2019
November
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Will our Solar System soon have its sixth dwarf planet?

According to the definition of the International Astronomical Union (IAU), dwarf planets are celestial bodies that do indeed have the round shape of a planet, but do not have sufficient mass to dominate the area around their distance to the Sun. The most well-known example of a dwarf planet is surely Pluto (with a diameter of 2400 kilometers (1490 miles)). Eris, Makemake, and Haumea are three other dwarf planets orbiting in the outer regions of our Solar System. At 950 kilometers (590 miles), Ceres is the largest object in the Asteroid Belt and simultaneously the smallest dwarf planet.

But maybe not for much longer, because the asteroid Hygiea also appears to be approximately spherical. The asteroid discovered by Annibale de Gasparis on April 12, 1849 in Naples was named after Hygieia, the daughter of the god Asclepios from Greek mythology. It is only the fourth largest object in the Asteroid Belt. However, differently than the somewhat larger asteroids, Vesta and Pallas, it actually appears to be spherical, as observations with the SPHERE instrument of the Very Large Telescope of the European Southern Observatory, ESO, have shown.

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At the end of the Solar System, there’s a surprisingly high pressure

Our Sun emits particles and radiation around the clock. These emissions propagate far into space in all directions and form the heliosphere. At the same time, our Solar System is constantly bombarded from interstellar space by cosmic radiation from a wide range of sources. Way out in the far outer edges of our Solar System, a few billion kilometers from the Sun, these streams of radiation meet each other from both directions in the so-called heliosheath.

The pressure appears to be significantly higher there than researchers previously thought. This was discovered by astronomers with the help of the two Voyager probes that have had only one goal since 1977 – to leave the Solar System. At the time of the measurements, Voyager 1 had already reached interstellar space (but was still within the Solar System as defined by its gravitational effects), while Voyager 2 was still flying through the heliosheath.

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