Inner Planets

Inner Planets - Mercury, Venus, Earth, Mars
Inner Planets – Mercury, Venus, Earth, Mars

The Inner Planets are Mercury, Venus, Earth, and Mars.  The following Table indicates the spacecraft that have been sent to the planets, the most recent is at the top of the list.  More information on each planet is given below……

Mercury Venus Earth Mars



Venus Express



Vega 2

Vega 1

Mariner 10

Mariner 5

Mariner 2


Hubble Telescope Recon. Orbiter   Opportunity Spirit

Phoenix Mars


Beagle 2



Global surveyor

Viking 2

Viking 1

Mariner 9

Mariner 7

Mariner 6

Mariner 4

Mars Series

Color represents the Satellite ownership, as follows:

USA (NASA) European Space Agency China India Japan Russia





Twice as close to the Sun as the Earth, it is about the size of our moon.  Mercury is a highly cratered planet, similar to the Moon.  It has a solid inner core, a liquid outer core, and a crust, just like the Earth.  However, Mercury is more dense, consisting of predominantly the heavier elements, like iron.  The recent flyby of the spacecraft Messenger October 2008, has revealed active volcanoes.   It has essentially no atmosphere, what little there is thought to be helium.

There are no moons.


Closest to the Sun….and way too hot!  The mean surface temperature is 347F.  During the day  the temperature can reach 800F.  Bring Sun screen, although  you could settle near the poles that are always in shadow and where the temperature may never exceed -300F..that’s minus 300 degrees! Otherwise, there is no atmosphere, so no wind, no rain, no clouds… weather!


If you are to have any chance of seeing it from Earth, it’ll have to be right after the sun sets, or just before the sun rises, and only at select times during the year.  When visible, it can be seen fairly easily but will be close to the horizon, due to the fact that it is close to the sun.


(Names in Bold are still operational)

BepiColombo – future.  The European Space Agency has named a future Spacecraft planned for Mercury exploration … it arrived at Mercury in 2011 and set up orbit around the planet.
Messenger – January 2008.  Messenger flew pass Mercury in January, 2008.  Only the second craft to explore Mercury since Mariner 10 in 1975, Messenger will  settle into orbit around Mercury in 2011, 3 years from now, and begin the real exploration of this hot, barren planet.
Messenger =  MErcury Surface Space ENvironment, GEochemistry, and Ranging.  (yes indeed…kind of clumsy.)
Mariner 10 – the first Spacecraft to visit the planet in 1974 and 1975.  It made 3 fly-bys  to map less than half of it’s surface.




Venus is totally covered in clouds and cannot be directly seen with our eyes.  However radar scans from several space probes have revealed most of the surface features to us.  The planet has many impact craters and is also covered with volcanic rock and lava flows from the active volcanoes on the planet.  It is thought that the lava flows have erased the evidence of older impact craters.  Also, as result of the volcanoes, the atmosphere consists of carbon dioxide (96%) and sulfuric acid.  This results in a very dense atmosphere with very high pressure on the surface of the planet.  As beautiful as it is from Earth, it is not a very hospital place.

There are no moons.  As a possibility however, some scientists believe that Mercury may have been a moon of Venus in the early days of the solar system.  Take a look at the relative sizes….I suppose it could have been a moon of Venus at some time.


Venus is in a global warming situation.  The atmosphere is mostly Carbon dioxide and as a result is much like a Greenhouse….very warm indeed.  The mean surface temperature is 847F, which means it gets a lot hotter than that on a summer day!  Note that it is warmer on Venus than on Mercury which is closer to the sun, due of course to the Greenhouse gases.  The upper atmosphere does contain water vapor which creates sulfuric acid.  This acid however does not reach the surface since the water evaporates due to the high temperature.  The weather for Venus is hot and cloudy, with the possibility of very heavy winds, and no rain in sight.


My favorite planet……the “morning star”, or, “evening star” depending on when it’s visible. Very easy to spot just after sunset or before sunrise…it is the brightest object in the sky, after the sun and moon of course and looks like a diamond in the sky.  Most people will think it is the lights on a commercial jet plane far in the distance.  Actually Venus is fairly close to us….equivalent to 1,000 times around the earth.


(Names in Bold are still operational, strikethrough were not successful missions.)

Venus Express – April 11, 2006.  European Space agency. Currently in orbit.  Atmospheric studies
Galileo – 1990.  Single flyby at 10,000 miles on way to Jupiter.
Magellan – August 10, 1990 – Established orbit around Venus and radar-mapped 98% of the surface.  Remained operational  for over 4 years.
Vega 2 – June 15, 1985.  USSR landing on Venus and analyzed soil sample.
Vega 1 – June, 1985.  USSR landing on surface and two weather balloons.  Lander functioned for 56 minutes.  Balloons operated for 46 hours.
Mariner 10 – February 5 1974 single flyby at 3,600 miles. Studied atmosphere and photos.  Continued on to Mercury.
Mariner 5 – October 19, 1965 single flyby at 2,400 miles. Studied atmosphere.
Mariner 2 – December 14, 1962 single flyby at 20,000 miles for 42 minutes.  First successful Interplanetary mission.
Mariner 1 – July 22, 1962.  Destroyed at launch.




