SpaceAtlas Space Object Data
NASA JPL SBDB · 1998 US18

1998 US18

1998 US18 belongs to the Apollo group of near-Earth asteroids, whose orbits cross the path of Earth; with a semi-major axis of 2.602 AU it takes 4.20 yr to circle the Sun.

Apollo Observations: 68
Orbital Period · P
4.20 yr
v(q)
42.2 km/s
v(Q)
8.1 km/s
Diameter · ≈
0.23 km
TJ
3.02
Eccentricity · e
0.6783

Orbit and dynamics

Between its closest point (0.837 AU) and its farthest (4.367 AU), the heliocentric distance changes by 3.53 AU over every revolution.

One full revolution takes 4.20 yr (1,533 days), computed from the semi-major axis of 2.602 AU.

The high eccentricity (0.678) produces a strongly elongated orbit, so the object spends most of its time far from the Sun.

The orbital plane is tilted 9.67° relative to the ecliptic.

By the vis-viva equation its orbital speed rises to 42.2 km/s at perihelion and falls to 8.1 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

No direct size measurement is available; from an absolute magnitude of H = 20.9 and an assumed geometric albedo of 0.14, the diameter works out to roughly 0.23 km.

Observation record and orbit quality

Astrometry from 68 individual observations underpins this orbit; the fit leaves an RMS residual of 0.4858 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
2.602 AU
Eccentricity
0.6783
Perihelion
0.837 AU
Aphelion
4.366937 AU
Inclination
9.67°
Orbital Period
— yr
Epoch
2461200.5
Mean Anomaly
215.35°

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

Predicted close approaches to Earth, from NASA's Center for Near-Earth Object Studies (CNEOS).

Date (UTC)Miss distanceVelocity
2036-May-21 07:07 0.415732 AU
62192682 km
27.19 km/s
2040-Oct-19 11:00 0.078612 AU
11760144 km
19.09 km/s
2061-Jul-14 17:38 0.218348 AU
32664350 km
12.58 km/s

Distances in astronomical units (AU) and kilometres. Source: NASA/JPL CNEOS Close Approach Data API.

Physical Parameters

Diameter
— km
Albedo
—
Density
— g/cm³
Rotation Period
— h
Absolute Magnitude
20.9

Orbit Quality

RMS
0.4858
Condition
0
Orbit ID
—
Data source: NASA JPL Small-Body Database · NASA CNEOS. 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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