You open your eyes and stumble backwards sending grey dust and rocks cascading down in front of you, with a steading breath you take a step forwards again. Take a look! You are standing on the precipice of a colossal mountain range; nearly 2 km below you and stretching out over 1500 km in front of you is the Caloris basin, “The basin of heat”. Though the Sun is noticeably absent, the sky is not completely black, but littered with the light of millions of stars left un-obscured by Mercury’s lack of permanent atmosphere. This of course also means that it is also intolerably cold, with temperatures reaching as low as -200°C.
You shut your eyes again and when you open them you are transported to an icy plane. You are now in a region of the planet permanently shrouded in darkness. Standing at the base of this icy polar crater, an ancient scar left by impacts deep in the planets past, the stars above you rotate with the seasons. Yet with no atmosphere to weather a storm, no surface activity to effect change, and little axial tilt to alter the solar irradiation through the seasons the landscape around you does not change and no sunlight ever reaches your feet.
In a blink of your eye, you are once again transported across the planet to the edge of vast a canyon, you look up and in the distance you can just see the enormous mountain range on which you started your journey. You are now inside “the basin of heat” and about to witness the reason for its namesake, for every two Mercurian years the Suns light floods the basin for over 50 Earth days.
With no atmosphere to scatter the sunlight above your head in a welcoming glow alerting you to the coming day, there is no advanced warning as the Sun begins to rise over the eastern horizon. The Sun is a bright sliver of fire above the distant mountain ridge slowly edging its way into full view. Once it is above the horizon you can fully appreciate the sheer size of it as it illuminates the blackness of space and obscures the once visible array of stars. But this time of year is special, the planet is approaching perihelion, its closest approach to the Sun, and as it does the speed at which it proceeds through its orbit increases by one and a half times. The consequence of this happenstance is what you are about to witness, and it is one of pure astronomical wonder. As the Sun rises above the mountain ridge headed toward the western sky it momentarily stops and makes its way back towards the eastern horizon. The orbital motion causing the Sun to appear to move from west to east has overcome the rotational motion that causes it to move from east to west. As the planet continues on its journey past the perihelion point the rotational motion takes over bringing the sun once again back up above the horizon to make its full journey across the sky. You have just witness the only double sunrise in our solar system.
As you fast-forward through the day you will see the Sun appear to shrink in the sky, by nearly one and a half times, as you move towards aphelion, the point in the orbit farthest from the Sun. It is over six Earth weeks until the Sun is at the midday point over the center of the Caloris basin, and with the Sun un-obscured during its total daytime trip from eastern to western horizon the surface can reach temperatures of over 400°C. That is a temperature range of over 600° from coldest to hottest and is the most extreme in the solar system.
You have just fast forwarded through a year on Mercury; that is 88 earth days, on the fastest planet in the solar system. You have witnessed the unchangeable seasons, the extremes of temperature, and the wonder of a double sunrise, and with a blink of your eye you are back on terra ferma ready for the next adventure.
Where would you like to go next?
For more information on Mercury check out some of these link:
- Bob the Alien is a fun one for kids and is full of fantastic facts