Mercury

Average distance from Sun: AU (57,910,000 km/35,980,000 mi) Length of Year:88 days Rotation period:58.65 days Mean orbital velocity:48 km/s (30 mi/s) Inclination of axis:2° Average temperature:800° F (427° C) day -300° F (-183° C) night Diameter:4,878 km (3,031 mi) Number of observed satellites: Magnetic field 0 weak Mercury Facts

Mercury Facts – cont. Closest distance to Earth – 77 million km Farthest distance from Earth – 222 million km Mass – 3.3 X kg Density – 5.43 g/cm 3

EARTHMERCURYMOON Mercury’s diameter is 4,880 km. That’s 40% smaller than Earth and 40% larger than the moon

Mercury’s core is 75% of its mass, and consists of iron and molten lava Rocky mantle Scientists think Scientists think Mercury’s dipolar magnetic field is produced by its partially molten core. Mercury’s density is similar to that of Earth’s at 5.42 gm/cm^3

Mercury is one of the five planets known to the ancients. They called these planets "wandering stars". Mercury may be seen as an evening "star" near where the sun has set, or as a morning "star" near where the sun will rise. The ancient Greeks called the evening star Hermes and the morning star Apollo, believing them to be different objects. The planet is named for Mercury, the Roman messenger of the gods. Historical Facts

Named after Mercury, the Roman god of commerce and delivering messages His name comes from the Latin word "mercari" meaning to deal or trade. The planet was named Mercury because it appeared to move faster in the sky than any other planet. We now know that this was because of its small orbit.

Mercury is not much bigger than our Moon. It is the smallest planet. The hazy atmosphere near the horizon on Earth spoils the view of Mercury for ground-based telescopes. Earth-based telescopic photo of Mercury taken from Catalina Observatory 1.5 meter (61 inch) telescope. It is so close to the Sun that it can be seen only in the twilight sky of the Earth.

Mercury Orbital Facts Until 1965, scientists thought that the same side of Mercury always faced the Sun. Mercury takes only 88 Earth days to complete one orbit Rotates slowly, once every 59 Earth days. This means that it rotates precisely three times for every two orbits

More Orbital Facts… orbits the Sun in a highly elliptical orbit at about one third of the Sun-Earth distance. 46 million kilometers from the Sun at perihelion (closest), 70 million kilometers away at aphelion (furthest). Rotates vertically, so Mercury does not have opposite seasons in each hemisphere like Earth does. “Seasonal” temperatures vary with distance from the sun. Extremely hot days and very cold nights. Mercury has very little atmosphere so the surface cools down rapidly on the night side.

Transit of Mercury Visible from Earth about every 8 years.

Image of May 7, 2003 Mercury Transit was taken by NASA/ESA's SOHO (Solar & Heliospheric Observatory)

Transit of Mercury on November 8,2006. Sunspot #923, which is just below the equator at the left-hand side, is much bigger than Mercury is. Two more sunspots at the right- hand side at the equator. Mercury appears as a small black dot in the lower middle of the solar disk.

Next transit: May 9, 2016

Mariner 10 10,000 pictures with 57% planet coverage reveal an intensely cratered, Moon- like surface and a faint atmosphere of mostly helium, resulting from solar wind bombardment. 3 Flybys Mariner 10 was the first to use the gravitational pull of one planet (Venus) to reach another (Mercury). Instruments on board the spacecraft were designed to measure the atmospheric, surface, and physical characteristics of Mercury and Venus.

Incoming View of Mercury This photomosaic of Mercury was constructed from photos taken by Mariner 10 six hours before the spacecraft flew past the planet on March 29, These images were taken from a distance of 5,380,000 kilometers (3,340,000 miles).

Close Encounter This two-image mosaic of Mercury was constructed from photos taken by Mariner a few hours before the spacecraft's closest and first encounter with the planet on March 29, 1974.

Outgoing View of Mercury This mosaic of Mercury was created from more than 140 images taken by the Mariner 10 spacecraft on March 29, The images were acquired after the spacecraft exited Mercury's shadow.

