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Saying 'Goodbye' to Voyager 1 & 2 | the Week 2016NoCoAstro SAYING ‘GOODBYE’ TO VOYAGER 1 & 2 | THE WEEK NASA uses modern technology in the fight to keep our dying spacecraft alive. OUR JOURNEY CONTINUES Neptune was the first planet located by mathematical predictions instead of direct observations of the sky. How do you discover a planet, anyway? EDITOR Amanda Bell CONTACT Questions, comments, submissions, photos or just to say ‘hello’: ObjView at NoCoAstro dot org November NoCoAstro NOCOASTRO MEETING Date: Thursday December 1st, 6:15pm Location: Fort Collins Museum of Discovery Speaker: Earth’s Aurora and Radiation Belts: Exploration on the Edge of Space with Dr. David Malaspina DID YOU KNOW…? All meetings are FREE & open to the public! Just stop by the Fort Collins Museum of Discovery. NOCOASTRO OUTREACH* 3rd & 17th, Saturday Fossil Creek Reservoir, 7pm 7th, Wednesday Poudre Learning Ctre, 7pm November 30th, Friday Fossil Creek Reservoir, 7:30pm DECEMBER * more details online at: NoCoAstro.org T RUE BLUE ORIGIN OF NAME: Discovered 23 September 1846, Neptune was named after the Roman god of the sea (which equates to the Greek god of the sea, Poseidon). MOONS: A few weeks after Neptune’s discovery, astronomers began to notice moon(s). Only Triton - the largest & only spherical moon - could be observed by technology at the time. Later, mid-20th century improvements in ground-based telescopes and space probes allowed discovery of Neptune’s 13 (maybe 14) satellites, all named for minor Greek water deities. ATMOSPHERE: Even though Neptune is the farthest planet from the sun (and so receives the least energy from the sun), Neptune’s weather patterns are driven by the strongest sustained winds in the solar system — recorded at over 1,200 mph (or 2,000 km/hr). Earth’s most powerful storms reach only 250 mph! During Voyager 2’s visit in 1989, the ‘Great Dark Spot’, a storm large enough to contain the entire Earth, was seen moving at an incredible 750 miles per hour. You will probably not be surprised to hear that, as an ice giant, Neptune’s atmosphere is composed mostly of hydrogen, helium and methane. Like Uranus, Neptune is visibly blue because of the methane in its atmosphere. MAGNETOSPHERE: Neptune’s magnetic field is tilted about 47 degrees off the planet’s rotation axis. Like Uranus, with an equally off-balance magnetic field and axis of planetary rotation, Neptune’s magnetosphere experiences wild variations. At an amazing 25x Earth’s magnetic field strength, it is believed to originate in an ionized convecting fluid-ice mantle. SIZE: SURFACE AREA: over 2.9 billion square miles [14.98x Earth SA]. EQUATORIAL CIRCUMFERENCE: ~96k miles [3.86x Earth]. VOLUME: 6.25 x 10^13 km cubed [almost 58x Earth volume]. MASS: 1.02 x 10^26 kg [17.15x Earth mass]. MEAN DENSITY: 1.638 g/cm cubed [almost 30% Earth density]. Neptune, as expected, is much larger than earth but also much less dense. November NoCoAstro RINGS: It wasn't until the mid 1980s and the Voyager 2 mission — around 140 years after astronomers discovered Neptune — that scientists discovered Neptune had rings! Neptune GRAVITY: Neptune, though much larger than Earth, has a surface gravity of only 11.15 m/s Rules: squared [that's just 1.14x Earth’s surface gravity of 9.807 m/s squared or 1 g]. Do you know why? Which Kuiper Belt DISTANCE FROM SUN: Neptune has an almost perfectly circular orbit approximately objects are under 30 AU or roughly 30x Earth distance from sun of 1 AU. Traveling at just 0.182x Earth’s orbital speed, its influence? Neptune orbits the sun once for every 164.79 Earth orbits. Neptune’s weirdly-circular orbit means that other celestial bodies with far more eccentric orbits may actually cross Neptune’s path! Such