November 9, 2018

On Oct. 20, 2018, an Ariane 5 rocket blasted off from French Guiana, an overseas possession of France on the northern coast of South America. The rocket carried a pair of probes bound for Mercury, the planet in our solar system closest to the sun, as part of a mission called BepiColombo. The mission’s name honors Giuseppe “Bepi” Colombo, an Italian scientist who contributed greatly to the study of Mercury. ESA missions frequently launch from French Guiana at a site called Europe’s Spaceport. The site’s remote geographic location offers advantages in launch trajectory as well as a “slingshot effect” created by the speed of Earth’s rotation near the equator.

The Mercury Planetary Orbiter is one of two probes included in the BepiColombo mission that will study the planet Mercury. Credit: ESA/ATG medialab

The European Space Agency (ESA) developed and organized the BepiColombo mission. ESA led the construction of the Mercury Planetary Orbiter (MPO), the main probe. But two other space agencies contributed to BepiColombo. The United States National Aeronautics and Space Administration (NASA) built an instrument called a mass spectrometer for the MPO. And the Japan Aerospace Exploration Agency (JAXA) built the mission’s second orbiter, the Mercury Magnetospheric Orbiter (MMO). Magnetosphere is the zone of strong magnetic forces that surrounds a heavenly body.

BepiColombo will study Mercury, the innermost planet of the solar system. Credit: NASA Goddard

Mercury, about 48 million miles (77 million kilometers) from Earth, is not a well-studied planet. Only two NASA spacecraft—Mariner 10 and MESSENGER—have reached it so far. In 1974 and 1975, Mariner 10 discovered that Mercury has a strong magnetic field. Scientists had previously thought the planet too small to host a magnetic field. Japan’s MMO is specially designed to study this feature. MESSENGER, which orbited Mercury from 2011 to 2015, learned many things about the scorched planet’s surface and confirmed that water ice existed in permanently shadowed craters at its poles.

Mercury’s magnetic field hints at our solar system’s turbulent early history and unusual composition. Most planetary systems have planets all about the same size and spaced evenly apart. In our solar system, Jupiter, the largest planet, is almost 25,000 times larger than Mercury, the smallest. Mercury might once have been larger, but layers of the planet’s surface could have worn away over billions of years. Alternatively, the planet may simply be the remnant of a collision of earlier inner planets. The BepiColombo mission hopes to learn more about Mercury as well as the formation of our solar system.

BepiColombo is powered by ion propulsion, a method of propelling space vehicles by ejecting charged particles called ions. Ion propulsion increases travel time compared to traditional chemical propulsion, but it costs much less. Ion propulsion also allows a probe to avoid the sun’s powerful gravitational field by taking a long, winding path to Mercury’s orbit. BepiColombo will fly by Earth once, Venus twice, and Mercury six times before it finally enters into orbit around the planet in late 2025.

June 12, 2017

Hermes was one of the busiest ancient Greek gods who lived on Mount Olympus. Hermes was the messenger of the gods, the god of roads and doorways, and the protector of travelers. He was also the god of shepherds and literature, specifically poetry. In addition, he was honored among some believers as the inventor of music. Hermes served as the guide for dead souls on their way to the underworld. He protected boundaries and assisted public speakers and merchants. Hermes was also a god of fertility and found time to conduct numerous love affairs with mortals, goddesses, and nature sprites called nymphs. The Greeks believed Hermes brought good or unexpected luck. He had a clever and cunning personality and a reputation as a trickster, which accounted for his being a patron of vagabonds, criminals, and thieves. Hermes is similar to Rome’s Mercury, a god with his own lively list of responsibilities.

Mercury (a.k.a. Hermes) rides the mythical winged horse Pegasus in the Jardin des Tuilieries in Paris, France. Credit: © Zoran Karapancev, Shutterstock

Hermes was born in a cave on a mountain in Arcadia, a region in southern Greece. There he was associated with the protection of sheep and cattle. He was conceived and born in a single day. On that first day of his existence, Hermes invented a stringed instrument called the lyre, stole the cattle of the god Apollo, and may have invented fire as well. Hermes inherited his vast capacity for industry from his parents—Zeus, the king of the gods, and Maia, a minor goddess. Hermes had several children himself, including Pan, the half man-half goat god of woods and pastures.

Hermes is generally portrayed as a handsome young man wearing a winged hat and winged sandals (adding to his fleetness of foot while delivering messages). He carried a caduceus «kuh DOO see uhs», a staff with snakes wrapped around it. Snakes were a symbol of fertility.

May 1, 2015

There’s a new crater on Mercury. Yesterday, the MESSENGER space probe crashed into the surface of the closest planet to the sun. It was a planned crash, as the spacecraft had spent all of its fuel.

MESSENGER’S last image before the crash. (NASA)

MESSENGER (Mercury Surface, Space Environment, Geochemistry, and Ranging) was a probe sent to study the planet Mercury. The U.S. National Aeronautics and Space Administration (NASA) launched the probe in 2004. On its way to Mercury, the probe flew past Venus in 2007. During this flyby, MESSENGER worked with the European Space Agency (ESA) probe Venus Express to detail Venus’s surface. In 2008, the craft flew by Mercury twice and photographed areas of its surface that had never been seen by a spacecraft. MESSENGER flew by Mercury again in 2009. It took this long, complex route in order to enter into orbit around Mercury using minimal fuel, which it accomplished in March 2011. The probe mapped Mercury’s surface and studied its composition, interior structure, and magnetic field for four years.

