Posted on by Jerry Coffey

What is the Diameter of Jupiter?

Jupiter seen from Voyager. Image credit: NASA/JPL

The diameter of Jupiter at its equator is 142,984 km. Since it rotates very quickly, completing a full rotation in just 10 hours, it is an oblate spheroid and bulges at the equator. If you measure the diameter through the poles it is 9,276 km smaller at 133,708 km. Solely based on diameter, Jupiter is 11.2 times the size of the Earth and larger than any other body in our Solar System other than the Sun.

The diameter of Jupiter is amazingly large for our Solar System, but is easily eclipsed by some extrasolar planets. According to Dr. Sean Raymond at the Center for Astrophysics and Space Astronomy at the University of Colorado the largest terrestrial(rocky like Earth) planets can be up to 10 times the size of Earth. Since Jupiter is a gas giant, let’s compare apples to apples and talk about the largest known gas giant in the universe. As of this time(August, 2011) the largest gas giant known is TrES-4. This planet is 1,400 light years away in the constellation Hercules. It has been measured to be 1.4 times the size of Jupiter, but it only has 0.84 times Jupiter’s mass. A gas giant can get about 14 times more massive than Jupiter before they ignite fusion and become brown dwarf stars.

A common question that people ask is ”can Jupiter ever become a star?”. That is a reasonable question given its size and mass. Fortunately for humans, the answer is no. Jupiter would need to add about 80 times its current mass in order to ignite fusion. While the planet occasionally accretes more matter, there is not enough available in our Solar System to add that much mass. If it did ignite, it would scorch our world

Jupiter interests scientists for many reasons. Its moons are a major draw for research. The planet has 64 moons that have been confirmed and a few more that have rarely been observed. The moons in the Jovian system account for 50% of all of the moons in our Solar System. A few of those moons are larger than some dwarf planets and others show evidence of subsurface oceans. Scientist are not sure if they are oceans of water as we know it, but they do believe that they exist.

The diameter of Jupiter is an awesome number in itself, but, once you consider the planet as a whole, you see that knowing the diameter is just scratching the surface. Hopefully, it is enough to spark an interest in researching the planet further.

Here’s more information on the diameter of Earth, if you’d like to compare and see how big Jupiter really is. Jupiter’s big, but extrasolar planets are thought to be able to get even bigger. Here’s an article about how big planets can get.

As I’ve mentioned above, Jupiter is the biggest planet in the Solar System, and here’s Hubblesite’s News Releases about Jupiter.

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.

Sources:
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Jupiter&Display=OverviewLong
http://planetquest.jpl.nasa.gov/news/tres4.cfm

Posted on by Matt Williams

What are Temperatures Like on Jupiter?

A true-color image of Jupiter taken by the Cassini spacecraft. The Galilean moon Europa casts a shadow on the planet's cloud tops. Credit: NASA/JPL/University of Arizona

Jupiter, which takes its name from the father of the gods in ancient Roman mythology, is the largest planet in our Solar System. It also has the most moon’s of any solar planet – with 50 accounted for and another 17 awaiting confirmation. It has the most intense surface activity, with storms up to 600 km/h occurring in certain areas, and a persistent anticyclonic storm that is even larger than planet Earth.

And when it comes to temperature, Jupiter maintains this reputation for extremity, ranging from extreme cold to extreme hot. But since the planet has no surface to speak of, being a gas giant, it’s temperature cannot be accurately measured in one place – and varies greatly between its upper atmosphere and core.

Currently, scientists do not have exact numbers for the what temperatures are like within the planet, and measuring closer to the interior is difficult, given the extreme pressure of the planet’s atmosphere. However, scientists have obtained readings on what the temperature is at the upper edge of the cloud cover: approximately -145 degrees C.

Because of this extremely cold temperature, the atmosphere at this level is composed primarily of ammonia crystals and possibly ammonium hydrosulfide – another crystallized solid that can only exist where conditions are cold enough.

However, if one were to descend a little deeper into the atmosphere, the pressure would increases to a point where it is ten times what it is here on Earth. At this altitude, the temperature is thought to increase to a comfortable 21 °C, the equivalent to what we call “room temperature” here on Earth.

Descend further and the hydrogen in the atmosphere becomes hot enough to turn into a liquid and the temperature is thought to be over 9,700 C. Meanwhile, at the core of the planet, which is believed to be composed of rock and even metallic hydrogen, the temperature may reach as high as 35,700°C – hotter than even the surface of the Sun.

