163693 Atira

As mentioned in a recent post on observing Atira-class minor planets, I had tried to observe Atira herself last fall but was not able to pick it up. So I was interested to spot it on the MPC Bright Recovery List a few weeks ago, where it looked like it would be observable from the Slooh Canary Island Observatory.

I scheduled a couple of sessions before dawn on the night of 7 Feb and was glad to see nice images come back. But they were quite crowded with stars! Turns out the object was near the edge of the Milky Way between Cygnus and Lyra. Still, the object was clearly visible and did not overlap any stars in a few of the images, so I was able to measure and submit a few observations from that session. I was successful again a couple of nights later, so there are visible observations on Atira from a couple of nights this year. The previous reports are from May 2015.

2017-02-17-01-atira

Atira is numbered and has an uncertainty factor of 2, so the orbit was not updated by the MPC. Still, it’s probably useful to confirm she is on track!

A few days later, I happened across the Arecibo Planetary Radar Science page and saw that they had observed Atira by radar a couple of weeks earlier on 20 Jan. At the time, she was passing 0.20 AU from Earth and reaching zenith around 1 PM, so I’m guessing they acquired the radar data during the day.

In the radar return image, a small satellite to Atira can be seen nearby, so the group discovered that 163693 is a binary system. From a Twitter posting on the finding:

It looks like Atira is continuing to move away from the Sun and should be well situated to try again on or after the next New Moon, so I’ll try to follow up.

I’ve made observations of a few other close approachers in 2017. In January I tried to pickup the NEO Confirmation object LM06iuE and was able to find it. I submitted the observations the following morning and just made the discovery publication for 2017 BQ6. The new Apollo-class PHA was first observed by the Space Surveillance Telescope, Atom Site on 2017-01-26. The NEO is estimated to be around 180m in size and passed by Earth at around 6 LD (Lunar Distances) on 7 Feb.

2017 BQ6 was imaged by the Goldstone radar site at that approach, showing a rough, jagged body compared to Dungeon and Dragon dice! It’s been a few years, but I seem to recall the game having a number of different kinds of dice. I suppose they meant the 20-sided die, but they did not mentioned whether or not we’d get a save through if 2017 BQ6 is ever on a collision course, as they measured it to be around 200m across.

More recently, I reported observations on 2017 BW which was pinged by Arecibo on 14 Feb. It was also imaged at Goldstone over several days and estimated to be around 40 m across on it’s longest axis. I also happened to catch 2015 BN509 which was imaged from Arecibo as well.

Though it was pure coincidence, it’s nice to see that a few of my recent observations may have contributed to refining the orbits of these radar candidates. Will have to keep an eye out on the radar groups’ sites to check for more!

 

 

 

Atiras

In my last post, I described a utility called OrbBroswer I’ve developed to help identify minor planets that might be useful or interesting to observe. From time to time, I download the Near Earth Asteroid orbit elements file (NEA.dat) from the Minor Planet Center data page and run it through the utility to look for objects that may be in need of follow up observations.

One approach I’ve tried is to select from all NEAs those having an Uncertainty value of 2 through 5. This helps find NEOs that may need additional observations to improve their orbit, while being good enough not to require an extensive search. This filter brings the number of candidates from around 15,000 to 5,000. Next these are loaded into the planetarium program C2A and filtered to identify observable objects at an apparent magnitude of 20, reducing the count further down to about 150.

These can be viewed in C2A at their estimated positions from a given observing location and time. Checking the sky at the onset of (full) darkness and again before the sky starts to lighten should show all objects that will be observable during the night. Leaving out objects right on the horizon or in the Milky Way, and having a sufficient magnitude to detect, should indicate all of the reachable targets from this set.

Since I only have the name of the objects displayed, I then look up each one in the MPC Observation Database to see the type of object, it’s uncertainty value and the time of last orbit update and observation. Then I can select minor planets that might be useful to observe that have not been seen for a while or have a small number of recent observations.

When I tried this a while back in September, I noticed a numbered minor planet, 418265, belonging to the Atira or Inner Earth Object (IEO) class of minor planet.  It had an uncertainty value of 4 and was last observed on 10 December, 2014.

The Atira-class family of minor planets has their orbits entirely within that of Earth’s and is relatively recently known. The first known object in this class, 163693 Atira, was discovered in 2003 at the Lincoln Laboratory Experimental Test Site observatory in New Mexico. As of today, there are only 26 of these known out of nearly half a million asteroids. Six of these have been observed enough to receive a number designation, but at least two have sparse observations and are effectively lost. So these are pretty rare!

