Everyone’s heard of Jupiter’s four most famous moons Europa, Io, Callisto, and Ganymede—we’ve known about them for over 400 years, thanks to Galileo—but giant Jupiter has many more moons than that. To date there are thought to be 69 natural satellites orbiting Jupiter. 53 are officially named, while 16 are awaiting further confirmation. So you’d be forgiven for not being immediately familiar with all of them…it’s a big Jovian family!
The little world seen above is one of Jupiter’s smaller and lesser-known satellites and it holds a particular distinction. It’s called Metis (pronounced like “meet” in the present tense, not “met” in the past) and it’s only about 37 miles across and 21 miles high. It is the closest moon to Jupiter, orbiting within the planet’s main ring (yes, Jupiter has rings) at a distance of about 80,000 miles. It’s also Jupiter’s speediest moon—at 70,500 mph it completes a single orbit in just over 7 hours. That’s almost three hours less than a Jovian day!
If you think that Saturn’s polar storm systems are amazing then you’re gonna love this: Jupiter has them too, and not just a single central storm over each of its poles either. NASA’s Juno mission has revealed that Jupiter has not only polar vortices but also a ring of enormous cyclones spinning in formation around both of its poles—five around its south pole and a whopping eight around its northern one! Each of these cyclones is gargantuan in its own right, easily big enough to span the Atlantic Ocean, and somehow they all manage to avoid merging with their respective neighbors via some as-yet unknown process. It’s literally like nothing found anywhere else in the Solar System!
In November 1964 NASA launched Mariner 4, the fourth of its ambitious series of robotic explorations of our three inner planet neighbors. Mariner 1 was lost during launch; Mariner 2 successfully flew past Venus; Mariner 3 failed to deploy; but on July 14–15, 1965, the 575-lb Mariner 4 became the first spacecraft to fly past Mars and capture close-up images of another planet from space.
Of course the pictures that Mariner 4 captured were in greyscale and not like the beautiful color views we are used to seeing from spacecraft today. But thanks to one creative scientist at NASA (and a box of crayons) our first scenes of Mars from space were in brilliant color.
This animation is comprised of three images acquired by ESA’s Mars Express spacecraft on Sept. 12, 2017 with its High Resolution Stereo Camera (HRSC). It shows parts of the grooved and pitted surface of Phobos, the larger of Mars’ two natural satellites.
Can you feel the heat? NASA’s Mars Odyssey can see it! This is an image of Mars’ smaller moon Deimos, captured with Odyssey’s THEMIS (Thermal Emission Imaging System) instrument on Feb. 15, 2018. Part of the 7-mile-wide Moon was in shadow, but the sunlit surface area reached temperatures up to 200 K (that’s still pretty cold for us, though… –100ºF / -73ºC!)