Asteroids

161989 Cacus help

Last update: 2026-06-27 12:46 UTC

Orbital Properties

Epoch

61200.0

MJD

Orbit type

Apollo

Perihelion (q)

0.883

Aphelion (Q)

1.363

Eccentricity (e)

0.214

Inclination (i)

26.1

deg

Orbit period (P)

434.5

Earth MOID

0.01462

U parameter

0.0

A₂

-8.7

10^-15au/days²

Next Earth close approach

Date

2028-03-07

Nominal distance (from Earth center)

0.14763

22085632

Maximum Brightness

14.7

mag

Risk

Object is not in risk list

Physical Properties

Absolute Magnitude (H)

17.3

mag

Diameter

1126

Taxonomic type

Scomp

Rotation period (T)

3.75

Discovery Information

Discovery Date

1978-02-08

Observatory

European Southern Observatory, La Silla

ORBIT VISUALISATION TOOLS

External links

Proper elements

Epoch

Near present day

Near middle of observation arc

Orbit properties

Epoch
Semimajor Axis
Eccentricity (e)
Inclination (i)
Long. of Ascending Node (Ω)
Arg. of Perihelion (ω)
Mean Anomaly (M)
Perihelion distance
Aphelion distance
Asc. Node-Earth Sep.
Desc. Node-Earth Sep.
MOID
Orbit Period
U parameter

Value

1-sigma variation

Unit

Epoch

Value

61200.0000

1-sigma variation

Unit

MJD

Semimajor Axis

Value

1.122679

1-sigma variation

1.349E-9

Unit

Eccentricity (e)

Value

0.213866

1-sigma variation

2.564E-8

Unit

Inclination (i)

Value

26.0657

1-sigma variation

1.715E-6

Unit

Long. of Ascending Node (Ω)

Value

161.2028

1-sigma variation

5.892E-7

Unit

Arg. of Perihelion (ω)

Value

102.1008

1-sigma variation

5.280E-6

Unit

Mean Anomaly (M)

Value

115.93199

1-sigma variation

3.972E-6

Unit

Perihelion distance

Value

0.882576

1-sigma variation

Unit

Aphelion distance

Value

1.362781

1-sigma variation

Unit

Asc. Node-Earth Sep.

Value

0.130750

1-sigma variation

Unit

Desc. Node-Earth Sep.

Value

0.016262

1-sigma variation

Unit

MOID

Value

0.014621

1-sigma variation

Unit

Orbit Period

Value

434.4918

1-sigma variation

Unit

U parameter

Value

0.0

1-sigma variation

Unit

A₂

Value

-8.65202

1-sigma variation

2.79262

Unit

10^-15au/days²

Covariance Matrix

	a	e	i	Ω	ω	M	A₂
a	1.82008E-18	-2.03093E-19	-4.12539E-18	-4.03346E-17	1.10271E-15	-3.22348E-15	3.15021E-9
e	-2.03093E-19	6.57419E-16	-1.08303E-14	-9.21989E-16	-7.53044E-14	-3.73426E-15	-3.45124E-8
i	-4.12539E-18	-1.08303E-14	2.93995E-12	-8.01606E-13	1.40420E-12	6.58404E-13	5.42002E-7
Ω	-4.03346E-17	-9.21989E-16	-8.01606E-13	3.47215E-13	-1.19629E-12	7.74936E-13	-1.20729E-7
ω	1.10271E-15	-7.53044E-14	1.40420E-12	-1.19629E-12	2.78831E-11	-1.50089E-11	7.36151E-6
M	-3.22348E-15	-3.73426E-15	6.58404E-13	7.74936E-13	-1.50089E-11	1.57753E-11	-6.43902E-6
A₂	3.15021E-9	-3.45124E-8	5.42002E-7	-1.20729E-7	7.36151E-6	-6.43902E-6	7.79871E0

Date of computation: 2026-06-27 12:46 UTC

Note: The ASCII file is in a format suitable for Orbfit input.