is the case for Pluto, whose distance from the sun is generally greater than Neptune; however, for about 20 years of Neptune’s 164.79 year orbit, Pluto is actually nearer to the sun than Neptune! ROTATION: Neptune is rotating on its axis quickly, once every 16.11 Earth hours. [this is 0.67x Earth rotation]. EQUATORIAL INCLINATION: With an inclination very similar to Earth’s of 28.3 degrees, Neptune experiences similar seasonal variations in a response to variations in sunlight — yes, even at this distance! You learned last month that Saturn’s seasons last about 7 years each. On Neptune, where one orbit around the sun requires nearly 165 Earth years, seasons actuall last about 40 years! PLANETARY ALBEDO: Two common astronomical albedos used are geometric albedo & bond albedo, which can vary widely for any celestial body. Neptune’s bond albedo of 0.29, which includes all possible scattered light from Neptune, is the lowest of the solar system’s giant planets. TEMPERATURE VARIATION: The wild & windy atmosphere of Neptune receives 1/2 the solar radiation of Uranus and 1/1000th as much as Earth but isn’t actually the coldest planet in the solar system. Neptune averages -353 degrees November F or -214 degrees C [compare to Earth’s average temperature of 59 degrees F or 15 degrees C]! MISSIONS TO NEPTUNE: VOYAGER 2: In 1989, Voyager 2 became the first (and so far only) spacecraft to visit Neptune. This was also “the last picture show” of the Voyager mission’s tour of the solar system. NoCoAstro W HAT IS AN ICE C RYPTIC T RITON: C ONCEALED G IANT, ANYWAY? Triton: E XTRAORDINARY Short answer: it’s complicated. • is Neptune’s only moon containing C OMPOUNDS: enough mass to become spheroidal We classify ice giants separately from in shape. What surprises are Neptune & the gas giants because their Uranus hiding? composition is dominated by ice rather • is the only large moon in the solar than gas. system with a retrograde orbit At the high pressures typical inside (meaning it was captured instead of giant planets, exotic molecular and Sounds simple enough, doesn’t it? Don’t formed around Neptune!) polymeric compounds are formed. be fooled. • is the only moon in the solar Several substances, ‘forbidden’ in system with clouds and a planet-like classical chemistry’, may be stable at atmosphere! high pressures. These include previously-unknown variants of salt and • is extremely cold (-391 degrees F) even new oxides of magnesium, silicon yet has geysers spewing icy material and aluminum! 5-miles from its surface! • will one day reach the Roche Limit around Neptune, tearing itself apart. November EXTRA! EXTRA! READ ALL ABOUT IT! What can you look forward to in your next & final edition of this newsletter? KUIPER BELT: Disc-shaped region with (probably) hundreds of thousands of icy bodies. PLANET NINE: How do we know it’s there & what exactly is it? EXOPLANETS: Moving beyond our solar system, every Trekkies dream! THE LOCAL GROUP: over 30 gravitationally- November bound galaxies. OBSERVABLE UNIVERSE: Did it just get more crowded in here? PRESIDENT Trevor Moriarty: pres at NoCoAstro dot org VICE PRESIDENT Bob Michael: vp at NoCoAstro dot org TREASURER & OUTREACH Greg Halac: treas at NoCoAstro dot org SECRETARY Dave Karp: sec at NoCoAstro dot org NEWSLETTER EDITOR Amanda Bell: ObjView at NoCoAstro dot org WEBSITE WE WANT Paul Fleming: web-edit at NoCoAstro dot org TO HEAR FROM YOU! November NoCoAstro “We each want to be the one to find it.” Scott Sheppard, Carnegie Institution for Science November January PLANET NINE IS PLAYING HIDE & SEEK | AAAS Objects beyond Neptune provide fresh evidence for Planet Nine. JOIN US! WWW.NOCOASTRO.ORG FACEBOOK.COM/NOCOASTRO SEE YOU ONLINE! November NoCoAstro.
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