Sedna, the mysterious reddish world that takes more than 11,400 years to orbit the Sun

Space exploration is a constant source of amazing things, and one of those things is right in our own space neighborhood.

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The exploration of the Solar System is a field open to many discoveries, including dwarf planets like Eris, Makemake, Ceres, and Haumea. In addition to these, there is one object in our system about which astronomers disagree. Some consider it a dwarf planet, although the International Astronomical Union has not recognized it as such. I'm talking about Sedna.

The discovery of Sedna is very recent. In 2001, three astronomers (Michael Brown, Chad Trujillo and David Rabinowitz) began a series of observations using the Samuel Oschin Telescope at the Palomar Observatory in San Diego, California, USA. On November 14, 2003, they discovered an object located 100 astronomical units (almost 15 billion kilometers) away, with a highly eccentric orbit around the Sun, which is why it had gone unnoticed until then. Due to its characteristics, Michael Brown initially named it "The Flying Dutchman", in honor of the famous ghost ship of legends, a vessel with no crew or known course that was a bad omen for sailors.

Considered a trans-Neptunian object, this object was initially designated 2003 VB12. It was eventually named after the Inuit goddess Sedna, a woman who lives at the bottom of the sea in an area called Adliden, where the Inuit believe the souls of the dead go. Like the dwarf planet Eris, Sedna is in a remote region of the Solar System known as the scattered disc, populated by objects (many of them icy) ranging in distance from us from about 30 to more than 100 astronomical units. In this region, the Sun appears as a bright, white, and distant star. Many of the comets that orbit the Sun in less than 200 years originate from the scattered disk.

These comets are much faster at completing this orbit than the small world in question: it has been calculated that Sedna takes 11,408 years to complete one orbit around the Sun, at a speed of 1.04 kilometers per second. Not much is known about this small world. It is believed to have a diameter between 800 and 1,100 miles (between 1,287 and 1,770 kilometers) (to give us an idea, the Moon has a diameter of 3,474.8 km). Its mass is unknown.

Furthermore, Sedna is one of the reddest objects in the Solar System, surpassed only by Mars, which could be due to the presence of tholins on its surface, a hydrocarbon sludge formed by millions of years of exposure to ultraviolet radiation. It also has a homogeneous surface, a sign of the absence of impacts from other objects, as well as a thin atmosphere. This object is believed to rotate every only 10 hours, so the days there would be very short and the years would be extraordinarily long... and very cold. The maximum temperature on Sedna would be −240°C.

It must be said that Sedna's discovery was somewhat fortuitous, since its very long journey around the Sun means we have a small window of opportunity to detect it. It is believed that there could be dozens of objects like Sedna in the scattered disc, whose detection has not been possible until now due to the eccentricity of their orbits.

Sedna’s very origin and the cause of its very long orbit are a mystery. One hypothesis is that another planet, roughly the size of Earth, was ejected out of the Solar System when it formed, pulling Sedna with it, but this hypothetical planet (which some astronomers call "Planet Nine") has not been detected by any astronomical observations.