What Planet is Closest to Earth in Size?

what planet is closest to earth in size

Most people would likely reply that Venus is closest to earth in size when asked which planet comes closest when passing by our solar system’s closest neighbor, the Sun.

Researchers have recently determined that, on average, Mercury outshines Venus by far. To reach their conclusion they conducted a computer simulation over thousands of years that detailed both planets’ orbits.


Mercury, our solar system’s smallest rocky planet, stands out in many ways. At just over 1,000 miles in radius, its radius approaches that of Earth’s moon but remains two-fifths smaller. Mercury also boasts the shortest year span in our solar system–just 88 days long!

Mercury lies so close to the sun that its surface can become scorching hot during the daytime; but at nighttime temperatures drop dramatically to an incredible 275-degree Fahrenheit difference, giving this planet its largest temperature swing of any in our solar system.

Mercury lacks an atmosphere, yet still boasts a thin exosphere made up of atomic particles blasted off its surface by solar radiation, solar wind, micrometeoroid impacts and micrometeoroid strikes. These particles escape into space where they form an equatorial ring known as the Mercury bow shock ring of dark streaks known as its unique “bow shock.”

Ancient Sumerians knew about Mercury, and associated it with Nabu, the god who introduced writing into our world. In 2016, scientists published the first global digital model of Mercury’s topography based on more than 10,000 images taken by NASA’s MESSENGER probe, showing its highest point as being located near Caloris basin (visible from space and larger than Northeastern United States) while its lowest point lies near its equator and includes Rachmaninoff basin which could hold water ice.

Astronomers use an approach that considers each planet’s average time at different distances from the Sun during its entire orbit to calculate which are closest. Scientists created a simulation of our solar system with all planets moving through their orbits and calculated their average distances over thousands of simulated years – they discovered Mercury is, on average, closer to our home planet than Venus and Mars – it even comes close to Jupiter Saturn Uranus Neptune! But Mercury doesn’t always stay close by as all of them spend some time being far apart!


Venus boasts one of the densest atmospheres in our Solar System, consisting primarily of carbon dioxide (96%), with small quantities of water and sulphur dioxide as well as other gases. Carbon dioxide traps heat in its dense atmosphere and produces an extreme greenhouse effect that has made Venus the hottest planet in our Solar System. Furthermore, its dense atmosphere also reflects light back out into space – making Venus one of the brightest objects visible in our skies after Moon and Sun. Studies of Venus can be difficult, although Magellan managed to map 98 percent of its surface in 1990 – including mountains, plains and thousands of volcanoes with long lava flows. Unfortunately due to Venus’ harsh environment spacecraft don’t last very long once landing; Venera 13 from Soviet space program only managed two hours of functionality after touchdown.

At its closest point to Earth, Venus experiences what’s known as an inferior conjunction. This occurs every 584 days and marks the only time it comes within 25 million miles of being adjacent – making this momentous event significant enough to call “closest to us than Mercury”. Although close at times, Venus still spends most of its orbit far away.

Venus was Galileo’s inaugural telescope observation, helping him confirm Copernican theory that all planets orbited around the Sun rather than Earth. Galileo noticed Venus had phases much like those seen on Earth – an indication of once being similar in climate terms to Earth and probably warmer as well. Later scientists learned of Venus’ thick atmosphere containing water vapor and sulfuric acid droplets trapping heat to create its runaway greenhouse effect; today its surface temperature stands at 465C or 900F which can melt lead.

Engineers from NASA, Los Alamos National Observatory and the US Army’s Engineer Research Development Center developed a computer simulation of the Solar System that allowed them to determine which planet was closest to Earth on average. After simulating each planet’s orbit for thousands of simulated years and then calculating their distance from each other on average, engineers were surprised to discover that Mercury actually stood as Earth’s closest neighbor!


This question of which planets are closest to our home planet in terms of size can be both fascinating and practical, particularly as humanity ponders sending manned missions to other worlds. Unfortunately, however, finding an answer doesn’t come easily: distance measurements vary considerably across planets.

As one example, one popular calculation involves comparing the average distances of Venus and Mars to that of Earth, but this doesn’t take into account that each planet reaches its closest point at different points during its orbit. To accurately identify which one is closer, calculate its distance over an entire orbit cycle.

On average, Mars lies approximately 142 million miles from our Sun and is commonly known as “the Red Planet.” As its name implies, Mars is composed of rock and dust; with two moons named Phobos (pronounced foe-BOS) and Deimos. Its vibrant red hue is due to the presence of oxidized iron deposits.

Mars doesn’t appear particularly hospitable to life as we know it today, with its freezing cold temperature and tenuous atmosphere not providing sufficient protection from ultraviolet radiation from space to support any form of life on the surface. But there are signs that it was once much more habitable; astronomers have found gullies on its surface which indicate flowing water once existed on Mars’ surface.

There is evidence of climate change on Mars. Scientists think it was once warmer and wetter, making conditions more hospitable to life on its surface.

Even so, no proof exists for any form of life on Mars; nonetheless it has captured human imagination for centuries and served as the target for rovers sent out by NASA and other space agencies as trailblazers for future human missions to Mars’ surface.


Earth is unique among its solar system in having liquid water and life forms that thrive, such as plants and animals. It consists of land, air and water surfaces and millions of different plant and animal species living here; all due to its distance from the Sun, physical properties, geological history and historical environment that allow life to exist here.

At approximately 4.5 billion years ago, gravity pulled together swirling dust and gases into place to form Earth. Like other terrestrial planets, Earth features a central core with rocky mantle enveloped by atmosphere and solid crust; oceans, lakes, rivers and streams supply water for plant and animal life; it spins on its axis once every 24 hours to cause night and day cycles; this makes the planet spin continuously on its axis and allows life on it to flourish.

The TRAPPIST-1 system, discovered in 2016, contains some of the closest Earth-sized exoplanets ever observed. They lie within the habitable zone of their star, meaning they could possibly contain liquid water on their surfaces and may provide temperatures suitable for microorganism life to flourish; although no evidence has yet been detected.

There are other Earth-sized exoplanets orbiting other stars, like Kepler-186f which is approximately 10 percent larger than Earth and located 1,200 light years away. Kepler-186f lies within its star’s habitable zone and receives approximately one third of the energy that the Sun gives Earth.

Gliese 667Cc, an exoplanet recently discovered by scientists, is about 22 light-years away and approximately 4.5 times greater in mass than Earth. It completes one orbit around its host star in 28 days and is thought to be a temperate planet with dense atmosphere.

TOI 700 e, which measures 95% of Earth in size and likely comprises rocks, orbits its host star every 28 days and lies within its habitable zone – meaning liquid water could potentially exist on its surface. TOI 700 e is also the first Earth-sized exoplanet discovered within such an orbit.

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