December 12, 2017

Astro-Event: Will Comet McNaught Perform?

During the month of June, keep your eye out for a pre-dawn visitor that may be the naked eye comet of the year. Comet McNaught C/2009 R1 starts the month out June 1st at about +8 magnitude near the star Beta Andromedae, and through the course of the month, skirts the constellations of Andromeda, Perseus, and Auriga. Views will get better starting June 4th, as the Moon passes Last Quarter on its way to New June 12th. The daily apparent motion of the comet will cause it to move semi-parallel to the horizon, never straying above 20° degrees elevation for mid-northern latitude observers about an hour before sunrise.

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16.05.10- Gliese 710: A Future Stellar Threat?

Our quiet corner of the local galaxy may be in for a future interloper. A possible solar system side-swipe comes in the form of Gliese 710, an unassuming +10 magnitude orange dwarf star currently 63 light years distant in the constellation Serpens. As we swirl around the center of our galaxy, stellar neighbors come and go like in-laws during your favorite respective obligatory familial holiday season. The low proper motion of this star hid its true nature until about a decade ago; generally, the lower the apparent motion, the more distant the star. Gliese 710, however, fits into a different class; a star that shows a low apparent motion because it’s moving towards us. Closest approach has been calculated by astronomer Joan Garcia-Sanchez of JPL as about 1.3 light years in 1.5 million years time. Doesn’t sound like much? Well, this skirts the edge of our Oort Cloud, that vast reservoir of comets that extends out to about 1.6 light years distant…Gliese 710 stands an 86% chance of breaking this threshold. In addition, a 2007 review of Hipparcos data by Vadim V. Bobylev shows that this star may pass as close as 0.02 of a light year, about 50 times farther than the (sometimes) planet Pluto. This could make things really interesting, as Gliese 710 could really stir things up in our Oort cloud. And of course, there is the question of whether or not Gliese 710 has an Oort Cloud of its own. More than likely, this pulse of comets will last for about a several million year span of time. Could our inner solar system have sustained such shocks before? One only has to look at the crater-scarred surface of our Moon to realize the inner solar system has served as a shooting gallery over the eons. The statistical probability of a really (i.e. 1,000 AU) approach is about 1 in 10,000, so don’t max out those credit cards just yet… this uncertainly stems from incomplete knowledge of all the gravitational factors at work. As more sensitive astrometrical platforms, such as ESA’s Gaia spacecraft come online, the nature of the threat from Gliese 710 will be more precisely known. At its closest approach, this inbound star will be about as bright as the red giant star Antares… here’s to the neighbors!

08.11.09:Does Cometary Mass Extinction Need to be Rewritten?

Comets are cause all mass extinctions in Earth’s history, right? Maybe not, if new research is correct. Simulations run by the scientists at the University of Washington now suggest that the giant planets of Jupiter and Saturn may do a much more through job of cleaning up incoming debris than is generally realized. Short period comets such as Halley’s are generally accepted to be denizens of the Kuiper belt, which extends out to 100 Astronomical Units (A.U.s), while much more numerous populations of long period comets are theorized to come from the Oort cloud, a massive solar system-engulfing sphere at a distance of 1,000 A.U. to up to 3 light years distant. Traditional cometary mass extinction theory states that when a star passes close enough to the shell of the Oort cloud, a rain of comets are pried free and the inner solar system becomes a celestial shooting gallery for a million years or so. Simulations, however, suggest no more than three impacts could have occurred over the last 500 million years or so, fuel for at best maybe a minor extinction event or two. Then there’s the pesky affair of some extinct species shown to exist above the K-T iridium layer… doubtless, the case of mass extinction is a thoroughly messy business. As reported earlier last month in this space, more than one impactor is suspected in the extinction of the dinosaurs. Examination of other inner solar system bodies should pin down the frequency, duration, and average number of killer comets, as the Moon, Mars and even Mercury have relatively little erosion and would be potential targets as well. Any incoming comet stands a 40% chance of having its orbit altered by Jupiter, as happened to Hale-Bopp in the late 90′s. Thanks, Jove!