169P/NEAT: A Comet or an Asteroid?

Two students from Our Lady and St. Patrick's College, Knock, and Bangor Grammar School in Northern Ireland worked with astronomers at the Armagh Observatory in January this year, observing comets and unusual asteroids. Read the report they wrote about their work here...

"The comet 169P was first observed by the Near-Earth Asteroid Tracking system. In order to observe this comet we had to figure out if it was possible to view it from Faulkes Telescope South, a 2m reflecting telescope which is used for research as well as for use by school students around the world over the internet. We found where this comet was predicted to be using the Minor Planet Center. Since 169P is such a bright object, we were able to use a red filter on some of our observations to provide a clearer image. We made five observations of the comet and could clearly see its orbital movement.

At 1400 hours on Monday 25th January we took control of the Faulkes Telescope South in Siding Spring, Australia. With the help of David and Tolis, we found that our exposure time should be at most 20 seconds, because the comet was moving quite fast. We decided 10 seconds exposure was long enough due to the comet's bright magnitude. We managed to take 5 photographs of the comet before moving on to a new observation. In order to distinguish between a star and our comet, we had to take more than one observation of the same position and then compare the images to see if any of the supposed stars moved. In our images it was very clear where 169P was as it moved a great deal.

An animation showing the movement of 169P. Images obtained using the Faulkes Telescope South, operated by Las Cumbres Observatory.

 169P was first thought to be an asteroid and was given the designation 2002EX12. After obtaining our images we made astrometric and photometric calculations and realised why this had happened. The easiest distinction to make between comets and asteroids is that asteroids are point source objects and comets are not. Most comets have comas, a visible, fuzzy atmosphere surrounding them. We compared the FWHM (Full Width Half Maximum) of our comet to the FWHM of the surrounding stars as we know that stars are point source objects. We found that our comet did have similar FWHM to the stars, showing no detectable coma and explaining why it was first classed as an asteroid.

 169P is the parent body to the alpha Capricornids meteor shower. The shower can be seen from July 15th to September 11th but is best observed at the beginning of August. The shower has the reputation of producing some of the brightest meteors of the major showers, with the average magnitude being estimated as about 2.2. There was confusion over the shower's parent body for over 50 years.

We had three more observing sessions booked for the week and hoped to make more observations of 169P/NEAT. Only two of these sessions were with Faulkes Telescope South and unfortunately both were cancelled due to bad weather. We did however get to observe five other asteroids using Faulkes Telescope North, including 21 Lutetia, an unusual main belt asteroid which will be the first M-Type asteroid passed by the European space probe Rosetta.

We had a wonderful time learning how to use the telescope and appreciate all the time that David, Tolis and everyone else at the Observatory spent helping us understand what we were doing."

Alison Hoy (Our Lady and St. Patrick's College, Knock, Belfast) and Ronan Smyth (Bangor Grammar School (Bangor)