Download ASCII file:

Physical properties

Rotation Period
Quality
Amplitude
Rotation Direction
Spinvector L
Spinvector B

Rotational properties

Value

Unit

Source

Rotation Period

Value

3.75

3.754

Unit

Source

[1]

[4]

Quality

Value

Unit

Source

[4]

Amplitude

Value

0.8

1.1

Unit

mag

Source

[4]

[1]

Rotation Direction

Value

Unit

Source

[-]

Spinvector L

Value

187

Unit

Source

[1]

Spinvector B

Value

0.000E0

Unit

Source

[1]

Taxonomy
Taxonomy (all)

Taxonomy

Value

Unit

Source

Taxonomy

Value

Scomp

Unit

Source

[2]

Taxonomy (all)

Value

S;Q

Unit

Source

[3]

Absolute Magnitude (H)
Slope Parameter (G)

H / G

Value

Unit

Source

Absolute Magnitude (H)

Value

17.301

Unit

mag

Source

[5]

Slope Parameter (G)

Value

0.15**

Unit

Source

[5]

Albedo
Diameter

Size and albedo

Value

Unit

Source

Albedo

Value

0.199

Unit

Source

[6]

Diameter

Value

1126

Unit

Source

[6]

Color Index Information

Color Index Information

Value

Unit

Source

Color Index Information

Value

0.88

0.46

Unit

B-V

U-B

Source

[7]

Sightings

Sightings

Value

Unit

Source

Sightings

Value

Visual S

Unit

Source

[8]

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Sources

No.	Name	Additional
[1]	EARN	1.) Lowell Observatory Near-Earth Asteroid Photometric Survey (NEAPS): Paper 4. Skiff, Brian A et al.
[2]	EARN	1.) DeMeo, F.E. et al. (2014) Icarus 227, 112-122. (Mars encounters cause fresh surfaces on some near-Earth asteroids) (contains taxonomic classification of 249 NEAs)
[3]	EARN	1.) Tholen, D.J. (1989) in "Asteroids II" (Eds. R.P.Binzel et al.), Univ.Ariz.Press, Tucson, USA, pp. 1139-1150. 2.) Thomas, C.A. et al. (2014) Icarus 228, 217-246. (Physical characterization of Warm Spitzer-observed near-Earth objects) 3.) DeMeo, F.E. et al. (2014) Icarus 227, 112-122. (Mars encounters cause fresh surfaces on some near-Earth asteroids) (contains taxonomic classification of 249 NEAs)
[4]	EARN	1.) Schuster, H.-E. et al. (1979) Astron. & Astrophys. Suppl. 37, 483-486. (Photoelectric observations of two unusual asteroids - 1978 CA and 1978 DA) 2.) Degewij, J. (1978) Messenger 13, 5. (The sizes of 1978 CA and 1978 DA) 3.) Petr Pravec's Ondrejov NEO Photometric Program Webpage "Prepublished Periods" 4.) Koehn, B.W. et al. (2014) MPB 41, 286-300. (LOWELL OBSERVATORY NEAR-EARTH ASTEROID PHOTOMETRIC SURVEY (NEAPS) - 2009 JANUARY THROUGH 2009 JUNE) (433,1943,3554,5011,5604, 5620,5693,8566,14402,16834,22753,35107,52768,68350,85867, 138883,141052,143651,154244,161989,162385,163758,175706, 194386,203217,207945,208023,212546,256412,2001FE90,2004LV3, 2005BC,2005SG19,2008QT3,2008WL60,2009DE47,2009DO111,2009EP2, 2009FD,2009JM2)
[5]	ESA Aegis	ESA orbit determination and impact monitoring system
[6]	EARN	1.) Mainzer, A. et al. (2011) ApJ 743, 156. (NEOWISE Observations of Near-Earth Objects: Preliminary Results) (albedo and diameters of 428 NEOs) 2.) Binzel, R.P. et al. (2002) in "Asteroids III" (Eds. W.F.Bottke et al.), Univ.Ariz.Press, Tucson, USA, pp. 255-271. (Physical Properties of NEOs) 3.) Nugent, C.R. et al. (2016) Astron. J. 152_63 (12pp) (NEOWISE Reactivation Mission Year Two: Asteroid Diameters and Albedos) (207 NEOs) 4.) Mainzer, A.; Grav, T.; Masiero, J.; Hand, E.; et al. (2011) Astrophys. J. 741, A90. See also Grav 2012b and Masiero 2012.
[7]	EARN	1.) Degewij, J. et al. (1978) I.A.U. Circ. HREF="http://www.cbat.eps.harvard.edu/iauc/03100/03193.html"> 3193. (1978 CA, 1978 DA - U-B, B-V, rotation period, sizes)
[8]	EARN	1.) Michelsen, R. et al. (2006) Astron. Astrophys. 451, 331-337. (Spectroscopy of near-Earth asteroids) (2329, 2002AG29,4957,35107,2002NY31,1917,25916,2002QE15,2002DB4, 2002TB58,1978CA,4954)

