Discovered in 1930 by the American astronomer Clyde Tombaugh, Pluto is out of the ordinary. Of an equatorial diameter lower than 2 500 km, it represents only tenth two of the Earth. Not satisfied to be, so far, the smallest member of the solar system, it also possesses an eccentric and very oblique orbit with regard to the plan of the ecliptic. Sometimes even, Pluto is closer of the Sun that Neptune. It is crossed in the perihelion in 1989, its passage in the aphelion is planned for 2113. Pluto is the second dwarfish planet of the solar system by the size. It orbits around the Sun at a distance varying between 29 and 49 astronomical units and belongs to the belt of Kuiper. It is about the first trans-Neptunian object of having been discovered. The solar system, which counted nine planets since 1930, contains no more than eight since August, 2006.
Further to this modification of the nomenclature, Pluto was added to the list of the minor objects of the solar system and saw attributing the number 134340 in the catalog of the minor objects.
Pluto and its Satellites
Mean diameter (km)
semi-major axis (km)
Orbital period (days)
Image: Composite photograph of Pluto and Charon photographed July 11, 2015 by the New Horizons probe. Image credit: NASA/JHUAPL/SWRI
Pluto lost his status of planet
The solar system has lost a member of the family of planets. "A planet is a celestial body that is in orbit around the Sun, has sufficient mass for its self-gravity to outweigh the cohesive forces of the solid body and assumes a hydrostatic equilibrium (spherical), which eliminated any body moving in a close orbit." This definition was approved on August 24, 2006, at the 26th General Assembly of the IAU (International Astronomical Union) by a show of hands of about 400 scientists and astronomers after ten days of discussions. In addition, the IAU has created a new class of objects: the dwarf planets. The first suspicions about the true nature of Pluto were born in 1992. This year, Americans David Jewitt and Jane Luu observed for the first time an object in the Kuiper Belt. The existence of such objects, very faint and gravitating beyond Neptune, was suggested by Gerard P. Kuiper in 1951. With a diameter of a few hundred miles, it would be the remains of the original nebula that gave birth to the solar system. However, the advent of increasingly powerful in recent year's telescopes led to the discovery of some seventy objects of this type. The largest trans-Neptunian objects (OTN) have obtained the status of dwarf planet. The four largest are: Eris (≈ 2400 km), Pluto (≈ 2300 km), Makemake (≈ 1600 km) and Haumea (≈ 1600 km).
Image: Diameters compared, big dwarf planets, relative to that of the Moon and Earth. Earth (≈12756 km), Moon (≈3474 km), Eris (≈2300 km), Pluto (≈2300 km), Makemake (≈1600 km) and Haumea (≈1600 km).
Image: The Pluto system, with three satellites seen by Hubble, 15 May 2005. In June 2011, another satellite was discovered by Hubble. The fourth is called Kerberos. The tiny moon Kerberos orbits Pluto in 32.1 days. The fifth, Styx, revolves in 20 days, it is between 10 and 25 km.
Image: Simulation rotations of Charon, Nix, Hydra, Kerberos and Styx around the icy dwarf planet Pluto. The tidal force of most of the inner solar system moons blocks the satellite, a side facing their central planet. This animation shows that this is not the case with small moons of Pluto, which behave like tops while Pluto and Charon are face to face. Pluto is shown in the center with, in order, from the smallest to the largest orbits Charon, Styx, Kerberos Nix and Hydra. The rotation of two nearby objects like Pluto and Charon (12% of the mass of Pluto) is around centroid or center of mass of the two objects, Pluto and Charon. The barycenter is located outside the main body, ie Pluto. Credits: NASA/JHUAPL/SwRI/M. Showalter
The surprising Pluto Mountains
The latest news reaching us from the New Horizons probe that flew Pluto in July 2015 and the first images reveals a surprise. In the region near the equator of Pluto, a chain of young mountains of 3500 meters high, rise above the ice surface. These Mountains were probably formed there are no more than 100 million years, they are very young compared to the age of 4.56 billion years the solar system. In addition, they can still be evolving, according to the team of Jeff Moore of the Ames Research Center of NASA in Moffett Field, California. This region, which covers less than one percent of the surface of Pluto, may still be geologically active today. Moore and his colleagues based the estimate of young age by the absence of crater in this view. Like the rest of Pluto, this region would probably have been pummeled by space debris during the billions of years past and would be filled craters. It seems that recent activity has erased the scars. "This is one of the youngest surfaces we have seen in the solar system," says Moore.
Unlike the icy moons of the giant planets, Pluto can not be heated by gravitational interactions with a much larger planetary body. Another process of generating this mountainous landscape. "It can bring us to rethink geological activity on many other icy worlds," says Deputy Team Leader GGI John Spencer of the Southwest Research Institute in Boulder, Colorado. The mountains are probably composed of water and ice, the "bedrock" of Pluto. Although the methane and nitrogen ice cover much of the surface of Pluto, these materials are not strong enough to build mountains, it is more likely that a more rigid material, such as water ice has created peaks. "At temperatures of Pluto (the average ground temperature is measured at -223 ° C), water ice acts like a hard rock" said Bill McKinnon of Washington University, St. Louis. The image was taken about 1.5 hours before New Horizons is closer to Pluto, the craft was 77,000 km from the surface of the dwarf planet.
Image: The surprising Pluto Mountains. Unlike the icy moons of the giant planets, Pluto can not be heated by gravitational interactions with a much larger planetary body. Another process of generating this mountainous landscape. Scientists suspect a geological activity, which would be very surprising.
Aphelion comes from the ancient Greek apo (distant) and Helios (sun). This is the furthest point from the Sun on heliocentric orbit of a planet or a solar
system object (comet, asteroid). The aphelion of the Earth is reached around July 4, when the Earth is at a distance of 152 097 701 km from the
date shifts on average about twenty minutes a sidereal year, due to the precession of the equinoxes and gravitational disturbances caused by the other
planets of the solar system. The sidereal year is the time it takes for the Sun finds the same position relative to the fixed stars on the celestial sphere,
it is 20 minutes and 24 seconds longer than the average tropical year (≈365,2422 days).
Aphelion comes from the ancient Greek peri (around) and Helios (Sun). It is the closest point to the Sun on the heliocentric orbit of a planet or a solar system object (comet, asteroid).
The perihelion of the Earth is reached on January 4, when the Earth is at a distance of 147 098 074 km from the sun.
This date shifts on average about twenty minutes a sidereal year, due to the precession of the equinoxes and gravitational disturbances caused by the other planets of the solar system.
The sidereal year is the time it takes for the Sun finds the same position relative to the fixed stars on the celestial sphere, it is 20 minutes and 24 seconds longer than the average tropical year (≈365,2422 days).