Re: another natural satellite of Earth... again.


Alan Harris
 

Paul Chodas has tentatively identified this with the Surveyor 2 Centaur rocket body, launched on September 20, 1966.  The very low Earth encounter velocity (0.6 km/sec is even low for lunar ejecta, so it is unlikely it is a natural body, even lunar ejecta, more likely space junk.

Alan

On 9/20/2020 2:30 PM, Sam Deen via groups.io wrote:
Hi all,

I'm surprised I didn't notice this any sooner, but a friend pointed out to me that the recently-discovered asteroid 2020 SO is on an orbit that, while not currently orbiting us, will be captured into Earth orbit for a few months later this year.

Current geocentric orbit:

Perigee 2020 Nov 3.251863 +/- 0.0224 TT = 6:02:41 (JD 2459156.751863)
Epoch 2020 Sep 18.0 TT = JDT 2459110.5 Find_Orb
q707812.420 +/- 2281 (J2000 equator)
H 28.3 G 0.15 Peri. 229.78793 +/- 0.10
Node 253.78959 +/- 0.0014
e 2.3556565 +/- 0.00905 Incl. 5.78461 +/- 0.0029
From 18 observations 2020 Aug. 19-Sept. 18; mean residual 0".16

Due to perturbations by the Moon, it will dip below e=1 on October 15th:

Perigee 2020 Nov 18.985389 +/- 0.0761 TT = 23:38:57 (JD 2459172.485389)
Epoch 2020 Oct 15.0 TT = JDT 2459137.5 Find_Orb
M 359.13451846 +/- 0.052 (J2000 equator)
n 0.02473837 +/- 0.0016 Peri. 344.83330 +/- 0.030
a 0.16830513 +/- 0.00725 Node 210.49792 +/- 0.0031
e 0.9989798 +/- 3.96e-5 Incl. 49.43843 +/- 0.026
P 39.84 H 28.3 G 0.15 U 8.4
q 25685.3859 +/- 123 Q 0.33643856 +/- 0.0165
From 18 observations 2020 Aug. 19-Sept. 18; mean residual 0".16

Then it will reach its first perigee on December 1, at which point the asteroid will peak at magnitude 14.0 (geocentric, it'll probably be higher from closer stations):

Perigee 2020 Dec 1.296073 +/- 0.182 TT = 7:06:20 (JD 2459184.796073)
Epoch 2020 Dec 1.3 TT = JDT 2459184.8 Find_Orb
M 0.01992107 +/- 1.3 (J2000 equator)
n 5.07228274 +/- 0.707 Peri. 176.20926 +/- 2.8
a724104.427 +/- 67503 Node 28.69067 +/- 0.45
e 0.9291863 +/- 0.000445 Incl. 34.04654 +/- 0.6
P 70.97d H 28.3 G 0.15 U 12.5
q 51276.5093 +/- 3999 Q 0.00933791 +/- 0.000683
From 18 observations 2020 Aug. 19-Sept. 18; mean residual 0".16

Then it will reach its second perigee on 3 February 2021, slightly higher and a fair bit more uncertain (at this point it will peak at magnitude 15.2):

Perigee 2021 Feb 3.752433 +/- 4.02 TT = 18:03:30 (JD 2459249.252433)
Epoch 2021 Feb 3.75 TT = JDT 2459249.25 Find_Orb
M 359.99300257 +/- 21 (J2000 equator)
n 2.87651669 +/- 0.739 Peri. 162.35558 +/- 8
a 0.00706480 +/- 0.00119 Node 27.66278 +/- 3.4
e 0.7963238 +/- 0.00654 Incl. 29.51607 +/- 0.29
P 125.15d H 28.3 G 0.15 U 12.5
q 215261.182 +/- 20314 Q 0.01269067 +/- 0.0015
From 18 observations 2020 Aug. 19-Sept. 18; mean residual 0".16

At this point, it will make another close approach to the Moon combined with just generally being ejected beyond Earth's hill radius, at which point its eccentricity will quickly increase and it will formally leave earth orbit (e=1) again in late May 2020, nominally May 21:

Perigee 2021 Mar 30.423267 +/- 49.1 TT = 10:09:30 (JD 2459303.923267)
Epoch 2021 May 21.0 TT = JDT 2459355.5 Find_Orb
q857161.590 +/- 556064 (J2000 equator)
H 28.3 G 0.15 Peri. 289.48583 +/- 70
Node 357.23445 +/- 20
e 1.0282245 +/- 0.209 Incl. 30.51023 +/- 16
From 18 observations 2020 Aug. 19-Sept. 18; mean residual 0".16

Running back its close approaches to Earth (half out of curiosity, half to see if it's an old artsat) nothing particularly stands out. With its orbit up to present, it typically made close approaches to Earth every 18 years or so (so 2002, 1984, 1966, 1948, etc):

Perigee 2002 Apr 13.269629 +/- 27.3 TT = 6:28:15 (JD 2452377.769629)
Epoch 2002 Apr 13.28 TT = JDT 2452377.78 Find_Orb
q 0.05376521 +/- 0.00687 (J2000 equator)
H 28.3 G 0.15 Peri. 334.16949 +/- 0.55
Node 185.70790 +/- 12
e 20.1117748 +/- 1.4 Incl. 158.19267 +/- 0.29
From 18 observations 2020 Aug. 19-Sept. 18; mean residual 0".16

Perigee 1984 Apr 6.864302 +/- 20.8 TT = 20:44:35 (JD 2445797.364302)
Epoch 1984 Apr 6.6 TT = JDT 2445797.1 Find_Orb
q 0.05414741 +/- 0.0158 (J2000 equator)
H 28.3 G 0.15 Peri. 337.88104 +/- 0.7
Node 186.47086 +/- 17
e 19.5215486 +/- 2.64 Incl. 157.57057 +/- 55
From 18 observations 2020 Aug. 19-Sept. 18; mean residual 0".16

It did, however, briefly nominally orbit Earth briefly in the 1960s:

Perigee 1966 Nov 9.304185 +/- 12.4 TT = 7:18:01 (JD 2439438.804185)
Epoch 1966 Nov 9.3 TT = JDT 2439438.8 Find_Orb
M 359.98843786 +/- 2100 (J2000 equator)
n 2.76250351 +/- Peri. 224.06218 +/- 51
a 0.00725787 +/- Node 36.30149 +/- 80
e 0.7800141 +/- 17248 Incl. 32.49146 +/- 7
P 130.31d H 28.3 G 0.15 U 17.4
q 238852.490 +/- 2.74e+7 Q 0.01291912 +/- 0.188
From 18 observations 2020 Aug. 19-Sept. 18; mean residual 0".16

Of course as you can see that approach is not very well constrained at all, but we can't rule it out. The only things to launch into heliocentric orbit during that time were (going backwards) Pioneer 6, Venera 3, Venera 2, Zond 3, and Luna 6, all in 1965, with nothing in 1966 or 1967. I think it's safe to say this object *most likely* isn't space debris. Furthermore thanks to its one-month observation arc it's possible to constrain its AMR to 0.023 +/- 0.035 m^2/kg- a very heavy spacecraft if not solid rock.

In summary: This 5-13 meter asteroid will be entering Earth orbit between October 15 this year and ~May 21 next year. It definitely hasn't been close relations with Earth since at least the mid 1960s, so is most likely natural.

~Sam



--
Alan Harris harrisaw@...
4603 Orange Knoll Ave. 818-790-8291
La Canada, CA 91011

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