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.

 

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