Interestingly enough, it may be this very temperature differential that leads to the intense storms that have been observed on Jupiter. Here on Earth, storms are generated by cool air mixing with warm air. Scientists believe the same holds true on Jupiter.

A close-up of Jupiter's great red spot. Credit: NASA/JPL-Caltech/ Space Science Institute
A close-up of Jupiter’s great red spot, an anticyclonic storm that is larger than Earth. Credit: NASA/JPL-Caltech/ Space Science Institute

One difference is that the jet streams that drive storms and winds on Earth are caused by the Sun heating the atmosphere. On Jupiter it seems that the jet streams are driven by the planets’ own heat, which are the result of its intense atmospheric pressure and gravity.

During its orbit around the planet, the Galileo spacecraft observed winds in excess of 600 kph using a probe it deployed into the upper atmosphere. However, even at a distance, Jupiter’s massive storms can be seen to be humungous in nature, with some having been observed to grow to more than 2000 km in diameter in a single day.

And by far, the greatest of Jupiter’s storms is known as the Great Red Spot, a persistent anticyclonic storm that has been raging for hundreds of years. At 24–40,000 km in diameter and 12–14,000 km in height, it is the largest storm in our Solar System. In fact, it is so big that Earth could fit inside it four to seven times over.

Given its size, internal heat, pressure, and the prevalence of hydrogen in its composition, there are some who wonder if Jupiter could collapse under its own mass and trigger a fusion reaction, becoming a second star in our Solar System. There are a few reasons why this has not happened, much to the chagrin of science fiction fans everywhere!

This cut-away illustrates a model of the interior of Jupiter, with a rocky core overlaid by a deep layer of liquid metallic hydrogen. Credit: Kelvinsong/Wikimedia Commons
This cut-away illustrates a model of the interior of Jupiter, with a rocky core overlaid by a deep layer of liquid metallic hydrogen. Credit: Kelvinsong/Wikimedia Commons

For starters, despite its mass, gravity and the intense heat it is believed to generate near its core, Jupiter is not nearly massive or hot enough to trigger a nuclear reaction. In terms of the former, Jupiter would have to multiply its current mass by a factor of 80 in order to become massive enough to ignite a fusion reaction.

With that amount of mass, Jupiter would experience what is known as gravitational compression (i.e. it would collapse in on itself) and become hot enough to fuse hydrogen into helium. That is not going to happen any time soon since, outside of the Sun, there isn’t even that much available mass in our Solar System.

Of course, others have expressed concern about the planet being “ignited” by a meteorite or a probe crashing into it – as the Galileo probe was back in 2003. Here too, the right conditions simply don’t exist (mercifully) for Jupiter to become a massive fireball.

While hydrogen is combustible, Jupiter’s atmosphere could not be set aflame without sufficient oxygen for it to burn in. Since no oxygen exists in the atmosphere, there is no chance of igniting the hydrogen, accidentally or otherwise, and turning the planet into a tiny star.

Scientists are striving to better understand the temperature of Jupiter in hopes that they will eventually be able to understand the planet itself. The Galileo probe helped and data from New Horizons went even further. NASA and other space agencies are planning future missions that should bring new data to light.

To learn more about Jupiter, check out this article on how weather storms on Jupiter form quickly. Here’s Hubblesite’s News Releases about Jupiter, and NASA’s Solar System Explorer.

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.

Sources:
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Jupiter&Display=OverviewLong
http://www.jpl.nasa.gov/news/news.cfm?release=2008-013

Posted on by Tammy Plotner

Simeis 147 by Davide De Martin

Simeis147 - By Davide De Martin

If you think we’re looking straight down the maul of the “Doomsday Machine”, you’d be pretty much correct. While the fictionalized Star Trek account had the planet killer slowly destroying a distant solar system, this particular “star eater” is very real and still exists along the Auriga-Taurus border…

Named Simeis 147, this ancient supernova remnant has expanded so much that it’s barely visible to larger telescopes. Why? Mostly because the diameter of the nebula is about 3-1/2 degrees, or about 7 times the size of the Moon – and the fact it’s one of the faintest objects in the night sky. Like many nebulous “sky scraps”, it is simply too large to be seen in its entirety – or beauty – except through the magic of astrophotograhy.