Most of the planets and minor planets have orbits outside of the earth’s, in the “Outer” solar system. When these are on the same side of the sun as the Earth, they are visible in the night sky. And when they are located directly behind us (relative to the Sun), they will rise in the evening, transit around mid night and set at dawn – just like the Full Moon. In this orientation they are said to be in “opposition”. They are also nearly fully illuminated and at their brightest at this time.

In contrast, the inner planets are only observed around the time of sunset or dawn. Mercury is quite close and never gets too far from the Sun in the sky, so it stays quite close to the horizon. But since it is a good-sized planet, it is possible to see it before the sky is fully dark, especially with a pair of binoculars – provided the Sun is safely below the horizon of course! Venus is the Morning or Evening “Star” and can range fairly high in the sky because it is further away from the Sun and can get closer to us. Currently it is near its greatest elongation and is high and bright at around 30 degrees from the horizon in the evening sky.

Ephemerides of Atira-class 418265 indicated that it would be low in the sky at 10-20 degrees above the horizon before dawn from the Slooh observatories in the Canary Islands. I was able to get a time slot around dawn on one night and give it a try. A moving object was visible around the expected position of the IEO but it was quite faint. Checking the predicted position on future nights, it looked like it would be a bit higher up in the sky later in September, so I tried again. This time I was able to get good positions on two nights and submitted them to the Minor Planet Center.

The observations were accepted and published and these stand as the only positions on the body since 2014. The orbital uncertainly remains at 4, but the positions I obtained agreed very closely to the expected positions determined by the find_orb package, so 418265 was right where it was expected. And since it has an estimated size of 2200 meters across, that’s a good thing to know!

Atira-class 418265 has an orbit that ranges from 0.4 AU to 0.8 AU. Its closest approach to Earth is a very safe 0.18 AU. But since it is fairly far from the Sun and gets somewhat close to us, it will can range fairly high up in the sky when it is in our neighborhood. That and it’s large size make it fairly easy to catch when it is nearby. It will have a fairly close approach in 2026 but hopefully it will be visible before then for more orbit updates.

A little later in the Fall, I noticed that Atira itself might be observable from the Southern Hemisphere, so I tried it from the Slooh observatory in Chile. I was able to get images at around 30 minutes before the end of complete darkness but was not able to see any moving objects. The estimated magnitude was 17.5 but this was probably not bright enough to pick it up with this telescope so close to the horizon.  I also tried from the iTelescope observatory in Australia but Atira was below the horizon limits of the scope I used. So these can be hard to get!

Looking over candidates again in November, I noticed another Atira-class object, 2008 UL90, deep in the southern sky at a declination of -60 and moving further south. I was able to capture some images at the expected location and then realized the object was in the southern end of the Milky Way and was not discernible in images containing many hundreds of stars. The object continued to move south as it passed close to the Earth and then started to move back quickly north in December after it’s closest approach on the 12th. I was not able to get observations for a few nights but then was able to catch it on the nights of the 20th and 21st from the iTelescope.net site in New Mexico.

A number of observatories from the Northern Hemisphere have also observed 2008 UL90, so it has had quite a few positions reported recently. This object will be visible well into January and is getting lots of additional observations on this pass. I think will be a candidate to receive a numeric designation since it has been seen on 5 “oppositions”.

Atira 2008 UL90 is considered an Potentially Hazardous Asteroid (PHA) because it has a considerable size of 800 meters, and also because it’s aphelion is in our neighborhood at 0.96 AU, with an estimated closest approach of 0.026 AU based upon it’s current known orbital elements. So this one is certainly worth keeping an eye on! As can be seen from the diagram below, the object ranges close to our distance from the Sun but is significantly inclined:

20170112-01-2008ul90-orbit

So I was able to get a look at and report on two Atira’s this past year. Since there are only 26 I think that’s pretty fortunate. Looking over all of the 26 known, it looks like (163693) Atira should be visible in March around a close approach. Another numbered Atira, 413563, may be visible around then too at mag 18.5. All of the others look to be hard to see or extremely faint over the coming year. But since two new Atira’s were discovered in 2016, so there’s always the chance of catching a new one!

