Mercury may seem distant compared to Venus and Mars, but in terms of size it actually ranks closer.
Scientists devised a mathematical formula to find which planet was nearest the earth in size, using data on distance between planets over time and then averaging their values to find which was nearest of all seven planets.
Mercury
Mercury may seem strangely near Earth in terms of size; in fact it’s about 1.5 times wider than the moon and only one-tenth the size of other major planets such as Mars and Venus.
Due to its small size, Earth is covered with numerous craters created by impacts with asteroids in its early days – most were created by impacts with Caloris which experienced an extremely massive asteroid impact some 4 billion years ago.
Mercury’s surface features not only craters but also impact basins – large depressions in its crust where chunks were removed by rock impacts or asteroids – as well as cliffs rising hundreds of miles above its surface.
An intriguing feature of Earth is its strange orbit, which can be explained by volatile gases like methane and ammonia present on its surface. Their molecules produce electrical charges which reflect sunlight back onto it to heat it further up the planet.
Scientists speculate that an eccentric rotation may have led to the planet appearing brighter when closest to the Sun (perihelion) than when farthest from it (aphelion).
Mercury lies nearer the sun than any of the other main planets in our solar system and therefore reaches temperatures up to 840F/450C during daytime hours, while at nightfall its temperatures drop dramatically to an astonishingly cold minus 275F (minus 180C), making it by far the coldest planet of them all.
Mercury’s extreme temperatures and lack of an atmosphere makes life unlikely on this planet, due to temperature fluctuation and intense solar radiation that would likely prove too much for any organisms living there.
Mercury may harbor habitable zones; to learn more, spacecraft such as NASA’s MESSENGER mission have successfully explored its surface.
This spacecraft has completed an exhaustive map of Mercury’s surface, providing us with unprecedented insights into its history and geology. It has revealed that Mercury once boasted a complex volcanic system which may have contributed to water ice being deposited into deep craters at either pole as well as contributing to shrinkage over billions of years.
Venus
Venus, which orbits our Sun in an elliptical path, is the closest large planet to Earth. At its perihelion point it comes closest to our sun while at aphelion point it stretches out as far as 67.7 million miles (108 million kilometers).
Planet Earth’s surface is covered with volcanic rock and lava flows that have transformed plains into mountains and valleys, as well as being geologically active due to a partially molten mantle and moving tectonic plates that have formed and reshaped its terrain.
Venus has an atmosphere composed largely of carbon dioxide that absorbs heat from the sun and holds onto it, trapping that energy for longer. Furthermore, its thicker atmosphere contains sulfuric acid clouds which block sunlight from reaching its surface, creating a powerful greenhouse effect and raising temperatures up to an average temperature of 860 F day and night.
Due to Venus’ dense atmosphere, liquid water cannot exist on its surface in its liquid state; instead, sunlight breaks it down into carbon monoxide which rises up through Venus’ cloud layer to become carbon dioxide and beamed back up toward Earth.
Venus’ surface pressure is 90 times that of Earth, making its atmosphere significantly denser and killing you quickly and painfully regardless of where you stood on its surface.
Scientists have deployed numerous spacecraft in order to gain a deeper understanding of Venus’ atmosphere, with ESA’s Venus Express taking up near-polar orbit around it since 2006.
Scientists are also using satellite imagery to map Earth’s surface and assess whether there are active volcanoes. These clues offer important insight into Earth’s past – its surface has been formed through millennia of volcanic activity; recent eruptions may have happened within just centuries or millions.
Earth
The Earth is the fifth-largest planet in our solar system, measuring at an impressive diameter of 6386 km and mass of 5.972x 1024 kg. Revolve around the Sun every 365 days on an axis slightly tilted so Northern and Southern Hemispheres can receive different amounts of light throughout the year, leading to seasonal change.
At approximately 4.6 billion years ago, Earth emerged when a giant cloud of gas and dust from the Sun’s nebula collided and collapsing under gravity to form a flat disk of material resembling our planet Earth. When that disk collapsed under its own weight, its particles stuck together to form what eventually became Earth.
Today, Earth is an immense rock and metal planet measuring roughly 12,000 kilometers (6,000 miles). Its surface features oceans, glaciers and ice caps which support life forms that call Earth home.
All day, our planet’s rocky core slowly rises and sinks at an estimated rotational speed of 790,000 miles per hour (12,000 km/h). Surface temperatures average 1,800F (7300C). Underneath its crust however, temperatures increase exponentially as one descends through its mantle layer.
Over one million years, our planet’s outer layers of mantle will gradually cool off until their temperatures match those in its core – this process is known as tectonic plate movement.
As well as Earth’s core, there exists another thick layer of rock known as the mantle which covers most of its surface. Measuring about 1,800 miles (2,900 kilometers), this mantle layer may vary between 50 to 200 miles thick depending on where you look on Earth. Not completely solid in form, its presence allows shuffled continents and earthquakes while creating volcanoes.
The Earth is composed of several layers. At its surface lies the crust, made up of rock thrown up by volcanic eruptions into its mantle layer, similar to wood floating on water. As this crust slowly sinks below its host layer, its slow movements shuffle continents while creating earthquakes, volcanoes, and mountain ranges.
Planet Earth’s outer crust measures roughly 6,000 miles (10 000 kilometers), while the innermost layer only extends for around 1,000 miles (2 000 kilometers). The mantle, however, stretches an amazing 1,800 miles (2900 kilometers). Crust and mantle are connected via an imperceptibly thin layer of liquid water in between.
Mars
Mars, located four solar system planets from our Sun, is slightly smaller than Earth in diameter at approximately 4,196 miles (6,752 km). Like Earth and other inner planets in our solar system, it completes one revolution around its axis every 24.6 hours.
Mars boasts a generally smooth surface at its equatorial latitudes while at the poles it becomes more cratered and volcanic. Its atmosphere consists primarily of nitrogen (78%), oxygen (21%), and argon with trace concentrations of water vapor and carbon dioxide.
Phobos and Deimos, two small satellites orbiting Mars in an almost circular pattern near its equator, may be captured asteroids that were plucked out of Mars’ atmosphere by spacecraft passing overhead.
Planet Earth is well known for its diverse weather patterns; in summertime its northern hemisphere experiences hot and dry conditions while its southern hemisphere experiences cold and damp wintertime conditions.
As well as being large in size, Mars features a thick metallic core and mantle/crust composed of less dense materials that give rise to higher surface gravity than Earth.
As our planet has such a thin atmosphere, it can quickly heat up and then quickly lose heat through radiation or the evaporation of liquid water on its surface. This makes earthquakes and landslides highly likely.
Mars’ geology varies significantly across its surface, from mountain ranges and volcanoes, scarps (trenches) and canyons, plains and even subterranean zones.
As is common with many planets in our solar system, Mars exhibits an unevenly distributed magnetic field which varies in strength between regions – an echo from its once vibrant magnetosphere formed through impacts and volcanism.
Mars is so similar to Earth that some scientists speculate it could once have supported life on its surface. Unfortunately, however, Mars today is dry and lacks liquid water sufficient for support of life on the planet.