Author: Fraser Cain

Words are one thing, but to really appreciate Jupiter, we’re going to want to see pictures.

This is a picture of Jupiter captured by NASA’s Cassini spacecraft, on its way to its final destination: Saturn. The black spot is a shadow cast by Jupiter’s moon Europa. Cassini was never able to capture this detailed a resolution image of Jupiter because the planet was too big to fit into its camera field of view. Instead, the spacecraft took 4 separate images which were then combined together on computer.

This Jupiter pic is a montage of the planet and its moon Io, captured by NASA’s New Horizons spacecraft on its way out to Pluto. The two objects were never actually lined up like this, instead, the separate images were combined together on computer.

Although this picture of Jupiter looks like it was taken by a spacecraft, it was actually taken by the Hubble Space Telescope, currently in orbit around the Earth. The photograph of Jupiter was taken to show the Great Red Spot, which has been decreasing in size over the last century.

This image of Jupiter was captured by NASA’s Galileo spacecraft. As Galileo was orbiting Jupiter, it didn’t take many large images of the planet. This photograph is a mosaic of many images stitched together, showing the boundary between a zone and a belt on Jupiter.

This is one of the most famous pictures of Jupiter and its Great Red Spot. This was captured by NASA’s Voyager 1 spacecraft as it was speeding past the giant planet.

Did you enjoy these images of Jupiter? There are many more on Universe Today. For example, this is a picture of Jupiter’s south pole captured by Cassini. And here’s Jupiter seen from Saturn.

Probably the best resource for pictures of Jupiter is from NASA’s Planetary Photojournal. You can access it here.

We’ve also recorded an entire show just on Jupiter for Astronomy Cast. Listen to it here, Episode 56: Jupiter, and Episode 57: Jupiter’s Moons.

A year on Earth is obviously 1 year long, since it’s the standard of measurement. But we can break it down further.

A year is 365.24 days. Or 8,765 hours, or 526,000 minutes, or 31.6 million seconds.

The tricky one is the number of days. Because the earth year doesn’t work out to exactly 365 days, we have the leap year. If we didn’t, days in the calendar wouldn’t match up with the position of the Earth in its orbit. Eventually, the months would flip around, and the northern hemisphere would have summer in January, and vice versa.

To fix this, we put on extra days in some years, called leap years. In those leap years, a year lasts 366 days, and not the usual 365. This gets tacked onto the end of February. Normally, February only has 28 days, but in leap years, it has 29 days.

When to you have leap years? It’s actually pretty complicated.

The basic rule is that you have a leap year if you can divide the year by 4. So 2004, 2008, etc. But years divisible by 100 are not leap years. So 1800, 1900 aren’t leap years. Unless they’re divisible by 400. So 1600 and 2000 are leap years. By following this algorithm, you can have an Earth orbit that lasts 365.24 days.

With the current system, it’s not actually perfect. There’s an extra 0.000125 days being accumulated. Over course of 8,000 years, the calendar will lose a single day.

Here’s an article about how astronomers might use cosmic rays to measure time on Earth.

And here is more information on how to calculate leap years from timeanddate.com.

We did an episode of Astronomy Cast just on the Earth. Give it a listen, Episode 51: Earth.

The driest place on Earth is in Antarctica in an area called the Dry Valleys, which have seen no rain for nearly 2 million years. There is absolutely no precipitation in this region and it makes up a 4800 square kilometer region of almost no water, ice or snow. Water features include Lake Vida, Lake Vanda, Lake Bonney and the Onyx River. There is no net gain of water. The reason why this region receives no rain is due to Katabatic winds, winds from the mountains that are so heavy with moisture that gravity pulls them down and away from the Valleys.

One feature of note is Lake Bonney, a saline lake situated in the Dry Valleys. It is permanently covered with 3 to 5 meters of ice. Scientists have found mummified bodies of seals around the lake. Lake Vanda, also in the region, is 3 times saltier than the ocean. Temperatures at the bottom of this lake are as warm as 25 degrees Celsius.

The next driest place in the world measured by the amount of precipitation that falls is the Atacama Desert in Chile and Peru. There are no glaciers that are feeding water to this area; and thus, very little life can survive. Some weather stations in this region have received no rain for years, while another station reports an average of one millimeter per year.

The lowest point on land is the Dead Sea that borders Israel, the West Bank and Jordan. It’s 420 meters below sea level.

The Dead Sea sits on top of the Dead Sea Rift, a tectonic fault line between the Arabian and the African plates. The movement of these plates causes the Dead Sea to sink about one meter per year! The Dead Sea used to be connected to the Mediterranean Ocean, but over a geologic time scale, it became cut off and evaporation concentrated the salt in the water so that today, the Dead Sea is 30 to 31 percent mineral salts. It has the highest level of salinity of any body of water in the world. Just a side note, I’ve had a chance to swim in the dead sea, and it’s one of the strangest experiences I’ve ever had.

The lowest point on land in the Western Hemisphere is Death Valley in California at 86 meters below sea level.

