1. Mercury

2. Similarities to the Moon The Moon and Mercury have several similarities: Both have heavily cratered surfaces Both are virtually unchanging Both have extreme temperatures Neither one has a permanent atmosphere

3. Orbital Properties Mercury is the closest planet to the Sun The Sun viewed from Mercury looks almost 3 times as large as it does from Earth Mercury is difficult to observe from Earth because of its closeness to the Sun Mercury has a very eccentric orbit (eccentricity-the amount by which an orbit deviates from a perfect circle) Mercury is 46 million km from the Sun at its closest point in orbit Mercury is as far away as 70 million km from the Sun

4. Rotation and Revolution Rates Until 1965, scientists thought that the same side of Mercury always faced the Sun Astronomers discovered that Mercury rotates 3 times in 2 of its years Mercury takes 88 days to orbit the Sun Mercury takes 59 days to rotate Mercury’s day is longer than it’s year Mercury has a solar day (time from noon to noon) of 176 Earth days Mercury’s speed is nearly 50 km/sec faster than any other planet

5. Imagine that at the beginning of a rotation, a feature is pointing directly to the Sun (this position is the equivalent of noon—position 1 in the diagram). When Mercury has completed one revolution around the Sun, this feature will end up pointing directly away from the Sun, or at midnight (position 4). It will take another full revolution before the feature points directly to the Sun again, ending up at noon. Therefore, the solar day in Mercury (noon to noon) is exactly twice its orbital period. If you lived on Mercury, you would be two years older every solar day! Rotation and Revolution Rates

6. The Name The planet Mercury is named after Mercury, the Roman god of commerce, travel, wrestling, and thieving This Roman god was based on the Greek god Hermes Hermes was the messenger for the other Greek gods The planet Mercury changes position in the sky from night to night more quickly than the other planets, which is probably why it was named after this speedy Roman god

7. Atmosphere Mercury is too small for its gravity to retain any significant atmosphere over long periods of time Mercury has a very thin atmosphere consisting of atoms blasted off its surface by the solar wind Because Mercury is so hot, the atoms quickly escape into space The atoms are continuously lost and replenished Contains oxygen, sodium, helium, hydrogen, calcium, and potassium There is no atmosphere to protect the surface Meteorites do not burn up due to friction

8. Surface Mercury’s surface is heavily cratered Shortly following its formation, Mercury was heavily bombarded by comets and asteroids The planet was once volcanically active There are also smooth plains and rugged highlands

9. Mariner 10 For a long time, astronomers could only speculate about the markings on Mercury because even the largest ground-based telescopes can resolve surface features on Mercury about as well as we can perceive features on the Moon with our unaided eyes The Mariner 10 probe is the only probe that has visited Mercury 1974-1975 The spacecraft used the gravity of Venus to adjust its orbital velocity so that it could approach Mercury Mariner 10 provided the first close-up images of Mercury’s surface, which immediately showed its heavily cratered nature, and also revealed many other types of geological features

10. Mariner 10 Images

11. Caloris Basin Largest feature on Mercury Impact crater about 1300 km (810 miles) in diameter Surrounded by mountains up to 2 km high Caused by an asteroid impact on the planet’s surface early in the solar system’s history The probable cause of the strange surfaces on the opposite side of the planet

12. Temperature The average surface temperature of Mercury is 354 o F The temperature ranges from -298 o F to 800 o F Largest surface temperature variation in the solar system The temperature range is so high due to the absence of an atmosphere and the incredibly long days and nights The sunlight on Mercury’s surface is 6.5 times as intense as it is on Earth

13. Structure One of the four terrestrial planets Second smallest planet (including Pluto) Earth is about 2.6 times bigger than Mercury Has the second highest density in the solar system The density is 5.43 g/cm³, which is slightly less than Earth’s Mercury’s core occupies 42% of its volume and 70% of its mass Earth’s core only occupies 17% The core is made of iron Surrounding the core is a 600 km mantle Mercury’s crust is 100-200 km thick

14. Magnetic Field Mariner 10 discovered a magnetic field Mercury’s magnetic field is about 1/100 that of Earth Scientists have no clear understanding of the origin of Mercury’s magnetic field

15. 1991 Astronomers used radar observations that showed: Mercury may have water ice at the poles Ice exists inside deep craters Floors of the craters remain in perpetual shadow so the Sun cannot melt ice

16. MESSENGER NASA has plans for a new mission to Mercury MErcury Surface, Space ENvironment, GEochemistry, and Ranging Launched on August 3, 2004 Will have three Mercury flybys in 2008 During the flybys, MESSENGER will map nearly the entire planet in color and measure the composition of the surface, atmosphere, and magnetosphere The MESSENGER mission, spacecraft, and science instruments are focused on answering six questions: Why is Mercury so dense? What is the geologic history of Mercury? What is the structure of Mercury’s core? What is the nature of Mercury’s magnetic field? What are the unusual materials at Mercury’s poles? What volatiles are important on mercury?

17. Bepi-Columbo Mission by the European Space Agency Composed of three parts A spacecraft in low orbit to make planet observations Another craft in eccentric orbit to study the magnetosphere Surface lander Planned to launch in 2013

18. Fast Facts NamesakeMessenger of the Roman Gods Mean distance from the Sun57.9 million km Orbital period88 days Rotational period58 days 39 minutes Diameter4,879 km Mass0.06 of Earth’s Gravity0.38 of Earth’s Atmosphere (primary contents) Oxygen, sodium, helium Temperature range-298 o F to 800 o F Number of Moons0 Number of rings0

19. Significant Dates 1610Galileo observed Mercury with a telescope 1631Pierre Gassendi observed the transit of Mercury across the face of the Sun with a telescope 1639Giovani Zupus discovered that Mercury has phases, which was evidence that the planet circled the Sun 1641Johann Franz Encke made the first mass determination using the gravity effect on the comet Encke 1889Giovanni Schiaparelli produced the first map of Mercury’s surface features 1965Gordon Pettengill and Rolf Dyce measured Mercury’s rotation period to be about 59 days 1968Surveyor 7 took first spacecraft pictures of Mercury from the lunar surface 1974Mariner 10 made first flyby within 705 km of Mercury 1975Mariner 10 made third and final flyby of Mercury at 327 km