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Increase in ‘Oumuamua’s speed through the solar system reveals it to be a comet

This illustration shows ‘Oumuamua racing toward the outskirts of our solar system. As the complex rotation of the object makes it difficult to determine the exact shape, there are many models of what it could look like. Image and Caption Credit: NASA / ESA/STScI

This illustration shows ‘Oumuamua racing toward the outskirts of our solar system. As the complex rotation of the object makes it difficult to determine the exact shape, there are many models of what it could look like.
Image and Caption Credit: NASA / ESA/STScI

Scientists observing the path of ‘Oumuamua,’ the first known interstellar object to pass through the solar system, discovered it to be traveling faster than expected, leading them to conclude it is actually a comet that received a boost in speed through outgassing.

When ‘Oumuamua was first seen last fall, scientists were uncertain as to whether it was an asteroid or comet. Based on its trajectory through the solar system, they determined it to be an interstellar visitor.

An international team of researchers who observed ‘Oumuamua using the Hubble Space Telescope (HST) and several ground-based telescopes, including the Canada-France-Hawaii Telescope in Hawaii, the Gemini South Telescope in Chile, and the European Southern Observatory‘s (ESO) Very Large Telescope (VLT), also in Chile, were surprised to see it increase its speed and alter its trajectory when they last observed it in early January. They found its speed boosted by 25,000 miles (40,000 km) from what it would have been if ‘Oumuamua were affected solely by gravitational forces.

“Our high-precision measurements of ‘Oumuamua’s position revealed that there was something affecting its motion other than the gravitational forces of the Sun and planets,” explained Marco Micheli of the European Space Agency‘s (ESA) Space Situational Awareness Near-Earth Object Coordination Centre in Frascati, Italy.

Davide Farnocchia of the Center for Near-Earth Object Studies (CNEOS) at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, recognized ‘Oumuamua’s increased speed and altered path as consistent with the actions of comets, which eject gas and dust as they approach the Sun. These jets of ejected material increase the comets’ speeds by giving them a slight push.

Gas and dust ejected from a comet as a result of solar heating form a cloud or coma at the front of the comet and a tail that trails behind it. Neither a coma nor a tail were observed with ‘Oumuamua, so scientists were unaware it was outgassing.

The fact that scientists did not see any signs of outgassing is likely due to ‘Oumuamua ejecting only a small amount of dust particles or giving off large, coarse dust grains not bright enough for Hubble to detect.

Even outgassing of a small amount of dust particles is likely enough to increase ‘Oumuamua’s speed.

‘Oumuamua may have once had the small dust grains typical of comets on its surface. Over time, as it traveled from its star system through interstellar space, these dust grains likely eroded away.

“The more we study ‘Oumuamua, the more exciting it gets. I’m amazed at how much we have learned from a short, intense observing campaign. I can hardly wait for the next interstellar object!” said Karen Meech of the University of Hawaii‘s Institute for Astronomy.

Now speeding out of the solar system at approximately 70,000 miles (114,000 km) per hour, ‘Oumuamua has passed beyond the orbit of Jupiter heading toward the outer solar system and can no longer be observed by Hubble.

A paper on the scientists’ findings has been published in the journal Nature.

Video courtesy: NASA





Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.

Reader Comments

Wow! Very interesting! Maybe one of the Voyagers or NH will run across it someday!!!!!

James Lunar Miner

“Astronomers estimate that several interstellar objects similar to ’Oumuamua pass inside the orbit of Earth each year,[47] and that 10,000 are passing inside the orbit of Neptune on any given day.[71] If correct, this provides possible opportunities for future studies of interstellar objects, although with the current space technology, close visits and orbital missions are impossible due to their high speeds.”

From: “’Oumuamua” Wikipedia

What kind of risk do the high velocity large, medium, or small interstellar objects pose to folks on Earth?

James Lunar Miner

“Recent research suggests that (514107) 2015 BZ509 may be a captured interstellar object from 4.5 billion years ago due it being in a co-orbital motion with Jupiter and its retrograde orbit around the Sun.”

And, “An interstellar comet can probably, on rare occasions, be captured into a heliocentric orbit while passing through the Solar System. Computer simulations show that Jupiter is the only planet massive enough to capture one, and that this can be expected to occur once every sixty million years.[16] Comets Machholz 1 and Hyakutake C/1996 B2 are possible examples of such comets. They have atypical chemical makeups for comets in the Solar System.[15][18]”

From: “Interstellar object” Wikipedia

If our Space Force and other folks ever need to investigate, deflect, or destroy an incoming high velocity interstellar object, the super high Isp and high delta-v deep space mission capabilities available with nuclear powered electric space propulsion systems could be quite useful.

Or we could just ignore such risks and keep our heads buried in the sand filled with dinosaur dreams and continue to hope and pray no interstellar object will ever impact our Home Planet.

James Lunar Miner

Probably any American Space Force effort to closely investigate or use nuclear explosive devices to deflect or destroy a high velocity interstellar object needs to have full access to the newly developing high delta-v deep space mission capabilities available with nuclear powered electric space propulsion systems.


“Masson said CNES is also working on a nuclear electric propulsion system that could be possibly used for a future mission to Mars. The project, called Democritos and funded through the EU’s Horizon 2020 research program, is a joint project between several European and Russian research institutes.”

And, “The Deep Space Gateway is expected to serve as a basis for the exploration of moon and a launching point for mission to Mars and further destinations.”

From: “European space officials outline desired contribution to Deep Space Gateway”
By Tereza Pultarova October 26, 2017

The “Deep Space Gateway” “launching point” for future missions to “Mars and further destinations” should include the missions of Space Force spacecraft with nuclear powered electric space propulsion systems that are headed out toward interstellar objects.

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