(90377) Sedna

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( 90377 ) Sedna is a transneptunisches object and probably belongs to the dwarf planet.

• 3.1 size
• 3.2 Surface

• 5.1 Discussion on the origin and history
• 5.2 Sedna hypothetical moon
• 5.3 Possible meanings of the red color

• 8.1 videos

Discovery and designation

Sedna was discovered on 14 November 2003 by Mike Brown ( Caltech ), Chad Trujillo (Gemini Observatory ) and David Rabinowitz ( Yale University) with the 1.2 -m Schmidt telescope at Mount Palomar Observatory. Further investigations were carried out with the Spitzer Space Telescope and the Hubble Space Telescope. On 15 March 2004, the discovery was published. Subsequently Sedna was found on several older recordings from the years 2001-2003, of which relatively precise orbit data could be calculated.

Because of its cold and distant nature explorers named the object after Sedna, the sea goddess of the Inuit, who lives according to the legend in the cold depths of the Atlantic Ocean. At its discovery it was given the provisional designation 2003 VB12.

Web properties

Orbit

Sedna orbits the sun on a prograde, highly elliptical orbit between 76 and about AE 1000 AE distance from its center. The orbital eccentricity is 0.86, the orbit is inclined 11.9 degrees to the ecliptic.

The current distance from the sun is about 12 light-hours, or 13 billion kilometers (about 90 times the distance from Earth to the sun). This corresponds to about three times the distance of Neptune ( the outermost planet ) to the sun. Sedna will reach its perihelion in mid 2076.

In aphelion Sedna is 20.5 times farther from the Sun than Pluto at its farthest point. This corresponds to 0.016 light years. So that the sunlight just over 5 days to reach Sedna when it is at aphelion, while at the point nearest the Sun are "only" about 10 hours. Sedna Apheldistanz would be approximately covered 262 times to get to the nearest star system Alpha Centauri.

The exceptionally large Apheldistanz the object is actually not the largest known - the much smaller, neptune track intersecting object 2000 OO67 outperforms Sedna in this regard.

The orbital period of Sedna is approximately 12,000 years..

The object probably have not heard due to the extreme orbital elements of the Kuiper Belt and is also only one tenth as far from the Sun as the assumed Oort cloud. Although the exact classification is still unclear, Sedna is definitely part of a whole new class of objects (see below).

Rotation

Sedna rotates in about 10 hours once on its axis.

Physical Properties

Size

Current estimates suggest that Sedna has a diameter of 995 km. Previously it was assumed much larger diameters of 1400 to even 1700 km. Since Sedna but obviously a larger albedo has originally assumed, this value has reduced greatly. Thus Sedna is slightly larger than the largest body in the main belt, the dwarf planet Ceres.

Surface

Sedna has a strong reddish color, which resembles that of the sun much closer centaur Pholus or the planet Mars. The cause of this coloration is not yet clear, it deviates significantly from the most carbonaceous color of the previously discovered Neptune from Trans.

The surface temperature is likely to be due to the large distance from the sun in only 30 K ( -243 ° C). The apparent brightness of Sedna is at perihelion 20.4 mag.

Dwarf planet candidate

In the media Sedna was often referred to as the 10th planet in our solar system - a statement which, however, by side of science found little support. Astronomers saw in Sedna because of their relatively small size and high orbital eccentricity no "real " planet.

Before there was an official and generally accepted definition of planet, was the question of when an object can be described as a planet, not clearly understood. If one went only on the size of the object, so familiar on 29 July 2005 made ​​object Eris, the diameter of which is currently estimated at 2326 km would, in any case, must be regarded as 10th Planet, assuming Pluto would retain its status. If, as a measure of a stable orbit, so Pluto and all other objects differ significantly from the other planet here through its highly eccentric orbit.

The official definition uses a third way, by establishing that an object is a planet only if it has already been cleaned its orbit of other objects by its attraction. This applies to any of the discovered in recent years to objects, making this the planet status is withdrawn, or the chance of a planetary status was denied. Instead, objects that do not satisfy this condition, now defined as the new class of dwarf planets.

It was a question of principle whether the solar system 8 or 10 ( and possibly more ) has planet. A commission of the International Astronomical Union published on 16 August 2006 in advance a definition of a planet was classified as a " planet candidate" after the Sedna. However, the vote on August 24 showed more than one possible classification as a dwarf planet Sedna.

Hypotheses and speculations

Being the most widely outsiders known large object in the solar system, moreover, on an unexpected path, Sedna encourages speculation - much more than other minor planets. The great distance from the Sun about raises questions about alternatives to existing development models. Thus, the current model for planet formation yields ( agglomeration of planetesimals ) already for previously known Kuiper belt objects due to the low density of the protoplanetary material, a development period that is longer by orders of magnitude ( more than 100 million years) than the lifetime of the protoplanetary disk (less than 10 million years). For an explanation of these and other previously misunderstood facts, there are various hypotheses, to judge it, however, still needs further research.

Discussion on the origin and history

The three explorers surmise, Sedna belong to an "inner Oort cloud". This may have formed from the original Oort cloud by a disturbance from outside. Possible causes would, for example, an earlier close encounter of the solar system with a nearby star. The unusually eccentric path but could also result from interference by an approximately Mars-sized body in our solar system farther out. Then Sedna would be an isolated incident and a scattered outside the Kuiper Belt object. As initial estimates show that such a disturbing object would, however, about 200 AU from the Sun circling away. The existence of such an object would be no less sensational than the discovery of the existence of Sedna itself

Sedna's hypothetical moon

First, it was observed that the reflected sunlight of Sedna changes periodically every 40 days, from which it concluded on an equally long period of rotation. For a small planet, this would be an unusually slow rotation, which raises the question of braking effects. One of the ways to slow a rapidly rotating body, would be a moon and the tidal forces caused by him. However, the examples of Venus and Mercury show that a slow rotation can also occur without a moon.

On 14 April 2004, NASA released new images from the Hubble Space Telescope, which, according to investigation no companion can be seen. A moon in the required size would have to be recognized, unless he would have been at the receiving immediately before or after Sedna. In addition, you could also from the observations with Hubble not derive exactly the rotation period of Sedna.

From October 2004 to January 2005, a group of Harvard - Smithsonian Center for Astrophysics to Scott Gaudi an observation campaign by the. , The results of Brown et al. could not confirm. This group determined rotation periods of 10 and 18 hours that do not require a braking effect of a moon to explain. By these measurements rotation periods can be eliminated in excess of 10 days. According to a conjecture of Gaudi originally measured period of 40 days could have been faked by background galaxies - but there are still more observations necessary to determine the exact rotation period accurately.

Possible meanings of the red color

The red color could indicate iron compounds or high concentrations of organic substances on the surface. In the first case would offer analogies to Mars, on the second to several comets. However, the formation of iron oxide is not necessarily an atmosphere necessary. A body that is so far out, perhaps to even be in the Oort Cloud, emerged so far would not expect a high iron content. Compounds of organic chemistry occur in the universe, regardless of life, such as alcohols in gaseous nebulae.