(also written 2015 SO2) is an

Aten Aten also Aton, Atonu, or Itn ( egy, jtn, ''reconstructed'' ) was the focus of Atenism, the religious system established in ancient Egypt by the Eighteenth Dynasty pharaoh Akhenaten. The Aten was the disc of the sun and originally an aspect of ...

asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...

that is a temporary

horseshoe A horseshoe is a fabricated product designed to protect a horse hoof from wear. Shoes are attached on the palmar surface (ground side) of the hooves, usually nailed through the insensitive hoof wall that is anatomically akin to the human toen ...

companion to the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

, the ninth known Earth horseshoe librator. Prior to its most recent close encounter with our planet (2015 September 30) it was an

Apollo asteroid The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, discovered by German astronomer Karl Reinmuth in the 1930s. They are Earth-crossing asteroids that have an orbital semi-major axis greater than that of the Earth ...

Discovery

was discovered on 21 September 2015 by B. Mikuž observing with the 0.6-m f/3.3 Cichocki telescope at the

Črni Vrh Observatory The Črni Vrh Observatory ( sl, Observatorij Črni Vrh, IAU code: 106) is an astronomical observatory located in western Slovenia, close to the settlement of Črni Vrh, near the town of Idrija. The current observatory was built in 1985 and stan ...

Slovenia Slovenia ( ; sl, Slovenija ), officially the Republic of Slovenia (Slovene: , abbr.: ''RS''), is a country in Central Europe. It is bordered by Italy to the west, Austria to the north, Hungary to the northeast, Croatia to the southeast, an ...

.Discovery MPEC
/ref>
/ref> As of 30 November 2015, it has been observed 84 times with an

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 ...

of 9 days.

Orbit and orbital evolution

is currently an

Aten asteroid The Aten asteroids are a dynamical group of asteroids whose orbits bring them into proximity with Earth. By definition, Atens are Earth-crossing asteroids . The group is named after 2062 Aten, the first of its kind, discovered on 7 Januar ...

(Earth-crossing but with a period less than a year). Its semi-major axis (currently 0.999115 AU) is similar to that of Earth (0.99957 AU), but it has a relatively low eccentricity (0.108105) and moderate orbital inclination (9.181°). Gravitational interaction with Earth causes its orbit to change so that its average period is one year. It alternates between being an Aten asteroid and being an Apollo asteroid, changing dynamical status every 113 years approximately. As of 30 November 2015, this object is the 14th known Earth

co-orbital In astronomy, a co-orbital configuration is a configuration of two or more astronomical objects (such as asteroids, moons, or planets) orbiting at the same, or very similar, distance from their primary, i.e. they are in a 1:1 mean-motion resonan ...

and the 9th known object following a horseshoe path with respect to our planet. Its orbital evolution characterized by alternating horseshoe and

quasi-satellite A quasi-satellite is an object in a specific type of co-orbital configuration (1:1 orbital resonance) with a planet (or dwarf planet) where the object stays close to that planet over many orbital periods. A quasi-satellite's orbit around the Sun t ...

episodes.

Physical properties

With an

absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse Logarithmic scale, logarithmic Magnitude (astronomy), astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent mag ...

of 23.9, it has a diameter in the range 50–111 meters (for an assumed

albedo Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...

range of 0.04–0.20, respectively).

Notes

* This is assuming an albedo of 0.20–0.04.

References

;Further reading
Understanding the Distribution of Near-Earth Asteroids
Bottke, W. F., Jedicke, R., Morbidelli, A., Petit, J.-M., Gladman, B. 2000, ''Science'', Vol. 288, Issue 5474, pp. 2190–2194.
A Numerical Survey of Transient Co-orbitals of the Terrestrial Planets
Christou, A. A. 2000, ''Icarus'', Vol. 144, Issue 1, pp. 1–20.
Debiased Orbital and Absolute Magnitude Distribution of the Near-Earth Objects
Bottke, W. F., Morbidelli, A., Jedicke, R., Petit, J.-M., Levison, H. F., Michel, P., Metcalfe, T. S. 2002, ''Icarus'', Vol. 156, Issue 2, pp. 399–433.
Transient co-orbital asteroids
Brasser, R., Innanen, K. A., Connors, M., Veillet, C., Wiegert, P., Mikkola, S., Chodas, P. W. 2004, ''Icarus'', Vol. 171, Issue 1, pp. 102–109.
From horseshoe to quasi-satellite and back again: the curious dynamics of Earth co-orbital asteroid 2015 SO₂
de la Fuente Marcos, C., de la Fuente Marcos, R. 2016, ''Astrophysics and Space Science'', Vol. 361, Issue 1, article 16 (10 pp).

External links