‘Oumuamua’ — 1st interstellar asteroid observed from Earth

This past month, a ghostly visitor passed through the solar system, and astronomers still are observing it fade away into the night, hoping to gather more information as it leaves our system. It was a cosmic first — the first observed interstellar asteroid.

We know that in our own solar system, leftover pieces of the early materials that formed the planets remain.

Close to the sun, where it is too warm for ices to freeze solid, these leftovers are called asteroids. Farther out, where ices remain solid, these bodies become the cores of possible comets.

We also know that, on occasion, gravitational interaction between these objects and the larger planets of our solar system can hurl them into interstellar space fast enough to escape the gravity of our sun. When this happens, they become interstellar wanderers, lost in the emptiness of the galaxy.

This month, astronomers are studying the first of these wanderers from another planetary system discovered passing through our own.

When the object initially was detected by the Pan-STARRS telescope in Hawaii on Oct. 19, observers first believed it to be a comet, one of many that fall in from the outer reaches of our own solar system to be discovered each year as they approach the sun.

The newly-detected object, however, already had swung around close to the sun. When observations showed none of the fuzziness normally associated with a thawing comet, it was re-classified as an asteroid.

But further examination of its orbit showed that this object was not gravitationally bound to the sun at all. It simply was passing through — the first observed asteroid from another planetary system.

It was given the name Oumuamua, which in Hawaiian means something similar to “first messenger from afar.”

Oumuamua entered our solar system from the direction of the star Vega, though astronomers have not been able to trace its origin to any particular stellar system. After swinging around the sun, it now is on its way out of the solar system in the direction of the constellation Pegasus.

After its close encounter with the sun, Oumuamua is rocketing away at about 86,000 mph, and astronomers are scrambling to get as many observations as possible and to learn more about what this interstellar voyager is like.

They have confirmed it is relatively small, only about a quarter of a mile long, and its coloring shows it to be dark reddish similar to certain asteroids in our own planetary system. The way its brightness varies indicates it is rotating and gives clues regarding its shape, which is very unusual — much more elongated than any asteroids that have been seen before, possibly as much as 10 times longer than it is wide.

Even though it’s on its way out, scientists hope to learn even more as they attempt to image Oumuamua with the Hubble and Spitzer Space telescopes before it is too far away to observe.

This passers-by obviously has been traveling for quite a long while to reach us, and anything we can learn from it might give us glimpses as to the conditions of planetary systems around other stars.

Before any readers jump to conclusions about possible interstellar alien spaceships, let me say again that the object is moving exactly like an inert rock under the influence of gravity, is not sending out any signals and, by all indications, is indeed a rock —- though a very interesting one.

Even if it was a probe from an alien civilization sent to spy out our planetary system, it already has passed us by and is on its way out, having made its closest approach to the sun on Sept. 9, before it was even noticed by us here on Earth.

New Christmas show

Oumuamua only is one ghostly messenger in our Christmas skies though, and we’ll be talking more about this wanderer, as well as other visitors this month at Strickler Planetarium as we premier a new version of our classic Christmas show, “The Stars of Christmas.”

The show will be presented on Saturdays, Dec. 9 and Dec. 16, at 6 and 7:30 p.m. and also will include a showing of “Let it Snow,” a Christmas musical extravagance on the dome.

Tickets for this combo show are $3 per person and available at the door. Visit our website at strickler.olivet.edu for more information.

December highlights

Wednesday, Dec. 13: Moon passes Mars in predawn sky.

Thursday, Dec. 14: Moon passes Jupiter in predawn sky.

Geminid meteor shower peaks evening of 13th and morning of 14th.

Thursday, Dec. 21: Winter solstice.

Friday, Dec. 22 and Saturday, Dec. 23: Ursid meteor shower peaks.