A Little Upset That Jupiter Is Missing But Still Awesome

ISS Symphony

Solar System: Things to Know This Week

1. See Shadows on Jupiter

Jupiter dominates the evening sky this month, rising at sunset and setting at dawn. On the nights of March 14 and 15, Jovian moons Io and Europa will cross the planet’s disk. When the planet is at opposition and the sun shines on Jupiter’s moons, we can see the moons’ shadows crossing the planet. There are actually 11 of these double shadow transits in March.

2. One Year of Dawn at Ceres

NASA’s Dawn spacecraft gently slid into orbit around Ceres just over one year ago, becoming the first spacecraft to reach a dwarf planet. Since then, the spacecraft has delivered a wealth of images and other data that open an exciting new window to this previously unexplored body in the asteroid belt.

3. The Latest from Saturn

Days ago, on Mar. 11, 2016, Cassini’s Ultraviolet Imaging Spectrograph (UVIS) watched as the plume of gas and icy particles from the moon Enceladus passed in front of the central star in Orion’s Belt. Such observations, known as stellar occultations, provide information about the density and composition of the plume.

4. The Equinox is Upon Us

March 20 is the vernal equinox–the start of spring in the northern hemisphere, and the start of fall in the southern hemisphere. During the two equinoxes each year, the line between day and night is vertical, so all over the planet, the length of the day and night are nearly equal. For the rest of the year, the Earth’s tilt angles the line between day and night, culminating with the solstices, in which the poles receive weeks of unending sunshine or darkness depending on the time of year.

5. Up Close with a Comet

Before Rosetta crash lands into comet Comet 67P/Churyumov-Gerasimenko in September, 2016, it will continue taking pictures and detailed measurements of this mysterious comet to study the origin of comets and how they relate to the origin of the solar system.

Want to learn more? Read our full list of the 10 things to know this week about the solar system HERE.

Make sure to follow us on Tumblr for your regular dose of space: http://nasa.tumblr.com

In last week’s episode of It’s Okay To Be Smart, I talked about why the moon orbits the Earth. If you haven’t watched it yet, give it a look. I’ll wait.

There’s some pretty interesting and counterintuitive astrophysics keeping the moon orbiting Earth and not getting gobbled up by the sun. But I left one thing out of that video. The moon doesn’t really orbit the Earth. Strictly speaking, the moon and the Earth orbit each other.  

Just like the Earth exerts a gravitational force on the moon, the moon and its mass are “tugging” right back on us. As a result, the two bodies are actually orbiting a point in between, called the barycenter.

If you’ve ever watched pairs figure skating, you’ve seen this in action. When spinning through this move, called a “death spiral”, the two skaters are actually rotating around a barycenter in between their two centers of mass:

This is true of any two orbiting objects, whether it’s a pair of binary stars, a planet and its star, or a planet and its moon(s). You can think of it just like a playground see-saw, with the masses and distance between the two orbiting objects determining where the “balance” point is. 

The Earth/Moon barycenter is about 1,700 km beneath the crust:

Jupiter, despite being more than five times farther from our central star than Earth is, is so massive that its barycenter lies outside of the Sun:

The Earth-Sun barycenter, on the other hand, is effectively in the center of the sun. Our mass is just peanuts compared to that of that huge burning ball of hot gas:

When two orbiting bodies have similar masses and are relatively close to each other, it can be tough to figure out who’s orbiting whom. This is one reason that some astronomers think Pluto and its moon Charon are more of a double-dwarf-planet system:

Scientists use the see-saw physics of barycenters to study planets in distant solar systems, observing these wobbly waltzes to discover planets that we can’t see with telescopes.

The dig deeper into this cool bit of astrophysics, check out this article from my friend Chris Crockett. And cue the Dead or Alive…

The Great Red Spot

Animations of Saturn’s aurorae

Earth isn’t the only planet in the solar system with spectacular light shows. Both Jupiter and Saturn have magnetic fields much stronger than Earth’s. Auroras also have been observed on the surfaces of Venus, Mars and even on moons (e.g. Io, Europa, and Ganymede). The auroras on Saturn are created when solar wind particles are channeled into the planet’s magnetic field toward its poles, where they interact with electrically charged gas (plasma) in the upper atmosphere and emit light. Aurora features on Saturn can also be caused by electromagnetic waves generated when its moons move through the plasma that fills the planet’s magnetosphere.  The main source is the small moon Enceladus, which ejects water vapor from the geysers on its south pole, a portion of which is ionized. The interaction between Saturn’s magnetosphere and the solar wind generates bright oval aurorae around the planet’s poles observed in visible, infrared and ultraviolet light. The aurorae of Saturn are highly variable. Their location and brightness strongly depends on the solar wind pressure: the aurorae become brighter and move closer to the poles when the solar wind pressure increases.

Credit: ESA/Hubble (M. Kornmesser & L. Calçada)

Jupiter’s moon, Callisto.