Anyone who has read Arthur C Clarke’s 1973 science fiction book “Rendezvous with Rama”¹ will have immediately thought of it when the discovery of ‘Oumuamua² was revealed in 2017. Some may have hoped, as in that book, that it was an investigating space craft from another star. In true honesty, Roger O’Brien, our speaker for the evening, admitted that he was such a person; then went on to outline all that had been confirmed about this interstellar traveller up to date.
Roger O’Brien is an Open University tutor in Astronomy and Planetary Science. Although a keen amateur astronomer since 1957, his first 26 years were in a bank. He then took a degree in Astronomy which became his profession. Roger is a Fellow of the Royal Astronomical Society and lectures at many prestigious science organisations. I was looking forward to this talk and was not disappointed. Roger has a casual and self-effacing presentation technique with interjections of, sometimes speculative, personal thoughts which draws you in and belies his wide professional knowledge. I don’t envy his students!
Discovered on 29th October 2017 by Robert Weryk using the Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) telescope in Hawaii, the object was initially missed by the auto detection system but then spotted when reviewed. By then the object had passed its closest point to the Earth of about 15 million miles and was heading away. Its speed was substantial at about 27 km per second and along with its strongly hyperbolic trajectory was quickly realised to have come from outside the Solar System; roughly from the direction of Vega. Originally given the nomenclature of a comet, it was reclassified as an asteroid as A/2017 U1. This has now been updated as the first official interstellar object as AI/2017 U1. The name ‘Oumuamua is Hawaiian for ‘Scout’.
ESO’s (European Southern Observatory) Very Large Telescope (VLT) was quickly called into action to assess the object as by then it had passed its closest point to the Sun and was heading away into interstellar space. The rapidly receding object was shown to be tumbling about every 7.3 hours and displaying a difference in albedo by a factor of 10. Measurements indicated a 10:1-ratio ellipsoid shape with the length about 400 metres. Roger described the shape as an elongated rugby ball.
It is dark red in colour, as are many space travelling objects, with a coating described as ‘organic’. However, in this case, ‘organic’ means something that is carbon based and the colour probably comes from deposited poly-carbons built up over millions of years travelling through space. Importantly, despite substantial scanning, no transmissions of any type were discovered emanating from the object.
Although first thought to be a metallic or rocky object as no comet-like signs were obvious, the current location of ‘Oumuamua is slightly further away than it should be and this is now thought to be because of some outgassing from the object’s surface, giving it additional speed. This additional evidence now supports the theory that it is probably a comet type object with a mainly icy construction.
Whilst ‘Oumuamua is the first ‘confirmed’ interstellar object, thus its IAU designation, Roger segued to other interesting objects such as 2015 BZ509, identified in 2014, which is an asteroid type object co-orbital with Jupiter. However, unlike the Trojans, it is in an extreme but stable retrograde motion, same period orbit as Jupiter. Given its estimated age as greater than that of the Solar System and its retrograde motion, it has been posited that this is also an interstellar object captured by the planet.
There has been some reticence by the scientific community in the past to recognise the passage of interstellar objects through the Solar System but this is now changing and surveys have been widened accordingly. Likely, there have been many similar ‘visitors’ in the past but these have not been identified due to their speed and size offering little opportunity of recognition.
Roger raised the potential of many such objects passing us by each year but, if a probe, was this the way to communicate with others ‘out there’. Perhaps more efficient ways would be available, such as light modulation of stars with some mathematical link? Compared to radio transmissions this was a more efficient way to transmit over such large distances as would be needed within the galaxy. Kepler is looking for such starlight modulation but would this be identified against the search for exoplanets?
The Gaia probe is charting up to 1.7 billion star positions, well in excess of its original target, with a subset 7 million having fully reconstructed trajectories. Could this assist in identifying ‘Oumuamua’s origins?
Coming to a close, Roger précised the identification of ‘Oumuamua, its acknowledgement as an interstellar object, the confirmation of its composition and possible point of origin all within one year.
Yet, the speculation of it being something more than just an ‘astromet’, perhaps a space probe, was tempting for Roger! An ice-based probe might seem an unlikely form of construction but was actually an eminently suitable material for space travel. Leaving us a little intrigued, he decided to be unsure about it overall!
Thanks for a good evening Roger.
Hugh Alford FRAS – Vice Chair
¹:- See the following links for information:-
²:-Try saying “HO u mu a mu a” all as one word. Or listen for the accurate pronunciation via the link below: ~