Venus

 

Venus, Earth's twin, is the second planet from the Sun.  In terms of size, it is the sixth largest planet, larger than Mercury and Mars.  It is 95% the size of Earth and 81.5% the mass of Earth.  If you were to stand on Venus, besides dying, you would weight 90% of what you do on Earth.

 

Venus has a relatively young surface which indicates that it is geologically active.  It has active volcanoes, as evidenced by the amount of sulfur in its atmospher.

 

Venus has two contintents, named after two goddesses of love, the Greek Aphrodite and the Babylonia Ishtar.  It has a large mountian, Maxwell Montes, one of the few features not named after historical or mythological females.

Venus also has a much thicker atmosphere than Earth, even though it is smaller than Earth, as mentioned above.  This thick atmosphere actually makes Venus the hottest planet, hotter than Mercury.

 

When Galileo Galilei first turned his telescope to the sky, little did he know that he would prove the heliocentric model of the solar system, and disprove the geocentric model.  One of his key discoveries was the phases of Venus.  The phases helped show that Venus went around the Sun and not around the Earth as had been previously believed.

The last thing that is strange about Venus, and may be the strangest of them all, is how the Sun transverses the Venutian sky.  One most planets, the Sun rises in the east and sets in the west.  Sometimes, it can go retrograde (but only on Mercury), but on Venus, the Sun only goes from west to east in the sky, rising in the west and setting in the west.

Space Station Idea

This is something I came up with about 8 years ago.  The physics is sound.  However, the engineering is not quite there yet.

Rim Space Station

Mercury and General Relativity

Albert Einstein proposed General Relativity in 1916. In it, he states that time and space re not separate geometric entities, but combined into one entity called space-time. Space-time is not flat, but curved and is heavily influenced by mass sitting in space-time. The larger a mass is, the larger its gravitational influence on space-time.

from Space.com

 

A consequence of General Relativity is that the apside of an object orbiting another object will move as the smaller object moves in its orbit. The apside in our Solar System can be thought of as being similar to the perihelion of a planet relative to the Sun. However, apsides are the point closest to the center of mass of a two-body system, like the Sun and a planet. Since the Sun is much more massive than any planet, we can equate the apside of a planet to the perihelion.

 

What we mean by the precession of the apside is that as the planet moves in its orbit, the planet goes deeper into the space-time well as shown above. This causes the planet's apside to move farther along as it orbits the Sun.

 

This is why full moons vary in size from month to month and why solar eclipses can vary from total, annular, or partial.  The apside of the Earth-Moon system precesses as the Moon orbits the Earth.

 

Since this post is about Mercury proving General Relativity, we should discuss how this is so. Back in 1859, French Mathematician Urbain Le Verrier discovered that Mercury's orbit had some strange anomalies. It was at first thought that the anomalies were due to a planet closer to the Sun than Mercury. This explanation helped in the discovery of Neptune by Le Verrier and two others: John Couch Adams and Johann Galle earlier in the century. But once Einstein's theory came out, the equations describing the precession of the asides calculated the anomalies present in Mercury's orbit.

 

There are other examples of observations proving the Theory of General Relativity. They can be found in the above Wikipedia link.

 

 

 

Mercury's Orbit

Mercury has a unique orbit around the Sun.  It was long believed that Mercury had a 1:1 resonance with the Sun, much like the Moon has a 1:1 resonance with Earth, i.e. the same face is always facing the Sun.  However it was discovered that Mercury has a 3:2 resonance, i.e. for every three complete rotations, Mercury completes two full orbits around the Sun.  This resonance, its proximity to the Sun, and its highly eccentric orbit leads to some strange phenomena.

Mercury, by far, has the highest eccentricity of all the planets (e=0.206). What does this mean?  An orbit that is eccentric means that the orbit is elliptical, or oval. The closer the eccentricity of an orbit is to zero, the more circular the orbit is. For reference, the orbital eccentricity of the Earth is 0.017.

Click here for more information.

Eccentricity leads us to mention Johannes Kepler's three laws of planetary motion, specifically Kepler's Second Law:

• A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.

This is just a fancy way of saying the closer the planet is to the Sun, the faster it goes.