MESSENGER, seen in an illustration (right), was the first probe to study the planet Mercury up close since Mariner 10 in 1974. MESSENGER took this photograph (left) during its first flyby of Mercury in January 2008. NASA/APL; NASA

MESSENGER made many important discoveries about Mercury. It showed that the planet has shrunk slightly since its formation. It also found that volcanic forces played a major part in the formation of Mercury’s surface. Finally, MESSENGER discovered small regions of ice at permanently shaded craters near the planet’s poles.

Despite MESSENGER’s fuel-saving maneuvers, the sun’s closeness posed challenges for the probe. The sun has an incredible amount of mass and thus a powerful gravitational pull. The sun’s gravity disrupted MESSENGER’s orbit, forcing the craft to fire its engines occasionally to keep from being pulled into Mercury. The probe ran out of fuel earlier this month and crashed into Mercury yesterday at 8,750 miles (14,000 kilometers) per hour. The crash made a crater some 50 feet (15 meters) in diameter. Talk about going out with a bang!

Other World Book articles

• Rediscovering Mercury
• Space exploration (2004-a Back in time article)
• Space exploration (2011-a Back in Time article)
• Space exploration

April 2, 2015

Scientists at Brown University  in Providence, Rhode Island, have proposed that the dark surface of Mercury, the closest planet to the sun in the solar system, formed from a steady “rain” of carbon-rich dust from passing comets, which has “painted” the surface of the planet for billions of years. The darkness of the planet’s surface has long puzzled planetary scientists.

Mercury’s dark surface, photographed from NASA’s Messenger probe. (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

Mercury is dry, extremely hot, and almost airless. Like the moon, Mercury is covered by broad, flat plains; steep cliffs; and many deep craters similar to those on the moon. The craters formed when meteoroids or small comets crashed into the planet. However, unlike the moon, the surface of Mercury reflects only about 6 percent of the sunlight it receives.

Many asteroids and moons in the solar system get their dark color from iron-bearing minerals on their surface. But scientists know Mercury is covered by a thin layer of minerals called silicates that contain almost no iron. The Brown University scientists theorized that carbon-rich dust from passing comets could be the cause of Mercury’s dark color. The amount of comet dust in the solar system increases near Mercury as the icy bodies release great amounts of gas and dust approaching the sun.

Oddly, the scientists found that comets that struck Mercury would have no affect on the coloration of the planet’s surface. A direct hit by a comet would blast all of the surface impact material into space. The scientists calculated impact angles and speeds and found that a gentle rain of dark comet dust would accumulate on Mercury’s surface as the icy bodies passed in their journey around the sun.

The scientists are hoping that NASA’s Messenger probe can obtain information on the carbon content of Mercury’s surface next month as it continues to come closer to the planet. Launched in 2004, the Messenger flew by Mercury in 2009 and went into orbit around the planet in March 2011. The probe was designed to map Mercury’s surface and study its composition, interior structure, and magnetic field for one year. As of March 2015, Messenger was still sending information about Mercury back to Earth. Scientists expect the probe will crash into Mercury by May 2015.

Other World Book articles: 

• Carbon
• Iron
• Silicate
• Space Exploration

March 27, 2012

Sometimes things are not as simple as they appear. Take the planet Mercury, for instance. In a very short time, the smallest planet in the solar system (sorry Pluto, you’re no longer a planet) has gone from a simple hunk of rock, much like Earth’s moon, to one of the most unusual planets ever studied. For years, most astronomers thought that Mercury formed early in the solar system’s history and has since remained pretty much unchanged. New evidence shows a planet whose more recent history includes active volcanoes, a shifting crust, and other activities once thought to have ended billions of years ago. Some of these activities may result from the fact that Mercury is slowly shrinking. The shrinking would explain why the outer layer of the planet is buckling and cracking. A closer look at the surface also shows evidence of lava flows having occurred much more recently than previously thought.

The MESSENGER space probe has revealed surprising new findings about the smallest planet in the solar system. (Courtesy of NASA)

The planet’s surface is not the only surprise. Mercury may also have an internal structure like no other planet yet studied by scientists. Mercury appears to have a core consisting of three layers. Earth has only two such inner layers. Both Mercury and Earth have an inner core of solid metal surrounded by a second layer of liquid metal. Unlike Earth, Mercury appears to have a third layer made of solid iron and sulfur. Many scientists now speculate that this possible third layer of core explains one of the great mysteries concerning Mercury. Scientists have long wondered how the planet could be so small and yet have a much greater mass than the other inner planets–Venus, Earth, and Mars–for its size.

The new data on Mercury was collected by the MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) space probe. Launched in 2004 by NASA, MESSENGER began a one-year mission orbiting Mercury in early 2011 (which NASA scientists have now extended). The probe reached the planet after a more than five-year tour of the inner solar system. The long, looping route involved three close fly-bys of Mercury along with close approaches to Venus and Earth.

Just how loopy was the route MESSENGER took? Mercury is only about 20 percent farther from Earth than Mars when those planets pass closest to Earth. Yet, a probe going to Mars travels for less than a year. By comparison, MESSENGER took more than five years to reach Mercury.

Additional World Book articles

• Probing the Planets (a special report)
• Space Exploration 2004 (Back in Time article)
• Space Exploration 2008 (Back in Time article)
• Space Exploration 2009 (Back in Time article)
• Space Exploration 2011 (Back in Time article)