In this week’s image by Davide De Martin, we take an up close and personal look at Simeis 147. The intricate filaments of this faint supernova remnant spans over 160 light years of interstellar space and is around 3900 light years away. With an apparent age of about 100,000 years, this awesome explosion occurred around the time of Peking Man, and like our distant ancestor left more than one artifact behind. In this case, the expanding remnant is not all. Deep within the folds and rifts lay a spinning neutron star. This pulsar is all that’s left of the original star’s core.

Unlike many things unexplored, more study was indicated and newer estimated gauge Semeis 147’s age at about 30,000 years. The pulsar itself has recently been detected and has been cataloged as PSR J0538+2817. Imagine something that rotates completely on its axis seven times per second! And think about what happened… The outer layers of this exploding star initially carried outward at speeds of 10,000-20,000 km/s–a tremendous amount of energy released in a blast wave.

Supernovae are divided into classes based upon the appearance of their spectra: hydrogen lines are prominent in Type II supernovae; while hydrogen lines are absent in Type Ia supernovae. Put simply, this means the progenitor stars either had hydrogen in their outer envelopes or did not have hydrogen in their outer envelopes. Type II supernovae are the territory of massive stars while Type Ia supernovae more than likely originated with white dwarf binary star systems – a place where the accreting white dwarf is driven above the Chandrasekhar Mass Limit, collapses and explodes.

So how often do events like the Simeis 147 type happen? According to Rudolph Minkowski; “As regards the supernovae frequency, there are two types of supernovae. The Supernovae I seem to occur about every 400 or 500 years per galaxy and the Supernovae II about every 50 years per galaxy, with considerable leeway. But, the Supernovae II are certainly much more frequent than Supernova I.” In recent studies done the 610.5 MHz Contour Maps of the Supernova Simeis 147, by Dickel and McKinley, the integrated flux densities show that the radiation is probably non-thermal and incredibly old.

As old as the Star Trek “Doomsday Machine”? Its origins were also unknown and it produced mass destruction. Maybe Simeis 147 isn’t quite the same as the neutronium hulled, antiproton beam firing planet killer of Gene Roddenberry’s fictionalized story… But it is definitely as intriguing to the imagination!

This week’s awesome image was done by Davide De Martin.

Posted on by Jerry Coffey

How Long is a Year on Jupiter

The answer to ”how long is a year on Jupiter” is 11.86 Earth years. There is so much more to know about the Jovian system, that we can not just leave you with one fact, so here are some more interesting facts about Jupiter.

At perihelion Jupiter is 741 million km from the Sun(4.95 AU). At aphelion it is 817 million km from the Sun(5.46 AU). That gives Jupiter a semi-major axis of 778,340,821 km. Jupiter’s orbit varies by 76 million km, but it has one of the least eccentric orbits in the Solar System.

Jupiter has 2.5 times the mass of all of the other objects in the Solar System except the Sun. It is so massive that if it gained any more mass it would shrink. Gravitational compression would take over making the planet more dense instead of larger.

There are some conspiracy theorists who like to propose that Jupiter will become a star and destroy Earth. That can never happen. Jupiter would have to accrete about 80 times more mass than it has now and experience a huge increase in temperature in order to ignite fusion. The planet has the hydrogen it needs, but not the wherewithal to fuse it into helium and become a star.

Earth’s magnetic field is generated by its core through a dynamo effect. Scientist are not even sure that Jupiter has a rocky/metallic core, yet the planet has a magnetic field that is 14 times stronger than Earth’s. Astronomers think the magnetic field is generated by the churning of metallic hydrogen near the center of Jupiter. This magnetic field traps ionized particles from the solar wind and accelerates them to nearly the speed of light.

One of the most well known aspects of Jupiter is the Great Red Spot. Astronomers have been documenting it for nearly 350 years. It seems to grow and shrink over time. It is actually a giant storm that would totally engulf the Earth. At one time the storm covered an area that was 40,000 km long. It is slowly getting smaller, but astronomers do not know if it will ever disappear.

Knowing the answer to ”how long is a year on Jupiter” is just one minor detail about the planet. The others above are just a few facts that do not even scratch the surface of the Jovian mystery. None of Jupiter’s 67 moons or it ring system have been mentioned. Imagine the stories yet to be told.

Here’s a great image of Jupiter, captured by amateur astronomer Mike Salway, and an interesting hypothetical article about how Jupiter’s orbit could mess up the Solar System.

Here’s some general information on Jupiter from the Nine Planets, and more information from Solar Views.

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.

