Jupiter and Saturn, the largest and second largest planets of the solar system, respectively, returned to the evening sky.
At around 9:30 p.m., look for Saturn as a pale yellow spot of light heading straight south. The planet will be about a third of the way from the horizon to the top, the top of the sky. Even though the ringed planet is much darker than Jupiter, you shouldn’t have a problem seeing it in its starless section especially.
Jupiter is the very bright “star” to the southeast and about the same distance above the horizon.
Jupiter is brighter than Saturn, mainly because it is closer to us. Saturn is twice as far from Earth as Jupiter is now.
Astronomers like to express distances in the solar system in terms of the average distance between the Earth and the Sun, about 93 million miles. Astronomers call that distance an astronomical unit, abbreviated AU. Currently, Jupiter is 4 astronomical units away from Earth. Saturn is 9 AUs.
Another way to look at distances is to measure the time it takes for light to reach us. 33 light minutes away, you see Jupiter the way it was 33 minutes ago. By comparison, Saturn is about 75 light-minutes away.
Since light from a planet (or something else, for that matter) is scattered as it recedes from its source, Saturn ends up being four times dimmer than its companion in the brighter sky.
Both planets are fundamentally different from a planet like Earth. Our planet is basically a ball of rocks mixed in with some minerals.
Jupiter and Saturn are called “gas giants”, and this is only partially true. They are actually made of materials that would be gases if we found them on Earth. It has no solid surfaces because it is mainly composed of the simplest element in the universe, hydrogen, sprinkled with helium and traces of other elements.
However, these substances can hardly be called gases in relation to Jupiter and Saturn. Beneath their gaseous atmosphere, hydrogen is so compressed by the immense pressure of planetary gravity that the planets are mostly liquid, giant droplets of fluid rapidly orbiting in space.
When I say giant, I mean giant. Jupiter is the largest planet at about 88,000 miles across, a true giant compared to Earth’s 8,000 miles in diameter. More than 1,400 terrestrial planets can be placed in the confines of Jupiter. Saturn is smaller than Jupiter, but not by much. It’s roughly 75,000 miles wide, and can hold 860 or so of Earth.
Jupiter and Saturn reveal the strengths and weaknesses of the various visual aids available to stargazers. Of course, both planets can be easily seen using the binoculars you were born with, your eyes.
Those planets were visible to the first humans to look up at the sky. It took all of human history until 1781 to discover Uranus, the next planet from Saturn.
There are no surface details visible to the naked eye. The planets may be giants, but they are very far away.
Galileo was the first astronomer to solve the problem of the planet’s disk. In 1610, he saw Jupiter as a small point, which was not surprising, given the primitive quality of his telescope.
When Galileo first looked at Jupiter with his telescope, he was shocked to find four tiny dots hovering around the planet.
Even a pair of binoculars will show you Galilee satellites if you can keep the binoculars steady enough. A small telescope operating at medium magnification is required to see the planet’s disk.
You’ll also notice thin and dark streaks that run in the same direction as the planet’s rotation. They are bands of cloud that are pulled all the way around Jupiter by its rapid rotation. Small Earth rotates once on its axis in 24 hours. The massive Jupiter orbits only once every 10 hours.
Following the ancient tradition, astronomers gave the names of the four brightest moons of Jupiter. Io, Europa, Ganymede, and Callisto are named after (how am I going to say this) good friends of Jupiter, the Roman king of the gods.
You can repeat Galileo’s discovery even with the simplest of telescopes. The three or four spots that line up near the planet are the Galilean moons.
The microscopic view is remarkable in part because of the Earth’s distance from the Jovian system. Moons are, after all, little things, the average diameter of the Earth’s moon.
We see it well because it reflects the distant sunlight. They are mostly covered with glossy icicle paint.
We know very little about the moons. Two spacecraft, Voyager 1 and 2, went through planetary bypasses a few decades ago. Recently, the Galileo space probe orbiting Jupiter provided more detailed information.
Io is the closest satellite to Jupiter. Io is practically skating on the surface of the giant planet Jupiter, only 261,000 miles away.
The small moon’s proximity to its massive parent planet is horrific news for Io. Jupiter’s immense gravity bends and stretches Io, like Earth’s moon raising tides on Earth’s liquid-dominated surface.
As a result, Io is torn from the inside out. Tidal forces are heating the planet’s interior and melting the long-suffering core of the satellite.
The liquid core of the Moon is emitted by giant volcanoes, which have returned to the surface of the Moon completely within ten million years or so. Volcanoes mostly spew hot sulfur, which quickly freezes into a lunar dust of sulfur ice.
Io’s volcanic activity even affects Jupiter’s second moon, the mysterious Europa. Its 1,925-mile diameter is slightly smaller than Earth’s moon.
The icy exterior of Europe would be as smooth as a billiard ball if it were about 2,000 wide. Nowhere on this planet do we find hills more than 300 feet high or pits more than three miles deep. It is also the most highly reflective of the Jovian satellite.
The most notable feature of Europa’s ice crust is a series of long canyons that are 600 miles long in some places and up to 185 miles wide. Initially, the grooves were probably fractures in the ice caused by the same gravitational flexion that caused volcanoes to appear on Io. These cracks are now filled, but they must be up to 100 miles deep.
Some planetary astronomers suggest that beneath the ice is a deep ocean of liquid water. As with Io, Jupiter’s great gravity bends Europa and heats its water ice into a liquid. Then the water seeps through cracks in the surface of Europa.
We cannot rule out the possibility of life where there is liquid water and heat. As a result, some seekers of life in our solar system have pinned their hopes under the ice of Europe.
The Galileo spacecraft discovered what must be called Europa’s strangest feature – the presence of sulfuric acid covering most of Europa’s surface. As anyone who has been in contact with its most common form in our culture, car battery acid, will attest, sulfuric acid is a corrosive chemical.
The cause of all this acid is still a mystery, but the volcanoes of Io may provide an answer. Volcanoes may spew sulfur and sulfur compounds at such tremendous speeds that some of the material is dumped into space, resulting in a poor supply of sulfur compounds into besieged Europe.
The heavy presence of battery acid might seem to eliminate any possibility of simple life in or within Europe, but strange things have happened in our solar system.
On Earth, for example, some “extreme” bacteria think sulfuric acid is very tasty, thank you very much.
Saturn is smaller and farther away, so binoculars won’t help you much.
Galileo’s small telescope revealed two small masses on either side of the planet. Fortunately, telescope technology has improved significantly in the past 390 years. A small telescope operating at medium magnification will resolve masses in a bright ring around Saturn.
You’re looking at a large field of debris, the cause of which remains undetermined, even with data from an orbiting spacecraft.
This is the most reasonable explanation. The rings were caused by one or more of Saturn’s moons that were mostly smashed into small pieces by the planet’s massive gravitational pull.
Jupiter also has a ring system, but you’d need a $1.5 billion spacecraft getting close to the planet to see it. Instead, Saturn’s unforgettable ring system is bonus enough.
Tom Burns is the former director of the Perkins Observatory in Delaware.