But then in 2006, just seven months after New Horizons started its journey, Pluto was unceremoniously kicked out of the solar system club

It was reclassified as a minor planet, mostly due to the technical reason that there may be similar-sized trans-Neptunian objects in the same region

King of the Kuiper Belt

Pluto is named after the god of the underworld, and much like its namesake it inhabits a dark, obscure world.

Pluto is the biggest object in the icy Kuiper Belt, which is in the outerreaches of the solar system beyond the orbit of Neptune. The place is home to comets and other small frosty objects.

There are at least two more recognised dwarf planets here-- Haumea and Makemake. Beyond the Kuiper Belt and the hypothesised Oort's cloud, interstellar space begins.

Pluto has five moons

Big moon Charon was discovered in 1978, followed by little moons Nix and Hydra in 2005, Kerberos in 2011 and Styx in 2012. The Hubble Space Telescope revealed all four baby moons. Astronomers stuck to underworld undertones when it came to the names.

New Horizons will hunt for more moons, but at this point, they would have to be pretty elusive. The Pluto empire, complete with six bodies, at least for now, is like its own mini solar system.


Photo: NASA website

Even to Hubble, Nix and Hydra appeared as points of light, and that’s how they looked to New Horizons until the final week of its approach to Pluto.

Now, the latest LORRI images show the two diminutive satellites not as pinpoints, but as moons seen well enough to measure their sizes. Nix is estimated to be about 35 kilometers across, while Hydra is roughly 45 kilometers across.

What about Pluto’s two smallest moons, Kerberos and Styx? Wait for more pictures from New Horizons.

Pluto is very far away

Pluto is so far from the sun - between 2.8 billion and 4.6 billion miles - that twilight reigns. At high noon on that planet, it looks as though it would be dawn or dusk on Earth.


Photo: NASA website

It takes about 5.5 hours for sunlight to reach Pluto at its average distance. Compare that with the time sunlight takes to reach Earth: 8 minutes, 20 secs

New Horizons took a tiring 9 1/2 years to cover the three billion miles to that planet. And that spacecraft travels at about 31,000 mph.

Pluto has eccentric orbit

Pluto's orbital characteristics are substantially different from those of other planets, which follow nearly circular orbits around the Sun It is highly inclined relative to the ecliptic paths of other planets , and highly elliptical.

This chaotic path occasionally takes Pluto closer to the Sun than Neptune. Last time this happened was from February 1979 to February 1999.

The pictures from New Horizons in the coming days will help scientists see the icy planet in a different light. And help answer an important question -- should Pluto be reinstalled as the ninth planet of the solar sytem?

( with agency inputs)

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