Sources:
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Jupiter&Display=OverviewLong
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Jupiter&Display=Facts

Posted on by Jerry Coffey

How Long is a Day on Jupiter

Jupiter and moon Io (NASA)

The Universe Today readers are always asking great questions. ”How long is a day on Jupiter?”, is one of them. A day on Jupiter, also known as the sidereal rotation period, lasts 9.92496 hours. Jupiter is the fastest rotating body in our Solar System. Determining the length of a day on Jupiter was very difficult, because, unlike the terrestrial planets, it does not have surface features that scientists could use to determine its rotational speed.

Scientists cast about for ways to judge the planet’s rotational speed. An early attempt was to do some storm watching. Jupiter is constantly buffeted by atmospheric storms, so the theory was that you could locate the center of a storm and get some idea of the length of a day. The problem scientists encountered was that the storms on Jupiter are very fast moving, making them an inaccurate source of rotational information. Scientist were finally able to use radio emissions from Jupiter’s magnetic field to calculate the planet’s rotational period and speed. While other parts of the planet rotate at different speeds, the speed as measured by the magnetosphere is used as the official rotational speed and period.

All of the planets are oblate spheroids with varying degrees of flattening. Jupiter’s extremely fast rotation flattens it more than any other planet. The diameter of the equator is 9275 km more than the distance from pole to pole. Another interesting effect of Jupiter’s rotational speed is that, because Jupiter is not a solid body, its upper atmosphere features differential rotation. The atmosphere above the poles rotates about five minutes slower than the atmosphere at the equator.

Jupiter is almost a solar system unto itself. Many astronomers believe the the planet is simply a failed star, just lacking the mass needed to ignite fusion. Many people are aware of its four largest moons, the Galilean moons Io, Europa, Ganymede, and Callisto, but few realize that Jupiter has 50 confirmed moons and at least 14 provisional moons. The four largest moons are all very interesting to scientists. Io is a volcanic nightmare. Europa is covered in water ice and may have oceans of slushy ice underneath. Ganymede is the largest moon in the Solar System, even bigger than Mercury, and is the only moon known to have an internally generated magnetic field like Earth’s. Callisto is interesting because its surface is thought to be very ancient; perhaps original material from the birth of the Solar System.

Knowing ”how long is a day on Jupiter” just scratches the surface of the intrigue that is the Jovian system. You could spend months researching the planet and its moons, yet have more to research to do.

Here’s an article on Universe Today that shows how Jupiter can be very flattened, and an article about how the powerful windstorms are generated from its rotation.

NASA’s Ask an Astronomer also has an answer for the question, “how long is a day on Jupiter?” And a cool video of Jupiter’s rotation.

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.

Sources:
NASA
Caltech Cool Cosmos

Posted on by Matt Williams

What is the Diameter of Earth?

Our beautiful, precious, life-supporting Earth as seen on July 6, 2015 from a distance of one million miles by a NASA scientific camera aboard the Deep Space Climate Observatory spacecraft. Credits: NASA
Our beautiful, precious, life-supporting Earth as seen on July 6, 2015 from a distance of one million miles by a NASA scientific camera aboard the Deep Space Climate Observatory spacecraft. Credits: NASA

For those people who have had the privilege of jet-setting or traveling the globe, its pretty obvious that the world is a pretty big place. When you consider how long it took for human beings to settle every corner of it (~85,000 years, give or take a decade) and how long it took us to explored and map it all out, terms like “small world” cease to have any meaning.

But to complicate matters a little, the diameter of Earth – i.e. how big it is from one end to the other – varies depending on where you are measuring from. Since the Earth is not a perfect sphere, it has a different diameter when measured around the equator than it does when measured from the poles. So what is the Earth’s diameter, measured one way and then the other?

Oblate Spheroid:

Thanks to improvements made in the field of astronomy by the 17th and 18th centuries  – as well as geodesy, a branch of mathematics dealing with the measurement of the Earth – scientists have learned that the Earth is not a perfect sphere. In truth, it is what is known as an “oblate spheroid”, which is a sphere that experiences flattening at the poles.

Data from the Earth2014 global relief model, with distances in distance from the geocentre denoted by color. Credit: Geodesy2000
Data from the Earth2014 global relief model, with distances in distance from the geocentre denoted by color. Credit: Geodesy2000

According to the 2004 Working Group of the International Earth Rotation and Reference Systems Service (IERS), Earth experiences a flattening of 0.0033528 at the poles. This flattening is due to Earth’s rotational velocity – a rapid 1,674.4 km/h (1,040.4 mph) – which causes the planet to bulge at the equator.

