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10 Amazing Facts About Our Solar System

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Man has been fascinated by the stars since ancient times. The careful observation and diligent study of the night sky over the centuries has given us extensive knowledge about what's going on above us. Check out these curious as well interesting facts about our solar system.

1. Venus and Uranus Spin Retrograde

All eight planets in our solar system orbit the sun counterclockwise (as seen from above the north celestial pole). Normally they also rotate about their axis in this direction, i.e. they spin counterclockwise. Standing on a planet's surface this means the sun normally rises in the east and sets in the west, just as on Earth.

Yet there are two exceptions: the second and seventh planet from the sun, Venus and Uranus respectively, spin in the opposite direction. These planets are also said to have retrograde rotation.

Uranus is furthermore eccentric because of its orbital tilt of 82 degrees rotating almost on its side.

Uranus' eccentric rotation: spinning backward and on its side

Uranus' eccentric rotation: spinning backward and on its side

2. Saturn Would Float in Water

The four planets closest to the sun (Mercury, Venus, Earth, Mars) are also called terrestrial planets as they are mostly made of rock and metal. The next four are gas giants (Jupiter, Saturn, Uranus, Neptune) and have no solid surface.

The inner terrestrial planets have, obviously, a higher density than the outer planets. Yet Saturn has a remarkably low density even for a gas giant: just 687 kg/m3. This means Saturn is so light it would float in water! (in reality, this experiment wouldn't be so straightforward, but it can be safely said that the average density of Saturn is lower than the density of water on Earth).

Saturn: much lighter than it looks

Saturn: much lighter than it looks

3. The Hottest Planet Is Not the One Closest to the Sun

One would expect the planet closest to the sun to be also the hottest. Yet Venus, the second in the order, is even hotter than Mercury. This is due to Venus' thick atmosphere which traps the sun's heat that is reflected back from the planet's surface.

Both planets are far too hot to sustain life. The average surface temperature on Venus is 467°C (872°F), while the temperature on Mercury varies widely from 180°C (290°F) during night-time to peaks of 430°C (800°F) during day-time due to the planet's lack of an atmosphere.

If man is ever to become a multi-planet species he is well advised to head outward in search of new frontiers.

Venus: the Morning and Evening Star

Venus: the Morning and Evening Star

4. One Day on Mercury Lasts Two Mercurian Years

Mercury revolves around the sun rather quickly in 88 Earth days but rotates around its axis very slowly. Each Mercurian sidereal day (i.e. one rotation on its axis with respect to distant stars) takes 58.65 Earth days or about 2/3's of its year.

Yet with respect to the sun one day on Mercury, sunrise to sunrise, actually lasts two Mercurian years or 176 Earth days.

Once it was thought that Mercury always kept the same side towards the sun but in fact, it is daytime for one Mercurian year and nighttime the following year.

Mercury: a day lasting longer than its year

Mercury: a day lasting longer than its year

5. Mount Olympus Dwarfs Mount Everest

Mars is notably smaller than Earth with its diameter being only slightly more than half the size of the Earth's. Yet the Red Planet's topography is truly XXL size.

With a peak of 22 km (13.6 mi) Mount Olympus dwarfs Mount Everest about two and a half to one. The Martian version of the Grand Canyon is Valles Marineris and has an astonishing length of 4,000 km (2,500 mi).

Olympus Mons: over twice the height of Mount Everest

Olympus Mons: over twice the height of Mount Everest

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6. The Sun Makes up Almost All the Mass of Our Solar System

It takes 1,000 times the Earth to fill Jupiter, the largest planet in our solar system. Yet the mass of all planets combined, including asteroids, is only a tiny 0,14% of the mass of our solar system. The remaining mass of 99.86% is entirely made up of the sun.

* natural satellites with a diameter < 10 km (6.2 mi) are not taken into account

PlanetDistance from the sun (AU)MassDiameterDensityRotation Period (Days)Moons













- 243






















16 *







18 *






- 0.718

15 *







8 *

7. Pluto Is Nowhere Near the Edge of Our Solar System

Before being demoted to a dwarf planet Pluto on older charts was featured as the ninth and most outer planet of our solar system. Pluto is certainly far away from Earth, yet the edge of the solar system still extends a 1,000 times farther out.

If the Earth's average distance from the sun is one astronomical unit (AU) by definition, Pluto on average is distant from the sun 39.5 AU, while the Oort cloud further extends out to 50,000 AU or 0.79 light-years. By comparison, the closest star Proxima Centauri is 4.2 light-years away.

8. Jupiter Spins Super Fast

Jupiter, usually the third brightest object in the night sky (after the Moon and Venus) is the biggest planet in our solar system. In fact, Jupiter's mass is two and half times that of all the other planets combined.

Yet great mass doesn't mean sluggishness. Jupiter rotates on its axis faster than any other planet in the solar system, completing a rotation in slightly less than ten hours. This equals an equatorial rotation velocity of 45,000 km/h (7.8 mi/s).

Completing a rotation on its axis in 9h 55m 30s

Completing a rotation on its axis in 9h 55m 30s

9. Planets Appear as Stars

Ancient people simply distinguished the sun, the moon, and the stars.

Among the stars, Sirius is the brightest having the lowest apparent magnitude (the scale is inverted by definition: low magnitude values stand for a high level of brightness).

Yet there are other celestial objects that 'outshine' Sirius: Venus, Jupiter, and sometimes even Mars appear brighter than Sirius. Further out Saturn shines brighter than most stars.

The planets, of course, simply reflect the sunlight and get their apparent brightness due to their relative nearness to the sun and the Earth.

10. Perfect Conditions for Life

It is estimated the universe contains some 200 billion galaxies. The Milky Way, i.e. the galaxy that contains our solar system, alone contains some 100-400 billion stars. Yet the only place where life exists we know of so far, is Earth.

Although that might change someday, at least it can be said that the conditions provided by the solar system for our Blue Planet are very special. This includes an adequately sized host star with little variation and a planet located at an appropriate distance in the habitable zone. The Earth's magnetic field shielding against solar winds and the proper tilt of its axis are also indispensable cosmic parameters for the existence of life.

The European Southern Observatory in Chile pointing a laser towards the center of the Milkyway

The European Southern Observatory in Chile pointing a laser towards the center of the Milkyway

Star Trek for Real


  • The Stargazer's Guide to the Night Sky, by Jason Lisle, Master Books, Green Forest, AR, USA (2012)
  • The New Astronomy Book, by Danny R. Faulkner, Master Books, Green Forest, AR, USA (2014)
  • Wikipedia

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2016 Marco Pompili


Greensleeves Hubs from Essex, UK on November 16, 2016:

Many people's knowledge of astronomy is very limited, so it's nice to have these extraordinary facts presented in a quick, easily digestible form Marco. One of the fascinating things about the Solar System is how uniquely different, each and every one of the planets and moons are.

Re-your poll, I am absolutely sure that - assuming we survive as a species - we will eventually go to the stars. It is human nature to be curious and to want to explore, and that is the ultimate exploration.

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