Mercury’s Atmosphere Mercury has almost no atmosphere and no water. The trace gases (oxygen, sodium, helium) that are there are made up of atoms or ions blasted off its surface by the solar wind. Mercury's extreme surface temperature enhances the escape of these volatile atoms into space. No erosion from wind or water. Might have water ice at its north and south poles inside craters where the sun cannot reach. Meteorites do not burn up due to friction because there is no atmosphere.

Mercury’s Surface Highly cratered with smooth areas. Relatively ancient, volcanic surface. Similar to Earth’s Moon, but fewer craters and more “plains”.

Caloris Basin Largest structure on Mercury ~1300 km Asteroid-size impactor early in solar system history Basin contains smooth plains but is highly ridged and fractured.

"Weird terrain“, hilly, lineated region. The shock wave produced by the Caloris impact caused ripples in the crust. Antipodal from Caloris

Discovery Rupes Linear feature may be a thrust fault. Many rupes on Mercury Likely formed as the rock cooled and shrunk 200 km

Mercury’s Interior Mercury’s density is much higher than Earth’s, but planet is only ~1/3 the size of Earth. Large iron core, 75% of radius (~1850 km), Silicate mantle only ~550 km thick.

Origin of Mercury’s Large Core Unknown, but hypotheses include: 1.Radial compositional (iron) zonation of the inner solar system. 2.Perhaps young Mercury was a larger planet, but giant impact removed much of mantle.

Messenger Discovery Mission MErcury Surface, Space ENvironment, GEochemistry, and Ranging mission. MESSENGER was launched in 2004 and entered Mercury’s orbit in 2011 to carry out comprehensive measurements. It began its 2000 th orbit of Mercury on May 22, html

MESSENGER’s “Science Drivers”: First Mission Why are the characteristics of the core and why is it so large compared to the mantle? What is the geological history of Mercury? What is the nature and origin of Mercury's magnetic field? What are the materials at Mercury's poles? What are the characteristics of Mercury’s gases?

Figure 2. MESSENGER mission timeline featuring major trajectory adjustments (DSM dates may change) At the end of MESSENGER’s initial mission, further studies were approved. Now 100% of Mercury’s surface has been photographed

Science Payload

MESSENGER’s “Science Drivers” Current Mission Sources of gases and how they move How long ago was Mercury volcanically active? How did Mercury's surface features change with time? What is the origin of Mercury's energetic electrons?

MESSENGER’s WAC multi-spectral images to study compositional variations across the surface of Mercury. The white arrows identify areas of Mercury’s surface that are interpreted to be relatively young volcanic plains, and the black arrows point to reddish areas interpreted to be volcanoes. Most of the color differences studied here are believed to indicate variations in the mineral composition and physical state of the rocks at different places on Mercury.

Capturing Mercury through MESSENGER's Dual Cameras Date Acquired: September 29, 2009 Image Mission Elapsed Time (MET): , Instrument: Narrow Angle Camera (NAC) and Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS) Resolution: Top WAC image: 24.5 kilometers/pixel (15.2 miles/pixel). Bottom NAC image: 3.5 kilometers/pixel (2.2 miles/pixel). Scale: Mercury's diameter is 4880 kilometers (3030 miles) Spacecraft Altitude: 137,000 kilometers (85,000 miles)

Date Acquired: September 29, 2009 Image Mission Elapsed Time (MET): Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS) Resolution: 410 meters/pixel (0.25 miles/pixel) in the lower right corner of this image Scale: This image is about 420 kilometers (260 miles) across Spacecraft Altitude: 16,200 kilometers (10,100 miles)

The mission is named in honor of Giuseppe (Bepi) Columbo, an Italian scientist who explained Mercury's unusual rotation (three turns for every two trips around the Sun). He also suggested to NASA the way to make multiple fly-bys of Mercury during the Mariner 10 mission. BepiColumbo European Mission to Mercury Planned launch ~2016, 1 Lander and 2 Orbiters