Close Approach of (415029) 2011 UL21

[PMSchu]

CNEOS predicts that the large NEO, (415029) 2011 UL21, will make a close approach on 2024-Jun-27 20:16 ± < 00:01 UT at a distance of 0.04439 AU. This is a 'Rarity'=3 event.

I'll post an update closer to the event. This is a kilometer sized object that's on the MPC's Potentially Hazardous Asteroids List.

Phil S.

[PMSchu]

Here's the promised update for the close approach of the kilometer-sized NEO (415029) 2011 UL21. The orbit is well defined and the parameters haven't changed. CNEOS predicts that the NEO will make a close approach on 2024-Jun-27 20:16±<00:01 UT at a distance of 0.04439 AU moving with V Relative=25.88 km/sec, H=15.9 magnitude, diameter 1.7 km - 3.9 km and 'Rarity'=3. This object has a 12872 day observation arc, the Condition Code=0 and the Earth MOID=0.0171455 AU The solution date was 2024-Apr-03 05:49:27 PDT. This MP was discovered at Kitt Peak on 2006-05-27 by Spacewatch. It's not surprising that the close approach parameters haven't changed since April 30, since CNEOS performed the close approach calculations on Apr 3. 

Using MPC's elements for the epoch 2024 May 15 0000 UT, ST4v predicts that this NEO will reach a peak brightness of 11.7 magnitude on the evening of June 28 at a distance of 0.05 AU traveling through Virgo at ~40"/minute. Close approach is predicted (to the nearest hour) on 2024 Jun 27 at 1600 EDT when the MP will be 11.9 magnitude traveling through Hydra at ~48"/minute in daylight as seen from Columbus, Ohio. Africa looks like the best place to observe the close approach, but this NEO is predicted to be brighter than 15.5 magnitude from June 21 to July 17, so there's plenty of opportunity to observe this large rock as it passes by. It might be worth adding to the Current Bright & Interesting Minor Planets OL for June and July before it fades from view. It will start out best from the southern hemisphere, but steadily move north heading toward Hercules so everyone will have a chance to view this MP. 

Here's the Interactive Atlas chart for this NEO as seen from Columbus, Ohio: [attachment=3104]

Here's the Object Info dialog for this NEO: [attachment=3105]

As a 'Rarity'=3 event, a close approach of a NEO this large and close is very rare. Typically there's only 1 or 2 per year. On 2089 Jun 25 (415029) 2011 UL21 will be 0.01782 AU distant. I wonder what the 'Rarity' will be for that!

Good hunting,

Phil S.

[bigmasterdrago]

What will be interesting for me, is if I can nail this rock (2011 UL21) in the middle of Nautical twilight (21:30CDT), Friday June 28th, and then snag 2024 MK twenty four hours later low in the west, it'll be a grand double hit!

They will both be into the darker part of my sky and out of the southern light domes.
Kenneth Drake

[PMSchu]

Two 'Rarity'=3 events in 24 hours. That's something that doesn't happen often. I wonder if these 2 NEOs have similar orbits.

Good luck & clear skies!

Phil S.

[bigmasterdrago]

Two 'Rarity'=3 events in 24 hours. That's something that doesn't happen often. I wonder if these 2 NEOs have similar orbits.

Good luck & clear skies!

Phil S.

Phil, the rocks have similar orbits is several ways except for inclination and size. UL21 has a radius of ~1.4Km while MK sports a tiny 0.101Km. Their inclinations are vastly different. UL21 having an i=34.88° while the tiny rock is 8.46°. UL21 is an Apollo class so its orbit crosses inside that of ours. MK is an Amor class, so does not. Most Amors cross the orbit of Mars.

Most of their other orbital elements are similar, although the Longitude of perihelion stands out a bit - UL21 = 200° vs MK = 291°

Again, it will be very interesting if I can nab UL21 moving ~3.5'/min into the west edge of Hydra out of Corvus.

   

Then next head to the Tail of the Scorpion to tag a much faster moving but brighter tiny rock - 2024 MK.

Unfortunately, I'm unable to get a proper ephemeris for 2024 MK at this time.

I've added this track but recommend doing your own from your location using date of observation osculating elements.

   

[PMSchu]

Hi BMD,

Thanks for the info about the differences in the orbital elements of 2024 MK and (415029) 2011 UL21. I don't know that I'd consider a 0.1 km object tiny. It would certainly leave a mark. NEOs with H=22 magnitude are generally considered to be ~140 m diameter and 2024 MK is slightly larger than that with H=21.76 magnitude. CNEOS has q=1.009168587376742 AU and lists it as an Apollo object and a PHA.

I saw your entry in the Support section regarding the use of kilometers where SkyTools expects AUs. As a temporary fix, can you manually convert the km units to AUs? Only a and q would need to be converted. I haven't used HORIZONS to obtain elements in a while. Can you request that the a and q parameters are generated as AU instead of km?

(415029) 2011 UL21 is already 13.9 magnitude according to ST4 Visual, but in Pyxis.

Phil S.

[bigmasterdrago]

Phil, I guess I meant tiny compared to UL21. LOL

Yes, I can manually convert. Horizons even indicated the math to do it. For some reason the inquiry page https://ssd.jpl.nasa.gov/horizons/app.html#/ does not provide for the option to display A in AU. I had used the method that Greg mentioned b4 Greg even mentioned it - Copy/Paste from a set of osculating elements generated at Horizons. It's always worked splendidly No screwing around with pasting in a bunch of singe lines of els. All of a sudden no worky. And today, I cannot even create a set of osculating elements like I did couple days back.

As you know 2024 MK will pass inside the orbit of the Moon. We need the latest els for the time of obs.

Not sure what is going on over at Horizons

Kenneth Drake

[PMSchu]

Yes I saw your post on the Support page. Maybe using the body-centered elements is OK. SkyTools will correct for your location on earth's surface.

Phil S.

[PMSchu]

Using MPC's elements for the epoch 2024 Jul 17 0000 UT, ST4.1.11.10 Visual predicts that this NEO will reach opposition on 2024 Jul 18 when it will be 15.5 magnitude in Hercules. It's currently 0.3 AU distant traveling at ~1"/minute. It's now well past the close approach, but still visible even in moonlight because of its ~2km diameter.

The NEO 2024 MK that had its close approach 2 days after (415029) 2011 UL21 is currently 20.2 magnitude and 0.10 AU distant in Andromeda traveling at 8.4"/hour. Size really does matter  .

Phil S.