A new telescope study of Hygia – the fourth largest object in the main asteroid belt – suggests that it is a dwarf planet, due to its surprisingly spherical shape.
Discovered in 1849 by the Italian astronomer Aniballe de Gasparis, Higia is located in the main asteroid belt between Mars and Jupiter. This is the fourth largest object in the belt, with Ceres, Vesta and Palace being the only larger ones (of the three, only Ceres is a dwarf planet ). Despite its size, Hygia remains a poorly researched site and is easily the most mysterious of the big four.
A new study published today in Nature Astronomy revisits much of what we know about Hygia, including its shape, size, rotation, and origin history. The study, led by astronomer Pierre Vernaca of Laboratoire d & Astrophysique de Marseille in France, was made possible by recent observations made by the European Space Agency's SPHERE Instrument on the Very Large Telescope (VLT) in the Chilean Atacama Desert.
Most importantly, new research indicates that the state of Hygiene needs to be improved from an asteroid to a dwarf planet. If that happens, Hygia will replace Ceres as the smallest dwarf planet in our solar system.
According to criteria developed by the International Astronomical Union (IAU) in 2006, a celestial object must satisfy four requirements in order to earn its designation as a dwarf planet: it must be in its own orbit around the Sun, cannot be the moon, vacuuming other material in close proximity and achieving "hydrostatic equilibrium" – in other words, mostly a spherical shape with enough gravity to overcome a solid, irregular shape.New research suggests that Hygiene is fulfilled la all four of these requirements, including hydrostatic equilibrium.
"Comparing the sphericity of Hygia with that of other objects of the solar system, it seems that Hygia is almost as spherical as Ceres, which opens the possibility of reclassifying this object.
An improved estimate of Hygia's diameter places its latitude at 430 kilometers (267 miles). For comparison, Pluto and Ceres – two other dwarf planets – have diameters of 2,400 kilometers (990 miles) and 950 kilometers (590 miles), respectively. The revised estimate of the site rotation period shows that one day of Hygiene lasts 13.8 hours, which is approximately half of the previous estimate.
Two relatively small craters were observed on the surface, one about 180 kilometers (112 miles) wide and the other about 97 kilometers (60 miles). Going into the project, astronomers expected to find a massive crater associated with the origin of the object. Hygiea is the largest member of the Hygiea family of asteroids – a collection of nearly 7,000 objects related to the same parent body. Accordingly, scientists expected to see a large impact pool on Hygia, similar to that found in Vesta with a diameter of approximately 500 kilometers (310 miles).
"Neither of these two craters could be caused by the effects of asteroids of the Higia family, whose volume is comparable to that of a 100-kilometer site [60 miles]. They are too small, ”says Miroslav Broz, co-author of the new book and research at the Astronomical Institute at Charles University in Prague, Czech Republic, in an ESA release.
Using computer simulations, researchers showed that the family of asteroids from Hygiea could be generated by massive collision collisions between 75 to 150 kilometers (46 to 93 miles). The resulting collision wipes out Hygia's parent body (which, as noted, was about 100 kilometers or 62 miles wide). But through the eons, much of the resulting waste is re-assembled to form (mostly) a sphere-shaped object that we see today. According to the collision, this collision happened more than 2 billion years ago.
In the future, the IAU will have to decide whether Hygiea should be granted dwarf planet status. Perhaps more importantly, Hygias, with its relatively fresh surface, differs from other major belt objects, including Vesta and Ceres, making it a mandatory target for further exploration and possibly even a robotic mission.