 

 

OrbBrowser – a Minor Planet Orbit Browsing Utility

In my “day job”, I’m a scientific applications developer working in the life sciences domain. I have a science background but have always used computers in one form or another in research, from time sharing main frames, to Unix workstations and servers to Linux clusters.

So I wanted to write a utility to extract orbital elements of minor planets from the flat-file distributions provided by the IAU Minor Planet Center, to help identify candidates for observation. I started with a basic PERL utility to filter the full MPCOrb data file based on input criteria. That was useful but not very exciting! So I’ve started to write an HTML/Javascript based utility to browse and filter some of the existing subsets provided by the MPC in an interactive fashion. The current version can be found on a demo site I’ve setup for the utility which is named OrbBrowser.

The site is quite simple to use. First, you need a data file in the MPC Minor Planet Orbit format containing the subset of interest. The current set of Near Earth Asteroids is available on the MPC data page in the file NEA.txt. Or you can download the DAILY.DAT file for the daily orbit updates to see what’s new and newly updated.

From the OrbBrowser site, select Choose File and select the local file of interest. After a few moments, the file should be read in and displayed in a table showing all of the fields present in the data file including orbital elements, orbital uncertainty and observation stats, etc. You can even see the published MPC “bit flags” giving the orbit type classification, PHA, NEA and critical flags.

Selecting the header of any column will sort the data by that column. At the bottom of the column are input fields to enter a min and max value for numerical fields, or a pulldown for categorical fields for filtering. So, for example, you can select U >= 2 and U <= 5 to see all objects in the data file with that range of uncertainty values. Adding another filter such as Orbit Type = Aten will intersect with the first filter to give all Atens having U from 2 to 5. And so on!

Once you have a subset of interest, you can export the filtered set back out to a file in MPC format or a text-delimited format. The MPC subset can then be loaded into a planetarium package such as C2A so you can see which objects in the list are currently visible from your favorite observing site at a given apparent magnitude limit. A text delimited export can be loaded into Excel or other data management programs to add additional information or more refined filtering and sorting.

Because OrbBrowser runs totally in a browser, there is no need to install any additional software to use the utility. However, you are subject to the javascript performance of your browser! On 64-bit Windows 10, I’ve had better luck with Chrome and Firefox for viewing the full NEA file with 15,000 some entries.

Also, you can download the main page of the site and supporting javascript and CSS files to your local desktop and run it totally off line. All of the source is available to read and it is available under an open source license, so you are free to modify it in any way and make use of it in your own site if that is of interest! See the Download and More Info tab for a link to the current ZIP archive and instructions to run it locally.

I’ve found the utility quite useful to help identify some of the Aten-class objects I’ve observed and submitted. I’ve even found and observed a couple of Atira-class bodies as well, which are totally within the Earth’s orbit and fairly elusive.

I hope OrbBrowser is of use to others. Feel free to send questions, suggestions and tomatoes to the email address listed on the site!

Screen shot example showing the current NEA.dat loaded, and filtered for Atens with U=2 through 5 to suggest potential objects that may need updating. (Of course, not all of these will be observable).

20161229-01-orbbrowser

Screen shot showing all NEA’s with U from 2 through 5 loaded into C2A with a magnitude filter. Objects can be selected that are well above the horizon – and out of the Milky Way.

20161229-02-c2a

Loading and working with the full MPCOrb database does not appear to be practical in javascript. So I’m working on another browser-based utility to filter and save subset of interest for interactive browsing. So stay tuned for a companion utility!

PHA 2016 WJ1

[Updated 3 Dec with new data available – see below]

As mentioned previously, the Spaceguard Priority List at the ESA is a great resource for finding Near Earth Objects (NEOs or NEAs) that are useful to observe – even by amateurs! The site assigns priorities to observable NEOs ranging from “Urgent” down to “Low Priority” in order to help triage candidates for the larger observatories (and others) for follow up, based upon a number of criteria.

One reason an NEA might be assigned to the Urgent category is having a narrow time window for observation. The surveys for minor planets often pick up smaller, bright objects that are only detectable because they are passing close by. These will tend to be moving fast and will only be visible for a relatively short time. So it’s important to get observations on these while they are still visible to determine a reasonably accurate orbit so they can be found again later. Also, some of these may even pass close enough to become targets for radar observation. In this case, priority visual observations can be made to help locate an asteroid well enough to point a radar at it. Radar observations can provide highly accurate locations and a variety of physical data for general research.

