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Our Solar System’s First Known 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.

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.

Observatories including NASA’s Hubble Space Telescope found that the interstellar object named ‘Oumuamua gained an extra boost of speed, which likely comes from comet-like jets of gas. Hubble found that ‘Oumuamua gained a speed boost when passing through the inner solar system. Credit: NASA Goddard Space Flight Center

“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 Centre in Frascati, Italy, and lead author of a paper describing the team's findings.

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.

animation of oumuamua and solar system orbits

An animation of 'Oumuamua as it passed through our solar system.

NASA

“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.”

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!"

Artist impression of the interstellar object ‘Oumuamua.

ESA/Hubble, NASA, ESO, M. Kornmesser

′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 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.

NASA/JPL-Caltech

NASA will host a Reddit Ask Me Anything (AMA) about the ′Oumuamua observations from 4 to 6 p.m. EDT Thursday, June 28. To participate, go to:

https://reddit.com/r/IAMA

The international team of astronomers used observations from Hubble, the Canada-France-Hawaii Telescope in Hawaii, and 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.

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.

Learn more about asteroids and near-Earth objects at: https://www.jpl.nasa.gov/asteroidwatch

For asteroid and comet news and updates, follow AsteroidWatch on Twitter at: https://twitter.com/AsteroidWatch

For more information from Hubble, go to: https://www.nasa.gov/hubble

Contacts:

Claire Andreoli
NASA's Goddard Space Flight Center, Greenbelt, Maryland
301-286-1940
claire.andreoli@nasa.gov

Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-1821
calla.e.cofield@jpl.nasa.gov

Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu