Asteroids with Satellites Database--Johnston's Archive
(99918)
1998 SQ2
compiled by Wm. Robert Johnston
last updated
23 September 2026
--Orbital and physical data--
(See this page for definitions of quantities; source codes in brackets, see this link for full references; *A, *D, and *E indicate assumed, derived, and estimated values, respectively.)
dynamical type, primary:
main belt asteroid
orbital data, primary (osculating elements)
[JPL]
: |
semimajor axis a: |
2.53660630774 AU
| |
orbital period P: |
4.0400599013 yr
(= 1475.63187895 d)
| |
eccentricity e: |
0.3165962377
| |
perihelion distance q: |
1.7335262943 AU
| |
aphelion distance Q: |
3.33968632117 AU
| |
inclination i: |
16.667994965°
| |
argument of perihelion ω: |
38.18018359°
| |
ascending node Ω: |
296.04930841°
| |
mean anomaly M: |
336.80989507°
| |
perihelion passage TP: |
2026 Sep 12.05571698
| |
Epoch: |
2026 Jun 09
| |
data arc: |
1996-2026
(2819 obs.)
| |
Earth MOID: |
0.748464 AU
| |
Jupiter Tisserand invariant TJ: |
3.320
|
orbital data, secondary:
|
semimajor axis as: |
11
km
[*E]
| |
separation/primary radius as/rp: | 5.9 [*E] | |
separation/Hill radius as/rH: | 0.021 [*E] | |
orbital period Ps: |
1.5038
± 0.0017
d [D26b]
| |
eccentricity es: |
?
| |
normalized ang. mom. αL: |
?
|
|
other data, system (combined):
|
absolute mag. H: |
14.75
[MPC]
| |
slope parameter G: |
(0.15) [*A]
| |
effective diameter dE: |
3.84
± 0.02
km [M19a]
| |
geometric albedo: |
0.149
± 0.028
[M19a]
| |
color index U-B: |
?
| |
color index B-V: |
?
| |
taxonomic type: |
| |
mass m: |
?
| |
density ρ: |
(1.6
g/cm3) [*A]
| |
Hill radius rH: |
490 km [*E]
|
other data, primary:
|
diameter dp: |
3.60
± 0.02
km [*D]
| |
dimensions : | ~3.9 x ~3.3 km [*E] | |
axial ratios a/b, b/c: | 1.2, ? [*E] | |
rotation period RPp: |
3.6815
± 0.0004
h [D26b]
| |
amplitude in mag., rotational ΔM: |
0.16
[D26b]
| |
amplitude in mag., mutual events ΔM: | 0.14 [D26b] | |
pole direction Β, λ: |
?
,
?
|
other data, secondary:
|
diameter ds: |
>1.33
km [*D]
| |
diameter ratio ds/dp: |
>0.37
[D26b]
| |
component mag. difference ΔM: |
<2.16
[*D]
| |
rotation period RPs: |
?
| |
|
|
--
(99918) 1998 SQ2
--discovery and notes:
Primary discovered
1998 Sep 18
from
Catalina Station, Arizona, USA
by
Catalina Sky Survey.
Alternate designation(s):
1996 AM20.
Linked to prediscovery observations from 1996 Jan 14.
Permanent number assigned 2005 Jun 22.
Companion discovered
2026 Jul 25
by R. Durkee, P. Pravec, P. Kusnirak, V. Benishek, A. Leroy, S. Bouley, and A. Rajaonarivelo
using
lightcurve
observations from Shed of Science South Observatory, Pontotoc, Texas, USA; Sopot Observatory, Serbia; Observatory of Besely, Ecole du Monde, Madagascar.
Announced
2026 Sep 23 [D26b].
--Links, more technical:
--Links, less technical:
--Links to ADS abstracts:
©
2026
by Wm. Robert Johnston.
Last modified
23 September 2026.
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