1. Venus and Mercury
Inner Planets, Solar System
Laura Pickering

2. venus
Left photo: Cloud structure on Venus in 1979, revealed by observations in the UV band by Pioneer Venus Orbiter
Right photo: Global radar view of Venus between 1990 and 1994 by Magellan

3. Venus Shrouded by opaque, cloud-like surface
Appears as brighter point of white light
Best seen during crescent phase, sun low or setting
150x OK for viewing
Closest planet to Earth
Synodic period = 584 days (time for Venus to return to same position relative to Earth)
Right photo: what you would see from the ground during the best seeing time (crescent)
Opaque layer of highly reflective sulfuric acid, making it hard to see the surface from space in visible light
Brightest point of light alongside the moon at night
Closest planet to Earth, and also most similar to Earth
Synodic period: the amount of time that it takes for an object to reappear at the same point in relation to Earth (full to full) = 584 days
Sidereal period: amount of time that it takes an object to make a full orbit around Sun = 225 days
Photo of Venus from ground

4. Venus orbit

5. Venus Closest planet to Earth, most similar planet to Earth
Diameter = km
640 km less than Earth
Mass = E+24 kg
81.5% of Earth’s mass
Angular diameter = ° to °
Apparent magnitude = -4.5
Diameter: km less than earth’s
Mass: 81.5% of earth’s
Apparent magnitude: measure of object’s brightness, brighter the object, lower the magnitude

6. Venus Atmosphere: Surface: 3° axial tilt
Densest terrestrial planet, 96% carbon dioxide
Pressure 92x greater than Earth’s
Surface:
Mean Temperature = 735 K
Dry, desert, with slab-like rocks shaped by volcanic activity
Other 3.5% of atmosphere is nitrogen
Surface is isothermal, maintaining a constant temperature between night and day and between equator and poles – only significant temperature variation occurs with altitude
3 degree axial tilt contributes to LESS seasonal temperature variation
Surface of Venus

7. Venus Visited by Mariner 10 spacecraft in 1962
Landed on in 1970 by Venera 7
Hostile surface conditions hindering future exploration
Photo uses UV light
Photo of Venus by Mariner 10

8. Mercury Left photo: Mercury taken by MESSENGER
Right photo: Mercury photo by MESSENGER enhanced to see the different chemicals in the planet

9. Mercury Best seen during morning or evening twilight
Observed during total solar eclipse
Viewing greatly hindered by proximity to sun
> 150x best for viewing
Synodic period around Sun = 116 days (time for Venus to return to same position relative to Earth)
Viewing highly difficult due to the proximity to the sun, Hubble can’t take any photos of mercury due to proximity to sun
Best viewing = x
Can be observed during total solar eclipse
Synodic period = 116 days
Sidereal period = 88 days
Observed from the ground- professional

10. Mercury
orbit

11. Mercury & venus
Can view Venus more/longer because of the greater distance from the Sun relative to the Earth

12. Mercury Smallest planet, closest to the Sun Diameter = 4879.4 km
38% of Earth’s diameter
Mass = E+23 kg
5% of Earth’s mass
Angular diameter = ° to °
Average apparent magnitude = 0.23
Smallest planet
Diameter: 38% of Earths
Mass: 5% of Earth’s
Difficult to view at night due to lower altitude and short viewing span of the planet, but easier to track during the day when the planet has higher altitude with an infrared filter to darken the image – amateur trick
Observed from ground – amateur during day

13. Mercury 1/30° axial tilt Surface: Absence of atmosphere
Temperature varies more than any planet (100 K to 700 K)
Heavily cratered = inactive for billions of years
Evidence of water ice where sun does not see
Absence of atmosphere
Smallest axial tilt of all planets, means some regions do not see the sun
These regions are therefore much colder, some around 102 K, and the MESSENGER found evidence of large volumes of water ice in the crater in these regions
However, the amount of craters also shows evidence that the planet has been inactive for billions of years
The temperature has such a large gradient due to the absence of an atmosphere
North Pole of Mercury, large volume of water ice

14. Mercury Mariner 10 flew by in 1974
MESSENGER orbited times ( )
Crashed into Mercury
Proximity to Sun and necessary speed to reach makes exploration difficult
MESSENGER crashed into Mercury due to fuel exhaustion after orbiting the planet for about 4 years, starting orbit in 2011 after travel to Mercury for three years and then fly bys for a few more years
Increased speed required to reach it is relatively high and due to proximity to sun, orbits around it are rather unstable
MESSENGER was first probe to orbit Mercury
MESSENGER Probe

15. Thanks!
Questions?