Monthly Archives: January 2010

Pluto has been Plutoed

300px-pluto_discovery_plates

 

In our school text-books we had read that there are nine planets. We all remember their names in increasing order of their distance from the sun. And we know that Pluto is the ninth planet. Well, it was the ninth planet. There has been a change in the planetary situation and we ( or rather I) at VERITAS thought that we must inform you about this change. When Pluto was discovered in 1930 it was added to the list of planets. It’s mass was not accurately known but scientists estimated that it would be of a comparable size to Mercury.In 1978 its moon, Charon was discovered and that made it possible to calculate Pluto’s mass.Pluto is one-twentieth the size of Mercury making it the smallest planet!
Now Pluto did not also behave like other planets. It has a huge orbital eccentricity and high orbital inclination. An orbit has less eccentricity when it is closer to a circle in shape. A more eccentric orbit is more elliptical or elongated. Pluto’s orbit is so elongated that for about 14 years of its 248 year orbit, it is closer to the sun than Neptune. So for 14 years out of its 248 year orbital period it is the 8th planet and Neptunebecomes the 9th. It’s orbit crisscrosses Neptune’s orbit but there will never be a collision between the two planets because their orbits are locked in a resonance( See VERITAS: Resonance in orbits- posted in year 2000. Available on request). Now let me explain what is meant by high orbital inclination.
All planets revolve around the Sun in one plane called the ecliptic. Pluto’s orbit does not lie on its plane – it is inclined by 17 degrees. So it does not behave like other planets and that had caused astronomers a lot of embarrassment. And to make matters worse, astronomers detected a few “objects” in the solar system which were of a comparable size or even larger! Eris, for example, islarger than Pluto. So should these other objects be included in the list of planets or should Pluto be expelled from the list?
To resolve the issue, the International Astronomical Union( IAU) decided to make a set of criteria that an object must satisfy in order to be given the planet status. So an object is called a planet if it satisfies the following:

1) It should revolve around the sun( and not around any other object)
2) It should have enough mass for gravity to squeeze it into a sphere. In scientific language this is called “achieving hydrostatic equilibrium”.
3) It should have cleared its neighborhood i.e it should have captured all nearby objects or collided with them so that there is nothing else left in the neighborhood of its orbit.
If an object only meets criteria 1 and 2 i.e. it revolves around the sun and is spherical because of its own gravity but has not cleared its orbital neighborhood then it is classified as a dwarf planet.
And if you go by the above criteria, then Pluto is a dwarf planet. It revolves around the sun and is spherical in shape due to its own gravity but has not cleared its orbit’s neighborhood. We know that it has not cleared it’s orbit’s neighborhood because it shares its orbital neighborhood with several other objects in a ring or belt beyond Neptune. This ring/belt of objects is called the Kuiper belt. There are hundreds of small objects in the Kuiper belt and Pluto is one of them. The Kuiper belt is also the source of many comets. So Pluto has not cleared its orbit and is therefore a dwarf planet.
So Pluto is one of the five dwarf planets identified so far. The following is the complete list:
1) Pluto ( A Kuiper Belt object)
2) Ceres ( a part of the asteriod belt between Mars and Jupiter)
3) Haumea ( Kuiper Belt Object)
4) Makemake ( Kuiper Belt Object)
5) Eris ( A scattered Disk object. The scattered disk is beyond the Kuiper Belt and is the source of lots of comets. Eris is the largest dwarf planet)  So Pluto has been demoted from the status of planet to dwarf planet. The word “plutoed” or “to pluto” was coined in 2006 following Pluto’s demotion. “To pluto” means to “demote or devalue something or someone”. Therefore we can say that Pluto has been plutoed.

Kanwar
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Go, wondrous creature! mount where Science guides:
Go, measure earth, weigh air, and state the tides:
Instruct the planets in what orbs to run,
Correct old time and regulate the Sun;
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Tags : Universe, Unearthly, Pluto, 2010 VERITAS

Liger, Tiglon and Genomic Imprinting

Friends,

 

            A few days back I read about two very interesting animals- the liger and the tiglon. In this VERITAS I will tell you about these animals and also about a very interesting fact of genetics that makes these animals so different from each other.

            A liger is the offspring of a male lion and a female tiger. So it is a hybrid of a male lion and a female tiger. They are much larger than both lions and tigers. Ligers are the largest cats in the world! It takes the best characteristics from both parents. It is very sociable like lions and like tigers, it loves swimming. Of course, lions and tigers would never mate in the wild. So a liger are typically born of captive lions and tigers.

            A Tiglon is the offspring of a male tiger and a female lion. It is much smaller than both the lion and the tiger.

            Let’s compare the sizes of these animals: a lion is about 8 feet in length and weighs about 250 kg. A Tiger is about 10 feet in length and weighs about 300 kgs. A Liger is about 12 feet in length and can weight upto 500 kg. So a Liger is about twice the size of a Tiger or a Lion! A Tiglon is about half the size of a Tiger and weighs about 160 Kgs.

 

            That brings us to the most interesting question: when both are offspring of a tiger and a lion then what causes Ligers to be huge and Tiglons to be so small in comparison? The answer is amazingly interesting and due to a very interesting generic phenomena called genomic imprinting.

 

We inherit two copies of every gene: one from our mother and the other from our father. Usually both genes are active. It is true that the characteristics produced by these genes may show a particular domination but that is because the effect of one gene overrides the effect of the other. Both genes are active. But in a very small number of genes, one copy is turned off depending on whether it came from the mother or the father. So the fact that the copy came from the mother or father is “imprinted” on these genes and that turns it off or on. So for most genes, there is no information regarding which parent it came from. But some genes behave differently depending on whether they came from the mother or father. These genes have their “source” imprinted on them and that makes them turn off or turn on. In the human genome there are about 23000 genes out of which only 80 are imprinted.

 

Now, lets look at how Lions live. They live in prides. There are several male and female lions in a pride. Now, each male lion wants his offspring to be the biggest and most powerful. Only then would his future survival in the pride or group be assured. So an imprinted gene from the male lion promotes growth- an extraordinary growth. But the lioness’ concern is different- she will give birth to several cubs at once and does not want any one of them to grow at the others’ expense. Also a larger cub would mean danger for her also. So there is an imprinted gene from the lioness that curbs too much growth. When a lion and lioness mate and produce an offspring, the growth enhancing gene of the male lion is countered by the growth diminishing gene from the lioness to produce “normal” sized cubs.

 

Lets now look at how Tigers live. They are solitary creatures. Since they do not live in prides so male tigers do not have the “super-growth” imprinted gene. There is no question of competition within the group. And since male tigers do not have the “super-growth” imprinted gene so the tigress does not need the growth diminishing imprinted gene.

When a male lion mates with a tigress, he gives the “super-growth” imprinted gene. But the tigress has nothing to counter it. So we get a liger- a huge creature that the tigress finds it difficult to deliver naturally. Frequently a c-section is required to deliver this giant which becomes much bigger than a lion or a tiger.

 

When a male tiger mates with a female lion, he does not have a “super-growth” gene but the lioness has a growth diminishing gene which diminishes the growth of the offspring unchecked producing the much smaller tiglon.

When I first read the reason, I was delighted and amazed at the same time. It was 2 AM in the morning and I could not control my excitement at such an interesting fact! Knowledge is a great source of joy. In fact, the greatest source of joy!

 

Curioser and Curioser,

Kanwar

 

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Go, wondrous creature! mount where Science guides:

Go, measure earth, weigh air, and state the tides:

Instruct the planets in what orbs to run,

Correct old time and regulate the Sun;

 

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