Venus and Mercury Inner Planets, Solar System Laura Pickering

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 https://www.businessinsider.com/venus-gravity-wave-akatsuki-2017-1 https://en.wikipedia.org/wiki/Venus

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 https://en.wikipedia.org/wiki/Venus

Venus orbit http://demo.webassign.net/web/Student/Assignment-Responses/last?dep=3522

Venus Closest planet to Earth, most similar planet to Earth Diameter = 12103.6 km 640 km less than Earth Mass = 4.8675E+24 kg 81.5% of Earth’s mass Angular diameter = 0.002694° to 0.018333° Apparent magnitude = -4.5 Diameter: 634.8 km less than earth’s Mass: 81.5% of earth’s Apparent magnitude: measure of object’s brightness, brighter the object, lower the magnitude https://en.wikipedia.org/wiki/Phases_of_Venus

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 https://en.wikipedia.org/wiki/Venus

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 https://en.wikipedia.org/wiki/Venus#Exploration

Mercury Left photo: Mercury taken by MESSENGER Right photo: Mercury photo by MESSENGER enhanced to see the different chemicals in the planet https://en.wikipedia.org/wiki/Mercury_(planet)

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 = 200-250x Can be observed during total solar eclipse Synodic period = 116 days Sidereal period = 88 days Observed from the ground- professional https://www.skyandtelescope.com/observing/celestial-objects-to-watch/catching-the-messenger-of-the-gods/

Mercury orbit https://www.universetoday.com/

Mercury & venus Can view Venus more/longer because of the greater distance from the Sun relative to the Earth http://jwilson.coe.uga.edu/EMAT6680Fa09/Yoon/EMAT%206690/First%20Task/3rd%20page%20-%20find%20orbit%20mercury/plotorbitmercury.html

Mercury Smallest planet, closest to the Sun Diameter = 4879.4 km 38% of Earth’s diameter Mass = 3.3011E+23 kg 5% of Earth’s mass Angular diameter = 0.00125° to 0.00361° 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 http://www.danielegasparri.com/Inglese/beyond_standard.htm

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 https://en.wikipedia.org/wiki/Mercury_(planet)

Mercury Mariner 10 flew by in 1974 MESSENGER orbited 4000 times (2004-2015) 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 https://www.thedailybeast.com/messenger-probe-crashes-into-mercury

Thanks! Questions?