The mysteries of the Oort cloud at the edge of our solar system

The Oort cloud represents the very edges of our solar system. The finely dispersed collection of icy matter begins about 200 times farther from the sun than Pluto and extends halfway to our closest starry neighbor to our sun, Alpha Centauri. We know so little about it that its very existence is theoretical – the matter that makes up this cloud has never been seen even by our most powerful telescopes, except when part of it breaks free.

“For the foreseeable future, the bodies in the Oort Cloud are too far away to be directly imaged,” a NASA spokesperson said. “They are small, weak and move slowly.”

Theoretical models aside, most of what we know about this mysterious area comes to us from visitors who sometimes turn to us every 200 years or so – long-lived comets. “[The comets] have very important information about the origin of the solar system, ”says Jorge Correa Otto, a planetary scientist from the Argentine National Council for Scientific and Technical Research (CONICET).

A light cloud, in theory

The inner edge of the Oort Cloud is thought to begin at around 1,000 to 2,000 astronomical units from our sun. Since an astronomical unit is measured as the distance between the Earth and the sun, it means that it is at least a thousand times farther from the sun than we are. The outer rim is believed to extend up to 100,000 Astronomical Units, which is halfway to Alpha Centauri. “Most of our knowledge of the structure of the Oort cloud comes from theoretical modeling of the formation and evolution of the solar system,” the NASA spokesperson said.

Although there are many theories about its formation and existence, many believe that the Oort Cloud was created when many planets in our solar system formed around 4.6 billion years ago. Similar to how the Asteroid belt between Mars and Jupiter springing to life, the Oort cloud probably represents the material left behind by the formation of giant planets like Jupiter, Neptune, Uranus and Saturn. The movements of these planets as they occupied their current positions pushed this material beyond Neptune’s orbit, explains Correa Otto.

Another recent study argues that some of the matter in the Oort cloud can be gathered like our sun “flies comets” in orbit around other stars. Basically, the theory is that comets with extremely long distances around our neighboring stars turn away as they get closer to our sun, at which point they stay in the Oort Cloud.

The icy objects that form the Oort Cloud are thought to be similar in composition to that of the Kuiper Belt, a flat, disc-shaped area beyond Neptune’s orbit that we know best. The Kuiper Belt is also made up of icy objects from the formation of planets early in the history of our solar system. Pluto is probably the most famous object in this region, although NASA’s New Horizons space probe flew over another double-lobe object in 2019 called Arrokoth – currently the most distant object in our solar system explored closely, according to NASA.

“The bodies of the Oort Cloud, the Kuiper Belt, and the Inner Solar System would all have formed together, and gravitational dynamics in the Solar System kicked some out,” the NASA spokesperson said.

Visitors from the edge of our solar system

Estonian philosopher Ernst Öpik first hypothesized that long-period comets could originate from an area on the outskirts of our solar system. Then, the Dutch astronomer Jan Oort predicted the existence of his cloud in the 1950s to better understand the paradox of long-lived comets.

Oort’s theory was that comets would eventually strike the sun or a planet, or be ejected from the solar system when they came into closer contact with the strong orbit of one of these large bodies. In addition, the tails that we see on comets are made up of gases burnt by solar radiation. If they made too many passes near the sun, this material would have burned. They should therefore not have spent their entire existence in their current orbits. “Sometimes the Oort cloud bodies will be kicked out of their orbits, possibly due to gravitational interactions with other Oort cloud bodies, and will come to visit the inner solar system as comets,” the carrier said. word of NASA.

Correa Otto says that the direction of comets also supports the spherical shape of the Oort cloud. If it were disc-shaped, similar to the Kuiper Belt, comets would follow a more predictable direction. But the comets passing by are coming from random directions. As such, it appears that the Oort Cloud is more of a shell or bubble around our solar system than a disk like the Kuiper Belt. These long period comets include C / 2013 A1 Siding Spring, which passed near Mars in 2014 and will not be seen again for 740,000 years.

“No objects have been observed in the distant Oort Cloud itself, making it a theoretical concept for the moment. But it remains the most widely accepted explanation for the origin of long-lived comets.” , NASA says.

The Oort Cloud, if it does exist, is probably not unique to our own solar system. Correa Otto says some astronomers believe these clouds exist around many solar systems. The problem is, we can’t even see our own yet, let alone those in our neighboring systems. The Voyager 1 spacecraft is heading in that direction – it is expected to reach the inner edge of our Oort Cloud in about 300 years. Unfortunately, Voyager will have long ceased to function.

“Even if it was the case [still work], the sunlight is so dim and the distances so vast that it would be unlikely to fly close enough to something to imagine it, ”said the NASA spokesperson. In other words, it would be hard to tell that you are in the Oort Cloud even if you were there.

Arline J. Mercier

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