As readers might have guessed, I love the idea of humans crossing the interstellar void, even if it takes ten thousand years to get anywhere. My fan poster of the Interstellar movie is here:
http://disaster-wise.blogspot.com/2014/10/interstellar-ice-fan-poster.html
And I love books like Alfred Bester's The Stars My Destination (the audio version of which came out last month on Audible!).
So I was excited to read about the object that passed through our solar system, first reported on October 19. The IAU had to invent a scheme to indicate interstellar origin: designated 1I/2017 U1, now it's known as 'Oumuamua, a Hawaiian word meaning scout from a distant land. Although no telescope captured its portrait, the blue circle marks what astronomers saw (image combined from ESO's Very Large Telescope, and the Gemini South instrument):
Here's a Nature article with the science.
curve range is very unusual.
Authors in a conservative journal like Nature or Science don't label something as "very unusual" very often, but that label fits 'Oumuamua. Here's my take from journal articles to date, in FAQ format.
Q. Was it verified as interstellar?
A. Yes. That's based on its speed and the "hyperbolic" path, a hyperbolic path being one that doesn't close up into an ellipse. And it came in at too high a speed to be bound to our solar system. While it seems to have come from the star Vega, that belief doesn't account for how stars move through the galaxy over time, relative to the sun. Given the asteroid's (relatively) low speed, Vega wouldn't have been in that spot at the time when 'Oumuamua was in the area. We'd need a lot more information to figure out where it originated. Here's the trajectory, from SciAm.
Q. Have astronomers seen any other interstellar objects passing through?
A. This is the first one confirmed. The problem is that interstellar visitors come in very fast. That makes them hard to spot, particularly the low-reflecting asteroids. And even interstellar chunks of ice would be hard to see unless they approach the sun. It's a tribute to modern science that 'Oumuamua was detected at all.
Q. Is it likely we'll see more interstellar objects?
A. Thanks to the rise of vastly greater computing power and new telescopes, yes. It's a sure thing that lots have already passed through our solar system over the eons, because interstellar space must have lots of loose rocks. The reason is that stars regularly pass near enough to other solar systems -- even through them -- to toss out planets and asteroids. That must have happened many times around the Milky Way galaxy, given the passage of billions of years.
Q. Did observations show any sign of alien works?
A. It was scanned by radio telescope for artificial emissions, but nothing turned up. That doesn't prove a great deal since we had so little time even to look at it, and when we did have the chance, it was already so far away we couldn't resolve details. Other than the trajectory, the information we have is from the color of the light reflected and the timing of how that light dimmed over time, cycling about every seven hours.
Q. Why did its light change over time?
A. Most likely because it was rotating.
Q. Is there anything really unique about it, other than its origin?
A. The inferred shape of 'Oumuamua is by far the most unique feature. A year ago, experts would have guessed that the first observed interstellar object should be a garden-variety hunk very much like the thousands we see in our neighborhood. 'Oumuamua didn't fit that expectation in at least one respect, its shape. Though we couldn't resolve details, evidence from the way its brightness changed with rotation points to it having the proportions of a cigar: about 110 yards in diameter, and two-thirds of a mile long. While we know of some narrow asteroids in our solar system, none has a ratio that extreme. That means 'Oumuamua is unlike any of the 20,000 solar-system asteroids about which we've gathered info on shape. Since we don't know how it was oriented compared to Earth, it's possible that the ratio is even more extreme than 10:1. So 'Oumuamua is a strange beast in that respect.
Q. How about its surface?
A. Its color (apparently a dull red) is nothing special compared to local asteroids. The color points to it being an asteroid of rock or metal, but the surface could be a mineral crust over ice. The insulating properties of such a crust would explain why, even if the object contains lots of ice, the ice didn't off-gas like a comet would. Many astronomers would have dearly loved to get a close-up look at the surface.
Q. Is there any chance of taking a closer look?
A. Not 'Oumuamua. It came and went, and won't be back. Its speed and distance mean that none of today's chemical-fueled rockets could catching up. But with more advanced technology, such as nuclear propulsion, we might be able to get a close look at future drop-ins. That's the plot of Arthur C. Clarke's Rendezvous with Rama, a novel about a spaceship that goes to explore a vast, dormant alien craft that's passing through the solar system. In a striking coincidence, Rama is also cylinder shape.
