Yarkovsky effect
Encyclopedia
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s, which carry momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
. It is usually considered in relation to meteoroid
Meteoroid
A meteoroid is a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteoroid reaches the ground and survives impact, then it is called a meteorite...
s or small asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s (about 10 cm to 10 km in diameter), as its influence is most significant for these bodies.
The effect was discovered by the Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
n civil engineer Ivan Osipovich Yarkovsky
Ivan Osipovich Yarkovsky
Ivan Osipovich Yarkovsky was a Russian-Polish civil engineer. He worked for a Russian railway company and was obscure in his own time. Beginning in the 1970s, long after Yarkovsky's death, his work on the effects of thermal radiation on small objects in the solar system was developed into the...
(1844–1902), who worked on scientific problems in his spare time. Writing in a pamphlet around the year 1900, Yarkovsky noted that the diurnal heating of a rotating object in space would cause it to experience a force that, while tiny, could lead to large long-term effects in the orbits of small bodies, especially meteoroid
Meteoroid
A meteoroid is a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteoroid reaches the ground and survives impact, then it is called a meteorite...
s and small asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s. Yarkovsky's insight would have been forgotten had it not been for the Estonia
Estonia
Estonia , officially the Republic of Estonia , is a state in the Baltic region of Northern Europe. It is bordered to the north by the Gulf of Finland, to the west by the Baltic Sea, to the south by Latvia , and to the east by Lake Peipsi and the Russian Federation . Across the Baltic Sea lies...
n astronomer Ernst J. Öpik (1893–1985), who read Yarkovsky's pamphlet sometime around 1909. Decades later, Öpik, recalling the pamphlet from memory, discussed the possible importance of the Yarkovsky effect for moving meteoroids about the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
.
The Yarkovsky effect is a consequence of the time needed for the surface to warm up or cool down. In general there are two components to the effect:
- Diurnal effect: On a rotating body (e.g. an asteroidAsteroidAsteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
) illuminated by the Sun, as on the Earth, the surface is warmer in the afternoon and early night, than in the late night and morning. The result is that more heat is radiated on the "dusk" side than the "dawn" side, leading to a net radiation pressureRadiation pressureRadiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light...
thrustThrustThrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
in the opposite "dawn" direction. For prograde rotators, this is in the direction of motion on their orbit, and causes their semi-major axisSemi-major axisThe major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape...
to steadily increase, spiraling away from the Sun. RetrogradeRetrograde motionRetrograde motion is motion in the direction opposite to the movement of something else, and is the contrary of direct or prograde motion. This motion can be the orbit of one body about another body or about some other point, or the rotation of a single body about its axis, or other phenomena such...
rotators spiral inward. The diurnal effect is the dominant component for larger bodies greater than about 100 m diameter.
- Seasonal effect: This is easiest to understand for the idealised case of a non-rotating body orbiting the Sun, for which each "year" consists of exactly one "day". As it travels around its orbit, the "dusk" hemisphere which has been heated over a long preceding time period is invariably in the direction of orbital motion. The excess of thermal radiation in this direction causes a "braking" force which always causes spiraling inward toward the Sun. In practice, for rotating bodies, this seasonal effect increases along with the axial tiltAxial tiltIn astronomy, axial tilt is the angle between an object's rotational axis, and a line perpendicular to its orbital plane...
. It dominates only if the diurnal effect is small enough. This may occur because of very rapid rotation (no time to cool off on the night side, hence an almost uniform longitudinalLongitudeLongitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....
temperature distribution), small size (the whole body is heated throughout) or an axial tiltAxial tiltIn astronomy, axial tilt is the angle between an object's rotational axis, and a line perpendicular to its orbital plane...
close to 90°. The seasonal effect is more important for smaller asteroid fragments (from a few metres up to about 100 m), provided their surfaces are not covered by an insulating regolithRegolithRegolith is a layer of loose, heterogeneous material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids, and other terrestrial planets and moons.-Etymology:...
layer and they do not have exceedingly slow rotations. Additionally, on very long timescales over which the spin axis of the body may be repeatedly changed due to collisions (and hence also the direction of the diurnal effect changes), the seasonal effect will also tend to dominate.
The above details can become more complicated for bodies in strongly eccentric orbits.
The effect was first measured in 1991-2003 on the asteroid 6489 Golevka
6489 Golevka
6489 Golevka is an Apollo, Mars-crosser and Alinda asteroid, discovered in 1991 by Eleanor F. Helin.Its name has a complicated origin. In 1995, Golevka was studied simultaneously by three radar observatories across the world: Goldstone in California, Yevpatoria RT-70 radio telescope in Ukraine and...
. The asteroid drifted 15 km from its predicted position over twelve years (the orbit was established with great precision by a series of radar observations in 1991, 1995 and 1999).
In general, the effect is size dependent, and will affect the semi-major axis
Semi-major axis
The major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape...
of smaller asteroids, while leaving large asteroids practically unaffected. For kilometre-sized asteroids the Yarkovsky effect is minuscule over short periods: 6489 Golevka
6489 Golevka
6489 Golevka is an Apollo, Mars-crosser and Alinda asteroid, discovered in 1991 by Eleanor F. Helin.Its name has a complicated origin. In 1995, Golevka was studied simultaneously by three radar observatories across the world: Goldstone in California, Yevpatoria RT-70 radio telescope in Ukraine and...
is estimated to be subjected to a force of about 0.25 newton, for a net acceleration of 10−10 m/s². But it is steady; over millions of years an asteroid's orbit can be perturbed enough to transport it from the asteroid belt
Asteroid belt
The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets...
to the inner Solar System.
For a specific asteroid, it is very hard to predict the exact impact of the Yarkovsky effect on its orbit. This is because its magnitude depends on many variables that are hard to determine from the limited observational information that is available. These include the exact shape of the asteroid, its orientation, and its albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...
, along with its variations over the surface and with wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
. Calculations are further complicated by the effects of shadowing and thermal "reillumination", whether caused by local craters or a possible overall concave shape. The Yarkovsky effect also competes with radiation pressure
Radiation pressure
Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light...
whose net effect may cause similar small long-term forces for bodies with albedo variations and/or non-spherical shapes.
As an example, even for the simple case of the pure seasonal Yarkovsky effect on a spherical body in a circular orbit with 90° obliquity, semi-major axis changes could differ by as much as a factor of two between the case of a uniform albedo and the case of a strong north/south albedo asymmetry. Depending on the orbit and spin axis
Rotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...
, the Yarkovsky semi-major axis change may be reversed simply by changing from a spherical to a non-spherical shape.
Despite these difficulties, utilizing the Yarkovsky effect is one scenario under investigation to alter the course of potentially Earth-impacting near-Earth asteroid
Near-Earth object
A near-Earth object is a Solar System object whose orbit brings it into close proximity with the Earth. All NEOs have a perihelion distance less than 1.3 AU. They include a few thousand near-Earth asteroids , near-Earth comets, a number of solar-orbiting spacecraft, and meteoroids large enough to...
s. Possible asteroid deflection strategies
Asteroid deflection strategies
Asteroid mitigation strategies are "planetary defense" methods by which near-Earth objects could be diverted, preventing potentially catastrophic impact events. A sufficiently large impact would cause massive tsunamis or an impact winter, or both...
include "painting" the surface of the asteroid or focusing solar radiation onto the asteroid to alter the intensity of the Yarkovsky effect and so alter the orbit of the asteroid away from a collision with Earth.
See also
- YORP effect
- Poynting–Robertson effect