SiMDA»Main

Summary for : (24) Themis

Dyn	T.T	T.B	T T.L B	T.D	Density (g/cm^3)	Δρ/ρ	Diameter (km)	ΔD/D	Mass (kg)	ΔM/M	Ref	Avg.M
MBA	C	B	B \| C	C	1.81 ± 0.73 (C)	40 %	183.8 ± 11.4	6.2 %	5.89e+18 ± 2.12e+18	36 %	S	EVM
MBA	C	B	B \| C	C	2.43 ± 0.83 (C)	34 %	180.0 ± 16.0	8.9 %	7.42e+18 ± 1.60e+18	22 %	S	w.avg
MBA	C				1.81 ± 0.67 (C)	37 %	183.8 ± 11.4	6.2 %	5.89e+18 ± 1.91e+18	32 %	C	?

Average asteroid densities (g/cm^3):
C = 1.3 ± 0.6, B = 2.4 ± 0.5, S = 2.7 ± 0.5, M = 3.5 ± 1.0, P = 2.8 ± 1.6, X = 1.9 ± 0.8, Xc = 4.9 ± 0.9, Xk = 4.2 ± 0.7 (Ref)

Object is a Gaia target for mass determination !

Additional resources:

3D Model | JPL New Horizons | Minor Planet Center | Wikipedia (these auto-generated links might not work)

Note: The density estimates have been ranked from (A) to (E), corresponding to the relative error: (B) less than 20%, (C) between 20 and 50%, (D) between 50 and 100%, and (E) more than 100%. (A) stands for (presumably) reliable estimates (accuracy better than 20%), based on more than 5 mass estimates and 5 diameter estimates, or a spacecraft encounter. Apparently unrealistic densities (ρ > 8) are tagged with (X).

EVM: average by using the Expected Value Method (Ref). w.avg: weighted average (with w = 1/err^2).

T.T: Tholen Tax Class. T.B: Bus & Binzel Tax Class. T T.L: S3OS2 Lazarro (Tholen) Tax Class. T.L B: S3OS2 Lazarro (Bus & Binzel) Tax Class. T.D: DeMeo Tax Class.

Ref: S = SiMDA, C = Carry (2012)

Diameter estimates

Designation	Diameter / Err (km)	ΔD/D	Method	Year	Ref	N	χ²	Use
(24) Themis	176.80 ± 2.29	1.3 %	TPM	2011	D83		9.37	1
(24) Themis	202.33 ± 6.05	3.0 %	NEATM	2011	D72		9.37	2

plot, average diameter and derived density

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Notes (N):
1: This estimate is discarded for the average diameter (and derived density) calculation in Carry (2012).
2: This estimate is discarded for the average diameter (and derived density) calculation in SiMDA (catalog).

NEATM : Near-Earth Asteroid Thermal Model. TPM : Thermophysical Model.

EVM diam. average D = (183.8 ± 11.39) km (ΔD/D = 6%, SNR = 16.13) Derived bulk density ρ = (1.81 ± 0.73) g/cm³ (Δρ/ρ = 40%, SNR = 2.5)

References

D72	(2011):	Masiero, J.R., Mainzer, A.K., Grav, T., Bauer, J.M., Cutri, R.M., Dailey, J., Eisenhardt, P.R.M., McMillan, R.S., Spahr, T.B., Skrutskie, M.F., Tholen, D., Walker, R.G., Wright, E.L., DeBaun, E., Elsbury, D., Gautier, IV, T., Gomillion, S., Wilkins, A., 2011. Main Belt Asteroids with WISE/NEOWISE. I. Preliminary Albedos and Diameters. Astrophysical Journal 741, 68.
D83	(2011):	Usui, F., Kuroda, D., Müller, T.G., Hasegawa, S., Ishiguro, M., Ootsubo, T., Ishihara, D., Kataza, H., Takita, S., Oyabu, S., Ueno, M., Matsuhara, H., Onaka, T., 2011. Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey. Publications of the Astronomical Society of Japan 63, 1117–1138.

