Bright Spots on Ceres

I have previously posted about asteroid/dwarf planet Ceres before. The Dawn Spacecraft recently arrived at Ceres and began a comprehensive study of the dwarf planet that has never been done before. One of the strange things that Dawn found on Ceres were bright spots that confounded scientists at first. What were they?

Via NASA/Dawn

 

The bright spots were discovered in a crater now known as Occator, an 80-km diameter crater at 19.5° latitude on Ceres. They are called faculae which means “bright spots”. Faculae are more commonly known as the bright regions on the Sun surrounding a sunspot. Where do the faculae on Ceres come from?





One theory is that they are ice spots in the crater that are reflecting sunlight or salt deposits left over after salty water on the surface evaporated away. These spots might have come from Ceres actually having a dusty surface, and minor impacts on the surface exposed the underlying ice or salt.



Another theory, which is more widely accepted, is that the spots are actually ice geysers or cryovolcanoes (volcanoes that spew ice rather than lava). This is believed to be the true cause as Dawn has seen haze above the spots.





We will probably learn more as Dawn continues its reconnaissance around Ceres. And if these are ice features, Ceres could be a great place to build a future way station in the Solar System.

 

Io

Mosaic of the Voyager Missions

Image Credit: 

NASA/JPL

 

Io is the third largest Galilean moon and the closest to Jupiter. It has vey little water and ice, making it the dryest body in the Solar System. It is mostly rocky material which is reflected in its density, 3.55 g/cm³, comparable to the density of the Moon. It is has a larger diameter than the Moon, with an average radius of 1816 km (the Moon has a radius of 1737 km). It only takes 1.77 days to orbit Jupiter, at a semi-major axis distance of 421,700 km. Io has a very hot surface even though it is at the same distance from the Sun as Jupiter. Why?

The quick and simple answer is that tidal forces from Jupiter's immense gravity pull and squeeze Io, keeping the interior hot. As Io orbits Jupiter, those differential forces from Jupiter, as well as the other Galilean moons, keep the interior hot and molten. As we know from Earth, molten interiors lead to volcanoes on the surface and Io has plenty of those. At least 150 active volcanoes have been observed on Io, erupting continuously.

Jupiter also has a much stronger magnetic field than Earth, so large, that Io itself orbits within its confines. The magnetic field lines actually capture ionized particles from the solar wind also ionizes atoms in the thin atmosphere of Io. This ionizing radiates the surface and helps keep it hot even at its extreme distance from the Sun.

The combination of the volancism and the magnetic field of Jupiter gives Io one of the youngest surfaces in the Solar System. The surface is estimated to be only a million years old and making it a place that would not be fun to visit. Io does have an atmosphere, making it one of the few satellites in the Solar System to have an atmosphere. The atmosphere is composed of mainly sulfur compounds, so would not be a pleasant place to smell, even if you could stand the heat and didn't have to breathe.

A comparable place to Io, and Io is in fact the inspiration for this place, is Mustafar in the Star Wars universe. At the end of Episode III: Revenge of the Sith, Obi-Wan and Anakin fight on the surface of Mustafar which is covered in lava lakes and has a lot of volcanic activity. Mustafar is compressed and pulled in the same way as Io, but with two gas giant planets in neighboring orbits providing the gravity, rather than a gas giant and fellow satellites.

Eruption on the surface of Io

Image Credit:

NASA/JPL/University of Arizona

Plume on the limb of Io

Image Credit:

NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

The Geography of Mars

Technically, the correct term for the title of this post is Areology, from Ares (the Greek god of war) and -logy (the study of something).
Mars has mountains much like Earth.  However, unlike many of the mountain ranges on Earth, Martian mountains were not created by plate techtonics.  Olympus Mons, Ascraeus Mons, Arsia Mons, and Elysium Mons are all taller than Mount Everest. Pavonis Mons is slightly shorter, but has a much wider base.

All five of those mountains are shield volcanoes, which erupt but have low viscosity lava. The lava flows down the sides of the volcano, which lead to wide bases and low profiles.  For the Martian volcanoes, lack of plate tectonics lead to all the shield volcanoes on Mars to get really wide and really tall.

Olympus Mons is the largest of these volcanoes.  It is 21.4 km tall (from the peak to average surface elevation around its locality)and as shown in the picture below, the base has an area equivalent to the size of Arizona.  This means that the slope of Olympus Mons is only 5 degrees from base to peak.  Olympus Mons is not the tallest mountain in the solar system. That honor belongs to Rheasilvia on the asteroid Vesta. It has a height from base to peak of 22 km, though only 12 km are above the average surface elevation of Vesta.  Mauna Kea and Mauna Loa are two shield volcanoes in the Hawaiian island chain. They have peaks only 4.2 km above sea level, but from base to peak they are 10.2 km.


Olympus Mons

Tharsis Montes

Elysium Mons

Mars is also home to one of the most extensive canyon systems in the solar system.  Valles Mariners is a huge scar running across the landscape in the southern hemisphere.  If we were able to place it on Earth, it would run from New York to Los Angeles.  It is approximately 4000 km long send has a maximum depth of 7 km.  Compare this to the Grand Canyon in Arizona, which is "only" 446 km long and 1.8 km deep.  The Grand Canyon was shaped by the Colorado River, but it is unknown what formed the Valleys Marineris.  It is believed that liquid water or volcanism formed it, but it could be a combination of both.

Valles Mariners



Lastly, Mars may have at one time liquid oceans. It does not anymore because of the atmospheric pressure (future post) and the low temperature. Images from Martian probes show evidence of ancient shorelines.

Astronomy Picture of the Day 

Mars Global Surveyor