Comet from interstellar space discovered moving in our Solar System

Another alien visitor

Photo: Wilikipedia

Comets, such as Hale–Bopp, seen here after passing perihelion in April 1997, are often detected in our Solar System.

Astronomers have discovered yet another alien visitor to the Solar System.

This one appears to be a comet, a ball of dust, ice and various volatile materials. It is rapidly approaching the sun and has just passed within the orbit of Jupiter. The object, designated Comet 3I/ATLAS, has an estimated diameter of about 20 kilometres. It is moving at around 240,000 kilometres an hour, which means it is not a member of our Solar System. It is moving far too fast to be held by the Sun's gravity.

That means it has come in from interstellar space, will fly past the Sun and return to the abyss. If we consider the chances of one of these lonely interstellar wanderers randomly drifting into the Solar System, and that this has happened at least three times in the last few years, there must be a lot of them.

These bodies probably originated in the same way as their counterparts in our Solar System—from the collapse of a cloud of gas and dust. If so, they would start their existence cosily orbiting a newly- born star somewhere out there. However, a close encounter with a fellow orbiting body could result in one of them being launched into an orbit taking it much closer to its star, or even into a collision with it, while the other was thrown out into space.

There are lots of objects similar to this one orbiting the Sun out beyond Pluto. We know there are close encounters that result in one body being thrown into the inner Solar System, where we see them as comets. It is possible the others get thrown out, maybe out of the Solar System altogether, to spend thousands or millions of years in the cold and dark.

Comet 3I/ATLAS is now far enough into the Solar System for the Sun's gravitational attraction to have accelerated it a bit. However, if we just assume it has been travelling through space at that measured speed of 240,000 km/h, we can get a better picture of its journey to us. It is arriving from the direction of the constellation of Sagittarius, but at this point we have no idea of where it has come from. It might even have had some close encounters with other stars en route. It probably originated in our galaxy.

The nearest star to us after the Sun is Proxima Centauri, which lies 4.3 light years away, which in cosmic terms is "sitting on our doormat". A light year is the distance light travels in a year. Light travels at just under 300,000 kilometres a second, so Proxima Centauri is just under 43 million million kilometres from us.

To make that cosmically tiny trip would take Comet 3I/ATLAS over 20,000 years. It is more likely the object has been drifting through interstellar space for thousands or even millions of years.

If we could get a sample of its material, we could estimate when it solidified. Comparing its makeup with that of bodies in our Solar System could tell us what other planetary systems are like. Having travelled deeply frozen, they should be excellently preserved. However, getting that sample is unlikely. We have nothing capable of reaching, and then achieving a soft landing, our fast-moving visitor.

A high-speed, close fly-by is a possibility. We could get lots of pictures and maybe an impact probe would throw off a material that could be analyzed.

Journey times ranging from centuries to millions of years would tend to rule out intelligent, alien visitors arriving in our neighbourhood this way. However, improbable as it might seem, the possibility cannot be ruled out.

Science fiction writer Arthur C. Clarke described such a scenario in his book Rendezvous with Rama. It might still be a good idea that, as our spacecraft flies past some future visitor, we make sure it is not a spacecraft before we start firing probes at it. After this visit, Comet 3I/ATLAS will be heading back out in the direction of the constellation of Gemini.

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Saturn will rise around midnight and Venus around 2 a.m. Mars is very low in the west after sunset. The Moon will reach last quarter on July 17.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.