Asteroids

6491 1991OA help

Last update: 2026-07-30 09:40 UTC

Orbital Properties

Epoch

61200.0

MJD

Orbit type

Amor

Perihelion (q)

1.021

Aphelion (Q)

3.982

Eccentricity (e)

0.592

Inclination (i)

6.2

deg

Orbit period (P)

1445.0

Earth MOID

0.03773

U parameter

0.0

Next Earth close approach

Date

2086-08-01

Nominal distance (from Earth center)

0.09001

13465604

Maximum Brightness

15.9

mag

Risk

Object is not in risk list

Physical Properties

Absolute Magnitude (H)

18.7

mag

Diameter

700

Taxonomic type

Rotation period (T)

2.690

Discovery Information

Discovery Date

1991-07-16

Observatory

Palomar Mountain

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

2.501429

1-sigma variation

2.682E-8

Unit

Eccentricity (e)

Value

0.591813

1-sigma variation

3.242E-8

Unit

Inclination (i)

Value

6.1574

1-sigma variation

7.362E-6

Unit

Long. of Ascending Node (Ω)

Value

299.9757

1-sigma variation

0.0001

Unit

Arg. of Perihelion (ω)

Value

326.3202

1-sigma variation

0.0001

Unit

Mean Anomaly (M)

Value

289.66627

1-sigma variation

0.00001

Unit

Perihelion distance

Value

1.021051

1-sigma variation

Unit

Aphelion distance

Value

3.981807

1-sigma variation

Unit

Asc. Node-Earth Sep.

Value

0.072854

1-sigma variation

Unit

Desc. Node-Earth Sep.

Value

2.217863

1-sigma variation

Unit

MOID

Value

0.037729

1-sigma variation

Unit

Orbit Period

Value

1445.0424

1-sigma variation

Unit

U parameter

Value

0.0

1-sigma variation

Unit

Covariance Matrix

	a	e	i	Ω	ω	M
a	7.19232E-16	-9.02806E-17	-1.45488E-15	-5.75774E-14	-1.30597E-13	-1.43068E-13
e	-9.02806E-17	1.05082E-15	-5.06327E-14	-4.19062E-13	4.33497E-13	-1.08860E-14
i	-1.45488E-15	-5.06327E-14	5.41929E-11	2.40679E-10	-2.40561E-10	7.19001E-12
Ω	-5.75774E-14	-4.19062E-13	2.40679E-10	4.37050E-9	-4.34443E-9	6.08319E-11
ω	-1.30597E-13	4.33497E-13	-2.40561E-10	-4.34443E-9	4.37852E-9	-4.61018E-11
M	-1.43068E-13	-1.08860E-14	7.19001E-12	6.08319E-11	-4.61018E-11	7.90992E-11

Date of computation: 2026-07-30 09:40 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

2.690

Unit

Source

[1]

Quality

Value

Unit

Source

[1]

Amplitude

Value

0.09

Unit

mag

Source

[1]

Rotation Direction

Value

Unit

Source

[-]

Spinvector L

Value

Unit

Source

[-]

Spinvector B

Value

Unit

Source

[-]

Taxonomy
Taxonomy (all)

Taxonomy

Value

Unit

Source

Taxonomy

Value

Unit

Source

[-]

Taxonomy (all)

Value

Unit

Source

[-]

Absolute Magnitude (H)
Slope Parameter (G)

H / G

Value

Unit

Source

Absolute Magnitude (H)

Value

18.719

18.77

Unit

mag

Source

[2]

[3]

Slope Parameter (G)

Value

0.15**

Unit

Source

[2]

Albedo
Diameter

Size and albedo

Value

Unit

Source

Albedo

Value

medium

Unit

Source

[4]

Diameter

Value

700

Unit

Source

[4]

Color Index Information

Color Index Information

Value

Unit

Source

Color Index Information

Value

0.7

Unit

B-V

Source

[5]

