We now know that 1I/(‘Oumuamua), aka A/2017 U1 is an even more extraordinary object than we believed. It is shaped more or less like a cigar: ten times as long as it is wide. This creates some real physical problems as it is far more elongated than any solar system object, asteroid, comet, or satellite, that we know and is far too elongated to be made up of two bodies in contact, as they would fly apart with its rotation.
The latest JPL solution to the orbit of A/2017 U1 is JPL#14, calculated on November 21st based on 115 observations over 34 days. There are just two additional observations since the last calculation and these have barely changed the calculated orbit. As it becomes more distant and fainter it seems unlikely that there will be many more observations.
We know that it entered the solar system with a velocity of 26.3 km/s, equivalent to 1 light year every 11000 years and will leave the solar system in a direction more or less towards the star 16 Pegasi, in the constellation of Pegasus.
Just how extraordinary is the orbit of ‘Oumuamua?
I can’t remember who was the colleague who asked the question but I have checked the velocity of the five NASA missions on solar system escape trajectories compared to 1I/’Oumuama.
The velocity of ‘Oumuama in the distant future will be (almost) identical to its entry velocity in the solar system: 26.3 km/s.
In contrast, the five NASA probes are all much slower. From fastest to slowest their velocity is:
Voyager 1 – 16.9 km/s
Voyager 2 – 15.0 km/s
New Horizons – 13.6 km/s
Pioneer 10 – 11.9 km/s
Pioneer 11 – 11.2 km/s
Voyager 1 is the fastest ever artificial satellite leaving the solar system, its velocity boosted by close approaches to Jupiter and Saturn, but even so, in an interplanetary race, will be caught and passed quickly by ‘Oumuamua. This will happen around the year 2080, when ‘Oumuamua will be further from the Sun than Voyager 1 although, by then, Voyager 1 will have fallen silent as its nuclear power plant is expected to fail to be able to generate enough power to maintain contact with Earth long before this date.
There are 327 comets that have been calculated reliably to have a hyperbolic, or open orbit that will escape from the solar system. Most of these orbits are just barely hyperbolic with a typical escape velocity from the solar system – that is, their speed in the future, far from the Sun – around 2-3 km/s.
- The most hyperbolic comet ever observed, is C/1980 E1 (Bowell), which is leaving the solar system with a velocity of 4.1 km/s.
- Comet Arend-Roland, which was a bright naked-eye object in 1957, is leaving the solar system at 2.2 km/s.
In other words, ‘Oumuamua is leaving the solar system more than 6 times faster than the fastest escaping comet that we have observed and about 10 times faster than an average comet in a hyperbolic orbit.
Truly, both its physical characteristics and its high velocity make it a quite extraordinary object.