Observational Information

Arc Length
Unobserved
Normalized RMS of residuals

Arc Information

Value

Unit

Source

Arc Length

Value

16425

Unit

Source

[1]

Unobserved

Value

1254

Unit

Source

[1]

Normalized RMS of residuals

Value

0.547281

Unit

Source

[1]

Astrometry Summary

First Observation
Last Observation
Total Optical Observations (Discarded)

Optical

Value

Unit

Source

First Observation

Value

1978-02-08.24581

Unit

Source

[2]

Last Observation

Value

2023-01-28.098291

Unit

Source

[2]

Total Optical Observations (Discarded)

Value

1816 (22)

Unit

Source

[1]

Radar Summary

First Observation
Last Observation
Delay (Discarded)
Doppler (Discarded)
Total Optical Observations (Discarded)

Radar

Value

Unit

Source

First Observation

Value

2022-08-24

Unit

Source

[3]

Last Observation

Value

2022-09-02

Unit

Source

[3]

Delay (Discarded)

Value

5 (0)

Unit

Source

[1]

Doppler (Discarded)

Value

0 (0)

Unit

Source

[-]

Total Radar Observations (Discarded)

Value

5 (0)

Unit

Source

[1]

Note: The ASCII file is in a format suitable for Orbfit input.

Sources

No.	Name	Additional
[1]	ESA Aegis	ESA orbit determination and impact monitoring system
[2]	MPC	Minor Planet Center: https://www.minorplanetcenter.net
[3]	JPL Radar Observations	Jet Propulsion Laboratory: https://ssd.jpl.nasa.gov/dat/radar_data_ast.txt

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Final Date: *

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Final Date: *

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Note: Ephemerides requests are limited to a maximum of 1000 points and a final date not exceeding 2040/12/31 00:00.

Close Approaches for 161989 Cacus from 1950 to 2126

Body	Date in UTC	Time uncert. in min	Nominal distance in au	Min. possible distance in au	Distance uncert. in au
EARTH	1953-03-07 23:24	< 1 s	0.1248586	0.1248577	0.0000003
EARTH	1966-09-07 01:47	< 1 min	0.1071072	0.1071056	0.0000005
EARTH	1972-08-28 11:03	< 1 min	0.1521225	0.1521212	0.0000004
EARTH	1978-03-08 05:18	< 1 s	0.1284205	0.1284201	0.0000001
EARTH	1997-09-01 23:44	< 1 s	0.0310729	0.0310724	0.0000002
EARTH	2003-03-07 06:17	< 1 s	0.1802421	0.1802420	0.0000000
EARTH	2009-03-07 03:35	< 1 s	0.1812750	0.1812748	0.0000001
EARTH	2022-09-01 06:53	< 1 s	0.0575393	0.0575393	0.0000000
EARTH	2028-03-07 09:18	< 1 s	0.1476333	0.1476331	0.0000001
EARTH	2041-09-08 17:05	< 1 s	0.1500369	0.1500360	0.0000003
EARTH	2047-08-29 00:23	< 1 min	0.1633202	0.1633189	0.0000004
EARTH	2053-03-08 07:58	< 1 s	0.1144535	0.1144534	0.0000000
EARTH	2066-09-04 23:29	< 1 min	0.0452159	0.0452129	0.0000010
EARTH	2078-03-08 13:09	< 1 s	0.1289361	0.1289357	0.0000001
EARTH	2091-09-05 08:48	< 1 min	0.0464763	0.0464751	0.0000004
EARTH	2103-03-10 02:12	< 1 s	0.1172244	0.1172243	0.0000000
EARTH	2116-09-09 19:48	< 1 min	0.1525663	0.1525654	0.0000003
EARTH	2122-08-31 16:05	< 1 s	0.1094927	0.1094921	0.0000002

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Stationary Points

Ecc. an. ast.	Ecc. an. Earth	Distance in au	Classification
65.32638855	236.85039831	0.01462074	MINIMUM
277.30381287	62.30642048	0.11419866	MINIMUM
350.97291587	147.13797805	0.44625790	SADDLE
170.97349811	332.53098049	0.64081932	SADDLE
357.42009918	336.20645990	1.82096636	SADDLE
188.30812214	167.71108401	2.32340796	MAXIMUM

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