Close Approach of 2025 SS5

[PMSchu]

CNEOS predicts that the newly discovered Apollo class NEO, 2025 SS5, will make a close approach on 2025-Sep-28 22:08±00:05 UT at a distance of 0.00070 AU  moving with V Relative=7.96 km/sec, H=27.8 magnitude, diameter 7.5 m - 17 m and 'Rarity'=1. There is a 3 day observation arc, the Condition Code=6 and the Earth MOID=0.000771147 AU.  The solution date was 2025-Sep-26 06:52:08 PDT. The initial reported observation was by Mt. Lemmon Survey on 2025-09-23. This object is too small to make MPC's list of Potentially Hazardous Asteroids (PHAs). CNEOS predicts close approaches on 2038 Sep 30 and 2053 Apr 2, but the uncertainties are > one day for the time of close approach.

Using MPC's orbital elements for the epoch 2025 Sep 26 0000 UT, ST4.1.11.18 Visual Pro predicts that 2025 SS5 will reach a peak brightness of 14.5 magnitude on September 28 at 1600 EDT (2000 UT) with the NEO 129.7k km distant traveling through Cygnus at 10.2"/second, but in daylight in Columbus, Ohio. Close approach is predicted (to the nearest hour) on 2025 September 28 at 1900 EDT (2300 UT) with the NEO 111.64k km distant traveling through Draco at 15.2"/second and 15.5 magnitude, but still in daylight. The best view of 2025 SS5 will be on the morning of September 28 from Columbus and eastern North America. 2025 SS5 should be well placed for European observers, if it's dark enough.

Here's the Object Info dialog for 2025 SS5:    

This NEO will pass very close so parallax will be an issue. Observers should follow the instructions in the 'Important Thread' at the top of this forum section to download the most accurate orbital elements. The elements are still being refined for this object, but I don't think that I'll be able to post an update for this NEO tomorrow.

Good hunting,

Phil S.

[Dennis]

Thanks for the heds up Phil, this proved to be a tough assignemnt.

I managed to grab a few frames of 2025 SS5 through intermittent cloud on 2025-09-28, from 8:58PM-9:01 PM AEST.
2025-09-28T10:58 to 2025-09-28T11:01 UT. 

Unfortunately, I was not able to Track on the NEO as the software that controls the mount placed the NEO some 4 or 5 FOV’s off target.

However, I was able to GoTo the correct RA and DEC coordinates, leapfrogging ahead of 2025 SS5 and grab these 5x30 sec frames before the clouds set in.

A Plate Solve gave the following for the full FOV
Center RA (2000.0): 23h 50m 50.01s
Center Dec (2000.0): +19° 09' 39.2"
Scale: 0.5460 arcseconds/pixel
Size (pixels): 3124 x 2088
Angular Size: 0° 28' 26" x 0° 19' 00"
Position Angle: 359° 52' from north through east
Mirror Image: No
RMS: 0.32 (X: 0.27 Y: 0.18)
Number of Stars Used in Solution: 47 (100%)
FWHM: 5.22 pixels, 2.85 arcseconds
 
Celestron C11 Edge HD at F10, ASI2600MM Pro camera. Full res 1920x1200 crop from the middle of the frame.

The star “pierced” by 2025 SS5 is:
Object Name: GSC 1725:1387
RA (Topocentric): 23h 52m 13.7s
Dec (Topocentric): +19° 17' 29"
RA (2000.0): 23h 50m 53.7s
Dec (2000.0): +19° 08' 44"
Magnitude: 13.58
Constellation: Pegasus
 
Despite the clouds, I continued to play leapfrog and grab sets of exposures but very few showed the trail of 2025 SS5, most were just photos of clouds…

Cheers

Dennis.

   

[PMSchu]

Thanks Dennis,

That's very impressive imaging. 2025 SS5 was moving very fast at that time. Where did you get your orbital elements that they were off by that much?

That's a lot of motion for only 150 seconds of exposure time isn't it?

I hope that you can take a stab at imaging 2021 RW9. ST4 now has it at 16.8 magnitude in Taurus, if it's really there.

Phil S.

[Dennis]

Thanks Phil, the session was dominated by thin, low clouds with the occasional sucker hole that I was able to take advantage of. The clouds gradually thickened and made imaging impossible, so I could not make an attempt to record NEO 2021 RW9 which transited around 3:00am the next morning.

The Paramount MX+ and control software is an enclosed ecosystem, where the mount models the sky and can then make on the fly adjustments for several variables, to allow for long focal length unguided imaging and set tracking at a custom rate for imported objects.

But when the software plots the object in the wrong place, then you miss it! In this case, the real 2025 SS5 was some 1 degree off at a PA of 269 degrees.

This has happened previously with these close approaches, where SkyTools plots the NEO accurately whereas the mount SW misses the mark.

I wonder if the mount SW is using geocentric coordinates rather than the site-specific Lat and Long?

Here is a single frame taker later, cropped 1920x1200 around the trail of NEO 2025 SS5 through a sucker hole at 2025-09-28T11:09:56. Imaging through the thin, low cloud made this fainter than I had expected.

This was 9:09:56 PM AEST.

Dennis.

   

[PMSchu]

Hi Dennis,

Does the mount allow you to input your LAT & LON? If not, then it can't use anything but geocentric calculations. That's sort of a short coming, but it likely only matters for these close approaches where parallax becomes important. I've noticed that for really close approaches, the NEO's track is different for different observing locations. Are you using MPC's Elements at Today's Epoch or are you downloading elements from HORIZONS?

Your second image looks great too. Thanks for sharing.

Phil S.

[Dennis]

Hi Phil
 
The mount location is set in the mount control SW to my GPS coordinates. To download the NEO I just input the name (e.g. 2025 SS5) via an under the hood function that queries an MPC database then creates the object in the mount sky chart (in the wrong place for close NEOs).
 
I am wondering if this operation might be bypassing the mount Lat and Long and using geocentric coordinates in the “hidden” query process?
 
The next time, I might test the following:
 

• Decouple the mount from the native Driver and set it to choose the ACCOM Driver, then connect with SkyTools via ASCOM and perform the GoTo using SkyTools to obtain the correct pointing location.
  
• Locate the “false” position plotted by the mount SW and set the Custom Track Rate on the “false” object in that SW.
  
• See if the mount will then perform Custom Tracking and remain faithful to the accurate SkyTools pointing location. A kind of “offset” or “bypass” experiment.
  

 
If this works, I retain the benefits of the mount modelling but have the accuracy and functionality of SkyTools to place the target on the camera sensor.
 
Cheers
 
Dennis.

[PMSchu]

Hi Dennis,

The mount would need to know your location to point the telescope correctly, but you're right that it may not correct its NEO ephemeris calculation for the position on earth and just assume geocentric coordinates. That won't give accurate positions for close passes. What does SkyTools predict for positions if you use the geocentric option for the ephemeris calculations? Does it match what the mount's predicting? If so, that would confirm your supposition. Can you contact the manufacturer and ask about how they handle minor planet position calculations?

The MPC had 2025 SS5 at 0.27 LD at close approach.

Phil S.