New study shows what interstellar visitor 'Oumuamua can teach us

March 27, 2018 by Jeanette Kazmierczak, NASA
An illustration of ‘Oumuamua, the first object we’ve ever seen pass through our own solar system that has interstellar origins. Credit: European Southern Observatory/M. Kornmesser

The first interstellar object ever seen in our solar system, named 'Oumuamua, is giving scientists a fresh perspective on the development of planetary systems. A new study by a team including astrophysicists at NASA's Goddard Space Flight Center in Greenbelt, Maryland, calculated how this visitor from outside our solar system fits into what we know about how planets, asteroids and comets form.

On Oct. 19, 2017, astronomers working with the NASA-funded Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1) at the University of Hawaii spotted an object zipping through our solar at a very high speed. Scientists at the Minor Planet Center, funded by NASA's Near-Earth Object Observations Program, confirmed it was the first object of interstellar origin that we've seen. The team dubbed it 'Oumuamua (pronounced oh-MOO-ah-MOO-ah), which means "a messenger from afar arriving first" in Hawaiian—and it's already living up to its name.

"This object was likely ejected from a distant star system," said Elisa Quintana, an astrophysicist at Goddard. "What's interesting is that just this one object flying by so quickly can help us constrain some of our planet formation models."

On Sept. 19, 'Oumuamua sped past the Sun at about 196,000 mph (315,400 km/h), fast enough to escape the Sun's gravitational pull and break free of the solar system, never to return. Usually, an object traveling at a similar speed would be a comet falling sunward from the outer solar system. Comets are icy objects that range between house-sized to many miles across. But they usually shed gas and dust as they approach the Sun and warm up. 'Oumuamua didn't. Some scientists interpreted this to mean that 'Oumuamua was a dry asteroid.

Planets and planetesimals, smaller objects that include comets and asteroids, condense out of disks of dust, gas and ice around young stars. Smaller objects that form closer to their stars are too hot to have stable surface ice and become asteroids. Those that form farther away use ice as a building block and become comets. The region where asteroids develop is relatively small.

"The total real estate that's hot enough for that is almost zero," said lead author Sean Raymond, an astrophysicist at the French National Center for Scientific Research and the University of Bordeaux. "It's these tiny little circular regions around stars. It's harder for that stuff to get ejected because it's more gravitationally bound to the star. It's hard to imagine how 'Oumuamua could have gotten kicked out of its system if it started off as an asteroid."

The distance from a star beyond which water stays ice, even if it's exposed to sunlight, is called the snow line or ice line. In our own solar system, for example, objects that developed within three times the distance between the Sun and Earth would have been so hot that they lost all their water. That snow line contracted a little as the Sun shrank and cooled over time, but our main belt asteroids are located within or near our snow line—close enough to the Sun that it would be difficult to be ejected.

"If we understand planet formation correctly, ejected material like 'Oumuamua should be predominantly icy," said Thomas Barclay, an astrophysicist at Goddard and the University of Maryland, Baltimore County. "If we see populations of these objects that are predominantly rocky, it tells us we've got something wrong in our models."

Scientists suspect most ejected planetesimals come from systems with . The gravitational pull of these massive can fling objects out of their system and into interstellar space. Systems with giant planets in unstable orbits are the most efficient at ejecting these smaller bodies because as the giants shift around, they come into contact with more material. Systems that do not form giant planets rarely eject material.

Using simulations from previous research, Raymond and colleagues showed that a small percentage of objects get so close to gas giants as they're ejected that they should be torn into pieces. The researchers believe the strong gravitational stretching that occurs in these scenarios could explain 'Oumuamua's long, thin cigar-like shape.

The researchers calculated the number of interstellar objects we should see, based on estimates that a star system likely ejects a couple of Earth-masses of material during . They estimated that a few large planetesimals will hold most of that mass but will be outnumbered by smaller fragments like 'Oumuamua. The results were published March 27 in the journal Monthly Notices of the Royal Astronomical Society.

The findings have already been partially confirmed by observations of the object's color. Other studies have also noted that star systems like our own would be more likely to eject comets than asteroids. Future observatories like the National Science Foundation-funded Large Synoptic Survey Telescope could help scientists spot more of these objects and improve our statistical understanding of planet and planetesimal formation—even beyond our solar system.

"Even though this was flying through our solar system, it does have implications for extrasolar planets and finding other Earths," Quintana said.

Explore further: 'Oumuamua likely came from a binary star system

More information: Sean N Raymond et al. Implications of the interstellar object 1I/'Oumuamua for planetary dynamics and planetesimal formation, Monthly Notices of the Royal Astronomical Society (2018). DOI: 10.1093/mnras/sty468

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24volts
not rated yet Mar 27, 2018
How about it was simply a piece of regular solid rock that got knocked out of some system when two planetoids hit each other like what happened to the Earth to create the Moon a long time ago? It wouldn't have all melted. Some of it would have been solid bits that simply got blasted out into space at high speed.

Some of that material is probably still moving along somewhere out in the solar system and possibly even the galaxy by now.
Parsec
not rated yet Mar 27, 2018
@24volts - objects do not acquire such huge velocities by impacting other objects. It just isn't possible.

The only mechanism to endow such an object with the observed velocity is some sort of gravitational slingshot as described in the article. The energy involved would completely destroy the object if it was deposited in the form of an collision.
24volts
not rated yet Mar 27, 2018
It still could have happened. It could have been gravitationally slung out of the system it was in. Who knows. It was probably millions or even billions of years ago. We have no idea where it actually came from originally.

No, the energy involved would not have instantly melted every rock if two planetoids had hit. A lot of material would have been simply knocked away into space. Especially stuff that wasn't right at the impact site.
Molecular hydrogen
not rated yet Mar 28, 2018
I agree with 24 volts a direct hit head on of two planetoids could melt all the rock but a glancing blow would release some solid debris and transfer the kinetic energy... with colliding galaxies anything is possible ..
J-n
not rated yet Mar 28, 2018
I think the point is that if it was given the velocity it has via the transfer of kinetic energy, that ammount of energy would destroy the object. Things further from the impact as you suggest would get less energy and survive ... but less energy ... so not the speeds we see.

24volts
not rated yet Mar 28, 2018
I think the point is that if it was given the velocity it has via the transfer of kinetic energy, that ammount of energy would destroy the object. Things further from the impact as you suggest would get less energy and survive ... but less energy ... so not the speeds we see.


we have no idea how many times that thing has slingshotted around planets, stars, etc... Exactly why would that destroy it? It obviously hasn't. It's a solid piece of rock. It could have been molten for all we know when it was first created or blasted off of some other rock. No one knows where it came from, no one knows what it's been through in all the years it's been zooming around the universe and no one knows where it will eventually end up at. We know almost nothing about it other than it was rock that zoomed into our solar system and is now zooming back out.

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