There's a lot happening above our heads. The discovery of water on the moon is the latest in a series of dramatic explorations in the last two
decades that have changed the way we humans view our small corner of the universe. It's as if we are living in a zoo of bizarre objects with complex personal lives. Some live beyond the known boundaries of the solar system while others are much closer, prowling around well-known planets.
Earlier, the solar system — loosely defined as the chunk of space under the sun's gravitational pull — was thought of as nine planets with an asteroid belt between Mars and Jupiter. Mike Brown, astronomer at Caltech, recalls that when he was in school, kids were given a handy mnemonic to remember the planetary order: Martha Visits Every Monday And Just Stays Until Noon Period. Then there were a dozen or so satellites orbiting the planets, including our moon. Sometimes comets would appear, behave like streakers in a cricket match, and disappear.
But all this started changing in 1992. The combined might of powerful telescopes and super computers led to the discovery of one of the most bizarre regions in the solar system — the Kuiper Belt (pronounced kwiper), named after a Dutch astronomer. Beyond Neptune, some 3 billion miles from the sun, millions of rocks were found floating in a gigantic two-billion-mile-wide belt which goes right around the sun. Current estimates say that at least 70,000 of these rocks are spread over 100 miles across and the total number may run into billions. The biggest of them, Eris, is even larger than Pluto. In fact, it is now thought that Pluto might be just one of the Kuiper Belt Objects (KBOs). This
contributed to its demotion from planethood in 2006.
The Kuiper Belt is deathly cold, with an average temperature of about minus 225 degrees Celsius. The objects in this belt come in diverse colours — grey, black, red. Many have a bluish tinge, probably because their rocky core is overlaid with frozen methane or ammonia. There is one KBO, discovered in 2000, which is named Varuna, the Hindu god of oceans.
Once in a while, a gravity jolt from passing Neptune may bump one of the rocks out of this backwater and hurl it towards the sun. As it warms up, the ice evaporates and trails behind it, giving it a glow and a tail — eventually becoming a comet.
How did all this debris collect here? It is thought that the Kuiper Belt is leftover material from 4.6 billion years ago when a giant molecular cloud clumped together to form the Solar System. Firsthand information from this weird region will become available after 2015 when Nasa's New Horizons spaceship reaches the Kuiper Belt. Launched in 2006, it did a flyby of Jupiter last year and got a speed shake-up for its long journey to Pluto and beyond.
The Kuiper Belt ends abruptly at about 7.5 billion kilometres from the sun. Scientists are still puzzling over this boundary, called the Kuiper Cliff. One theory is that there is a massive object —an unknown planet — out there that has swept away the debris. But there is no proof of this as yet.
The solar system, though, continues beyond the Kuiper Cliff. Scientists predict that beyond this lies the Oort Cloud (pronounced Ort), a gigantic bubble of dust and tiny pieces of debris extending some 9 trillion kilometres further and completely surrounding the solar system. It is thought that this debris once lay between the planets and got pushed out by gravity about a billion years ago, making the Oort Cloud a relatively young structure. In the coming years, as robotic spaceships come closer to this eerie region, more details will emerge.
Between the Kuiper Belt and the Oort Cloud lies the boundary of the heliosphere, a giant bubble blown out by charged particles streaming out of the sun at over a million kilometres per hour. The speeding particles suddenly slow down after colliding with particles from the interstellar medium — mostly hydrogen and helium which permeate the space between the stars. This is known as the Termination Shock, experienced only by two man-made spaceships — Voyager 1 and 2. Further on is the heliosheath, the outer limits of the heliosphere.
In the near future, as space missions like New Horizons reveal more mysteries of space, some may miss the simplicity of the past. But these discoveries not only reveal a new grandeur of the cosmos, they also reaffirm the beauty of science, which has made it possible for us to observe and explore.
Five Bizarre Objects
Haumea: The Spinning Potato
Named after the Hawaiian mother goddess, this dwarf planet from the Kuiper Belt is like an oblong potato — 2,000 km long but only about 1,000 km in width. This happened due to its jaw-dropping spin, probably as a result of a collision in the past. The potato goes around the sun in 283 earth years, dragging along two tiny moons, Hi'iaka and Namaka
Antipholus & Antipholus: the separated twins
These two identical bodies circle each other in the Kuiper Belt. Each is about 108 km wide. What makes them unique is that they are 125,000 km apart. They are named after the twins who are accidentally separated at birth in Shakespeare's Comedy of Errors
Mercury: not so hot
If you were to land on this planet be prepared for mind-boggling confusion. One day on Mercury is two Mercury-years long. It spins so slowly that by the time it completes one full spin, the planet has travelled twice around the sun. Strangely, though this planet is closest to the sun, it is not the hottest. The average surface temperature is 169 degrees C, while Venus sizzles at 460. This is because there is no atmosphere on Mercury while the soupy atmosphere on Venus traps heat to create a greenhouse effect
Sedna: The Red Hermit
This red object was once considered a part of the Oort Cloud but is now classified as a detached object (not fitting into any region). This is so because in its 12,000-earth-year journey around the sun, it drifts an unimaginable 15 billion km away from it. It is named after the Inuit sea goddess, the mother of all sea creatures
Janus & Epimethus: The Flipping Moons
These two small Saturn moons had scientists stumped for years until the mystery was solved. Given that their paths around Saturn are barely 50 km apart, less than their width, it was logical that they should collide. But in an arrangement unknown anywhere in the universe, what happens is that as they draw close, one rises, slows down and takes position behind the other. This flip happens every four years. The moons have unflattering names — Janus is the two-faced Roman god; Epimethus the Greek titan who lacked foresight.
New moons on the horizon
Some of the most spectacular new discoveries have been moons or natural satellites — objects that orbit around planets or other bodies, not the sun.
Till a decade ago only a few dozen moons were known, mostly orbiting the four gas giants – Jupiter, Saturn, Uranus and Neptune. Today, the number of moons has shot up to a stunning 330. Of these, 166 go around planets, while dwarf planets like Pluto account for another 6. Then there are 104 moons associated with asteroids and 58 with various objects beyond Neptune, mostly in the Kuiper Belt. Since 2000, 47 new moons of Jupiter and 43 of Saturn have been discovered. This large clan of moons is a menagerie of quirks. Some like Triton, one of Neptune's moons, spin opposite to the direction of their primary planet.
Others look as if they have been knocked sideways, and lie tilted. Some were created from the same matter as their primary — the object that they orbit. It is likely that others like our own moon, and Pluto's huge moon Charon, arose from a ‘Big Whack', a giant collision of bodies. Some have atmosphere, others are just rocks.
Recently, moonlets — small pieces of rock up to 100 metres in width — have been discovered. The Cassini spaceship discovered many such moonlets following Pan and Daphnis, two moons which are in one of Saturn's rings. Scientists believe that there may be millions of such moonlets bridging the gap between dust and actual moons.
The latest buzz is that some of these moons could have conditions that support life. Candidates being explored include Enceladus, Saturn's tiny moon famous for its stripes (cracks in water ice and plumes of liquid water) and Jupiter's moon Europa that has a five-km-thick ice layer on its surface. The Hubble telescope, with a new installed camera, will doubtless bring in many more details in the days to come.
No comments:
Post a Comment