Category Archives: PLANETS

A few facts about our planets


Mars is the fourth planet from the Sun, a terrestrial planet with a thin atmosphere composed primarily of carbon dioxide. It is often described as the “Red Planet” due to its reddish appearance.

The  most amazing recent news is that liquid water has been found to exist on Mars which have only until now appeared as dark streaks.

Mars is home to the tallest mountain in the solar system, Olympus Mons, a shield volcano, which is 21km high and 600km in diameter.

Mosaic of the Syrtis Major hemisphere of Mars: Credit USGS Astrogeology Science Center

A day on Mars is roughly equivalent to an Earth day. A Martian year takes over 680 days, compared with Earth’s 365 day orbit of the Sun.

Mars has two known moons, Phobos and Deimos.

Mars has a very thin atmosphere, which contains about 95.3% carbon dioxide (CO2) and 2.7% nitrogen, and a mixture of other gases. The temperature is very cold, and there is believed to be  frozen water at the poles in the form of permafrost.

The most recent missions to Mars include the Curiosity rover which has been roving the planet since Aug. 5, 2012 and sending back images, the MAVEN mission, which arrived on September 22, 2014 to study the martian atmosphere, and the Indian Space Research Organization’s MOM Mangalyaan orbiter, which arrived on September 24, 2014.

Explorations have revealed water in the soil and possibly flowing water in the warmest months on Mars.

The next missions to arrive will be the European Space Agency’s ExoMars mission, comprising an orbiter, lander, and a rover, followed by NASA’s InSight robotic lander mission, to be launched in March 2016 with a planned arrival in September, 2016.

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Venus is also known as the Morning Star and the Evening Star but it is not really a star.

It is the second planet from the Sun, the second brightest object in the night sky after the Moon, and the second largest terrestrial planet, sometimes referred to as the Earth’s sister planet due the their similar size and mass.


The surface of Venus is obscured by an opaque layer of clouds which reflects the sun brightly.Venus is the hottest planet in our solar system. The average surface temperature is 462 °C.

More than 1,000 volcanoes or volcanic centres larger than 20 km have been found on the surface of Venus.

Venus has no known moons and is unusual in that it rotates anti-clockwise, also known as retrograde rotation.

A day on Venus lasts longer than a year! It takes 243 Earth days to rotate once on its axis and 225 Earth days to orbit the Sun, compared to the Earth’s 365 days.

Mayan astronomers made detailed observations of Venus as early as 650 AD.

In 2006, the Venus Express space shuttle was sent into orbit around Venus by the European Space Agency, which is sending back information about the planet.

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Mercury is the closest planet to the Sun and it is the smallest planet in the Solar System, just 4,879 Kilometres across its equator, compared with 12,742 Kilometres for the Earth.

After Venus, Mercury is  the second hottest planet, experiencing temperatures of up to 427°C on the side which faces the sun, whilst on the alternate side it can be as low as -173°C.

Mercury has no moons and no rings.

mercury 3
Messenger spacecraft image: Credit: NASA/John Hopkins University

Mercury is very dense.  This is largely due to  being composed mainly of heavy metals and rock.
As the iron core of the planet cooled and co
ntracted, the surface of the planet became wrinkled. Scientist have named these ‘wrinkles’, Lobate Scarps. They can be up to a mile high and hundreds of miles long.

One solar day (the time from noon to noon on the planet’s surface) lasts the equivalent of 176 Earth days while the sidereal day (the time for 1 rotation in relation to a fixed point) lasts 59 Earth days.

One year on Mercury is just 88 days long. For every two orbits of the Sun, Mercury completes three rotations on its axis.

Due to Mercury’s proximity to the Sun,  it is not easily seen except during twilight.

Only two spacecraft have visited this rocky planet: Mariner 10 in 1974-5 and MESSENGER, which flew past Mercury three times before going into orbit around Mercury in 2011.

“Thirteen times a century Mercury can be observed from the Earth passing across the face of the Sun in an event called a transit, the next will occur on the 9th May 2016.”

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Neptune  is the eighth and most distant planet from the Sun.

The planet may have formed much closer to the Sun in early solar system history before migrating to its present position.


Neptune has 14 moons, the most interesting one being Titon, a frozen world,  probably the coldest in the Solar system.
Neptune is not visible to the naked eye,and therefore was unknown to the ancients. It was first observed by telescope in 1846, its position determined by using mathematical predictions.

Neptune is a gas giant, not a solid body. It spins on its axis very rapidly and takes 18 hours to make one rotation.

Neptune is also known as an ‘ice giant’, like the slightly larger planet Uranus. Although smaller than Uranus, Neptune has a greater mass.

