Which Planet Orbits our Sun the Fastest?

Question: Which planet in our solar system is orbiting the sun at the fastest speed?  — Mike

Answer: Mercury is the winner at an orbital speed of about 47.87 km/s (107,082 miles per hour), which is a period of about 87.97 Earth days.  Just for your information, here is a list of the orbital speeds (and periods) for all 8 (plus Pluto) planets:

  • Mercury: 47.87 km/s (107,082 miles per hour), or a period of about 87.97 days
  • Venus: 35.02 km/s (78,337 miles per hour), or a period of about 224.7 days
  • Earth: 29.78 km/s (66,615 miles per hour), or a period of about 365.256365 days
  • Mars: 24.077 km/s (53,853 miles per hour), or a period of about 686.93 days
  • Jupiter: 13.07 km/s (29,236 miles per hour), or a period of about 11.86 years
  • Saturn: 9.69 km/s (21,675 miles per hour), or a period of about 29.42 years
  • Uranus: 6.81 km/s (15,233 miles per hour), or a period of about 83.75 years
  • Neptune: 5.43 km/s (12,146 miles per hour), or a period of about 163.72 years
  • Pluto: 4.74 km/s (10,603 miles per hour), or a period of about 247.92 years

Jeff Mangum

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Does the Coriolis Effect From the Milky Way Rotation Influence the Orbits of Planets in our Solar System?

Question: I read that our solar system orbits the center of the Milky Way Galaxy and am wondering if orbital direction of the planets was initially influenced by the Coriolis effect.  — Jack

Answer: Two comments to your question.  First, the net orbital angular momentum axis of the Sun or the Solar System turns out not to be aligned with the “spin axis” of our Milky Way galaxy.  The plane of the disk of our Solar System is inclined by an angle of about 63 degrees relative to the plane of the Milky Way within which our Solar System resides.  Second, the Coriolis effect, sometimes referred to as a “fictitious force”, refers to motion which is really in a straight line, but which appears to be curved when viewed from a reference frame that is accelerating (i.e. rotating).  So, if you are in a rotating disk, like our Solar System, you experience a Coriolis force, but if you step away from our Solar System and look at it from a point that is not accelerating, you would see planets in motion but with no Coriolis effect.

Jeff Mangum

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Building a Pyramid on Io for Maximum Durability

Question: If I were to build a 146 meter tall pyramid on the surface of Io, what material(s) would you recommend I use for maximum durability with respect to the satellite’s terrain and climate?  — Evan

Answer: I think that steel would be a good material to use to build a pyramid on Io.  It has good strength-to-weight, and it would likely be resistant to the sulfur-heavy conditions on Io.

Jeff Mangum

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Did Our Solar System Originally Include a Fifth Gas Giant?

Question: Read an article that researchers at the University of Toronto believe that Jupiter in the solar system early days kicked a planet out of the solar system . Do you believe this could be the one? Many thanks  — Bill

Answer: This scenario, whereby the early solar system was comprised of more than the four gas giants we have today, has been hypothesized since 2011.  The early solar system was an evolving place, with lots of gas and dust forming young planets which ultimately have to compete, in a gravitational sense, for a place in the solar system.  It is entirely plausible that a fifth gas giant existed early in the evolution of the solar system, but was ejected by the heavyweights in this environment, Jupiter and Saturn.  In fact, the prime suspect from the University of Toronto study appears to be Jupiter.

Jeff Mangum

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How Many Earths Can Fit in the Volume of the Milky Way?

Question: How many earths can fit in one galaxy and if the earth were about the size of galaxy how many planets, moons, etc. would be able to fit on earth.  — Xondra

Answer: To answer this question you need to know the volume of the Earth and a galaxy.  Let’s take the Milky Way as our galaxy example.  The Earth’s volume is a little over 10^(12) km^3.  To calculate the volume of the Milky Way, we assume that it can be approximated by a disk with a thickness of 1000 light years and a radius of 50,000 light years.  A light year is about 9.5 x 10^(12) km, while the volume of a disk is pi*(thickness)*(radius)^2.  Plugging in our thickness and radius we get about 6.7 X 10^(51) km^3.  Dividing the volume of the Milky Way by the volume of the Earth, you get (6.7 X 10^(51))/(10^12) =~ 6.7 X 10^(39) Earths that can fit in the volume of the Milky Way galaxy.

Jeff Mangum

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Why Are the Best Times to Observe Meteors Between Midnight and Dawn?

Question: Why are all the best times for viewing meteor showers between midnight and dawn?  As I imagine looking down on the solar system from above, I think of a stream of comet debris as impacting all of our outward-facing atmosphere (away from the sun) uniformly at the same time.  Why isn’t it as good as soon as it becomes dark?  — Steve

Answer: The main reason that the best viewing times are between midnight and dawn is due to the orientation between your location on the Earth’s surface and the direction of travel of the Earth in its orbit.  Starting around midnight your location on the Earth’s surface spins around to the forward-facing half of Earth, relative to the direction that the Earth is travelling in its orbit around the Sun. At dawn, your location on the Earth’s surface is pointed straight in the direction of the Earth’s travel in its orbit.  Therefore, between midnight and dawn you are moving head-on through the location of the meteors in space, which means that you will, on average, observe more of them.

Jeff Mangum

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Why is the New Horizons Spacecraft Slowing Down?

Question: Why is New Horizons slowing down? I check it on line every day and its speed is constant. Today its losing speed.  — Tom

Answer: I don’t know of any specific reason as to why New Horizons would have been slowing down on the particular date that you noticed it.  In general the spacecraft will need to make small course corrections as it travels to its next target, which often involve changes in speed.

Jeff Mangum

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Does the Sun’s Rotation Speed Dictate the Orbital Speed of the Planets?

Question: Are the planets orbiting the sun at the same speed as the sun revolves on its axis? Or are some planets moving slower or faster than the sun spins, of course the position in the solar system dictates how long it takes to complete one full orbit, but say they were all in the same position close to the sun are they moving at the same speed as the sun spins? When the solar system formed surely the sun dictated the speed at which the dust cloud revolved, so unless objects got bumped to move faster or slower they should all be revolving roughly the same yes??  — Sammy

Answer: The Sun takes about 26 days (at its equator) to 34 days (at its poles) to rotate on its axis at its equator, which is much faster than all of the planets orbit about the Sun.  In fact, the orbits of the planets are dictated (mostly) by the Sun’s gravity and their distance from the Sun.  Also, the speed at which the dust cloud from which the Sun and planets formed was determined by the mass and angular momentum of the cloud itself, as it was much more massive than the Sun and planets.

Jeff Mangum

 

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What Are Those Two Bright Lights on the Western Horizon?

Question: On July 15, 2015, observing from Las Vegas, Nevada, there are 2 objects (Low) in the Western sky. One is bright the other dim. Are they Venus and Jupiter?  — George

Answer: Yes!  Venus, the brighter of the two, is to the south (left when facing west) of the other bright guy, Jupiter.

Jeff Mangum

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What is that Bright Object in the Western Sky After Sunset?

Question: What bright light is in nepa’s sw sky at 30degrees above the horizion at 9:15 edt.  — Tom

Answer: Although I don’t exactly know what location you are observing from, I suspect that you are seeing Jupiter and Venus, which are both currently visible on the western horizon after sunset.

Jeff Mangum

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