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SciShow Space takes you on a tour of Mercury, the sun’s closest friend, where a year is just a day and half long, and the surface holds many surprises -- like ice!
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Have you ever wondered what it's like on other planets? What sights would await you on the red dunes of Mars? What it would be like to dance on Saturn? What's waiting beneath the swirling clouds of Jupiter? Yeah, lots of things would kill you before you ever found out: the heat, or the cold, or radiation, potentially crushing gravitation, and either a total lack of atmosphere or a miasma of poison gases. But, we're learning more and more about the conditions on our celestial neighbors all the time. So it's not hard to imagine what it would be like to pay them a visit.

(0:34) Take Mercury, for example, the Sun's closest pal. Because it's only fifty-eight million kilometers from the sun, compared to Earth's 150 million kilometers, on Mercury the Sun would appear three times larger than it does from Earth, and six times brighter. So, you know, wear sunscreen. And, because it's the closest, Mercury has the shortest orbital period in the solar system, completing one circuit around the sun in just eighty-eight Earth days. 

(0:59) But, as it travels around the Sun, Mercury actually rotates relatively slowly. One full rotation, which would be one day on Mercury, takes about fifty-eight Earth days, so the planet ends up experiencing roughly three days for every two of its years. It's also a cute little thing, as planets go, about 4,900 kilometers in diameter. That's about 40% larger that our moon, but it's still only as big across as the continental United States. 

(1:27) And, as you headed towards the planet, you'd see that it looks a lot like our moon: grey, rocky, and uneven. Unlike the moon, though, its surface is rippled with towering ridges called lobate scarps, which were created when Mercury rapidly cooled after it formed more than four billion years ago. In the process of cooling, the planet actually shrank by as much as eleven kilometers in diameter, giving it an appearance that's been compared to a dry apple. 

(1:52) As you get even closer to Mercury, you pass through its exosphere, a thin layer of oxygen, hydrogen, helium, sodium, potassium, and other materials, most of which were knocked off the planet's surface by solar wind and meteoroids. And, because it has no significant atmosphere to burn up any rocks flying at it from space, Mercury is also heavily cratered. One impact four billion years ago was so nasty it created a crater roughly 1,550 kilometers wide. Known as the Caloris Basin, it's basically the size of Texas. 

(2:24) Now you might well think that Mercury is the hottest planet in the solar system because it's the closest to the Sun, but you'd be wrong. That distinction actually goes to Venus. Since Mercury has such a weaker atmosphere, it's not very good at retaining heat, so it can get a lot colder than you might think. Daytime temperatures can reach 430°C, sure, but at night, they drop to -180°. That's the biggest temperature swing in our solar system. 

(2:54) And in fact, if you were to land in the right crater on Mercury, you might even find ice. Astronomers think they've found evidence of water-ice lurking at the north and south poles, where there are craters so deep that they're perpetually shadowed and cold. This water was probably delivered to Mercury by the same impacts that gave the planet its pockmarked complexion. 

(3:14) So, one last weird thing to keep in mind if you're planning a trip to Mercury is that you'd feel a lot lighter there, but not as light as you might expect. Even though Mercury is only 40% bigger than the Moon, it actually has about twice the gravitation. Standing on Mercury, you'd experience 38% the force of gravity that you'd experience on Earth, compared to just 16% on the Moon. What gives? Despite its small size, Mercury is actually the second densest planet in our solar system, thanks to its huge metallic core. At roughly 3,700 kilometers wide, its liquid iron core takes up about 75% of the planet's total diameter. Since it's so packed with mass, Mercury exerts stronger gravitation, resulting in a lighter step than you take on Earth, but not quite the bounce that you get on the Moon.

(4:04) Thanks for joining me for SciShow Space. If you wanna keep helping us explore the solar system and the rest of the universe together, just go to, and don't forget to go to and subscribe.