Jupiter is the largest planet in our solar system, boasting its Great Red Spot that nearly covers as much surface area as our own planet!
People typically calculate which planet comes closest to Earth in size by subtracting their average distances from the Sun; however, due to the nature of elliptical orbits, which one actually closes is subject to change over time.
Venus, the second planet from our Sun, is sometimes considered Earth’s twin; however, they couldn’t be any further apart. While Earth offers oceans and lakes for humans to enjoy, Venus offers only boiling hot temperatures with an inhospitable atmosphere billions of times more acidic than even our most acidic parts on Earth.
Venus may appear barren now, but scientists know otherwise. When our Solar System first formed two billion years ago, Venus once had liquid water covering nearly half its surface for two billion years or more. Due to Venus’ runaway greenhouse effect – trapping solar radiation into its interior environment which in turn raises surface temperatures – there was once liquid water there too, perhaps for two billion years or longer during those early times before life as we know it became impossible.
Venus is shrouded by a dense blanket of clouds, making direct observation impossible. Radar and spacecraft observations reveal that this cloud cover features both dark markings and global-scale bright bands; most likely made up of carbon dioxide along with some nitrogen or other gases.
Though we have yet to see evidence of life on Venus, there remains the possibility that some kind of microorganism or bacteria do inhabit its dense atmosphere. Scientists from MIT and Cardiff University have discovered chemical signatures associated with such organisms present on Venus.
Venus rotates on an opposite axis than Earth, meaning its Sun rises and sets in opposite directions from its surface. Due to Venus’ thick atmosphere, studying its interior or formation history is extremely challenging; scientists believe it may have formed similarly to ours by gathering rock and metal from objects orbiting around a young Sun and gradually accreting onto itself over time. Venus stands out among terrestrial planets due to lacking evidence of plate tectonics on its surface while its core is thought to be divided between an inner core (solid) and outer core (low viscosity liquid).
Mercury, like Venus, was initially thought of as two distinct objects in the sky: The Evening Star and Mourning Star. But as astronomers learned more about its orbit, they discovered it spent most of its time closer to Earth than any of the other planets and was the closest planet in our solar system. Galileo couldn’t see Mercury during its phases like Venus or the Moon do; these happen when its inferior conjunction and superior conjunction occur – either when its brightest or darkest phases appear respectively.
Like Earth’s moon, Mercury features a rocky core, silicate mantle and metallic crust with numerous impact craters from heavy bombardment during its formation 4.5 billion years ago. Many of these impact craters bear names of deceased artists or writers while their scarred surfaces serve as visible evidence that there hasn’t been any volcanic activity on Mercury since.
Mercury rotates slowly around its axis, taking 59 days to complete one rotation. Given its proximity to the Sun, Mercury experiences hotter days than Earth when sunlight shines directly overhead and shorter nights when sun rays move toward its horizon. Without an atmosphere to store heat during daylight hours, temperatures on Mercury can reach 800 degrees Fahrenheit (430 Celsius), dropping as low as minus 290 Fahrenheit (179 Celsius) at nighttime.
Mercury boasts the second strongest magnetic field in our Solar System, with slightly stronger north pole magnetic flux than south. Polar regions of Mercury also display high radar reflection suggesting water ice accumulations.
Mercury, like other terrestrial planets, features an exosphere filled with gases such as oxygen, hydrogen, sodium potassium and hydrogen sulfide that is stirred up by solar wind. Furthermore, Mercury boasts a global magnetic field 1.1% as strong as Earth’s.
Mars can only be seen from close enough vantage points twice annually; the next time this will happen will be in 2035.
Mars, the fourth planet from the Sun, is best known for its reddish hue, which comes from finely ground iron(III) oxide dust in its soil. Furthermore, Mars’ thin atmosphere can only temporarily contain heat released from its rocky surfaces.
On July 31, Mars will come within 56 million km (35 million miles) of Earth, marking their closest encounter ever recorded history and thus making this occasion known as the perihelion – it will remain the closest distance until 2287 when they come even closer together.
Earth and Mars take roughly the same time to complete one orbit around the Sun, so sometimes they appear opposite one another – known as opposition.
Last June, when Mars last had an opposition, scientists used the Hubble Space Telescope to capture images of its polar caps, water ice clouds, and dust storms – these photos were the sharpest and clearest ever taken of Martian features! Due to this success, scientists plan to replicate this feat this summer – when Mar is closer by 7 million miles than 2001!
Although liquid water cannot exist on Mars’ surface due to its extremely low atmospheric pressure (less than one percent that of Earth), evidence exists for its former presence underground – such as in hematite concretions or Ma’adim Vallis which appears to have been formed by flowing water.
Weather permitting, Mars should be visible in the night sky this month. It emerges just after sunset in Capricorn and remains visible through most of the night as it moves across from east to west across the sky. At midnight local time it reaches its highest point and becomes easier than ever to spot; being one of the brightest objects visible.
Pluto is one of nine known planets in our solar system once classified by astronomers as planets before discovering other interesting icy worlds deeper in the Kuiper Belt – filled with thousands of rocks and ice objects larger than 62 miles (100 kilometers) across. Pluto is known to possess a thin atmosphere consisting of mostly nitrogen, methane and carbon monoxide molecules.
Before New Horizons flew by Pluto in 2015, scientists could only observe it from afar. Now that this spacecraft had reached Pluto and taken pictures of its surface, scientists could observe an intricate world full of mountains, valleys, plains and craters – not at all what scientists had been expecting!
Astronomers also discovered a cluster of 357 regularly spaced pale ridges and six darker wind streaks stretching 46 miles over Sputnik Planitia, Pluto’s biggest plain. These features resemble Earth’s penitentes – erosion-formed features on mountainous terrain – but differ by changing in color and location over time, possibly being caused by winds.
Pluto features snow- and ice-capped mountains dotted across its landscape as well as irregularly-shaped depressions, thanks to its relatively low gravity of only 6% of Earth. Pluto’s relatively weak gravity allows sublimated ice to sublimate and rise to create an atmosphere, thought to mostly consist of nitrogen.
Pluto boasts four moons, including Charon which is two times as large as Pluto and is tidally locked to it, always facing in one direction. Hubble also helped discover two more moons named Nix and Hydra which lie roughly 26 and 70 miles (42 and 113 kilometers) away from Pluto respectively – New Horizons mission will explore these moons as well as any nearby icy regions.
Pluto lies so far from the Sun that light takes 5.5 hours to reach it. Although its orbit can sometimes bring it closer than Neptune, a stable orbital resonance prevents any collision between Pluto and Charon – dwarf planets in orbit around each other – thus keeping both from colliding. Astronomers hope New Horizons can capture that iconic Kodak moment when Charon rises from behind Pluto for the first time!