Cover story: Pluto demoted!-DAWN - Young World; September 09, 2006

Come wander with me, she said,
Into regions yet untrod;
And read what is still unread
In the manuscripts of God.
-- Longfellow

Science is self-correcting. After years of wrangling and a week of bitter debate, the International Astronomical Union voted on a sweeping reclassification of the solar system. Pluto was demoted to the status of a “dwarf planet”.

The ‘new’ solar system has eight planets, three dwarf planets and tens of thousands of “smaller solar system bodies”, like comets and asteroids.

It is time to grab a magic marker for the classroom charts and rip off the very last ball on the solar system model.

A logical question that arises here is why was the solar system down-sized?

According to the new rules a planet must fulfil the following three criteria:

1. It must orbit around the sun.
2. It must be big enough for gravity to squash it into a round ball.
3. It must have a clear orbit of its own.

Dwarf planets only have to be round
Pluto was discovered on February 18, 1930 by Clyde W. Tombaugh, named so by an 11-year-old girl from England, Venetia Phair ( Pluto is the Roman God of the under world). Quite interestingly, Minerva was one of the suggested names (remember Harry Potter). Situated at a distance of 5,900 million km from the sun, it completes one revolution in 248 years.

The diameter of Pluto is only about 1,440 miles, smaller than our moon and its elongated (oblong) orbit is tilted with respect to the other planets. Twenty years of its 248-year journey around the sun is inside the orbit of Neptune. Latest being from 1979-1999. Pluto is a giant snowball of methane and water mixed with rock.

In the dark realms beyond Neptune, is a zone of icy debris known as the Kuiper Belt. Planetary scientists say that there are dozens of potential dwarf-planets in that zone. For now, the three dwarf plants are:

1. Pluto.
2. Ceres, the largest asteroid.
3. UB 313, an object nicknamed Xena.

This isn’t the first time that the astronomers have rethought a planet. The asteroid Ceres was considered as the eighth planet after its discovery in 1801 by Giovanni Piazzi and retained this status for about half a century.

The image was taken by the Hubble Space Telescope on February 21, 1994, when the planet was 4.4 billion kilometres from the earth.

Pluto’s surface is believed to reach temperatures as low as -240 degrees centigrade. From Pluto, the sun appears to be a very bright star.

The dwarf-planet Pluto has a rotation period of six days, nine hours and 18 minutes, the same as that of its moon, Charon. Pluto rotates synchronously with its moon; hence they continually face each other as they travel through space.

The decision to demote Pluto to the status of a ‘dwarf planet’ will have cultural and economic impact. The psyche of generations brought up with the knowledge of nine planets in the solar system will have to adjust. But this isn’t that big an issue when compared with the economic impact on the astronomy-related toys, models, education and publications. The World Book Encyclopaedia had been holding the printing of its 2007 edition for this decision.

Children, however, are flexible and will probably adjust far quicker than us old- timers!

THE PLANETS OF THE SOLAR SYSTEM

Mercury
The planet was named after the winged messenger, a Roman god. It is roughly two-fifths the size of earth, second smallest in the solar system and closest to the sun. Mercury’s atmosphere is a thin mixture of helium (95 per cent) and hydrogen. Completing its orbit in 88 days, Mercury alternatively bakes and freezes depending on which side is lit by the sun.

Venus
The second planet from the sun was named after the Roman goddess of love and beauty.

Venus is also known as the ‘morning star’ and ‘evening star’ since it appears as a bright white disc to the unaided eye at these times. Its atmosphere is a mixture of carbon dioxide (95 per cent), nitrogen and sulphuric acid. It completes its rotation around the sun in 225 Earth days.

Earth
From outer space, our planet looks blue with white swirls, created by water and clouds. Earth is the third planet from the sun and not perfectly round as it bulges at the equator and flattens at the poles. Its diameter is 12,756 km with an atmospheric content of 78 per cent nitrogen, 21 per cent oxygen. We are at a distance of 149.6 million kilometres from the sun, completing the travel around it in 365.2 days (hence the leap year every fourth year). Earth rotates on its axis in 23 hours, 56 minutes and four seconds. Earth has a satellite, commonly called the moon.

Mars
The fourth planet from the sun, Mars was named after the Roman god of war because of its blood-red colour which comes from the iron-rich dust. It is about one-half the size of the earth.

The atmosphere is 95 per cent carbon dioxide. Completing its orbit in 687 days, it has a day of 24 hours and 37 minutes.

Jupiter
The fifth and the largest planet of our solar system is so named for the most important Roman god because of its sheer size. About 1,300 Earths would fit into it.

Jupiter is stunningly colourful with bands of blue, brown, pink, red, orange and yellow. “The Great Red Spot” is its single most distinguishing feature, which is actually a windstorm larger than the Earth and has continued for centuries without any signs of dying down.

Saturn
The sixth and the second-largest planet of the solar system, has seven flat rings around it made up of billions of ice particles. Named for the Roman god of farming, it is 10 times larger than the earth with an atmospheric content of hydrogen and helium. Saturn takes 29 years to complete its orbit and has a day of 10 hours and 40 minutes.

Uranus
The seventh planet from the sun is twice as far from it as its neighbour. It was discovered in 1781 and named after ancient sky god. This greenish-blue planet is four times larger than the earth and has an atmosphere of hydrogen, helium and methane. It has a 17 hours long day and takes 84 years to complete its orbit around the sun.

Neptune
The eighth planet appears stormy-blue, about 30 times farther from the sun than Earth, named after the Roman god of the sea. It was discovered in 1846. Neptune is almost four times the size of the Earth and has a liquid layer on its surface with thick clouds and constant raging storms. It takes 165 years to complete its orbit around the sun and has a 16 hours long day.

Dr Summaiya Syed-Tariq