Category Archives: comet

A Comet!

Coming Soon to a Sky Near You

Comet PANSTARRS (C/2011 L4), which has been dazzling southern hemisphere skygazers for a couple of weeks now, is making its way around the Sun. It will make its closest approach (perihelion) to the Sun on March 10th,  and a couple of days later it should be visible in the post-sunset skies for those of us in the northern hemisphere to enjoy.  Here’s a little gazing chart (courtesy of Astronomy Magazine and Gary A. Becker) to help you find it.  The view could be quite lovely on March 12th and 13th, when it will appear not too far from a crescent Moon low in the western sky. The comet should be visible through most of the month, although later on it will be competing with the Full Moon, which could wash out the sky a bit. It may likely have two tails — a whitish dust tail and a bluish plasma tail, so it’s worth making the effort to take a look at PANSTARRS.

Where Comet PANSTARRS will appear in the western sky for northern hemisphere observers starting around March 10th, 2013. Check it out!  Map courtesy Astronomy Magazine and Gary A. Becker.
Where Comet PANSTARRS will appear in the western sky for northern hemisphere observers starting around March 10th, 2013. Check it out! Map courtesy Astronomy Magazine and Gary A. Becker.

Astronomer Fred Espenak also has some extraordinarily gorgeous finder charts on his Website AstroPixels.com. Check ’em out! And, while you’re there, check out some of his other work, too.

Back in the day, when I was in graduate school, I spent a lot of time studying images of Comet Halley. We were interested in its plasma tail (also known as the ion tail).  This is a stream of gas molecules that form as the Sun heats the icy nucleus of the comet. The ices start to “sublimate” (similar to how dry ice “melts”) and creates a cloud of gas and dust.  The material flows off the comet, forming a dust tail and the plasma tail. The materials in the plasma tail interact with the solar wind, which causes the plasma tail to glow in a process called ionization. It also creates structures in the plasma tail, and in the right conditions, can cause what is called a “disconnection event”. This occurs when the existing plasma tail encounters changes in the solar wind that are different from the conditions in which it was originally formed. Think of it as forming in one electrical polarity and when it encounters a different polarity, it can’t exist anymore. So, the plasma tail breaks off and a new one forms. This happens over and over again as the comet rounds the Sun. We studied this occurring in Comet Halley as it passed through in 1985 and 1986, and that allowed our team to analyze conditions in the solar wind by looking at the tail, as well as letting us chart what was once thought of as a “pathological” condition in comets.  Turns out it happens to comets with active plasma tails during the inner parts of their orbits around the Sun.  Comet PANSTARRS was showing a pretty active plasma tail as it went to perihelion. I’ll be watching it later this week to see how it fared. So, if your skies are clear later this week and early next, step outside after sunset and check out the comet. It could be quite lovely!

 

 

 

 

Crystalline Entities Found in Distant Solar System

Herschel Discovers Cometary Crystals around Beta Pictoris

We all know about comets in our own solar system. They’re conglomerates of ices mixed with dust and rock. As they get close to the Sun their gases sublimate, the dust is freed and that action creates dust and plasma tails streaming out behind the comet.  Astronomers see comets as repositories of information (in the form of those ices and dust particles) about conditions in the early solar system, since those materials have survived until this time. In particular, comets often contain materials that formed close to the Sun in the early history of the solar system, but then were somehow transported out to colder regions where comets seem to thrive.

This infrared view of the Beta Pictoris solar system, was obtained by ESO’s 3.6-meter telescope and the NACO instrument on one of the 8.2-meter units of ESO’s Very Large Telescope (inner region), and then subtracting the overpowering glare of the central star. The image shows a planet orbiting at roughly the same distance from Beta Pictoris as Saturn is from our own Sun, and a prominent dust disc in the outer reaches of the system. Credits: ESO/A-M. Lagrange et al.

So, it’s rather cool that astronomers have now found cometary particles  in another solar system, the young star Beta Pictoris. The European Space Agency’s Herschel space telescope detected pristine materials in the dust disk surrounding this star. Those materials match the makeup of comets in our own solar system.

Beta Pictoris hosts a gas giant planet, in addition to a dusty debris disk that will likely spawn the formation of some icy bodies similar to the worldlets that astronomers are finding in our own Kuiper Belt.

So, what’s the material made of that Herschel found? First, the mineral olivine is present in the disk around Beta Pic.  Olivine forms in protoplanetary disk material close to newly formed stars.  In our solar system we find it in asteroids and comets, and of course it’s found on Earth, too.

The data collected by the Herschel telescope allowed astronomers to calculate that the olivine crystals in the Beta Pic disk make up about 4% of the total mass of the dust found in a region that lies between 15 to 45 astronomical units from the star.  In our solar system, that extends from well beyond the orbit of Saturn out beyond the inner limit of the Kuiper Belt. The 4% number is quite similar to such solar system comets as 17P/Holmes and 73P Schwassmann-Wachmann 3.

Astronomers concluded that the olivine was originally bound up inside comets and released into space by collisions between the icy objects.  And, since since olivine can only crystallize  at a distance of not more than 10 astronomical units of the central star, finding it in a cold debris disc means that it must have been transported from the inner region of the system out to colder areas. A process called “radial mixing” could help push materials out away from the central star, and that could explain how the olivine crystals made it to the deep freeze of the Beta Pic system.  Want to read more about this find? Check out ESA’s Herschel Web page for the full story.

  Get Your Stargazing On for October!

This month’s edition of “Our Night Sky”, the star gazing video I produce for AstroCast.tv is now up for your viewing pleasure!  Check it out!