2016 BC14 and Jupiter’s Influence

After learning about and publishing a few observations of Near Earth Objects (NEOs), I came across cool website titled Earth’s Busy Neighborhood. My day job is a scientific software engineer and I really admire this stunning example of a data aggregation web site. The main page shows an HTML5 animation of all of the NEO’s currently passing close to the Earth and also lists details on each one, gathered from the MPC observation database, JPL orbits, links to articles and other sites and all sorts of detail. Also, summaries of confirmation candidates, Minor Planet Circulars and risk updates are gathered and published in The Tracking News section each day. Apparently the authors gather data from various sources using Python scripts to generate the HTML pages. Great stuff!

Many of the objects on the tracker are relatively small, 5-10 meters, and pose little risk of global destruction. Unless they are close by, these smaller bodies are generally very faint and are only accessible to 1 meter class telescopes.

But looking through the list a few weeks ago, I noticed an object 2016 BC14 classified as “Approaching” with an estimated size over 200 meters. So I figured this would be a good one to try to catch. The MPC Ephemeris service showed it to be readily accessible from the Slooh Canary Island Observatory on Mt Teide so I scheduled a set of “missions” on 7 March to try to spot it.

I have a couple of telescopes at home I like to take out from time to time. But conditions are often unfavorable living near the shore in Southern New England. It can be nice and clear out during the day only to cloud up and dew up after sunset. And I’m not as included to handle cold metal when it’s 20 degrees F outside! Having access to remote telescopes helps greatly, but even those are subject to clouds, snow and ice and even strong winds and there was a spell of all that at the Mt Teide site earlier this month. It took over a week of trying to get a couple of nights of pictures of BC14 but I did get there in time.

At that point, the object had brightened to around mag 17 and was clearly seen in each individual image. After selecting images from each timepoint on the 2 nights, I had a set of observations for a potential submission. Even after a week of trying, the object was listed as “Useful for orbit improvement” by the MPC, probably because of it’s status as a Potentially Hazardous Asteroid or PHA.

Before submitting the observations, I ran them through the find_orb Orbit Determination package from Project Pluto. One of the many things this software can do is to read in a series of observations of Solar Systems objects (of any kind) and determine potential orbit solutions. It will also report on orbit “residuals” which is the difference between the expected position (based on the orbit determined) and the measured position for a given observation. So to check my observations, I can download the current set of published observations on the object and add in my values in order to check for discrepancy with published results. If there are enough reliable observations, I can see if any of mine are out of whack due to some error – such as picking the wrong object on the screen when recording a measurement. Ideally, my values should be in line with the published values and have a reasonable small error – under 0.5 arc seconds or better. And for a newly or recently discovered object, adding “good” observations should improve the orbit fit and reduce the overall residuals in the combined set of published and new data points.

After running my observations through find_orb, the residual values in declination were quite good, but the RA delta was consistently over 0.5 arc minutes in all cases. This looked odd, so I went back and reviewed the workup in Astrometrica to see if anything was off there. I find that Astrometrica is rather robust and either returns a very good image solution, or no results at all. (And if no fit is obtained it usually means that I selected the wrong configuration file so the scale is way off!) Occasionally I find I need to tweak the magnitude setting used to select reference stars if the field is unusually sparse or crowded but that’s about it.

Since the workup looked OK so I loaded the observations again in find_orb. The program determines the orbit of minor planets around the Sun (or other bodies) and will also calculate perturbations caused by other objects such as the planets. By default, it will determine which bodies perturbing to use automatically. The fit of 2016 BC14 gave an orbit ranging from just over 1.0 AU to 0.7, so this is an Aten class asteroid staying rather close to Earth. The package determined that mainly Earth and Luna could be perturbing the object and selected those for the fit.

But when I selected to include perturbations from all planets in the orbit, the residuals for my observations improved greatly and varied +/- 0.2 arc seconds or less for all values. By selecting and deselecting the various planets, it looked like Jupiter had a pretty strong effect on the values, and including it gave a much improved fit. So how can Jupiter have such an effect of the asteroid only goes out to 1.03 AU?

Jupiter is currently rising in the evening and is up high in the sky around midnight, so it is currently in opposition to Earth. (The exact opposition was on 8 March not too far off from the date of these observations). Jupiter is 5.4 AU from the Sun and currently about 4.5 AU from us. It’s mass is about 1 thousandth of the mass of the Sun and it is farther away from us than the Sun, so I would expect it’s gravitational pull to be over 20,000 times weaker on the body then the Sun. I’m not sure if that is enough to cause the difference in the position of the minor planet.

Of course, the position I’m seeing is relative to Earth’s place in the sky. So if Jupiter is having an effect on the Earth’s position as well that could increase the effect on the observed location perhaps. I’m not sure how to sort this out – maybe it’s a good question to ask folks on the Minor Planet Mailing List.

Anyhow, after confirming the observations I formatted the report and submitted it to the MPC – with some help again from my friends on the Slooh A-team. Since this was my first report from the Canary Island location (observatory code G40), I’ll need to have a program code assigned for that location as well. So I’ll wait and check from time to time for the observations to be published, and think about what to look for next when the moon starts waning again.

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