Asteroids with Satellites Database--Johnston's Archive

(65803) Didymos and Dimorphos

compiled by Wm. Robert Johnston
last updated 9 October 2021

--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: NEA, Apollo (PHA)


orbital data, primary (osculating elements) [JPL] :
semimajor axis a: 1.6443941966 AU
orbital period P: 2.1087112032 yr
(= 770.206767 d)
eccentricity e: 0.3836974806
perihelion distance q: 1.0134442863 AU
aphelion distance Q: 2.275344107 AU
inclination i: 3.4077057°
argument of perihelion ω: 319.318868°
ascending node Ω: 73.199435°
mean anomaly M: 136.6502278°
perihelion passage TP: 2020 Sep 11.6418607
Epoch: 2021 Jul 01
data arc: 1996-2021 (1046 obs.)
Earth MOID: 0.0401437 AU
Jupiter Tisserand invariant TJ: 4.201


orbital data, secondary:
binary dynamical type:A [P07f]
semimajor axis as: 1.19 ± 0.03 km [N20b]
separation/primary radius as/rp:3.1 [*D]
separation/Hill radius as/rH:0.017 [*D]
orbital period Ps: 0.4971 ± 0.0004 d [N20b]
eccentricity es: <0.05 [N20b]
normalized ang. mom. αL: 1.16 [P07f]

other data, system (combined):
absolute mag. H: 18.07 [MPC]
17.7 ± 0.03 [K04a]
slope parameter G: (0.15) [*A]
effective diameter dE: 0.77 ± 0.1 km [*D]
geometric albedo: 0.16 ± 0.04 [P06b]
color index U-B: 0.211 [K04a]
color index B-V: 0.795 [K04a]
color index V-R:0.458 ± 0.009 [K04a]
color index B-R:1.253 [K04a]
color index V-I:0.82 ± 0.009 [K04a]
taxonomic type: Xk (SMASSII) [JPL]
mass m: 5.4x1011 ± 4x1010 kg [N20b]
density ρ: 2.17 ± 0.35 g/cm3[N20b]
Hill radius rH: 68 km [*D]

other data, primary:
diameter dp: 0.78 ± 0.03 km [N20b]
dimensions :0.832 x 0.838 x 0.786 km [N20b]
axial ratios a/b, b/c:1.01, 1.06 [*D]
volume :0.249± 0.03 km3 [N20b]
rotation period RPp: 2.26 ± 0.0001 h [N20b]
amplitude in mag., rotational ΔM: 0.24 [W14e]
pole direction Β, λ: 310 ± 20° , -84 ± 20° [N20b]


other data, secondary:
diameter ds: 0.17 ± 0.03 km [*D]
diameter ratio ds/dp: 0.22 ± 0.02 [P06b]
component mag. difference ΔM: 3.29 ± 0.20 [*D]
rotation period RPs: ?

-- (65803) Didymos and Dimorphos --discovery and notes:

Primary discovered 1996 Apr 11 from Kitt Peak Observatory, Arizona, USA by Spacewatch Program. Alternate designation(s): 1996 GT . Permanent number assigned 2003 Sep 10.

Named 2004 Jul 13 for the Greek word for "twin" [MPC052326].

Companion discovered 2003 Nov 20 by P. Pravec, L. A. M. Benner, M. C. Nolan, P. Kusnirak, D. Pray, J. D. Giorgini, R. F. Jurgens, S. J. Ostro, J.-L. Margot, C. Magri, A. Grauer, and S. Larson using lightcurve observations from Ondrejov Observatory, Czech Republic; Jet Propulsion Laboratory; National Astronomy and Ionosphere Center; Ondrejov Observatory, Czech Republic; Greene, Rhode Island, USA; University of California, Los Angeles, California, USA; University of Maine at Farmington, Maine, USA; University of Arkansas at Little Rock, Arkansas, USA; University of Arizona, Arizona, USA. Announced 2003 Nov 28 [P03b]. Permanent designation I Dimorphos, assigned 2020 Jun 23; named for the Greek word for “having two forms” [MPEC2020M83].

Shape model published [N20b].

--Links, more technical:

--Links, less technical:

--Links to ADS abstracts:


© 2003-2014, 2021 by Wm. Robert Johnston.
Last modified 9 October 2021.
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