The fast-moving NEOs can be hard to accurately observe with the modest telescopes I have access to, so I usually don’t try for things in the Urgent category. Observations on the “Needed” and “Useful” objects are often worthwhile, and even the Low Priority objects can be useful to observe for orbit improvement. But I was interested to see an object in the Urgent category this past week that was in a brighter magnitude range (around 18) and moving at the relatively modest rate of around 2 arcseconds per minute: 2016 WJ1. Certainly doable!

2016 WJ1 is likely listed in the Urgent category because it is identified as having a potential for a close approach or impact to Earth in the distant future and is of significant size to be designated a Potentially Hazardous Asteroid or PHA. It is not uncommon for newly discovered asteroids to be placed on the JPL and ESA “watch lists” for potentially hazardous NEOs. An orbit can be estimated for a solar system object after only 1 or 2 nights observation, but this will only be an approximate orbit until the it has been observed for an extended period of time. So newly discovered minor planets are sometimes found to have potential close approaches to Earth, based on a rough orbit, and so are placed on the watch list upon initial discovery. Sort of like a quarantine! These are often removed after more data comes in and more accurate tracks can be projected. For example, in the Sentry Risk Table maintained for NASA by the JPL, one can see that dozens of minor planets discovered in 2016 have been removed from the list after follow up observations, out of the 1700 or so that have been discovered this year in total. So it’s important to get data on these objects while they are still observable to help identify, or rule out, a close approacher as being a potential threat.

2016 WJ1 was in the northern sky this past week at with a declination of around +15. This would be best observed from the Slooh.com site in the Canary Islands, but they were closed due to an extended spell of bad weather. The object was lower in the sky from their observatory in the southern hemisphere near Santiago, Chile but still observable. And the weather has been very nice there of late, with sunny summer skies and warm temperatures, so this looked to be worth a try.

So I scheduled 4 “missions” on the night of Nov 27th from Santiago and got nice images back the next morning. After solving the images in Astrometrica, I could see a very faint moving object around the expected position for 2016 WJ1. To improve the signal and get a more accurate position I was able to stack the images from each set, giving 3-4 images taken about 1 minute apart for each stack. Here’s a portion of one of these stacks showing the presumed target, circled in purple:

20161202-1-2016-wj1-stack4

In this image stack, Astrometrica is shifting each image by the expected movement of our target object. The oval-shaped objects are stars that are offset between frames because they are moving relative to the asteroid. But the asteroid lines up between the images, giving a  nice circular shape and a better defined peak. (And the fact that it does also confirms we are seeing something moving at the expected rate and direction of our target). The red box marks the area where Astrometrica expected 2016 WJ1 to be. We are somewhat off (about 1.8 arc minutes in RA) but in the neighborhood. And this offset is consistent in each image, helping to confirm we are in fact seeing an object agreeing with the expected track of 2016 WJ1.

Now Astrometrica can give us the position in the sky at each time point for each stack, so we have 4 “observations”. I then ran these through the findOrb package along with other published observations to calculate the best orbit solutions for the combined set. This gives the position at each time point plus the delta or “residual” between the observed location and the location predicted for the orbit:

16 11 28.21566 W88 04 03 52.25 +14 38 35.3 .29+ .36+ .15613 1.1416
16 11 28.22933 W88 04 03 48.37 +14 38 24.5 .41- .34- .15603 1.1415
16 11 28.25381 W88 04 03 41.58 +14 38 06.4 .51+ .13- .15583 1.1413
16 11 28.27146 W88 04 03 36.61 +14 37 53.3 .06- .17+ .15570 1.1411

In the first line, the observed and predicted positions differ by around 0.3 arc minutes in RA and Dec respectively. This is pretty good accuracy for a stacked image and should be useful data. The second and third timepoints were a little more off but the 4th is good, so I submitted the first and last lines to the Minor Planet Center through their email submission mailbox.

The observations were accepted, but I missed that publication deadline for that day. A few more positions were obtained the next night and sent in on 29 November.  Both sets were published that later day in the MPC Minor Planet Electronic Circular (MPEC) 2016-W117.

These publications are rather technical and daunting to read. A more user-friendly form can be see in the Tracking News section of the Earth’s Busiest Neighborhood site here.

