SpaceAtlas Space Object Data
Cacus
NASA JPL SBDB · 161989

Cacus

Cacus belongs to the Apollo group of near-Earth asteroids, whose orbits cross the path of Earth; with a semi-major axis of 1.123 AU it takes 1.19 yr to circle the Sun.

Apollo Observations: 1,798
Encyclopedia excerpt
161989 Cacus is a stony asteroid, classified as a near-Earth object and a potentially hazardous asteroid of the Apollo group, approximately 1 kilometer in diameter. It was discovered on 8 February 1978, by German astronomer Hans-Emil Schuster at ESO's La Silla Observatory in northern Chile. Its orbit is confined between Venus and Mars.
Orbital Period · P
1.19 yr
v(q)
34.9 km/s
v(Q)
22.6 km/s
Diameter · ≈
1.23 km
TJ
5.45
Eccentricity · e
0.2139

Orbit and dynamics

Between its closest point (0.883 AU) and its farthest (1.363 AU), the heliocentric distance changes by 0.48 AU over every revolution.

One full revolution takes 1.19 yr (435 days), computed from the semi-major axis of 1.123 AU.

An eccentricity of 0.214 makes the orbit moderately elongated.

A steep inclination of 26.07° carries it well above and below the ecliptic plane.

By the vis-viva equation its orbital speed rises to 34.9 km/s at perihelion and falls to 22.6 km/s at aphelion.

Because q < 1 AU and Q > 1 AU, this orbit geometrically intersects the region of Earth's orbit.

Size and surface

The measured diameter is 1.9 km, a value from direct size determination rather than from brightness alone.

Its geometric albedo of 0.09 indicates a very dark, carbonaceous-type surface.

Observation record and orbit quality

Astrometry from 1,798 individual observations underpins this orbit; the fit leaves an RMS residual of 0.4733 arcseconds.

Condition code U = 0 means the orbit is very well determined, leaving only a small uncertainty in the future ephemeris.

About these computed values

Orbital periods, perihelion and aphelion speeds, and diameter estimates on this page are computed by SpaceAtlas from the JPL SBDB orbital elements. They are derived quantities, not values copied from the source catalogue.

Orbital Parameters

Semi-Major Axis
1.123 AU
Eccentricity
0.2139
Perihelion
0.883 AU
Aphelion
1.36321 AU
Inclination
26.07°
Orbital Period
— yr
Epoch
2461200.5
Mean Anomaly
115.93°

Orbit diagram

The Sun sits at the focus (orange). Earth's orbit is the grey circle at 1 AU. The red dot marks the object's position at the catalog epoch.

3D orbit (interactive)

Drag to rotate; scroll or pinch to zoom. The Sun is at the focus (orange), Earth's orbit is the grey ring at 1 AU, and the red dot marks the object's current position.

Close approaches

No close approaches to Earth are currently on record for this object.

Physical Parameters

Diameter
1.9 km
Albedo
0.09
Density
— g/cm³
Rotation Period
— h
Absolute Magnitude
17.31

Orbit Quality

RMS
0.47326
Condition
0
Orbit ID
—
Data source: NASA JPL Small-Body Database . Orbital periods, perihelion and aphelion speeds, and diameter estimates on this page are computed by SpaceAtlas from the JPL SBDB orbital elements. They are derived quantities, not values copied from the source catalogue.

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