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In late October 2017, astronomers announced the first ever discovery of an asteroid (or comet?) coming into our Solar System from another stellar system. The object was first spotted on 19 October by the University of Hawaii’s Pan-STARRS telescope, during its nightly search for near-earth objects. Based on its extreme orbit and its rapid speed, it was soon determined that the object has come into our Solar System from somewhere else, and this makes it the first ever asteroid/comet with an extra-solar origin to have been discovered. Originally given the designation A/2017 U1, the International Astronomical Union (IAU) have now renamed it 1I/2017 U1, with the I standing for “interstellar”. 

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The object, given the designation A/2017 U1, was deemed to be extra-solar in origin from an analysis of its motion.

In addition to its strange trajectory, observations suggest that the object also has quite an unusual shape. It is very elongated, being ten times longer than it is wide. It is thought to be at least 400 metres long but only about 40 metres wide. This was determined by the rapid and dramatic changes in its brightness, which can only be explained by an elongated object tumbling rapidly.

The object has also been given the name Oumuamua (pronounced oh MOO-uh MOO-uh), although this is not its official name (yet).  This means “a messenger from afar arriving first” in Hawaiian. In other respects, it seems to be very much like asteroids found in our own Solar System, and is the confirmation of what astronomers have long suspected, that small objects which formed around other stars can end up wandering through space, not attached to any particular stellar system.

To read more about this fascinating object, follow this link.

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Over the next few days we should be treated to the sight of one of the best comets in many years. Comet PANSTARRS is entering the inner part of the Solar System, and will be visible in the Western sky over the next week. Although we are not entirely sure, comet PANSTARRS should brighten over the next few days to become visible to the naked eye in the West just after sunset. The last good comet I saw was comet Hyakutake which was visible in 1997. Seeing a comet with its tail stretching across the sky is a memorable experience, so it is well worth making the effort over the next few days to try to see comet PANSTARRS.


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This image shows where we can expect to see the comet. For Northern Hemisphere observers it will be low in the Western sky just after Sunset.


This screen capture is taken from the website earthsky.org

This screen capture is taken from the website earthsky.org


Where do comets come from?

There are two basic types of comets, short period and long period comets. The short period comets come from the Kuiper Belt, which is a band of small objects just beyond the orbit of Pluto. In fact, Pluto is a Kuiper Belt object, and of course has been re-classified as a minor planet by the International Astronomical Union. The Kuiper Belt was postulated by Gerard Kuiper in 1951, but the first Kuiper Belt object (apart from Pluto) was not discovered until 1992. The Kuiper belt lies at between 50 and 100 Astronomical Units (AUs), where 1 AU is the distance from the Earth to the Sun.


The Kuiper belt lies beyond the orbit of Pluto, and is the reservoir of short period comets.

The Kuiper belt lies beyond the orbit of Pluto, and is the reservoir of short period comets.


Long period comets come from much further out in the Solar System, they come from the Oort Cloud. The Oort cloud is about 2,000 times further away than the Kuiper Belt, lying at about 100,000 AUs. The Oort cloud is so far away that we will probably never directly observe objects in the Oort cloud.


The Oort cloud is the reservoir of long period comets, lying about 2,000 times further away than the Kuiper Belt.

The Oort cloud is the reservoir of long period comets, lying about 2,000 times further away than the Kuiper Belt.


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