Interstellar Asteroid, a Cosmic Mystery

--by Robert Arvay

Something very strange has been seen in our neighborhood.  It came from very far away, and then departed at very high speed.  What is it?

On October 20th, 2017, the Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) detected an object in space, within our solar system, that, after further analysis, has been deemed to be an unusual asteroid, or “space rock.”  Its shape is elongated like a cigar, and its size is estimated to be in the range of 1300 feet long.  That is about a quarter mile, longer than any US Navy aircraft carrier, and almost as long as the largest oil tankers.

https://www.space.com/38838-interstellar-asteroid-oumuamua-space-cigar.html

What makes this observation very unusual is that the object’s speed and direction of travel indicate that in all likelihood, it could not have originated from within our solar system.  It probably entered our solar system from interstellar space, that is, from somewhere between the stars, far away in our galaxy.  Its trajectory was influenced by the sun’s gravity, causing its path to curve sharply, before it exited our planetary system at very high speed, so fast that it escaped the sun’s gravity, and then zoomed back into the galaxy, where it may wander for billions more years.

There are many levels to this mystery.  No such event has ever before been detected, and this one was almost missed.  Which brings up the question, how many more of these galactic interlopers have there been, without anyone noticing them?  How common are they?  How many more will possibly arrive?  Do they pose any danger?

The answer to the final question is probably, no.  The volume of space within our galaxy, even within our solar system, is vast beyond our ability to imagine.  If stars were the size of baseballs, for comparison, then the nearest star to our sun would be ten miles away.  It takes light more than four years to reach us from there, traveling at 186,000 miles per second. 

We are far more likely to be hit by a large space rock coming from inside our own solar system, and that has not happened on a planet-changing scale since 65 million years ago.  Of course, smaller “space rocks” are more common—the Tunguska event in 1908 destroyed a remote forest in Siberia the size of a major world city.  More recently, spectacular displays of meteor incursions have occurred without much more damage than sonic booms breaking windows—but even these are potential rocks of mass destruction, depending on the angle at which they strike..

Finally, astronomers are carefully tracking NEOs (near earth objects) such as asteroids that come close enough to earth to merit some degree of alarm.  While there may not be much we could do at present to stop them from striking the earth, they pose not only a direct, but also an indirect danger. 

For example, during the Gulf War, a large meteor exploded over the Pacific Ocean with enough power to mimic a small nuclear bomb.  Had that explosion occurred over the US or the Middle East, it could easily have been mistaken for a nuclear attack.  Had it been thought that we were under nuclear attack, a swift, defensive nuclear response might have been ordered.  Matters might have easily escalated from there, resulting in a global catastrophe.

Even without this scenario, the mystery of the galactic asteroid stands on its own.  It brings attention to the fact that astronomers know far less about the galaxy then we give them credit for—and they do know a lot.

Outer space, the voids between the stars, may be far more crowded than we (and astronomers) imagine.  Let’s consider rogue planets.  These are planets that do not revolve around any star, but instead, wander aimlessly (so to speak) through interstellar space.  It has been suggested that rogue planets may outnumber revolving planets, even by an order of magnitude.  How could that happen?

One theory is that rogue planets formed around stars.  As a star forms, it is surrounded by matter, which then condenses just as the star condenses.  This matter is already revolving around the star, so it can be expected that the revolving matter will form into revolving planets.  Because the planets exert gravitational influence on each other, some of them will be ejected outward, away from the star, to wander through space.

While this is possible, it seems unlikely, because most ejected planets would not completely escape their star.   Most would be dispersed into vast, elliptical orbits, returning back into the solar system every dozens of million years or so.

It also does not seem likely that most planets need to form in the proximity of a star.  They may form just as stars do—from matter that is dispersed in space.  This would result in the formation of a wide variety of bodies, from giant stars, to smaller stars, to gas giant planets, and downward in size to very small bodies, including rogue planets.

If there is a sufficient density of rogue planets in the galaxy, then we might expect some of them to have come close enough to the sun to have been captured, that is, made to orbit our sun.  If so, we might expect them to have elongated, elliptical orbits.  We might also expect that their orbits would be tilted, that is, not in the same plane (or “dish”) as the planets that formed around our sun.

In fact, two small planets (called dwarf planets) have been discovered that fit those descriptions.  One has been named Sedna, the other, Eris.  Also, many others have been detected, all of them smaller than the dwarf planet, Pluto.

It is speculated that numerous, and very large, planets may be orbiting the sun, too far distant to be detected, at least by present methods. 

It has also been speculated that a small star, or perhaps a super massive planet, one which does not emit light, is orbiting the sun at a distance of billions of miles.  Its orbit might bring it close enough to send very distant space rocks plummeting among the known planets, and in sufficient numbers to cause collisions that account for several mass extinctions in the earth’s history.

In other words, there is not only a lot that we do not know, but also, we don’t know how much we don’t know.

UPDATE
https://blogs.scientificamerican.com/observations/fly-by-of-interstellar-asteroid-portends-quadrillion-trillion-more-in-galaxy/?utm_source=newsletter&utm_medium=email&utm_campaign=space&utm_content=link&utm_term=2017-11-23_featured-this-week
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