What we see in the first section in the link above are observations of 6 different minor planets that have been recently discovered and being followed up as potential risks, including our 2016 WJ1. My observations from Slooh station W88 program code 7 are listed for both nights, along with data from other observatories from England, Germany, the Czech Republic and an ESA observatory in the Canary Islands. Adding in a few positions from the Southern Hemisphere is likely helpful to estimating the minor planet’s orbit as a balance to all of the other submissions from the North.

The Daily Orbit Update on the next date (MPEC 2016-W127) shows observations on 2016 WJ1 from over 10 observatories, so it’s certainly getting a lot of attention. I also submitted a third set on 30 Nov which was published in 2016-X07 on 1 Dec. As of today, there are 220 observations over a mere 12 days, so there are certainly a number of eyes on this NEO.

2016 WJ1 is still on the risk list, but certainly needs to be observed for a longer period of time to really understand how concerned we need to be about it. It’s discovery was confirmed and then published just recently on 22 November, so it’s still very “new”. It was one of 18 new designations published that day, ranging in estimated sizes from 10 meters up to 1000 meters, so it is of moderate size at around 180 meters. Fifty meters is considered to be a significance threshold in terms of potential damage, so the object is certainly worth tracking – but is not a monster! An object’s speed relative to the Earth is also highly important to consider when assessing risk.

Another factor is the number of potential encounters, which depends upon the orbit type. 2016 WJ1 is an Apollo-class minor planet which means that is primarily located outside of the Earth’s orbit but crosses it. It’s orbit is rather elongated and ranges from inside of Venus’ orbit to beyond that of Mars. In fact, it seems to make close passes to Venus, Earth and Mars on a fairly regular basis in an orbit close to the solar plane. We are seeing it now because it is in our neighborhood and will pass by at a very safe 0.05 AU (~ 5 million miles) around mid December.

It is projected to come back around in 2023 at an even safer distance but will observable. So we’ll get to check up on it again in a few years, which is re-assuring! Then it will continue to come around every 7-10 years or so for more viewing chances too, and can likely be seen in between those visits by the larger guns. Each of these approaches will help refine the orbit’s accuracy further and check against course changes caused by encounters with the 3 planets it interacts with.

A pass in 2065 looks like a close shave and that is currently contributing to much of the estimated risk. But, again, this is a very long extrapolation of a 3 week old orbit to really worry about just yet. And that fact that it is expected to make a series of close passes could well be an advantage. One could imagine launching missions to encounter it and study if further. And it could well be a good test or subject for risk mitigation – such as steering it away from us. I even wonder if somebody somewhere is thinking it might be a good candidate for asteroid mining. One could imagine valuable ore being offloaded each time it comes back in the vicinity perhaps.

2016 WJ1 is expected to have a much more rapid motion in the sky as it gets closer and then passes by over the next few weeks, so further observations are probably best left to the professional observatories. And there are always other candidates to follow up on. If the weather clears in the Canary Islands some time, I’d like to try another newly discovered ‘risk’ candidate – 2016 TF94. Unless there’s something more interesting on the list!

Update: new observations dated from 2003 were published yesterday from the observatory at Mauna Kea in MPEC 2016-X21. I’m guessing these are “pre-covery” data. When a new object of interest is discovered, observatories often go back through their data to see if was observed before. Perhaps they had seen it in 2003 but it was never confirmed and was not published as a new object at that time. But now, the older observations are found to be consistent with those of 2016 WJ1 and are now added to its history.

Now the known arc spans for about 13 years instead of a month, greatly reducing the long-term uncertainty of the minor planet’s trajectory. 2016 WJ1 was removed from the JPL Sentry list yesterday. The NEODyS close approach table shows that close approaches in the next 100 years will be just that – approaches that should safely pass us by.

More observations during this and subsequent passes will tighten this up further, but this is certainly good news!

Atens

Since February, I’ve been continuing to capture images of Near Earth Objects using the “internet” telescopes of Slooh.com with a few attempts from iTelescope.net. I’ve made over 20 submissions to the Minor Planet Center on some 18 different minor planets and comets. The observations have been fairly routine updates, so I’ve not felt compelled to blog about each submission, but will report from time to time on anything interesting observed.

