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