In Greek mythology, Nemesis and Tyche were two sisters and the daughters of Zeus or Oceanus. Nemesis was the goddess of divine retribution. So if you displayed hubris i.e considered yourself better than the gods, Nemesis would teach you a lesson. So Nemesis personified the revenge of fate against arrogance. Her sister Tyche was responsible for the fate of cities. Tyche was responsible for the sudden outburst of a disease or an earthquake or a flood.
But why am I telling you all this? But I do have the habit of telling people what they don’t want to know or don’t need to know. J Anyway, read on and I will tell you something more interesting.
We all know that a massive extinction event wiped out the dinosaurs and gave rise to the mammalian domination of earth. Actually there was not just one extinction event in the history of earth. There have been several and scientists have found that extinction events are regular and periodic. Scientists estimate that there is an extinction event every 26 to 30 million years.
Now, how do we explain these periodic extinction events?
In a VERITAS posted in 2004( VERITAS: The Belt and the Cloud see http://unvarnished-veritas.posterous.com/the-belt-and-the-cloud), I had told you about the places where comets originate from. Short range comets ( with orbits less than 200 years) come from a place known as the Kuiper belt which is a belt of icy bodies just outside Neptune’s orbit. Long range comets( orbits sometimes in thousands of years) originate in a huge spherical cloud of bodies which lies about 1 light year from the sun. The Oort cloud surrounds the solar system. Isn’t it amazing that the Sun does not just hold planets till Neptune/Pluto. Sun’s gravity goes far beyond that. To give you an idea of the distance- Astronomical distances are measured in light years and in Astronomical units. A light year is the distance covered by light in one year. Astronomical unit is the distance between Earth and Sun. It is written as AU. Light takes 8 minutes to travel from Sun to Earth. So 1 AU = 8 light minutes. Pluto is at a distance of 50 AU from the sun. That is about 6 light hours from the sun. Now imagine this: The Oort cloud is 50,000 times the distance from Earth to the Sun. This is 50,000 Astronomical Units or AU. Yes, the solar system does not end with Neptune or Pluto- there are things in the solar system far beyond the 9 planets( 8 now!) that we studied in school.
So the Oort cloud is a spherical ball of icy bodies with a radius of 1 light year with the sun at the center! Some people even estimate that the outer edge of the Oort cloud is about 100,000 AU to 200,000 AU. That is nearly 3 light years! So we have parts of the solar system nearly 3 light years away from the sun! And the interesting thing is that the nearest star to the Sun is Alpha Centauri and that is 4 light years away.
The proposal to explain the periodic ( 26 million year) extinction cycle on Earth is that every 26 million years, something perturbs some objects in the Oort cloud and hurls them towards the earth at a HUGE speed. These objects, which may become long range comets later change the seasons when they pass the earth and cause widespread extinction of the lifeforms that exist on earth at that time. Some may even hit the earth causing widespread damage. By the way, lots of comets have originated in the Oort cloud. Halley’s comet was once a Oort cloud object but now has an elliptical orbit with a period of 76 years.
Okay, so to come back to the theory: once every 26 million years something disturbs a Oort cloud object hurling it towards the earth causing extinction events. But what? There are many hypothesis. In this VERITAS we will talk about two of them: Nemesis and Tyche.
Scientists have postulated that there is a brown dwarf star just beyond the Oort cloud and revolves around the sun in a highly elliptical orbit. Its orbital period around the sun is 26 million years or so. When it comes near the Oort cloud, after every 26 million years, it disturbs the Oort cloud bodies and sends them hurling through space towards the sun. Some of these bodies hit the earth causing a huge amount of dust in the air, climate change and therefore mass extinctions. We know that dinosaur extinctions have been caused by such a body falling on the earth. The name of this hypothetical star is Nemesis. A brown dwarf star is a star that is not large enough to sustain nuclear fusion. So it does not shine. It is therefore practically invisible. If this is true than the Sun and Nemesis form a binary star pair- Binary stars are pretty common in the universe.
Some other scientists found that all mass extinctions have been caused by objects that have come from the same point in the sky- and that point lies in the orbital plane of the planets. Let me explain. All planets and the sun lie on a single plane. So if I were to take a huge sheet of paper and pass it through the sun and mercury, that sheet of paper will pass through all the other planets also. There are no planets “above” or “below” the planetary orbital plane( Pluto was an exception but now it has been plutoed. See VERITAS: Pluto has been plutoed, 20 January 2010 http://unvarnished-veritas.posterous.com/pluto-has-been-plutoed).
So if scientists find that the objects causing mass extinctions come from a point in the orbital plane of planets far away in the Oort cloud, what could that imply? Yes, scientists believe that there may be a planet revolving around the sun with an orbit so huge that it crosses the Oort cloud! And this planet dislodges objects in the Oort cloud and they hit the earth at high speeds causing mass extinctions every 26 million years or so. The name that scientists have given this hypothetical planet is Tyche.
So Nemesis and Tyche are the names of hypothetical objects( one star and one planet) which explain the periodic mass extinctions on earth. Scientists are trying real hard to confirm or deny their existence. This may take several years.
Our earth is a tiny spec of nothingness and our lives are even more tiny and insignificant. Yet, we go about our lives with the seriousness that is almost ridiculous and laughable! The only useful thing we can do in our lives is to use this short insignificant period of consciousness to admire the infinite beauty and mystery that surrounds us.
Here is a nice little poem by Jane Draper:
Stars have ways that I do not know,
Enormity that checks my thought,
Yet on the loom of their fine glow
The fabric of my dreams is wrought.
I look into the stars, and one
After one, convictions die,
While more than I have lost is spun
Delicately across the sky.
I look into the stars, and all
The fuming purposes life gives
Pass, like mists of evening fall,
And all life never has been, lives.
Go wondrous creature, mount where science guides
go measure earth, weigh air, state the tides,
instruct the planets in what orbs to run
correct old time, regulate the sun