Shashi M. Kanbur, Professor of Physics and Earth Science, SUNY Oswego

 

Isaac Newton later proved this with physics and calculus in his three laws of motion,

 

We also know that Mercury is 0.4 AU, on average, from the Sun. Because it is so close, it is by far the fastest moving planet in terms of orbital speed.  And from its highly eccentric orbit, when Mercury is at perihelion, it is moving its fastest.

Before we move on to the funky stuff, let's discuss more about Mercury's sidereal rotation and sidereal period, or its day and its year, A sidereal day is how long it takes a planet to rotate once on its axis completely, or how long it takes a star to appear at the same spot in the sky.  For Earth, this is about 23 hours and 56 minutes.  On Mercury, it takes about 58.5 Earth days.  A sidereal year is how long it takes to complete one complete orbit around the Sun.  Earth takes about 365.25 days to complete one sidereal year. Mercury has a sidereal year of approximately 88 days.  So for every three sidereal days on Mercury, Mercury completes two full orbits, hence 3:2 resonance.

But because of its unique position in the solar system, funny things happen on Mercury. As Mercury approaches perihelion, its orbital angular velocity increases.  At around four days before perihelion, the orbital angular velocity equals the rotational angular velocity. When these two angular velocities are equal, the Sun appears stationary in the Mercury sky.  As Mercury gets closer to perihelion, the angular orbital velocity increases and becomes larger than the rotational velocity. The Sun then appears to move backwards in the sky!  In some cases, it is possible that the Sun could actual set in the east.  At perihelion, the orbital angular velocity begins to decrease. Four days after reaching perihelion, the orbital rotational velocity once again equals the rotational orbital velocity. The Sun again appears stationary then again begins its apparent movement to the west.

Another interesting fact about Mercury's orbit, is that the time from true noon to true noon, what we call a solar day, is larger than a Mercury year. One Earth, our solar day is 24 hours. On Mercury, it is 176 Earth days, or two Mercury years.  Mercury has one of the slowest rotational angular velocities in the solar system, comparable to that of Venus, which is a topic for later.

NOAA

 

In conclusion, because of its proximity to the Sun, its highly eccentric orbit, and its tidally locked 3:2 resonance with the Sun, strange things happen in the sky of Mercury.

 

Evolution vs. Creationism

Here is a link to a post I made in January of 2006 where I give my thoughts on evolution vs. creationism.

Creation vs. Evolution

Barren Mercury

As mentioned before, Mercury is a planet.  But it is unique in our Solar System in that it is the only planet without any type of atmosphere.

There may be a couple of reasons for it:

1. It may be too small to hole an atmosphere.  Mars is the second smallest planet but has a very thin atmosphere.  Because of their small sizes, the escape velocity for the planets are relatively small.  Most gas molecules have a relatively fast speed when moving about in the atmosphere, so they could escape easily.  However, this explanation may not be true. Callisto, as you recall, is similar in size to Mercury. But it does have a thin atmosphere.  The next bullet point is probably the correct explanation.
2. Mercury is extremely close to the Sun, approximately 0.4 AU out.  The Sun has a very active solar wind and that solar wind is extremely hot.  Possibly in the early formation of the Solar System, the primordial solar wind stripped Mercury of its atmosphere, which would have likely been very tenuous to begin with.  If Mercury had an atmosphere, it would have been similar to that of Callisto, with probably and composition similar to that of Mars, mostly carbon dioxide.

Next time, we will learn about Mercury's strange orbit.

Lopsided Mercury

Generally, planets will be wider at their equatorial region than at their poles. Being flatter at the poles of a sphere creates what is called an oblate spheroid.  However, Mercury is strange.

There is a large crater on the surface of Mercury called the Caloris Basin or Caloris Planitia .  It is a large impact crater on the surface that was formed about 4 billion years ago.  The impact was so great, that it is believed that seismic waves from the original impact pushed up the area directly opposite the Caloris Basin.  This area is on the antipode of the impact crater and is referred to the Chaotic Terrain, or my favorite, Weird Terrain.  There are relatively few impact craters in this area which tells us that the area is relatively young.

Because of the uplift on the antipode of the Caloris Basin and the Basin itself, the radii from the center to the Basin and to the antipode are not the same.  So the planet is a little lopsided.

NASA.gov

 

NASA.gov

There is also a series of concentric rings around the Caloris Basin, much like any crater in the solar system.  These rings were created from ejecta from the impact.

And here are craters on Mercury that have a strange shape:

Space.com