The Solar System Just Had an Interstellar Visitor. Now It’s Gone

Hello, goodbye interstellar comet. The hyperbolic orbit of Comet C/2017 C1 as plotted by JPL’s Small-Body Database Browser (NASA/JPL-Caltech)

Update: At original time of writing, C/2017 U1 was assumed to be a comet. But Followup observations by the Very Large Telescope in Chile on Oct. 25 found no trace of cometary activity. The object’s name has now been officially changed to A/2017 U1 as it is more likely an interstellar asteroid, not a comet.

Astronomers using the PanSTARRS 1 telescope in Maui may have discovered an alien comet.

Comets and asteroids usually originate from the outermost reaches of the solar system — they’re the ancient rocky, icy debris left over from the formation of the planets 4.6 billion years ago.

However, astronomers have long speculated that comets and asteroids originating from other stars might escape their stars, traverse interstellar distances and occasionally pay our solar system a visit. And looking at C/2017 U1’s extreme hyperbolic trajectory, it looks very likely it’s not from around these parts.

“If further observations confirm the unusual nature of this orbit this object may be the first clear case of an interstellar comet,” said Gareth Williams, associate director of the International Astronomical Union’s Minor Planet Center (MPC). A preliminary study of C/2017 U1 was published earlier today. (Since this statement, followup observations have indicated that the object might be an asteroid and not a comet.)

According to Sky & Telescope, the object entered the solar system at the extreme speed of 16 miles (26 kilometers) per second, meaning that it is capable of traveling a distance of 850 light-years over 10 million years, a comparatively short period in cosmic timescales.

Spotted on Oct. 18 as a very dim 20th magnitude object, astronomers calculated its trajectory and realized that it was departing the solar system after surviving a close encounter with the sun on Sept. 9, coming within 23.4 million miles (0.25 AU). Comets would vaporize at that distance from the sun, but as C/2017 U1’s speed is so extreme, it didn’t have time to heat up.

“It went past the sun really fast and may not have had time to heat up enough to break apart,” said dynamicist Bill Gray. Gray estimates that the comet is approximately 160 meters wide with a surface reflectivity of 10 percent.

But probably the coolest factor about this discovery is the possible origin of C/2017 U1. After calculating the direction at which the comet entered the solar system, it appears to have come from the constellation of Lyra and not so far from the star Vega. For science fiction fans this holds special meaning — that’s the star system where the SETI transmission originated in the Jodie Foster movie Contact.

For more on this neat discovery, check out the Sky & Telescope article.

2 thoughts on “The Solar System Just Had an Interstellar Visitor. Now It’s Gone”

  1. Greetings. Thanks for covering this. Many astronomy blogs did not. And that is amazing, because this “interstellar rock” is a big, big deal.

    First the “boring stuff”. Apparently there was some confusion about whether the visitor was truly interstellar. This boiled down to the calculations of the orbit – so-called “residuals” by afficianados of orbit mechanics. I hope that people have managed to firmly establish whether this object is interstellar. It would be nice to see a final official confirmation. But let’s assume that it did come from deep space.

    Then next is your own point. Was it a comet, an asteroid, or something else? Again, it would be nice to see any official commentary. I suspect that probably this object was an asteroid – but that is speculation on my part.

    This was TRULY a remarkable event. It offered the scientific community a chance to “see” a nitty-gritty piece of space debris from some other part of our Galaxy. That’s no small deal. Ironically – we were caught napping. It appears that no-one spotted the “visitor” before its point of closest approach to the Sun. So our investigations are limited to “watching it disappear into the rear vision mirror”. That’s humbling. We were really “not ready” for an event like this. I gave some quick thought to … could we intercept one of these passing interstellar rocks? The answer seems to be … no easily, maybe not at all. First, the warning times are far too short. And second the velocity and approach angles (out of the Ecliptic plane) are so extreme, we don’t have any rockets that could “go and take a look”. Again … that’s a truly humbling confession. There is a huge amount of information that could be obtained, if we could get a piece (a sample) of an interstellar object like this.

    So apparently we have to be content with … humble pie. And perhaps we can let our imaginations run wild. WHAT IF that object happened to contain evidence of ancient life from another star system? Wow – it’s stunning to think about.

    HOPEFULLY – we will be watching Vega and Lyra a little more closely. It is just possible, another one of these objects might come along soon. If there was some kind of debris field, there might be more of these “visitors” in our future.

    Thanks for the coverage!

    (Dr.) Pete Pollock, California

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