Ever since space scientists first discovered the strange, cigar-shaped object called "Ium Oumuamua" in the sky, they've been discussing what exactly it is. Suggestions include an asteroid, a comet, and even an alien spaceship. Now, a study published in Nature suggests that it could actually be a comet ̵
The intriguing results complement recent discoveries that suggest that it's time to think about the division of asteroids into comets. Gravity keeps our feet on the ground, the moon orbits the earth and the planets orbiting the sun. It is also the main agent controlling the trajectory of comets as they swing through the solar system. It was his laws of gravity that allowed Newton's colleague Edmond Halley to predict the return of the comet, now known as the Halley Comet. The same laws allowed the Rosetta spacecraft to catch and fly the comet 67P / Churyumov-Gerasimenko.
There are non-gravitational effects that can affect the orbit of a comet, but in comparison to gravity they are so weak normally negligible. But in the case of the 1I / Oumuamua object, its orbit is so unusual that non-gravitational effects could play a role in its geometry.
1I /; Oumuamua was first spotted in October 2017. Calculations based on the laws of gravity showed that his trajectory was neither the ellipse of a comet nor that of an asteroid. Instead, Oumuamua appeared to have a hyperbolic orbit (see video), meaning that it was not gravitationally bound to the Sun. This means that it is most likely an intruder outside the solar system. Hence the "1I" part of his name: the first interstellar body.
O Oumuamua happened within 0.25 astronomical units (AU) of the Sun (1 AU is the distance between the Sun and the Earth). As a well-behaved comet, he should have developed a coma and a tail, like ice and dust, evaporating from the surface through a process called sublimation. But despite an organized and concerted observation campaign by the international astronomical community, no trace of coma or tail was seen.
In fact, measurements of its composition showed that it had more in common with asteroids than with comets: the low reflection from its surface indicated that there was little, if any, ice. It also seemed to have organic material that had been altered by cosmic rays – like many asteroids.
In addition to these observations, Oumuamuas was a very unusual shape: although the object was not directly visible, modeling its light curve (how the amount of reflected light changes as an object rotates) suggests that it is long and thin was – more cigar-shaped than the usual semi-rounded appearance of asteroids and comets. This made one more likely to say, "Oumuamua could be more fabricated than a natural visitor to the Inner Solar System, perhaps an extraterrestrial spaceship.
So, comets, asteroids, or spaceships? Devaluing the interstellar spaceship – it would certainly have stopped at least to study the signal mixing that emanates from our planet, leaving comets or asteroids as the remaining options. "The same group that published the discovery report from Oumuamua continued to observe the object and collected data from instruments on virtually all major earth-based telescopes in the world, as well as the Hubble Space Telescope.
Other options included an unusual mass distribution or perhaps a center of gravity that was shifted from the center of the body, and it could also be highly magnetized, interacting more strongly with the solar wind a razish and comprehensive series of observations, the team speculated that none of these effects were sufficient to explain the orbit of Oumuamua. Instead, they came to the conclusion that significant release of gas through sublimation was the most important possible mechanism – and this would suggest that it is a comet.
This is an important conclusion that is more general not only for Oumuamua but for comet and asteroid science. There were only a handful of earlier observations of non-gravitational effects on comet orbits, mainly because the measurements required for the calculations must be made over a very long distance. Assuming that Oumuamua went down like other comets, the body lost water and dust at a rate of about 2.4 kg per second.
This is similar to 20 kg per second for 67P / Churyumov-Gerasimenko. It seems that although Oumuamua appears to have a density similar to that of comets of the solar system, it must be much stronger given the small amount of dust released. Or perhaps the dust was more firmly bound to the surface by the organic compounds present.
Can we really say that Oumuamua is a comet, albeit with asteroidal properties? Or could it be an asteroid with comet properties? Is it important? I am not sure if it is so. The division between asteroids and comets in the solar system was obvious: asteroids had circular orbits, were of rock and metal and lived in the asteroid belt between Mars and Jupiter. Comets had inclined elliptical orbits, were of rock and ice and came from farther away.
But in recent years we have discovered families of asteroids scattered throughout the solar system, as well as Kuiper Belt objects. We also found comets with short and long orbits. And we've seen unusual features on objects that we thought we knew well. The asteroid Ceres, for example, has left behind salts that have been vaporized from the surface by sublimation – a process that is often observed in comets but not in asteroids.
Since Oumuamua, along with small bodies in the solar system and intestinal guests, seem to show a spectrum of compositional and dynamic qualities, it might be time to think beyond the division of asteroids and comets and to a new kind to seek to classify these objects. Maybe we need many more categories. Or maybe just one – the class of Small Body. Obviously, Oumuamua shows us that we have not yet discovered the diversity of objects in our neighborhood.
This article was originally published in The Conversation. Read the original article.
<p class = "Canvas Atom Canvas Text Mb (1.0em) Mb (0) – sm Mt (0.8em) – sm" type = "text" content = " Monica Grady is a professor of planetology and space science at the Open University and a research associate at the Natural History Museum, London, funded by the STFC, the UK Space Agency and the EU Horizon 2020. She is the CEO of MonicaGrady MeteoriteLady Ltd, a company which produces educational resources and educational events for schools and the public. "data-reactid =" 87 "> Monica Grady is a professor of planetary and space sciences at the Open University and a research fellow at the Natural History Museum in London. She is receiving financial support from the STFC, the UK Space Agency, and the EU's Horizon 2020 program. She is the CEO of MonicaGrady MeteoriteLady Ltd, a company that produces education resources and public relations for schools and the public.