Planetesimals of the Solar System

Asteroids are small, rocky objects, much smaller than planets. However they also orbit the Sun like the planets. There are lots of asteroids in our solar system most of which live in the region between the orbits of Mars and Jupiter, known as the asteroid belt.

The first asteroid was discovered on the first night of January 1901, by the astronomer Giuseppe Piazzi at Palermo. Italy. He named it “Ceres” after the patron Goddess of Sicily.

Astronomers were indeed jubilant on spotting a minor planet—as they referred to the asteroid—that filled in a large gap in the orderly spacing of the major Planets.

Slowly the other asteroids were discovered and by the year 1890, about 300 were known. Most had been given the names from international pantheon of Gods, and demigods. With the invention of photography the number of discoveries swelled and the supply of deities names was nearly exhausted. Hence the favourite names of wives, lovers, dogs, towns and even African shrubs had to be invoked for christening asteroids.

However few astronomers showed interest in these minor planets (asteroids) each less than 1000 kilometres across, playing cosmic bumper cars between Mars and Jupiter. Their total mass is believed to be hardly one-thousandth that of Earth’s. Most, never get close enough to be seen clearly and certainly none harbours life.

Their attractions, however, seem to be many; such as the chance to name some cosmic real estate, the continuing challenge of understanding how our solar family moves, the hope of studying primordial material, the prospect of finding mineral resources and setting up way stations to the outer planets.

But only in the past decade have astronomers come to realise that these bodies preserve an important record on the formation of the planets. Unlike the major planets which underwent vast changes since their original formation, these asteroids have remained unaltered for about 4.5 billion years though there have been some collisions. As veritable time capsules they should be similar to the preplanets that astronomers call planetesimals. They could be Rosetta stones to decipher our Solar System. Astronomers had been planning to send up an asteroid rendezvous probe.

Even four decades ago astronomers were able to list out 2042 asteroids with well known orbits. They now estimate that there are about 100,000 asteroids bright enough to be photographed from the Earth and that there are millions of undiscovered chunks.

Science fiction stories usually like to depict the asteroid belt as the “reefs of space” into which Rocket ships can only venture at great risk. Science fiction movies are also respon­sible for creating such an impression. However astronomers have sent several spacecraft through with fewer collisions than they would have anticipated. That’s not to say that a collision with a large rock—fist sized or large—would not destroy our probes but such encounters are rare in the vastness of space.

The composition of asteroids is still a puzzle. Some seem to be made of metal, the remains of bodies big enough to heat up and melt, thus forming an iron core similar to the Earth’s. Other asteroids are of a light rocky material quite unlike the moon but similar to one kind of meteorite.

Most of tiny fragments that appear as meteors are probably chips of asteroids flung free by collisions. So far they are the only pieces of asteroids scientists have been able to lay their hands on. It is the asteroids themselves that “would be space colonists” are after. According to one ambitious plan, astronauts are expected to travel to the asteroid belt, build rockets on a small asteroid and boost it back to the earth. Other asteroids might be hollowed out for use as space stations. The rocky asteroids could supply water, oxygen and other elements lacking in the lunar soils that colonists would be using. The metallic asteroids would supply almost pure iron alloy. (an asteroid only one kilometre in diameter contains as much iron as a produced on Earth in eight years i.e. about four hundred billion metric tons, and it’s already refined.)

As the world’s hunger problems seem to be getting worse every day, scientists are exploiting the possibilities of growing food in space. Our most cost effective measures of supplying electricity would be to build Satellite Solar Power Stations and send their output to Earth via microwave links. The stations could be built in space, of materials retrieved from the shallow gravity wells of the moon and asteroids. Recent studies have examined the possibility of retrieving Earth-approaching asteroids for space manufacturing. This resource is vast— there are probably 100,000 asteroids as stated above- some of them with diam­eters greater than 100 meters and masses around one million metric tons. The unit cost to retrieve asteroids may be many times less than one thousand US dollars per kilogram lift cost of Earthly materials using the shuttle or one dollar to two dollars for lunar materials .The small asteroids have zero- gravity fields. So the prospect of costly landings is avoided. Solar energy for processing and propulsion is continuously available on the asteroid.

The favourable economics of asteroid retrieval combined with the apparent attractiveness of space agronomy raise the possibility that food could be grown more cheaply and reliably in space than on Earth, given a highly developed programme of space manufacturing. Large quantities of dehydrated crops could be dropped out of orbit (possibly by an electromagnetic mass-driver device) enter the Earth’s atmosphere aboard a metal foam reentry body, land in the ocean near potential consumers and be towed ashore for use. Some astronomers have already experimented with this technique for recovering asteroidal materials on Earth.

A three-kilometre carbonaceous asteroid towed earth­ward by a Solar Powered mass driver (most of the mass driver’s mass and expense would go into a power plant and its radiator) could provide enough growing area to support six billion people. In the interim smaller asteroids could be turned into smaller growing areas as financial insurance.

A retrieval system would cost in the range of 100 billion US dollars to 200 billion US dollars spread over two to three decades. This compares favourably with the 700 billion US dollars it would cost between now and 2040 A.D. to provide irrigation to modernise agriculture in the developing world. Given a potential market of 200 billion US dollars to 500 billion US dollars a year the pay off would be rapid.

The Biggest Asteroid of 2021 (christened 2001 FO32,) zoomed past earth, at a distance of 2000 Kms, on the night of March 21st at a velocity of 123,876 Kmph which is much faster than the average asteroid. It had been first spotted in 2001 and had been in the watch list of the National Aeronautics and Space Administration (NASA).

It is nearly half a kilometre wide. To put it in perspective, it is more than twice the height of India’s Statue of Unity, the tallest statue in the world.

The asteroid did not get closer than 2000 kms, and therefore did not cause any damage to our planet. However NASA as an abundant caution regarded the distance close enough for it to be classified as “potentially hazardous asteroid” and put it on the “Asteroid Watchlist”.

The encounter which took place on March 23 provided astronomers with the opportunity to get a more precise reading on the space rock not only in terms of its size but also to determine its composition.

The bigger the asteroid, the bigger the threat to the Earth. As long it doesn’t get close enough to be pulled in by Earth’s gravity, Earthlings can breathe a sigh of relief.

Asteroids are much larger than comets and much heavier. An asteroid only 5 km across would be classified as small; Ceres, the largest, is 100 times bigger than this. They have a mean density twice that of water, considerable strength, and a composition based on rock and metals.

But in the past experience has shown that asteroids, even much smaller than 2001 FO32, have the potential to wreak havoc once they break through the atmosphere.

One example is the meteor that caused extensive damage to a town called Chelyabinks, in Russia. It was only 17 metres wide. The force unleashed by the explosion was enough to shatter glass, level trees and break down buildings within a radius of 500 square kilometres.

In the case of the 2002 FO32 asteroid no damage was caused. As the asteroid makes its way through the inner solar system — the region from Mars to Mercury — it will first pick up speed, then slow down before being flung back into space to continue its orbit around the Sun.

Dinosaurs first appeared on our planet between 247 and 240 million years ago. They ruled the Earth for about 175 million years until a major violent extinction event 65.5 million years ago wiped out all of them, except for birds (avian dinosaurs). From the sheer size and the extent of the damage caused by the impact of the meteorite, scientists infer that the celestial body that impacted the earth about 60 million years ago must have been a meteor which originated from a huge asteroid.