My goal here is NOT to explain the importance of these objects; there are plenty of places you can read about that. Instead, I'd like to focus on what we actually KNOW about the orbit. As usually happens for a newly discovered object, orbital parameters are being quoted as if they are known absolutely: closest distance to the sun, average distance, farthest distance from the sun, and orbital period. There are more orbital parameters than these, but they are mostly secondary to our understanding of the basic geometry of the orbit.
Our knowledge of an orbit is only as good as the observational data used to derive that orbit, and when the observations cover only a short period of time, the orbital uncertainties are high. Yet these uncertainties are usually glossed over when they are presented to the general public. This feeds into an impression already held by the general public that science can produce immediate results with almost magical precision. The CSI television series promote this view. It can also be seen in the movie Deep Impact, in which the young amateur astronomer takes a single observation of a comet to the learn'd astronomer on a mountaintop, who immediately realizes not only that the comet may hit the Earth, but also predicts the date, time, and location. I believe that all good citizens of the modern world should learn that all science involves uncertainty, and our job as scientists is to reduce those uncertainties with better processes and more data. In other words, science takes time to produce accurate results!
So, without further ado, here is my OrbitMaster visualization of approximately 1000 alternate possible orbits for 2012 VP113. Details about what this all means and why we care follow below...
So, how do we know the path that an asteroid takes through Solar System? We observe its position in the sky as viewed from the Earth over some period of time, and then we use computer programs to fit orbits (which obey Kepler's laws ) to these observations. And while there IS a single "best" orbit that fits the data, that's not really the whole story. The real test of how well we know the orbit is to try many different orbital parameters and see how well they fit the data.
To do this, I use a program called Find_Orb. The process is called Monte Carlo, and it works by adding small random errors to the observational data, and then producing new best-fit orbits. This works because the data themselves are not absolutely accurate. Each time we see the asteroid, its light is smeared out by the atmosphere, the telescope, etc. I ask Find_Orb to add random positional errors to each observation, and then I collect hundreds or thousands of results as alternate possible orbits. Collectively, they map out the uncertainty of our knowledge of the orbit. I am by no means the only person calculating uncertainties for asteroid orbits! But I may be one of the few who thinks it's important to discuss these uncertainties with undergraduate students and the general public.
To that end, I have spent the last few years building up online tools to help students visualize asteroid orbits and their uncertainties. In particular, I've spent quite some time hacking away at AstroArts' OrbitViewer Java applet to add new functionality. OrbitViewer has been made available for modification under the GNU General Public License and I intend to distribute the source code of my modifications under the same. The result is my OrbitMaster applet, which is available both at my CSU website and at my previous institution, where it lives as part of the Research-Based Science Education for Undergraduates curriculum. A few of the improvements over OrbitViewer are:
As you can see, the orbit is pretty well-constrained for the years 2012-2014 or so, but before and after those dates, the possible orbital paths start to diverge pretty wildly. Unfortunately, the OrbitMaster applet can only show undistorted orbits out to about 120 AU or so, based (I think?) on a limitation in the original OrbitViewer code. (If anyone knows how I might extend this out to 1000 AU or so, I would be most grateful!) But the dates are limited to the years 1600-2199 as well, so we weren't going to be able to see this guy make a full orbit around the Sun anyway. Fortunately, 2012 VP113 represents one of the most extreme cases that would butt up against this 120-AU limitation, and that's exactly why this object is so interesting! Other objects may reach greater distances from the Sun, but those objects start out closer to the Sun as well. Sedna and 2012 VP113 are remarkable because they are at their CLOSEST to the Sun when they are 75-80 AU out.
Simulation Curriculum's Starry Night software can also help us visualize the orbital uncertainties, which helps us see that we really don't know much about the long-term behavior of 2012 VP113 at all:
So that's the qualitative perspective We can get a more quantitative view by looking at summary statistics and histograms of the orbits, as shown in the spreadsheet screenshot below. I have cut off the perihelion/aphelion and semimajor axis graphs (min, max, and average distances from the Sun for each orbit) at 1000 AU, but as you can see in the green table, these 991 trial orbits have average solar distances up to almost 3900 AU, and max solar distances up to almost 7700 AU!
From these results, it would appear that the quoted perihelion distance for 2012 VP113 of 79.85 AU may vary by about +/- 3 AU. Fortunately, that still places this object in the Inner Oort Cloud, even if the perihelion were as low as my lowest value of 68.8 AU. It would not approach Neptune closely enough for that planet to have kicked it out into this orbit beyond the planetary region of our Solar System. The inclination of the orbit is pretty well constrained at 24.01 +/- 0.02 degrees, and such precision in inclination is pretty common in early orbital determinations. But we really don't know the orbital period better than to say that it's greater than about 3,600 years, and could reasonably be as much as twice that value. And as for the orientation of the orbit's semimajor axis line, we really don't know it any better than to within +/- 30 degrees.
I hope that in this blog post, I've provided some perspective on how LITTLE we know about the orbits of new discoveries in the Solar System. But as we watch this object move over time, Kepler's Laws will help us sort out the reasonable orbits from the unreasonable ones. And believe it or not, after just another year or two of observations, we'll have a pretty good idea of the behavior of 2013 VP113, even on the far side of its orbit.
To that end, I have spent the last few years building up online tools to help students visualize asteroid orbits and their uncertainties. In particular, I've spent quite some time hacking away at AstroArts' OrbitViewer Java applet to add new functionality. OrbitViewer has been made available for modification under the GNU General Public License and I intend to distribute the source code of my modifications under the same. The result is my OrbitMaster applet, which is available both at my CSU website and at my previous institution, where it lives as part of the Research-Based Science Education for Undergraduates curriculum. A few of the improvements over OrbitViewer are:
- Orbits can be altered to improve student understanding of the orbital parameters, or locked down to avoid changing a carefully-designed orbit during a lesson.
- The primary orbit can be "cloned" so that alternate possible orbits can be designed by hand and compared with one another.
- Hundreds or thousands of alternate "clone" orbits can be preloaded to visualize the uncertainty in our knowledge of the best-fit orbit.
- New speed and date calculations; detection of collisions of the best-fit orbit with the Earth; etc.
So again, here's that OrbitMaster visualization of approximately 1000 alternate possible orbits for 2012 VP113:
Simulation Curriculum's Starry Night software can also help us visualize the orbital uncertainties, which helps us see that we really don't know much about the long-term behavior of 2012 VP113 at all:
From these results, it would appear that the quoted perihelion distance for 2012 VP113 of 79.85 AU may vary by about +/- 3 AU. Fortunately, that still places this object in the Inner Oort Cloud, even if the perihelion were as low as my lowest value of 68.8 AU. It would not approach Neptune closely enough for that planet to have kicked it out into this orbit beyond the planetary region of our Solar System. The inclination of the orbit is pretty well constrained at 24.01 +/- 0.02 degrees, and such precision in inclination is pretty common in early orbital determinations. But we really don't know the orbital period better than to say that it's greater than about 3,600 years, and could reasonably be as much as twice that value. And as for the orientation of the orbit's semimajor axis line, we really don't know it any better than to within +/- 30 degrees.
I hope that in this blog post, I've provided some perspective on how LITTLE we know about the orbits of new discoveries in the Solar System. But as we watch this object move over time, Kepler's Laws will help us sort out the reasonable orbits from the unreasonable ones. And believe it or not, after just another year or two of observations, we'll have a pretty good idea of the behavior of 2013 VP113, even on the far side of its orbit.