The atmosphere of Neptune is made of hydrogen and helium with some methane. The methane absorbs red light, which makes the planet appear a beautiful blue. High, thin clouds drift in the upper atmosphere.

Neptune has a very active climate with large storms and high winds whirling around the upper atmosphere.Neptune is known for its ‘Great Dark Spot’, a massive storm which raged for about five years, recorded in 1989.

Neptune was flown by in 1989 by spacecraft Voyager 2.

The NASA/ESA Hubble Space Telescope has also studied this planet, as have a number of ground-based telescopes.

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Uranus is the seventh planet from the sun at a distance of about 2.9 billion km (1.8 billion miles) or 19.19 AU.

Uranus is an ice giant, with faint rings. The inner rings are narrow and dark and the outer rings are brightly coloured..

Uranus has an atmosphere which is mostly made up of hydrogen and helium with a small amount of methane which causes the planet to have a blue tint. Most of the planet’s mass is made up of a hot dense fluid of “icy” materials – water, methane and ammonia above a small rocky core.

Uranus is the only giant planet whose equator is nearly at right angles to its orbit. It is nearly the same size as the other ‘ice giant’, Neptune.

Uranus has 27 moons, many named after characters from the works of William Shakespeare and Alexander Pope such as Miranda, Titania, Oberon and Umbriel.

One day on Uranus takes about 17 hours (the time it takes for Uranus to rotate or spin once.)  A complete orbit around the sun takes about 84 Earth years.

Uranus is not visible to the naked eye but it became the first planet discovered with the use of a telescope. It was discovered by William Herschel.
Voyager 2  is the only spacecraft to have visited Uranus.


Sighting of Jupiter was first recorded by Babylonian astronomers in 7th or 8th century BC.
Jupiter is the fifth planet from the Sun and is the largest planet in the Solar System. It is made primarily of gases and is therefore known as a “gas giant”.


Jupiter is known to have at least 67 moons. Io is the largest, Europa, Ganymede and Callisto, are just three more. Jupiter has four thin rings which are hardly visible.

Jupiter has the shortest day of all the planets. It turns on its axis once every 9 hours and 55 minutes. It appears to move slowly in the sky, however, as it takes almost 12 Earth years to orbit the Sun.
Jupiter remains in each zodiac constellation for nearly twelve months.

Jupiter has unique cloud features. The upper atmosphere of Jupiter is divided into cloud belts and zones, primarily made up of ammonia crystals and sulphur.
Eight spacecraft have visited Jupiter: Pioneer 10 and 11, Voyager 1 and 2, Galileo, Cassini, Ulysses, and New Horizons missions.

The Juno mission is its way to Jupiter and will arrive in July 2016. Other future missions may focus on the Jovian moons Europa, Ganymede, and Callisto, and their subsurface oceans.

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Saturn is the sixth planet from the Sun and is the second largest in our Solar System.
It is a gas giant with a prominent ring system.
A Saturnian day is 10 hours 39 mins long. A year (the period of orbit around the Sun) takes the equivalent of 29.46 Earth years.
Saturn’s atmosphere is made up of 96% hydrogen and 4% mostly helium.

Saturn in Black2

There are known to be more than 53 moons, the largest being Titan, which scientists believe resembles a frozen version of what Earth was like several billion years ago.
Much of what is known about the planet is due to the US Voyager explorations in 1980-81 and much more from the later Cassini-Huygens mission of 2004 which continues to explore Saturn, its rings and its moons.
Saturn is named after the Roman god of agriculture, it’s astronomical symbol represents his sickle.

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Pluto may once more be a planet! It was once classified as the ninth planet but was reclassified to being  a ‘dwarf planet’ in 2006. when the IAU formalised the definition of a ‘planet’. But will they rethink this after the recent spectacular flyby?

New Horizons is now several million miles away from Pluto after  its closest flyby probe recently flew past the dwarf planet.

Pluto is the second closest dwarf planet,  to the Sun and is the second most massive dwarf planet (Eris is the largest dwarf planet).
Pluto is about two thirds the size of  Earth’s moon and 18% of its mass.

There are at least 5  known moons orbiting Pluto:  Charon, discovered in 1978, Hydra and Nix, both discovered in 2005, Kerberos originally P4 discovered 2011 and Styx originally P5 discovered 2012 .

The latest discovery of NASA’s New Horizons mission reveals that Pluto is host to flowing ice that have similarities to glaciers on active worlds such as Earth and Mars.

No spacecraft had ever visited Pluto until  New Horizons, which was launched in 2006 to fly by Pluto on its way to the Kuiper Belt, mission now completed.

There are many new images of Pluto now, which are  revealing amazing facts after this most recent visit by New Horizons.