Mercury A Scorched and Battered World
Starter • Take a moment and imagine yourself on Mercury, what would you see? What might you experience?
Mercury: Strange Days • Imagine looking up at a sun that is three times larger than what you see on Earth. • Even stranger, the morning sun would appear to rise briefly, set and rise again – and the same thing would happen in reverse at sunset. • This is due to Mercury’s wild elliptical (egg-shaped) orbit and weird rotation.
Strange Days • Part way through its orbit, the speed of Mercury’s orbital velocity matches its angular rotational velocity. When this happens, the Sun will appear to go backwards in the sky before it resumes its regular direction https://www.youtube.com/watch?v=gubNWJ5RlP4
Strange Days • The weird rotation: one day on Mercury (the time it takes for Mercury to rotate or spin once) takes 59 Earth days; whereas it makes a complete orbit around the sun (a year in Mercury time) in just 88 Earth days.
Things you should know about Mercury • Mercury is the smallest planet in our solar system (since Pluto’s downgrade) – and is only slightly larger than the Earth's moon. • It is the closest planet to the sun at a distance of about 58 million km (36 million miles) or 0.39 AU.
Things you should know . . . • Mercury is a rocky planet, also known as a terrestrial planet. Mercury has a solid, cratered surface, much like Earth's moon. • Mercury's thin atmosphere, or exosphere, is composed mostly of oxygen (O2), sodium (Na), hydrogen (H2), helium (He), and potassium (K). • According to NASA, atoms that are blasted off the surface by the solar wind and micrometeoroid impacts create Mercury's exosphere.
Mercury’s Exosphere • Mercury essentially does not have an atmosphere (very similar to our moon). • This is evidenced by its weak gravitational field. • Mercury has an escape velocity of only 4.3 km/s, as compared to Earth’s 11.2 km/s. • Our moon’s is only 2.4 km/s (indicating Mercury has more atmosphere (next slide) than our moon.
Mercury’s Exosphere • So, Mercury does not have much of an atmosphere but here is a continual reference to Mercury’s exosphere. • An exosphere is defined as the highest region of the atmosphere – where air density is so low that a fast moving air molecule has a > 50% likely of escaping into space (instead of hitting other molecules).
Things you should know . . . • Mercury has no moons. • Only two spacecraft have visited this rocky planet so far: • Mariner 10 in 1974-5 and • MESSENGER, which flew past Mercury three times before going into orbit around Mercury in 2011.
Mercury Missions http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=BEPICLMBO • The European Space Agency has a mission planned to reach Mercury in 2015 - BepiColombo. • Due to budget constraints part of the mission, the lander portion, was cancelled.
Things you should know . . . • No evidence for life has been found on Mercury (which goes without saying). • Daytime Temperatures can reach 430 degrees Celsius (800 degrees Fahrenheit) and drop to -180 degrees Celsius (-290 degrees Fahrenheit) at night. • Even the hardiest archea or bacteria probably could not stand these swings in temperature – though we shouldn’t count them out. • Mercury appears to have ice on its poles in areas that are permanently shaded.
A little bit about Mercury • https://www.youtube.com/watch?v=rZU8Y9DIBtI • So, let’s take a moment and think about where we are in our “knowledge” of Mercury.
Massive Asteroid Impact • The Caloris Basin is a massive impact crater on Mercury and one of the largest in our solar system (960 miles in diameter – 9 times the size of the crater that led to the dinosaur’s demise). • The impacting asteroid is estimated to have been 62 miles in diameter (Earth’s was only 6). • Could we deal with an asteroid that size? • The Basin is ringed with mountains formed by the impact.
Relativity and Mercury • Albert Einstein proposed three tests of general relativity, subsequently called the classical tests of general relativity, in 1916: • the perihelion precession of Mercury's orbit • the deflection of light by the Sun (Eclipse) • the gravitational redshiftof light
Relativity and Mercury • The General Theory of Relativity did successfully predict perihelion precession of Mercury’s orbit • Mercury deviates from the precession predicted from these Newtonian effects. • Einstein showed that general relativity agrees closely with the observed amount of perihelion shift – cementing Relativity, replacing Newton. • This was a powerful factor motivating the adoption of general relativity.
Relativity and Mercury • https://www.youtube.com/watch?v=hSXNE0pNtr8 Neal deGrasse Tyson – Relativity and Mercury.
Exit Ticket • What are three things you learned about Mercury?