AstronomyWorld Asteroid Day

Oumuamua : A Cigar Shaped Puzzle

Asteroids are essentially rocks in space that form the protoplanetary disk of dust and gas forming a ring about the sun. Their sizes can range from those as small as boulders and those which are as large as planets. During the early days of our solar system, debris was unstable, crashing and colliding with one another. Thus lead to the formation of rocks of different sizes. Asteroids may be made up of rock, metals and in some cases even water! The composition of an asteroid specifically depends on how near it is to the sun. The ones comparatively closer to the sun are dominantly made up of carbon with traces of nitrogen, hydrogen and oxygen while the ones farther away are made up of silicate rocks.

Below, we take a closer look at Oumuamua, an interstellar object that visited our solar system in the October of 2017. We shall also study how scientists developed various theories about its classification and composition with the passage of time.

When Oumuamua was first spotted in our solar system in the October of 2017, it caused quite the stir in the astrophysics community. Detected first in Hawaii using the Pan-STARRS1 telescope (funded by NASA’s Near Earth Observation program), it was named this way as ‘Oumuamua’ is Hawaiian for scout or messenger. It was the first ever interstellar object that our telescopes had ever detected.

Although scientists were excited to find out as much information that they could, using the Hubble telescope, they soon realized that they were too late and that Oumuamua has already started leaving our solar system. There wasn’t much time whilst mounting questions about its composition, origin and classification. There was a long list of permissions that required approvals before any kind of research could take place. Scientists at NASA worked day and night. Oumuamua was travelling at a speed of 110,000 meters per hour and moving farther from us every minute.

Oumuamua was dull red in colour, in the shape of a cigar, somewhat flattened and 1000 feet long unlike anything else in our solar system. While it was going at such a high speed, it was also spinning along its own axis. This would suggest that it was made of some very strong substance. It was irregularly shaped, and tumbling out of our solar system in a hurry. Its eccentric orbital path and surprising velocity suggested very clearly that it was something that had come to our solar system from beyond.

At first, astronomers thought it was an interstellar asteroid. It was very likely since it looked like a chunk of debris that could have been shed by another system probably due to being torn apart by gravitational forces of a flyaway star or a supernova explosion.

Astronomers were then led to believe that it was a comet that had flung loose from a faraway star as it was speeding up while exiting the solar system as if outgassing of gasses were giving it the required boost. However, it didn’t have the flash or glow of a comet. It also left no dust trails as it travelled which is characteristic for a comet. No dust trails could also suggest a difference in chemical composition and the size of dust particles. Its brightness also varied quite wildly.

It was acting like a comet while looking like an asteroid.

There was a brief period when Harvard scientists proposed that it may be an alien spaceship as its shape resembled that of a rocket cylinder. Astronomers turned their radio telescopes on it just in case, but our interstellar visitor remained silent. Hence an alien spaceship seemed like a far-fetched idea.

Imagine wanting to get to know someone very well, while they’re about to move to a part of the world from where communication is impossible. Such was the relationship between Oumuamua and astronomers. They were trying their hardest to study and find concrete information about our visitor but it was moving farther away. There just wasn’t enough time.

Even after Oumuamua had gone out of the range of even the Hubble telescope, the research and studies did not cease. After about three years of studying the weirdly shaped object that was roaming in our solar system, some astronomers from Yale suggested that it was neither an asteroid nor a comet. Rather, they proposed that it may be a cosmic iceberg made up of solid hydrogen and not a planetesimal ripped due to gravitational interactions or collision. Instead, it must have been formed inside a cold and dark interstellar cloud which consists of dense patches of dust and gas and where stars are said to be formed.

At the center of such interstellar clouds, there is no sun and hence temperatures can plunge to a few degrees above absolute zero. Hydrogen freezes only at temperatures such as 6 degree Celsius above the absolute zero. Such extreme temperature conditions could only be found at prestellar cores of such molecular clouds. These frozen particles of hydrogen may stick to interstellar dust and after thousands of years, form solid structures like ice cubes at least 30 meter wide.

Water and ice, which are the main constituents of a comet, could not have provided enough propellant for it to travel at the speed that it did. The classification of Oumuamua as a comet could be ruled out according to this theory. Frozen hydrogen, on the other hand, was capable of providing such humongous acceleration because it is more volatile. Subliming hydrogen could provide an additional energy boost of 61 m/s to the velocity of a cosmic ice ball already travelling at 64374 m/s. Thus scientists at Yale classified it as a chunk of solidified hydrogen with an icy core.

They also said that the peculiar shape of Oumuamua may have been formed while it was journeying in our solar system. Elaborating on that, they said that while it came closer to the sun, the hydrogen on its surface started subliming giving it the necessary stimulant to travel at speeds as high as 110,000 meters per hour. While this sublimation took place, parts of the icy surface corroded off, giving it a thin cigar shape.

As it fled from our reach in a jiffy, Oumuamua did not give us much time to study it with intricacy. All theories being made are, understandably, hypothetical assumptions due to the meagre data available. Nonetheless, everyone is on guard and waiting for another one of such visitors from the beyond in order to test their theories. Oumuamua also leaves us with so many questions about what lies in the cold dark nothingness of the sky. There is so much that is out of our reach, so much that we cannot see even with our most powerful telescopes. So much that is waiting to be discovered.

Oumuamua may be the very first interstellar object that was detected by our telescopes, but it will very definitely not be the last.

By: Swastika Thakur

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