You might say that planet Earth is a very large magnet. We have mentioned before Earth’s magnetic field that is generated by the iron core. The movement of that molten iron generates a magnetic field surrounding our planet. We can see the effect of that field every time we use a compass to find directions.
What you may not realize is that there is also a magnetic field generated by the ocean. Salt water is a good conductor of electricity. Moving electric currents generate magnetic fields. Hans Christian Ørsted discovered that by accident in 1820 when he noticed that placing a compass near a wire carrying an electric current caused deflection of the compass needle.
Salt dissolved in the oceans’ water creates ions, which are electrically charged particles. The movement of ocean tides causes those charged particles to move. Electric current is electrically charged particles in motion. Since electric current generates a magnetic field, the ocean tides generate magnetic fields. Because the movement of ocean currents and tides is complex, the magnetic fields generated by the oceans are more complex than the big magnetic field of the Earth. They are also 20,000 times weaker than Earth’s main magnetic field making them harder to measure.
Today’s satellite technology allows us to map the oceans’ magnetic field. The European Space Agency used three satellites to create a network called “Swarm.” They used the data from those satellites to create a 3-D digital map of this little-known magnetic field. The research shows how the field changes over time. Although the oceans create a relatively small part of Earth’s magnetic field, they play an important role. Mapping this field also give scientists a better picture of how the oceans flow all the way down to the seabeds. That information gives us a better understanding of Earth’s climate.
Combined with the magnetic field produced by the molten core and rocks in Earth’s crust, we are protected by a “cocoon” surrounding our planet. You might say, “Protected from what?” Our Sun frequently erupts in solar storms releasing charged particles that escape into space. Many of those particles travel to the Earth. We call it “solar wind.” Without a protective magnetic shield, those particles would reach Earth’s surface disrupting power grids and aircraft navigation. More basic than that, they would damage human cells causing cancers and other health problems.
In 1999 astronomers detected the first exoplanet–a planet in another solar system. The number of planets detected orbiting around stars other than our Sun has grown to more than 3,500 today. There are billions of stars in our Milky Way Galaxy so searching for other worlds is just getting started.
NASA’s main tool for finding exoplanets has been the Kepler space telescope. The method of detecting those planets is watching for occlusions. If there is a planet orbiting a star, it will sometimes pass in front of that star from our viewpoint causing an occlusion or mini-eclipse. The planets are too small for us to see, but we can see a small dip in the light coming from the star. If the dip comes on a regular interval that means it might be an orbiting planet. The amount of the dip in light level indicates the size of the planet in relation to its star. Using this method of detection, astronomers have compiled a catalog of detected planets.
As I said, until now the Kepler telescope has been the method for finding most of these planets, but it will soon end its life. However, 2018 will be the beginning of new opportunities to look for exoplanets because of two new satellite-based observatories. Very soon NASA will launch TESS. That stands for Transiting Exoplanet Survey Satellite. By the end of the year, the European Space Agency (ESA) will launch CHEOPS or Characterising Exoplanet Satellite. (Aren’t you glad we have acronyms.)
The Kepler telescope was very good at searching for other worlds, but only in a small area of the sky. TESS will take a much wider view with the hope of finding many more. For obvious reasons, so far most of the planets detected are giant planets. TESS will be targeting bright stars in the hope of finding smaller planets that more closely resemble Earth. Astronomers will be able to target TESS more precisely toward selected stars.
On the morning of September 15, 2017, Cassini ended its life in fiery destruction. Cassini was a space probe orbiting and studying Saturn, and by all measures, Cassini exceeded expectations.
NASA, the European Space Agency, and the Italian Space Agency worked together on the Cassini-Huygens space exploration project. The mission was to study Saturn along with its moons and rings. NASA launched the spacecraft in 1997, and it arrived near Saturn and went into orbit around that planet in 2004.
The Huygens (pronounced hoy-guns) lander module, provided by the ESA, separated from the Cassini probe and landed on Saturn’s largest moon, Titan, in 2005. The parachute landing was successful, and the probe sent out data for about 90 minutes. In that brief time, scientists learned much about the surface of that distant moon. Viewed from Titan’s surface, the Sun appeared about the size and brightness of a car headlight 150 meters away. The Huygens probe took pictures and told us that Titan’s surface is dotted with rivers, lakes, and oceans made of methane and ethane. It also has dunes up to 300 feet (91 meters) tall.
Meanwhile, the Cassini probe continued to orbit Saturn and send back amazing and beautiful pictures of its rings and moons for 13 years. Cassini helped us to learn more about the moons of Saturn. The planet has at least 53 moons and possibly eight more. We learned that the moon Enceladus is covered with a liquid water ocean with a surface layer of ice 19 to 25 miles (30 to 40 km) thick. Geysers of water erupt from cracks in the ice. The rings of Saturn are a constantly changing collection of ice particles and small rocks. Saturn has hurricane-like storms at both poles and a hexagon-shaped jet stream at the north pole. How long is a day on Saturn? That’s hard to determine because it is a gas planet and not all parts of it move at the same speed. Scientists estimate a little more than 10 hours.
Cassini exceeded expectations by surviving seven years of travel to Saturn plus 13 years orbiting the planet. As it ran out of fuel, scientists sent it hurtling into Saturn’s atmosphere to burn up so it could not contaminate any of Saturn’s moons by crashing into them.