2018 FE4

[bigmasterdrago]

This Apollo class rock from space discovered March of 2018 at Pan-STARRS makes a pass over the top at a distance of 2.7LD at mag 16.1. This is on the evening of Sept 25, ripping at 4 arc minutes per minute out of Cepheus, through Andromeda and into Pegasus b4 morning twilight on the 26th. It brightens somewhat to mag 15.5 as the phase angle improves b4 morning twilight ruins the view.

[PMSchu]

Neither CNEOS nor the MPC list a close approach by this object on their websites in September 2022. Interestingly the CNEOS's Orbit Viewer shows this NEO approaching within 0.061 AU on 2022 Sep 29. Their table of close approaches shows nothing in 2022. I've seen this happen with other objects. With H=24.7 it's unlikely to be 16.1 magnitude.

I've had many objects turn up in ST4v DB Power Searches that weren't on the CNEOS & MPC websites. Some objects like 2018 FE4 weren't in the close approach table, but the orbit viewer indicated that a close approach should have been expected. Frequently CNEOS was using an epoch of the elements around the time of discovery, but that doesn't explain why the MPC didn't indicate a close approach. They have elements calculated for today's date.

How did you find this one?

Phil S.

[bigmasterdrago]

It was at http://astro.vanbuitenen.nl/neos

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Most recent obs are in March 2018 at Mt Lemmon and Mauna Kea. Elements at Lowell epoch 2459800.5, MPC epoch 2459800.5, JPL unnumbered epoch 2458205.5.

Clearly this rock is lost and needs to be found again. For 0hr local time Sept 26, Lowell and JPL have the rock plotted 17° apart while the MPC position is 80° out from the central position of JPL & Lowell. Rather interesting.

[PMSchu]

Wow, that's a very impressive website there! Quite a gold mine of information.

It's quite disconcerting to see such large discrepencies in the predicted positions when using the elements provided by seemingly correct sources. It's hard to know who to believe. The JPL's HORIZONS elements are produced for the epoch of date, but so are the MPC's if you download the elements for the NEAs at Today's Epoch file. Both JPL & MPC apply purturbations to their calculations. Who to believe?

Which of the Lowell, JPL & MPC positions is closest to the NEO Approaches | astro.vanbuitenen.nl website?

I believe Dennis, but his weather sucks & he can't make many observations  . I need to use the iTelescopes more, but it's hard to capture 19th magnitude NEOs even with a 20" system. Since 2018 FE4 is predicted to be 27.5 magnitude currently, I've got no shot until Sep 25 by their predicted brightness chart.

Phil S.

[bigmasterdrago]

Both Lowell and the MPC are using current epoch whereas JPL is using those from 2018 Mar 28. The MPC agrees closest with that page. However JPL elements agree with those at Horizons as one would expect - both position and time of close approach and distance. And clearly including perturbations. It will be interesting to see if this rock is re-acquired.

As an experiment I used the elements from https://minorplanetcenter.net/db_search/...d=2018+FE4 (2458600.5). Nowhere close to either of the other sets using gravitational perturbation. I'm watching the news on this rock rather closely. Just for grins. Gives me stuff to do. LOL

[PMSchu]

The astro.vanbuitenen.nl site says that their elements come from the MPC. The MPC corrects for all of the planets & several of the larger MPs as well. There's a code for that on the page with the elements as you're probably aware.

Phil S.

[bigmasterdrago]

The astro.vanbuitenen.nl site says that their elements come from the MPC. The MPC corrects for all of the planets & several of the larger MPs as well. There's a code for that on the page with the elements as you're probably aware.

Phil S.

Lowell does similar after getting any new elements direct from the MPC - they epoch date them in-house with perturbations to the current epoch. But, Lowell can run behind.

[PMSchu]

Hi BMD,

Do you know the procedure that MPC follows when they produce their 'NEAs at Today's Epoch' data file? They wouldn't just precess their elements for 2022 Aug 9 00:00 UT to the current date would they? The new discoveries wouldn't have elements for the standard date, although they could generate them easily enough.

Here's a description of the perturbing bodies that the MPC considers for their NEO orbit calculations: Perturbing Bodies (minorplanetcenter.net)

They consider a lot of objects. I don't know why MPC & JPL give different positions, unless it's down to different elements.

Phil S.

[bigmasterdrago]

Phil, is that done in house via SkyTools? I think that's why it requires so much time on the PC to import and process the data file fetched from the MPC.

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ST grabs the near earth file which is small (29,761 currently) and then only processes those to the current (daily) epoch. If I understand it correctly. It takes my PC much less time to grab the MPC NEA.

[PMSchu]

BMD, my understanding is that SkyTools can import 2 MP element files from the MPC. The full file MPCORB containing all of the MPs that the MPC currently has, ~1.2E6 objects with the epoch 2022 Aug 9 00:00 UT, and the NEAs at Today's Epoch file that has all of the NEAs, currently 29,792 objects, with the epoch at today's date. There's also the ASTORB option & several other files from MPC as well.

I don't think that ST4v makes any changes to the epoch of the MP data file. It just uses the date provided. That date doesn't affect the calculations, it just indicates how reliable any calculations made using those elements might be. Old elements = less reliable. ST4v will complain if the elements are too old for that reason.

It's much easier to work on ~30k objects than 1.2 million .

Phil S.