Sightings

Sightings

Value

Unit

Source

Sightings

Value

Unit

Source

[-]

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Sources

No.	Name	Additional
[1]	EARN	1.) Erikson, A. et al. (2000) Icarus 147, 487-497. (The Near-Earth Objects Follow-Up Program III: 32 Lightcurves for 12 Objects from 1992 to 1995) (433,1917,2368,3753,4769, 4953,6491, 1995 EK1, 1995 FJ; 5738,7467,1995 LH) 2.) Harris(JPL), A.W. unpublished data
[2]	ESA Aegis	ESA orbit determination and impact monitoring system
[3]	EARN	1.) Erikson, A. et al. (2000) Icarus 147, 487-497. (The Near-Earth Objects Follow-Up Program III: 32 Lightcurves for 12 Objects from 1992 to 1995) (433,1917,2368,3753,4769, 4953,6491, 1995 EK1, 1995 FJ; 5738,7467,1995 LH)
[4]	EARN	1.) 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)
[5]	EARN	1.) Veeder, G.J. & E.F. Tedesco (1991) I.A.U. Circ. HREF="http://www.cbat.eps.harvard.edu/iauc/05300/05323.html"> 5323. (1991 OA - B-V)

Observational Information

Arc Length
Unobserved
Normalized RMS of residuals

Arc Information

Value

Unit

Source

Arc Length

Value

11898

Unit

Source

[1]

Unobserved

Value

1121

Unit

Source

[1]

Normalized RMS of residuals

Value

0.596769

Unit

Source

[1]

Astrometry Summary

First Observation
Last Observation
Total Optical Observations (Discarded)

Optical

Value

Unit

Source

First Observation

Value

1991-03-18.58486

Unit

Source

[2]

Last Observation

Value

2023-10-14.373049

Unit

Source

[2]

Total Optical Observations (Discarded)

Value

204 (2)

Unit

Source

[1]

Radar Summary

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

Radar

Value

Unit

Source

First Observation

Value

Unit

Source

[-]

Last Observation

Value

Unit

Source

[-]

Delay (Discarded)

Value

0 (0)

Unit

Source

[-]

Doppler (Discarded)

Value

0 (0)

Unit

Source

[-]

Total Radar Observations (Discarded)

Value

0 (0)

Unit

Source

[-]

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

Filters

Initial Date: *

Final Date: *

Normalised Only accepted

Max residual (arcsec):

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Computation parameters

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Initial Date: *

Final Date: *

Output option:

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Time step:*

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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 6491 1991OA 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	1963-06-08 15:05	2.9	0.1179952	0.1179830	0.0000041
EARTH	1967-07-08 11:24	1.5	0.1124283	0.1124143	0.0000046
EARTH	1971-07-04 00:30	1.2	0.0925030	0.0924971	0.0000019
EARTH	1975-07-05 07:01	< 1 min	0.0988220	0.0988173	0.0000016
EARTH	1979-07-20 02:38	< 1 min	0.1547518	0.1547450	0.0000023
EARTH	1983-07-06 17:09	< 1 min	0.0738694	0.0738680	0.0000005
EARTH	1987-06-22 03:51	< 1 min	0.0715009	0.0715002	0.0000002
EARTH	1991-07-04 22:56	< 1 min	0.0574918	0.0574915	0.0000001
EARTH	1995-05-27 01:42	< 1 min	0.1054872	0.1054866	0.0000002
EARTH	2086-08-01 00:46	5.7	0.0900120	0.0899055	0.0000355
EARTH	2121-08-14 10:57	1.7	0.1168603	0.1168282	0.0000107

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Stationary Points

Ecc. an. ast.	Ecc. an. Earth	Distance in au	Classification
9.42919808	180.48272943	0.03772923	MINIMUM
0.18105392	342.11988525	2.00447260	SADDLE
179.96190024	342.09977792	2.99982239	SADDLE
180.18545782	162.21459520	4.99640368	MAXIMUM

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MOID Plots

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