(5645) 1990 SP is an eccentric and tumbling

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

, classified as

near-Earth object A near-Earth object (NEO) is any small Solar System body orbiting the Sun whose closest approach to the Sun ( perihelion) is less than 1.3 times the Earth–Sun distance (astronomical unit, AU). This definition applies to the object's orbit a ...

of the

Apollo group Apollo Education Group, Inc. is an American corporation based in the South Phoenix area of Phoenix, Arizona, with an additional corporate office in Chicago, Illinois. It is privately-owned by a consortium of investors including The Vistria Grou ...

, approximately 1.7 kilometers in diameter. It was discovered on 20 September 1990, by Scottish–Australian astronomer

Robert McNaught Robert H. McNaught (born in Scotland in 1956) is a Scottish-Australian astronomer at the Research School of Astronomy and Astrophysics of the Australian National University (ANU). He has collaborated with David J. Asher of the Armagh Observato ...

at the

Siding Spring Observatory Siding Spring Observatory near Coonabarabran, New South Wales, Australia, part of the Research School of Astronomy & Astrophysics (RSAA) at the Australian National University (ANU), incorporates the Anglo-Australian Telescope along with a coll ...

in Canberra, Australia. Scientists have said that it has a '1 in 364 billion chance' of colliding with the

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

Orbit and classification

The asteroid orbits the Sun at a distance of 0.8–1.9 AU once every 1 years and 7 months (576 days). Its orbit has an

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-Centre (geometry), center, in geometry * Eccentricity (g ...

of 0.39 and an

inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Eart ...

of 14 ° with respect to the

ecliptic The ecliptic or ecliptic plane is the orbital plane of Earth's orbit, Earth around the Sun. It was a central concept in a number of ancient sciences, providing the framework for key measurements in astronomy, astrology and calendar-making. Fr ...

Close approaches

This near-Earth asteroid has an Earth

minimum orbit intersection distance Minimum orbit intersection distance (MOID) is a measure used in astronomy to assess potential close approaches and collision risks between astronomical objects. It is defined as the distance between the closest points of the osculating orbits o ...

of , only slightly above the threshold minimum distance of 19.5 lunar distances (0.05 AU) to make it a

potentially hazardous object A potentially hazardous object (PHO) is a near-Earth object – either an asteroid or a comet – with an orbit that can make close approaches to the Earth and which is large enough to cause significant regional damage in the event of impact. Th ...

. It also makes close approaches to Mars. On 14 April 1969, it passed the Red Planet at only .

Precovery

Published by the

Digitized Sky Survey The Digitized Sky Survey (DSS) is a digital data, digitized version of several photography, photographic astronomical surveys of the night sky, produced by the Space Telescope Science Institute between 1983 and 2006. Versions and source materia ...

(DSS), a first

precovery In astronomy, precovery (short for pre-discovery recovery) is the process of finding the image of a celestial object in images or photographic plates predating its discovery, typically for the purpose of calculating a more accurate orbit. This ha ...

was taken at the discovering observatory in 1974, extending the asteroid's

observation arc In observational astronomy, the observation arc (or arc length) of a Solar System body is the time period between its earliest and latest observations, used for tracing the body's path. It is usually given in days or years. The term is mostly use ...

by 16 years prior to its discovery.

Physical characteristics

The stony

S-type asteroid S-type (stony-type or silicaceous-type) asteroids are asteroids with a spectral type that is indicative of a siliceous (i.e. stony) mineralogical composition, hence the name. They have relatively high density. Approximately 17% of asteroids are ...

is also characterized as a P-type, based on post-cryogenic observations by the

Spitzer Space Telescope The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility (SIRTF), was an infrared space telescope launched in 2003, that was deactivated when operations ended on 30 January 2020. Spitzer was the third space telescope dedicate ...

, while observations at the

NASA Infrared Telescope Facility The NASA Infrared Telescope Facility (NASA IRTF) is a telescope optimized for use in infrared astronomy and located at the Mauna Kea Observatory in Hawaii. It was first built to support the Voyager program, Voyager missions and is now the US n ...

using its SpeX instrument during a follow-up campaign of the Spitzer-observed objects between 2009 and 2012, gave it a C/X/T spectral type.

Rotation

In April 2002, Czech astronomer

Petr Pravec Petr Pravec (born September 17, 1967) is a Czech astronomer and a discoverer of minor planets, born in Třinec, Czech Republic. Pravec is a prolific discoverer of binary asteroids, expert in photometric observations and rotational lightcurves ...

obtained a rotational

lightcurve In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis ...

from a photometric observations, which gave a relatively long

period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

of hours with a brightness variation of 0.7 in

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

(). The observations have also shown that the body is most likely in a tumbling motion.

Diameter and albedo

Estimates for the body's diameter range from 1.6 to 2.2 kilometers with an

albedo Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...

for its surface between 0.06 and 0.12, according to observations made by the

NEOWISE Wide-field Infrared Survey Explorer (WISE, observatory code C51, Explorer 92 and MIDEX-6) was a NASA infrared astronomy space telescope in the Explorers Program launched in December 2009.. . WISE discovered thousands of minor planets and nu ...

mission of NASA's

Wide-field Infrared Survey Explorer Wide-field Infrared Survey Explorer (WISE, List of observatory codes, observatory code C51, Explorer 92 and MIDEX-6) was a NASA infrared astronomy Space observatory, space telescope in the Explorers Program launched in December 2009.. . WISE L ...

and by the Spitzer Space Telescope. The ''Collaborative Asteroid Lightcurve Link'' takes the revised WISE data – an albedo of 0.0872 and a diameter of 1.65 kilometers – as the best of all available results.

References

External links

Asteroid Lightcurve Database (LCDB)
query form

)
Dictionary of Minor Planet Names
Google books

– Observatoire de Genève, Raoul Behrend * * * {{DEFAULTSORT:1990 SP 005645 Discoveries by Robert H. McNaught 19900920