Mass estimates

Designation	Mass / Err (kg)	ΔM/M	Method	Year	Ref	N	χ²	Use
(24) Themis	5.75e+18 ± 2.51e+18	44 %	Deflec	1997	M12		0.00	1
(24) Themis	1.99e+18 ± 3.98e+18	200 %	Ephem	2007	M62	2	0.96	2
(24) Themis	1.13e+19 ± 4.28e+18	38 %	Deflec	2008	M71	2	1.59	3
(24) Themis	6.04e+18 ± 6.04e+17	10 %	Ephem	2009	M86		0.06	4
(24) Themis	5.62e+18 ± 3.78e+18	67 %	Ephem	2010	M93		0.01	5
(24) Themis	3.96e+18 ± 2.81e+18	71 %	Deflec	2011	M97		0.47	6
(24) Themis	4.78e+18 ± 1.84e+18	38 %	Deflec	2011	M97		0.37	7
(24) Themis	6.16e+18 ± 1.85e+18	30 %	Deflec	2011	M97		0.02	8
(24) Themis	5.25e+18 ± 2.34e+18	45 %	Deflec	2011	M97		0.08	9
(24) Themis	1.06e+19 ± 4.57e+18	43 %	Ephem	2011	M100	2	1.06	10
(24) Themis	1.01e+19 ± 5.97e+17	6 %	OrbFitN	2014	M123	2	50.56	11
(24) Themis	3.73e+18 ± 1.57e+18	42 %	Ephem	2019	M126		1.90	12

plot, average mass and derived density

All

Notes (N):
1: This estimate is discarded for the average mass (and derived density) calculation in Carry (2012).
2: This estimate is discarded for the average mass (and derived density) calculation in SiMDA (catalog).
3: This estimate is an average of individual solutions listed before under the same reference (e.g. M125).

Deflec : Orbital deflection (close encounter) of one or several test asteroids (classical LSQ). Ephem : Planetary ephemeris solution. OrbFitN : Simultaneous multi-asteroid astrometric orbit solution (similar to 'Ephem').

EVM mass average M = (5.895 ± 2.117) × 10¹⁸ kg (ΔM/M = 36%, SNR = 2.8) Derived bulk density ρ = (1.81 ± 0.73) g/cm³ (Δρ/ρ = 40%, SNR = 2.5)

References

M12	(1997):	Lopez Garcia, A., Medvedev, Y.D., Morano Fernendez, J.A., 1997. Using Close Encounters of Minor Planets for the Improvement of their Masses, in: I. M. Wytrzyszczak, J. H. Lieske, & R. A. Feldman (Ed.), IAU Colloq. 165: Dynamics and Astrometry of Natural and Artificial Celestial Bodies, p. 199.
M62	(2007):	Aslan, Z., Gumerov, R., Hudkova, L., Ivantsov, A., Khamitov, I., Pinigin, G., 2007. Mass Determination of Small Solar System Bodies with Ground-based Observations, in: O. Demircan, S. O. Selam, & B. Albayrak (Ed.), Solar and Stellar Physics Through Eclipses, pp. 52–58.
M71	(2008):	Baer, J., Chesley, S.R., 2008. Astrometric masses of 21 asteroids, and an integrated asteroid ephemeris. Celestial Mechanics and Dynamical Astronomy 100, 27–42.
M86	(2009):	Folkner, W.M., Williams, J.G., Boggs, D.H., 2009. The planetary and lunar ephemeris de 421. IPN Progress Report 42, 1–34.
M93	(2010):	Fienga, A., Manche, H., Kuchynka, P., Laskar, J., Gastineau, M., 2010. INPOP10a. Scientific Notes.
M97	(2011):	Zielenbach, W., 2011. Mass Determination Studies of 104 Large Asteroids. Astronomical Journal 142, 120–128.
M100	(2011):	Fienga, A., Kuchynka, P., Laskar, J., Manche, H., Gastineau, M., 2011. Asteroid mass determinations with INPOP planetary ephemerides. EPSC-DPS Joint Meeting 2011 , 1879.
M123	(2014):	Goffin, E., 2014. Astrometric asteroid masses: a simultaneous determination. Astronomy & Astrophysics, Volume 565, id.A56, 8 pp.
M126	(2019):	Fienga, A., et. al, 2019. INPOP19a planetary ephemeris. Notes Scientifiques et Techniques de l'Institut de mécanique céleste,

Size, Mass and Density of Asteroids (SiMDA)

Summary for : (24) Themis

Diameter estimates

Mass estimates