Mars may have had water on the surface 3 to 4 million years ago.  Currently Mars appears to have water below the surface.   Since water is considered essential to life, the presence of water on Mars would increase the likelihood that life had existed there in the distant past …. and the occurrence of life twice in one solar system would then indicate that maybe life is common in the cosmos.  The surface of Mars is rocky with impact craters and there is evidence of erosion from past water floods.  As can be noted below, we have sent many space craft to explore Mars.  It will be the first Planet to be visited by man.  All of this because it has water and will be the easiest to adapt to.

The atmosphere consists of mostly CO2 (96%) with traces of Nitrogen and Oxygen, but at very low pressure.

When man visits Mars they will dress warm, explore the surface in pressurized suits, be able to jump maybe 3 feet high,

Mars has two moons, Phobos and Deimos, among the smallest moons in the solar system.



The atmosphere is very thin so that winds, although high in speed, do not pack much of a force.  Dust storms are common.  No free water so no rain.  The maximum  temperature is 98F and the minimum is -190F.  Cooler than Earth, no clouds, and no rain.


Pretty easy to spot…it is reddish in color.


Mars is the most often visited planet by mankind.  A total of 20 space craft have been successfully sent to Mars.  (Names in Bold are still operational, strikethrough were not successful missions.)

Mars Reconnaissance Orbiter – March 10, 2006.   Look for water and dust in Mars atmosphere and for evidence of ancient seas and climate changes.
Opportunity – January 24, 2004.  Sister rover to Spirit but on the other side of Mars.
Spirit – January 3, 2004.  Rover. Geologic survey from microscopic examination to panoramic views looking for evidence of water.
Phoenix – May 25, 2008.  Mars Lander intended to look for water beneath the surface and also analyzer the soil for organic matter.  The Lander was successful and creased operation on November 10, 2008 nearly 3 months beyond it’s design life.
Mars Express – December 24, 2003.  European Space Agency, successfully inserted into orbit and is currently operating to study the geology and atmosphere.
Beagle 2 -December 24, 2003.  United Kingdom Lander onboard the Mars Express.  The Lander lost contact after landing.  Failed.
Mars Odyssey – October 24, 2001.  Mission is to map the surface and search for signs of water.  It is still operational as of 2008
Deep Space 2 – December 3, 1999.  This was a microprobe which was onboard the Polar Lander intended to look for water beneath the polar ice cap.  It was lost when the Polar Lander crashed.
Mars Polar Lander – December 3, 1999.  The Lander apparently crashed on the surface of Mars due to premature engine shutdown during the landing.
Mars Climate Orbiter – September 23, 1999.  The Orbiter failed to be inserted into orbit due to inconsistent use of Metric and English units.
Nozomi – July 3, 1998.  Japan’s first interplanetary space craft intended to orbit Mars.  It failed to achieve orbit around Mars.
Mars Pathfinder – July 4, 1997. Pathfinder was a low-cost Lander with the first wheeled rover.  It obtained geology data and  performed soil analysis.  It lasted 3 months, several times beyond its design life and performed beyond expectations.
Mars Global surveyor – September 11, 1997.  It’s planned 2-year mission was delayed for 1 year due to solar array deployment problems.  However, it operated for 9 productive years giving data on the geology and atmosphere of Mars.
Mars Observer – August 22, 1993. Launched to carry out long term wave and particle investigation into the geology, atmosphere, and climate of Mars.  The Observer fell silent just two days before reaching Mars.
Fobos 1 – 1988.  USSR.  Two space craft were launched to orbit Mars and to put a Lander on the moon Phobos.  Fobos 1 failed enroute due to a programming error.
Viking 2 – August 7, 1976. Orbiter and Lander. Also flew within 10 miles of one of the moons, Deimos.
Viking 1 – June 19, 1976. Orbiter and Lander.  Sampled soil and atmosphere.  Also flew within 50 miles of one of the moons, Phobos.  High resolution photos.
Mariner 9 – November 14, 1971.  Orbit for 1 year taking photographs.
Mariner 7 – August 5, 1969.  Single flyby to photograph 10% of surface.
Mariner 6 – July 31, 1969.  Single flyby to photo graph 10% of surface.
Mariner 4 – July 15, 1965.  Single flyby to photograph and take field measurements.
Mars Series by the USSR.  From the 1960’s to the 1990’s the USSR sent 15 space craft to Mars….only 1 was successful and 4 were partially successful.