object that passed through our inner solar system late last

year? It was the first object we've confirmed to have come

from outside our solar system, and was given the name

'Oumuamua, Hawaiian for “scout or messenger from our distant

past.” Now, scientists have analyzed data from many

observatories, including NASA's Hubble Space Telescope, and

found that this interstellar object has gained an unexpected

boost of speed. After 'Oumuamua was discovered with Hawaii's

Pan-STARRS 1 telescope as it surveyed the skies for

near-Earth asteroids in October 2017, observatories all around

and above the world focused on the approximately half-mile long

object to learn as much as possible about this cosmic

visitor before it flew too far away to see. The Hubble Space

Telescope was used to collect observations to determine the

object's trajectory over two months in late 2017 and early

2018. The observations were combined with data from multiple

ground-based observatories, which showed 'Oumuamua to have a

small, continuous non-gravitational

“acceleration.” Something besides just the gravity from

the Sun and planets was affecting the trajectory of

'Oumuamua. A probable source of this acceleration is jets of gas

coming off the object. This behavior is similar to objects

we have already identified as comets – when they get close to

the Sun, ices in the comet sublimate into gas, and

streamers of gas can push the object along. Usually when

comets do this the outgassing can be seen because it ejects

large amounts of dust, which form a cloud around the object,

called a coma, and a tail. But with 'Oumuamua, no type of coma

or tail was seen. Maybe 'Oumuamua doesn't have much dust

left after its interstellar journey – an amount no more than

a couple coffee cans of material, making the dust too

sparse for us to see. Or, maybe the dust was much larger than

normal, making it hard for us to detect. I know that sounds

counterintuitive, but it's easiest to detect dust when the

particles are similar in size to the wavelength of light we're

using. Observatories were looking at 'Oumuamua in visible

light, where we have the most sensitive detectors, but larger

particles of dust would be easier to detect with microwave

or radio wavelengths. This is definitely an unusual object,

and unfortunately no more new observations of 'Oumuamua are

possible because it's already too dim and far away for even

Hubble to see. But when there's one weird object there are

probably more. Sky survey programs will keep an eye out

for other interstellar visitors, and the Hubble Space Telescope

will be ready to contribute observations to better

understand any more orphaned vagabonds traveling between the

the stars.

www.nasa.gov/hubble @NASAHubble