A curious asteroid

[Dr Paul Leyland]

The newly announced km sized Asteroid 2021 PH27 has a = 0.46148 +/- 0.00043 e = 0.7094 +/- 0.0023 and a 114.5 day orbital period. Is this the shortest period on record? It’s a Mercury and Venus crosser, but doesn’t make it out beyond 0.8 AU.

The current evening apparition is no longer accessible for folks with plausible telescopes but next March it may be possible for some of us. On 2022-03:01 it is predicted to be at an altitude of 18 degrees when the sun is 15 degrees below the horizon at 06:30 UTC here in La Palma. It won’t be easy to pick up a V=19.4 object in nautical twilight but neither is it obviously impossible.  At least the moon is out of the way around then.

One for your diaries?

Is it too late for the 2022 Handbook?

[Richard Miles]

Thanks Paul for highlighting this discovery, which is remarkable and shows what is possible when a large 4m scope (DECam Survey) searches the twilight sky. As well as the shortest known period, 2021 PH27 also has the highest precession rate of 53.5 arcseconds per century (a consequence of general relativity in operation), i.e. gretaer than that of Mercury.

As to the Handbook for 2022 that goes to the printers tomorrow! But in any case, it wouldn’t get a mention under any of the various categories. Usually we try and put stuff in that means they can be observed by amateurs. It might be worthwhile to list Inner Earth Objects provided that they can reach say mag 20 at some point in the year plus some criterion as to teh lowest practical solar elongation. Of course the two are inter-related so we might have to use a sliding scale of acceptability which is a function of both magnitude and elongation. If you have a go at reaching it next March and succeed that would help to set the limits. At about mag 16 the limit is an elongation of about 19 degrees for our UK latitudes. Ther may be a problem about adding a new category to the Handbook and that is the number of pages limit. To add the Exoplanet data I had to shorten the brighter asteroid Asteroid Ephemerides.

Richard

[Dr Paul Leyland]

Thanks Richard.  I will try to have a go next March. The elongation is 40 to 50 degrees that month if I read the MPC ephemeris correctly.

[Dr Paul Leyland]

There has been some speculation that it may have been a Venus Trojan in the past. It seems that Venus Trojans aren’t stable on gigayear timescales, largely due to perturbations by the Earth,  but may well  be metastable for a good number of megayears.

[Richard Miles]

Sounds a reasonable hypothesis to me.

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