2016 EL56 – a newly discovered PHA

After having my first NEO observations accepted and published, I’ve been looking to observe some other interesting objects and thought I would try some brighter entries on the MPC NEO Confirmation Page. This page lists newly discovered minor planets or comets thought to be in or potentially reaching our neighborhood in the Solar System. Most of these are very faint bodies picked up by large telescopes used in the various sky surveys and are typically confirmed by high powered professional or amateur observatories dedicated to follow up confirmation and recovery work.

Still, a few brighter objects can be found on the list, and it looks like these are a little more common in the Southern hemisphere. So I thought it would be worth trying some of these from the Slooh observatory in Chile.

The first one I tried was a NEO candidate designated M50sG6S on the list on March 8th. It had an estimated magnitude of 18.2 and a projected declination of 35S so it looked like it should be detectable from Chile. I scheduled missions from W88 that night but did not see any moving object in the images obtained. No confirmations were made for this object over the coming week so it was removed from the list and not confirmed.

The next day, I saw an entry A100jOx in the southern sky with an estimated brightness of 18.9 at declination 25S. This magnitude is a bit of a stretch but it looked to be fairly high up in the sky on a moonless night so I gave it a go. Image files came in the next day, and I also noticed that the object had already been confirmed and given the designation 2016 EL56 by checking on the previous designation page. So other observatories had already confirmed the object!

The images looked quite good, so I took a look in Astrometrica to see if I could pick up the new object. First, I updated the MPC orbit database since the object was just designated and should now have an orbit available. A faint moving object was seen in most of the images, near but not at the exact location predicted by Astrometrica. Since this was a newly discovered object with 2 days of observations, the orbit would have a significant degree of uncertainly and this discrepancy was to be expected.

Since the object was faint, I tried the “Stack and Track” feature in Astrometrica. Using the Slooh protocol “Faint Mono” normally produces 4 monochromatic or luminence files, though sometimes these are not all produced. I had 4 images from the first timepoint and 3 from the second, so I made 2 stacks from each set.

“Track and Stack” will read in a series of images and shift them according to the expected motion of the desired target. The motion can be entered, but if the object is known it can be looked up from the orbit database. So I selected the newly minted designation 2016 EL56 and the program shifted and stacked the images from the estimated motion rate and position angle or direction. Here is one of the stacked and shifted images:


In the picture above, the images are shifted so the stars in the picture show up as a series of dots or a solid line. An object moving at the expected rate and direction will fall around the same position and show up as a single spot. So the weaker peaks in the individual images can add up to give a stronger signal over the background. The position will be a little less uncertain but the curve fit will work better so it can enhance the measurement overall. I’ve noticed that noise on a single image will also show up as a single spot so it’s important to look over the individual frames!

Running the observations in find_orb showed consistency with the other observations made to date and a positive influence on the overall fit. So I prepared a report and submitted it to the Minor Planet Center that day. Since I had a program code already assigned, this time the observations were published the very next day in the Daily Orbit Update MPEC 2016-E112 and later in the Minor Planet Supplement MPS 690473.

Minor planet 2016 EL56 is a Potentially Hazardous Asteroid (PHA) with an estimated size of 150 meters. The ESA site classifies it as an Apollo class asteroid ranging from around 4 AU down to about 0.3, with the next expected close approach in 2045 at 0.15 AU from Earth. It looks like the object was picked up after it passed by us in February, so it is now heading away and fading in brightness. It is not expected to have in impact in the future but any observations made while it is still accessible will help greatly in predicting it’s position and recovery when it returns!


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