First Known Interstellar Object ‘Oumuamua Gets Unexpected Speed Boost

Interstellar Object Gets Unexpected Speed Boost

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. Credit: NASA/ESA/STScI

Using observations from NASA’s Hubble Space Telescope and ground-based observatories, an international team of scientists have confirmed ′Oumuamua (oh-MOO-ah-MOO-ah), the first known interstellar object to travel through our solar system, got an unexpected boost in speed and shift in trajectory as it passed through the inner solar system last year.

“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,” said Marco Micheli of ESA’s (European Space Agency) Space Situational Awareness Near-Earth Object Coordination Center in Frascati, Italy, and lead author of a paper describing the team’s findings.

This video explains how observatories, including NASA’s Hubble Space Telescope, found that ‘Oumuamua gained an extra boost of speed, likely from comet-like jets of gas. Credit: NASA

Analyzing the trajectory of the interstellar visitor, co-author Davide Farnocchia of the Center for Near Earth Object Studies (CNEOS) at NASA’s Jet Propulsion Laboratory (JPL) found that the speed boost was consistent with the behavior of a comet.

“This additional subtle force on ′Oumuamua likely is caused by jets of gaseous material expelled from its surface,” said Farnocchia. “This same kind of outgassing affects the motion of many comets in our solar system.”

This animation shows the path of `Oumuamua as it passed through the inner solar system, and its location on Jan. 2, 2018, when it was last observed by NASA’s Hubble Space Telescope. By then, ‘Oumuamua had been boosted by 25,000 miles (40,000 kilometers) compared to where it would have been if only gravitational forces were affecting its motion. Credit: NASA/JPL-Caltech

Comets normally eject large amounts of dust and gas when warmed by the Sun. But according to team scientist Olivier Hainaut of the European Southern Observatory, “there were no visible signs of outgassing from ′Oumuamua, so these forces were not expected.”

The team estimates that ′Oumuamua’s outgassing may have produced a very small amount of dust particles – enough to give the object a little kick in speed, but not enough to be detected.

Karen Meech, an astronomer at the University of Hawaii’s Institute of Astronomy and co-author of the study, speculated that small dust grains, present on the surface of most comets, eroded away during ′Oumuamua’s long journey through interstellar space.

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

This animation of `Oumuamua is one of many artist conceptions of what this object could look like. Credit: NASA/STScI

′Oumuamua, less than half a mile in length, now is farther away from our Sun than Jupiter and traveling away from the Sun at about 70,000 mph (113,000 kph) as it heads toward the outskirts of the solar system. In only another four years, it will pass Neptune’s orbit on its way back into interstellar space.

Because ′Oumuamua is the first interstellar object ever observed in our solar system, researchers caution that it’s difficult to draw general conclusions about this newly-discovered class of celestial bodies. However, observations point to the possibility that other star systems regularly eject small comet-like objects and there should be more of them drifting among the stars. Future ground- and space-based surveys could detect more of these interstellar vagabonds, providing a larger sample for scientists to analyze.


‘Oumuamua was too small to appear as anything more than a point of light, even in the largest telescopes. But we know that it must be a highly elongated object because it varied dramatically in brightness over every seven-to-eight-hour period. Credit: NASA/JPL-Caltech

The international team of astronomers used observations from Hubble, the Canada-France-Hawaii Telescope in Hawaii, the Gemini South Telescope, and European Southern Observatory’s Very Large Telescope in Chile.

The paper with the team’s findings will appear in the June 27 issue of the journal Nature.

Reference: “Non-gravitational acceleration in the trajectory of 1I/2017 U1 (‘Oumuamua)” by Marco Micheli, Davide Farnocchia, Karen J. Meech, Marc W. Buie, Olivier R. Hainaut, Dina Prialnik, Norbert Schörghofer, Harold A. Weaver, Paul W. Chodas, Jan T. Kleyna, Robert Weryk, Richard J. Wainscoat, Harald Ebeling, Jacqueline V. Keane, Kenneth C. Chambers, Detlef Koschny and Anastassios E. Petropoulos, 27 June 2018, Nature.
DOI: 10.1038/s41586-018-0254-4

JPL hosts CNEOS for the agency’s Near-Earth Object Observations Program, an element of the Planetary Defense Coordination Office within the agency’s Science Mission Directorate. Hubble is a project of international cooperation between NASA and ESA. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages Hubble. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations.

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