Equatorial vs Polar Diameter:

Because of this, the diameter of the Earth at the equator is about 43 kilometers (27 mi) larger than the pole-to-pole diameter. As a result, the latest measurements indicate that the Earth has an equatorial diameter of 12,756 km (7926 mi), and a polar diameter of 12713.6 km (7899.86 mi).

In short, objects located along the equator are about 21 km further away from the center of the Earth (geocenter) than objects located at the poles. Naturally, there are some deviations in the local topography where objects located away from the equator are closer or father away from the center of the Earth than others in the same region.

The most notable exceptions are the Mariana Trench – the deepest place on Earth, at 10,911 m (35,797 ft) below local sea level – and Mt. Everest, which is 8,848 meters (29,029 ft) above local sea level. However, these two geological features represent a very minor variation when compared to Earth’s overall shape – 0.17% and 0.14% respectively.

Meanwhile, the highest point on Earth is Mt. Chiborazo. The peak of this mountain reaches an attitude of 6,263.47 meters (20,549.54 ft) above sea level. But because it is located just 1° and 28 minutes south of the equator (at the highest point of the planet’s bulge), it receives a natural boost of about 21 km.

Mean Diameter:

Because of the discrepancy between Earth’s polar and equatorial diameter, astronomers and scientists often employ averages. This is what is known as its “mean diameter”, which in Earth’s case is the sum of its polar and equatorial diameters, which is then divided in half. From this, we get a mean diameter of 12,742 km (7917.5 mi).

The difference in Earth’s diameter has often been important when it comes to planning space launches, the orbits of satellites, and when circumnavigating the globe. Given that it takes less time to pass over the Arctic or Antarctica than it does to swing around the equator, sometimes this is the preferred path.

We have written many interesting articles about the Earth and mountains here at Universe Today. Here’s Planet Earth, The Rotation of the Earth, What is the Highest Point on Earth?, and Mountains: How Are They Formed?

Here’s how the diameter of the Earth was first measured, thousands of years ago. And here’s NASA’s Earth Observatory.

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

Sources:

Posted on by Fraser Cain

How Long is a Year on Earth?

The eccentricity in Mars' orbit means that it is . Credit: NASA

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.

Posted on by Nancy Atkinson

Wilkins Ice Shelf Continues Break-up, Even During Winter

Satellite images reveal the Wilkins Ice Shelf in Antarctica has experienced further break-up with an area of about 160 square kilometers breaking off during May 30 -31, 2008. ESA’s Envisat satellite captured the event. This is the first ever-documented episode to occur during the Antarctic winter. The animation here, comprised of images acquired by Envisat’s Advanced Synthetic Aperture Radar (ASAR) between May 30 and June 9, highlights the rapidly dwindling strip of ice that is protecting thousands of kilometers of the ice shelf from further break-up.

Wilkins Ice Shelf, a broad plate of floating ice south of South America on the Antarctic Peninsula, is connected to two islands, Charcot and Latady. In February 2008, an area of about 400 square km broke off from the ice shelf, narrowing the connection down to a 6 km strip; this latest event in May has further reduced the strip to just 2.7 km.

According to Dr. Matthias Braun from the Center for Remote Sensing of Land Surfaces, Bonn University, and Dr. Angelika Humbert from the Institute of Geophysics, Münster University, who have been investigating the dynamics of Wilkins Ice Shelf for months, this break-up has not yet finished.

“The remaining plate has an arched fracture at its narrowest position, making it very likely that the connection will break completely in the coming days,” Braun and Humbert said.
Long-term satellite monitoring over Antarctica is important because it provides authoritative evidence of trends and allows scientists to make predictions. Ice shelves on the Antarctic Peninsula are important indicators for on-going climate change because they are sandwiched by extraordinarily raising surface air temperatures and a warming ocean.

The Antarctic Peninsula has experienced extraordinary warming in the past 50 years of 2.5°C, Braun and Humbert explained. In the past 20 years, seven ice shelves along the peninsula have retreated or disintegrated, including the most spectacular break-up of the Larsen B Ice Shelf in 2002, which Envisat captured within days of its launch.

News Source: ESA

Posted on by Fraser Cain

What is the Driest Place on Earth?

Dry Valleys. Image credit: NASA

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.

Posted on by Fraser Cain

Lowest Point on Earth

The Dead Sea from space. Image credit: NASA

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.