Jumbos of the Solar System

Jumbos of the Solar System
Our Solar System is a wondrous place, full of astounding things. For example, most people know that its biggest planet is Jupiter, named for the king of the Roman gods. But did you know that the mass of Jupiter is two and a half times greater than that of all the other planets put together? And where is the biggest moon, tallest mountain or largest crater?

The biggest moon
It's appropriate that the biggest planet has the biggest moon, and Jupiter's moon Ganymede tops the list. However it's not the biggest by much. Ganymede's diameter of 5262 km (3270 mi) is only 112 km (70 mi) greater than the diameter of Saturn's moon Titan. In fact, for a long time astronomers thought that Titan was the biggest moon. It was only when the Voyager 1 space probe got close to Titan in 1980 that they realized that some of what had seemed to be Titan's surface was actually a thick atmosphere. Both Ganymede and Titan are bigger than Mercury and would qualify as planets if they orbited the Sun.

The biggest impact crater
Solar System bodies collide with each other. These bodies even formed through gentle collisions, though many were then destroyed by violent collisions. In the ancient Solar System a Mars-sized object hit the Earth, and the debris thrown out by the collision made the Moon. However, usually, the result of an impact is a crater.

On Earth old craters tend to be hard to find because geological processes erase them. The Vredefort crater in South Africa is usually listed as the largest impact crater on Earth, but we see its remains after two billion years of erosion. The original diameter was probably around 300 km (190 mi). Estimates of the size of the asteroid that caused it are around 15-20 km (9.3-12.4 mi) across. It must have made quite a bang.

Yet the Vredefort crater isn't even close to the size of Utopia Planitia impact basin on Mars, which is 3,300 km (2,100 miles) across. And the biggest one by far is the North Polar Basin on Mars. It's elliptical, showing that the impactor hit Mars at an angle, and is some 10,600 × 8,500 km (6,550 × 5,250 mi). It covers an area much bigger than the United States.

The biggest rift valley
Rift valleys are quite different to craters. They're not formed by impacts, but by internal geological processes which fissure the crust (a body's outer layer). For example, the Valles Marineris canyon system on Mars is a rift valley thought to have been created when the planet's crust was stretched and broken. It's over 4000 km (2500 mi) in length, and up to 7 km (4 mi) deep. It's often compared to the Grand Canyon on Earth, but the Grand Canyon is much smaller and was created by erosion, which is caused by surface processes such as wind and water. Nonetheless Valles Marineris can't match the size of rift valleys on Earth. The largest terrestrial one is at the bottom of the sea, running alongside the Mid-Atlantic Ridge for about 10,000 km (6000 mi).

The tallest mountain. The tallest volcano.
The craters and valleys are impressive, but what if we look up instead of down? Where is the Solar System's tallest mountain? It's tricky to work out the heights of mountains, especially on distant heavenly bodies. On Earth we use altitude above sea level, but that's not going to work elsewhere. The height from base to summit is best for making comparisons.

Everest may be the highest mountain on Earth with a peak at 8848 m (29,029 ft) above sea level. However the tallest mountain is Mauna Kea which is 10,203 m (33,476 ft) from base to summit. Yet it doesn't compare to some mountains elsewhere in the Solar System.

It seems that Mars's Olympus Mons and the central peak of asteroid Vesta's Rheasilvia crater are almost the same height. NASA's Dawn mission calculated that Rheasilvia is at least 22 km (14 mi) high. Using Mars Orbiter data and digital modeling, researchers put the height of Olympus Mons at slightly less than that of Rheasilvia. Rheasilvia may be the tallest mountain, but Olympus Mons is definitely the tallest volcano. They're both more than double the height of Mauna Kea.

The biggest body of water
Earth not only has the biggest known rift valleys, but it must surely have the biggest body of water. The interconnected seas, sometimes called the Ocean Sea covers 71% of the Earth, over 360 million km2 (140 million mi2). No other bodies in the Solar System have lakes or oceans on the surface.

However there are (as of March 2016) sixteen bodies which may have a subsurface ocean covering at least a million km2. The moon Ganymede could have a greater volume of water in its interior than Earth has on the surface, but we will need more evidence to determine if that's the case.

The biggest dwarf planet
With space probes visiting two dwarf planets, they were big news in 2015. And at last they resolved the question: Is Pluto bigger than Eris? The answer was good news for Pluto fans. Yes, Pluto is the biggest dwarf planet. It's larger than its rival Eris – but not by much. Its diameter is only 46 km (28 mi) greater. That's less than the distance across Greater London in the UK.

You Should Also Read:
Titan – Planet-sized Moon of Saturn
Dwarf Planets – a Tour
Jupiter's Galilean Moons

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