As mentioned, the first submission I made was for minor planet (163243) 2002 FB3 in February, which I found out after taking the images is an Aten-class NEA that was on the MPC Critical List for observation. The minor planet Aten-class asteroids are defined as having a semi-major axis of less than 1.0 AU with an aphelion of greater than 0.983 AU. So these have an orbit entirely or largely inside of the Earth’s orbit but have the potential to cross the Earth’s path or come to a close proximity. For example, here is the orbit of Aten 162117 described in more detail below. It’s orbit extends somewhat beyond Earth’s but has a high inclination:

20160904-01-162117

Out of 14,576 minor planet orbits listed in the MPC’s NEA data file as of today, 1056 are given the Aten orbit classification. The semi-major axis ranges from 0.63 AU for 325102 2008 EY5 to 0.9996724 AU for 2010 TK7. There are 49 Atens classified as being over 1 KM in size and 106 on the MPC critical list. These stats are as of 3 Sept 2016 and obtained using a utility I developed called OrbBrowser for filtering and browsing the MPC minor planet orbit files, that I’ll describe in more detail in a later post.

Back in April, I noticed Aten (308242) = 2005 GO21 on the MPC Bright Recovery Page.  Since it was visible in the southern sky, I tried to schedule “missions” from the Slooh observatory near Santiago, Chile designated W88. The site was experiencing clouds and rain for a spell so I got no results after trying for a few nights. I tried once more even though the forecast did not look so good. Luckily, there was a clearing later that night and I was able to get 2 sets of images before dawn when the object was up in the sky. Two observations from that night were submitted and accepted and published in MPEC 2016 H38 as the first new observations on the object since July 2014. The orbit was not updated at that time, but I suppose my data were used in the next orbit update later in the year.

I noticed another Aten on the Bright Recovery List, (136818) Selqet, that had not been observed since 2008! It was brightening in the southern sky, so I tried again from Slooh W88 but got shut out again by the weather. I had previously signed up and had tried a few missions from the iTelescope site in Siding Spring, Australia, so I gave that a try. I was able to get observations in on 2 successive nights, even with a fairly full moon in the sky and submitted them:

20160904-02-selquet-Q62-0514r1

The submissions were accepted, but I was not sure if they would be published without assignment of a Program Code, so I asked to MPC staff to check the observations for publication. After that they were published in MPEC K25 along with data from observatory Y00 SONEAR Brazil, and these were used in an orbit update. So I was excited to get observations on a NEO that had not been reported in nearly 8 years!

The Aten was brightening and visible in the southern sky for quite some time, so I submitted follow up observations from W88 in June as well.

Another Aten bright recovery I saw on the list was (2100) Ra-Shalom, last observed in 2013. This is a large body, estimated to be some 2.7 km in diameter and has been observed and studied in a number of light-curve and radar campaigns. Observations were published in MPEC 2016-L118.

Aten (5381) Sekhmet was also on the Bright Recovery page, last observed earlier in 2016. It’s a 1+ KM designated NEO also on the Critical List. Since the Orbit Uncertainty had a value of 3, I took and submitted observations from 1 night from W88, published in MPEC 2016-M17.

Recently, Aten (162117) 1998 SD15 was listed with a previous observation date in 2008. It was estimated at a visible magnitude of around 19 but it looked like it would be brightening over the next month or so. I scheduled missions from the Slooh Teide T1 telescope, and after trying for a few nights obtained 3 sets of images. The object was moving at around 4 arcsec per minute but was distinctly visible in each image. So I selected an observation from each set and submitted them and they were reported in MPEC 2016-R33.

After Googling this object, I noticed it is scheduled for radar observation from Arecibo on 21 September, so I decided it would be worth trying for more data on it. The object is currently right around 1.0 AU from the Sun, but 0.18 AU from the Earth. The orbit has a fairly high inclination of 26 degrees, so it is safely 25 million km “above” us as shown in the orbit diagram above. The object is moving south in the sky and will cross behind the Earth a little later this month and reach a closest approach of 0.12 AU around 19 September. The magnitude will increase to 16 at that time and the apparent motion will get somewhat faster at over 10 arcsec / minute.

Data were obtained from both the Slooh Teide observatory and the iTelescope Mayhill NM observatory the night of 3 Sept and submitted. I plan to follow up as the object brightens and picks up speed and try using stacking of short exposures to get locations as the relative motion brightens.

So far this year, I’ve reported on 8 different Aten class NEAs that had not been observed in 3 months to nearly 8 years! Will definitely keep an eye out for more including the archetype Aten itself. I’ve also caught a few Apollo-class minor planets and those are certainly of interest as well.

 

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.

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:

20160315-01-2016EL56-stack

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!