The lowest point on the Earth’s crust is the Mariana’s Trench in the North Pacific Ocean. It is 11 kilometers deep. Like many of Earth’s extremes, the Mariana’s Trench is caused by the Pacific tectonic plate subducting beneath the Philippine plate; this means that the Pacific Plate is sliding underneath the Philippine plate. The point where the Philippine plate overlaps is Mariana’s Trench.

When people learn that energy output from the Sun is increasing, and will boil away the planet’s oceans within a billion years, they wonder if there’s any way to stop the process. Obviously, we can’t stop the Sun from shining and increasing its energy output. But is there a way humans could move the Earth further away from the Sun?

The answer is yes. Well, it’s theoretically possible. Not with today’s technology, and not without an enormous amount of energy, but the laws of physics say it’s possible. In fact, nature does it all the time.

The trick is to replicate a natural process called a 3-body interaction. This is what happens when you have nice orbit perturbed by a 3rd object. In this case, we’ve got the Earth nicely orbiting the Sun. But if we could have an asteroid pass by the Earth in just the right way, its gravity would pull our planet out of its orbit just a tiny bit.

Instead of its current elliptical orbit, the Earth would start to spiral outward from the Sun, slowly drifting further and further away. This is very similar to how the Moon is slowly drifting away from the Earth.

If you timed things right, and used several asteroid passes, you could make the Earth spiral outward as the Sun’s energy output is increasing. Instead of getting roasted, we would slowly drift away from the Sun, matching the expanding habitable zone. This would give life on Earth billions more years, instead of a few hundred million.

Of course, playing pool with asteroids is a dangerous game. Give an asteroid the wrong trajectory and it could crash into our planet and end humanity in an instant. And if you get the calculations wrong, you could end up spiraling the Earth away from the Sun too quickly, and freeze the planet. You’ve got to get it just right.

Everyone has wanted to dig a hole down to the center of the Earth at some time in their lives. I think I was in the 3rd grade, and my friends and I tried to dig down as far as we could go. I never told them my goal, but in my heart, we were going all the way through. In the end we actually got down about 2 meters, but the bottom kept filling in with water.

Of course, digging down to the centre of the Earth was always out of reach.

In order to be able to dig down to the center of the Earth, my friends and I would have needed to dig our way through 6,378 km of rock, mantle, and iron. Most of this journey would be through temperatures hot enough to melt rock, getting as high as 7,000 Kelvin at the center.

The first 35 km or so of digging would be through the outer crust of the Earth. Assuming we could actually get through the solid rock, and keep water from filling back into our super deep hole, we might actually be able to make some progress through this.

Temperatures rise as you get deeper, though. One of the deepest mines in the world is the TauTona gold mine in South Africa, a mere 3.6 kilometers deep. Even though this just scratches the surface of the Earth, temperatures at the bottom of TauTona already get as high as 55°C.

Once you break through the crust, you’re into the Earth’s mantle. At this point, you’re looking at about 3,000 km of rock heated to such a high temperature that it’s a liquid. Volcanoes are points on the Earth when magma from the mantle breaks through to the surface.

How we’d dig through that… I have no idea. But let’s say we could.

Then we’d break through into the core of Earth. This region extends for another 3,500 km or so, and its comprised almost entirely of iron, with a little nickel, and some other trace metals. And it’s even hotter than the mantle above it. This is where temperatures get to 7,000 Kelvin. Assuming we could bore through the iron, and could withstand the heat, we could get down to the center of the Earth.

At this point, we would have traveled 6,378 km to complete our journey. And then another 6,378 km to get through the other side and visit the folks in China.

Sources:
http://en.wikipedia.org/wiki/Earth_radius
http://en.wikipedia.org/wiki/TauTona_Mine
http://en.wikipedia.org/wiki/Mantle_%28geology%29

Of all the features of Mars, its axial tilt is most similar to Earth. Mars’ tilt is 25 degrees, just a fraction away from the Earth’s 23.5 degrees. And because of this tilt, Mars has seasons, just like the Earth. Of course, since Mars takes twice as long as Earth to orbit the Sun, the seasons are twice as long.

Mars also has a very elliptical orbit. Because of this, the difference between its closest and most distant point along its orbit vary by 19%. This extreme difference makes the planet’s southern winters long and extreme. The northern winters aren’t as long or cold.

Astronomers know that the current tilt of Mars’ axis is just a fluke. Unlike Earth, the planet’s tilt has changed dramatically over long periods of time. In fact, astronomers think that the wobble in the tilt might help explain why vast underground reservoirs of water ice have been found at mid-latitudes, and not just around the planet’s poles. It’s possible that in the distant past, Mars was tilted at a much more extreme angle, and the ice caps were able to grow across the planet. When the tilt was less extreme, the ice remained, and was covered by a layer of dust.

Researchers have developed a model that accounts for the advance and retreat of the subsurface Martian ice sheets over 40 ice ages and 5 million years.

Here’s an article that explains how scientists track the Martian equator in the past. And the lopsided ancient oceans on Mars are explained by its tilt in the past.

Here’s some information about the tilt and seasons on Mars from MSSS. And the Wikipedia article about timekeeping on Mars.

Finally, if you’d like to learn more about Mars in general, we have done several podcast episodes about the Red Planet at Astronomy Cast. Episode 52: Mars, and Episode 91: The Search for Water on Mars.